363.7009773 C362 v.l cop. 2 llatural History Survoy Librar/ lllinoia Department of Energy and Natural Raaourcaa The Changif\g Illinois Environhient: Critical Trends Trends ^ort of the Project Resources June 1994 ILENR/RE-EA-94/05(1} Hphvai History Survey Library NOTICE: Return or renew all Library Materialsl The Minimum Fee for each Lost Book Is $50.00. The person charging this material is responsible for its return to the library from which it was withdrawn on or before the Latest Date stamped below. Theft, mutilation, and underlining of books are reasons for discipli- nary action and may result in dismissal from the University. To renew call Telephone Center, 333-8400 UNIVERSITY OF ILLINOIS LIBRARY AT URBANA-CHAMPAIGN LI61— O-1096 ILENR/RE-EA-94/05(1) The Changing Illinois Environment: Critical Trends Technical Report of the Critical Trends Assessment Project Volume 1: Air Resources Illinois Department of Enei^ and Natural Resources Illinois State Water Survey Division 2204 Griffith Drive Champaign, Illinois 61820-7495 June 1994 Jim Edgar, Governor State of Illinois John S. Moore. Director Illinois Department of Energy and Natural Resources 325 West Adams Sffeet, Room 300 Springfield, Illinois 62704-1892 Printed by Authority of the State of Dlinois Printed on Recycled and Recyclable Paper Illinois Department of Energy and Natural Resources 325 West Adams Street, Room 300 Springfield, Illinois 62704-1892 Citation: Illinois Department of Energy and Natural Resources, 1994. The Changing Illinois Environ- ment: Critical Trends. Summary Report and Volumes 1 - 7 Technical Report. Illinois Department of Energy and Natural Resources, Springfield, IL, ILENR/RE-EA-94/05. Volume 1: Air Resources Volume 2: Water Resources Volume 3: Ecological Resources Volimie4: Earth Resources Volume 5: Waste Generation and Management Volume 6: Sources of Environmental Stress Voliune 7: Bibliography Coo ."2— Volume 1 Air Resources CONTRIBUTORS Illinois State Water Survey Van C. Bowersox Donald A. Dolske Donald F. Gatz Kenneth E. Kunkel Stephen J. Vermette Wayne M. Wendland ABOUT CTAP ABOUT THE CRITICAL TRENDS ASSESSMENT PROJECT The Critical Trends Assessment Project (CTAP) is an on-going process established to describe changes in ecological conditions in Illinois. The initial two-year effort involved staff of the Illinois Department of Energy and Natural Resources (E^4R), including the Office of Research and Planning, the Geological, Natural History and Water surveys and the Hazardous Waste Research and Information Center. They worked with the assistance of the Illinois Environ- mental Protection Agency and the Illinois depart- ments of Agriculture, Conservation, Mines and Minerals, Nuclear Safety, Public Health, and Trans- portation (Division of Water Resources), among other agencies. CTAP investigators adopted a "source-receptor" model as the basis for analysis. Sources were defined as human activities that affect environmental and ecological conditions and were split into categories as follows: manufacturing, transportation, urban dynamics, resource extraction, electricity generation and transmission, and waste systems. Receptors in- cluded forests, agro-ecosystems, streams and rivers, lakes, prairies and savannas, wetlands, and human populations. The results are contained in a seven-volume technical report. The Changing Illinois Environment: Critical Trends, consisting of Volume 1 : Air Resources, Volume 2: Water Resources, Volume 3: Ecological Resources, Volume 4: Earth Resources, Volume 5: Waste Generation and Management, Volume 6: Sources of Environmental Stress, and Volume 7: Bibliography. Volumes 1-6 are synopsized in a summary report. The next step in the CTAP process is to develop, test, and implement tools to systematically monitor changes in ecological and environmental conditions in Illinois. Given real-world constraints on budgets and human resources, this has to be done in a practi- cal and cost-effective way, using new technologies for monitoring, data collection and assessments. As part of this effort, CTAP participants have begun to use advanced geographic information systems (GIS) and satellite imagery to map changes in Illi- nois' ecosystems and to develop ecological indicators (similar in concept to economic indicators) that can be evaluated for their use in long-term monitoring. The intent is to recruit, train, and organize networks of people — high school science classes, citizen vol- unteer groups — to supplement scientific data collec- tion to help gauge trends in ecological conditions. Many of the databases developed during the project are available to the public as either spreadsheet files OT ARC-INFO files. Individuals who wish to obtain additional information or participate in CTAP programs may call 217/785-0138, TDD customers may call 217/785-0211, or persons may write: Critical Trends Assessment Project Office of Research and Planning Illinois Department of Energy and Natural Resources 325 West Adams Street, Room 300 Springfield, IL 62704-1892 Copies of the summary report and volumes 1-7 of the technical report are available from the ENR Clearinghouse at 1/800/252-8955. TDD customers call 1/800/526-0844, the Illinois Relay Center. CTAP information and forum discussions can also be accessed electronically at 1/800/528-5486. FOREWORD FOREWORD "If we could first know where we are and whither we are tending, we could better judge what we do and how to do it..." Abraham Lincoln Imagine that we knew nothing about the size, direction, and composition of our economy. We would each know a little, i.e., what was happening to us directly, but none of us would know much about the broader trends in the economy — the level or rate of housing starts, interest rates, retail sales, trade deficits, or unemployment rates. We might react to things that happened to us direcdy, or react to events that we had heard about — events that may or may not have actually occurred. Fortunately, the information base on economic trends is extensive, is updated regularly, and is easily accessible. Designed to describe the condition of the economy and how it is changing, the information base provides the foundation for both economic policy and personal finance decisions. Typical economic decisions are all framed by empirical knowledge about what is happening in the general economy. Without it, we would have no rational way of timing these decisions and no way of judging whether they were correct relative to trends in the general economy. Unfortunately, this is not the case with regard to changes in environmental conditions. Environmental data has generally been collected for regulatory and management purposes, using information systems designed to answer very site-, pollutant-, or species- specific questions. This effort has been essential in achieving the many pollution control successes of the last generation. However, it does not provide a systematic, empirical database similar to the eco- nomic database which describes trends in the general environment and provides a foundation for both environmental policy and, perhaps more importantly, personal decisions. The Critical Trends Assessment Project (CTAP) is designed to begin developing such a database. As a first step, CTAP investigators inventoried existing data to determine what is known and not known about historical ecological conditions and to identify meaningful trends. Three genial conclu- sions can be drawn from CTAP's initial investiga- tions: Conclusion No. 1: The emission and discharge of regulated pollutants over the past 20 years has declined, in some cases dramatically. Among the findings: Between 1973 and 1989, air emissions of particulate matter from manufacturing have dropped 87%, those of sulfur oxides 67%, nitrogen oxides 69%, hydrocarbons 45%, and carbon monoxide 59%. • Emissions from cars and light trucks of both carbon monoxide and volatile organic com- pounds were down 47% in 1991 from 1973 levels. • Lead concentrations were down substantially in all areas of the state ovct the 1978-1990 period, reflecting the phase-out of leaded gasoline. • From 1987 to 1992, major municipal sewage treatment facilities showed reductions in loading of biological/carbonaceous oxygen demand, ammonia, total suspended solids and chlorine residuals that ranged from 25 to 72%. • Emissions into streams of chromium, copper, cyanide, and phenols from major non-municipal manufacturing and utility faciUties (most of them industrial) also showed declines over the years 1987-1992 ranging from 37% to 53%. Conclusion No. 2: Existing data suggest that the condition of natural ecosystems in Illinois is rapidly declining as a result of fragmentation and continual stress. Among the findings: • Forest fragmentation has reduced the ability of Illinois forests to maintain biological integrity. In one Illinois forest, neotropical migrant birds that once accounted for more than 75% of breeding birds now make up less than half those numbers. II FOREWORD • In the past century, one in seven native fish species in Lake Michigan was either extirpated or suffered severe population crashes and exotics have assumed the roles of major predators and major forage species. • Four of five of the state's prairie remnants are smaller than ten acres and one in three is smaller than one acre — too small to function as self- sustaining ecosystems. • Long-term records of mussel populations for four rivers in east central Illinois reveal large reduc- tions in numbers of all species over the last 40 years, ^parently as suitable habitat was lost to siltation and other changes. • Exotic species invasions of Illinois forests are increasing in severity and scope. Conclusion No. 3: Data designed to monitor compli- ance with environmental regulations or the status of individual species are not sufficient to assess ecosys- tem health statewide. Among the findings: • Researchers must describe the spatial contours of air pollutant concentrations statewide using a limited number of sampling sites concentrated in Chicago and the East St. Louis metro area. • Much more research is needed on the ecology of large rivers, in particular the effects of human manipulation. The length of Illinois' longest stream gaging records is generally not sufficient to identify fluctuations that recur less frequently than every few decades. • The Sediment Benchmark Network was set up in 1981 with some 120 instream sediment data stations; by 1990 the network had shrunk to 40 stations, the majority of which have data for only one to three years. CTAP is designed to begin to help address the complex problems Illinois faces in making environ- mental policy on a sound ecosystem basis. The next edition of the Critical Trends Assessment Project, two years hence, should have more answers about trends in Illinois' environmental and ecological conditions to help determine an effective and economical environmental policy for Illinois. Ui CONTENTS CONTENTS AIR RESOURCES: VOLUME SUMMARY 1 INTRODUCTION 5 CLIMATE TRENDS IN ILLINOIS 7 AIR QUALITY TRENDS IN ILLINOIS 91 ATMOSPHERIC DEPOSITION TRENDS IN ILLINOIS 155 AIR RESOURCES: VOLUME SUMMARY AIR RESOURCES: VOLUME SUMMARY REPORT OVERVIEW Although considerable progress has been made in im- proving the environment, national and state goals for environmental quality still have not been completely met, and additional effort and expenditures will be necessary. To use public funds as effectively as possi- ble, Illinois environmental officials must set priorities so that the most serious problems receive the most attention. The priorities should be based on an assess- ment of the current status of Illinois' environment. This technical report on air resources is one of a series aimed at documenting and assessing the status of Illinois' environment. It includes comprehensive infor- mation about Illinois' climate and air quality and the deposition of atmospheric constituents on the earth's surface. In each subject area, currently available data have been assembled to provide a picture of how air resources have changed over time and how they vary spatially from place to place around the state. SUMMARY AND SIGNIFICANT RESULTS Climate Trends This report presents an analysis of climate trends since the late nineteenth century in Illinois. This work is based on a variety of climate data and information from Illinois sites. Long-term daily temperature and precipitation data available from 41 locations formed the basis for much of the analysis of temperature and precipitation in this report. More detailed observations from National Weather Service office sites (including Chicago, Springfield, Peoria, Moline, St. Louis, and Evansville) were used to assess trends in cloud cover, freezing precipitation, and visibility. Citizen reports were used to assess trends in tornado frequency. Although long-term trends can be identified in various climate parameters, the dominant characteristic of Illinois' climate is the presence of variability on all time scales from decades to a few years or less. That is, the magnitude of long-term trends is in general consid- erably less than the changes that can occur from one year or a few years to the next. With that being said, how- ever, some identifiable long-term features can be noted. The most persistent and extreme period of summertime drought and heat occurred during the 1930s, the Dust Bowl era. This mirrors the long-term average tempera- tures in Illinois, which increased by 4 to 5"F from the mid- to late 1800s to the 1930s, and then cooled by about half that amount to the present. This trend in temperature is consistent with trends found in global records. Consistent with the cooling trend after about 1930, generally benign and moderate summers occurred during the 1960s and 1970s. However, since that time, the 1980s were characterized by more frequent hot and dry summers, similar to the first half of the century. In fact, the severity of the 1988 growing-season drought in Illinois has only been equaled in two other years since the turn of the century. In general, the frequency of extreme cold events has increased from about 1930 to the present. This upward trend reached its peak in the late 1970s and early 1980s, with an unprecedented string of extremely cold winters. However since the early 1980s, winters have generally been on the benign side. Tornado frequency records exhibit large variability. Reliable records of tornado frequencies are limited to the past three decades. In that time, no upward or downward frend in frequencies has been identified. It is clear that climate has not been stable in Illinois during the last 1 50 years, nor should it have been so anticipated. Many of the changes, although abrupt, were of relatively small magnitude. Yet those relatively small-scale changes levied a substantial toll on the inhabitants of the state through discomfort, lost income, increased costs, and impediments to commerce and agricultural production, in spite of major strides. TTie past gives little hint as to the direction and magnitude of any possible future changes, but it does suggest the degree to which climate may change in the future, and demonstrate the magnitude of that impact on human activities. Air Quality Air quality can have direct effects on human and ecosystem health. Thus it is necessary to examine current air pollutant concentrations and their spatial variations over the .state. We also need to know whether concentrations are increasing, decreasing, or remaining constant, especially in the major population centers. Finally, we seek to identify gaps in air quality data and research that need to be filled to permit wise planning for the future. AIR RESOURCES: VOLUME SUMMARY This assessment of air quality is based primarily on Illinois Environmental Protection Agency (lEPA) measurements of seven pollutants for which state or national standards have been set, plus eight additional pollutants for which standards have not been set. These data cover the time period from 1978-1990. Summary data published in EEPA annual reports were tabulated in computer spreadsheet and Geographic Information System (GIS) files and are available to others. Temporal changes in pollutant concentrations are depicted graphically using box plots, which concisely show several features of observed distributions of concentrations at sampling sites within various geo- graphic areas. Spatial variations of average pollutant concentrations in the Chicago area are shown by plots of concentration contours. Trends in concentrations over time were tested for statistical significance using the nonparametric Spearman Rank Correlation Coeffi- cient. Statistical tests were also carried out to identify significant differences in concentrations between geo- graphic regions. For the criteria pollutants tested for time trend in any geographic region of the state, results indicated only decreasing trends or no significant (5 percent) trends. No increasing trends in criteria pollutants were de- tected. For the state as a whole, seven of twelve pollutant/averaging time datasets tested for time trend showed significant trends (5 percent or better) toward decreasing concentrations over the 1978-1990 period. After accounting for temperature effects, O, showed a significant decreasing trend (2 percent level), rather than no trend. In the Chicago area, eight of the twelve datasets showed decreasing trends at the 5 percent level (all but one of these were at the 1 or 2 percent level). After accounting for temperature, Oj (ozone) in the Chicago area showed a decreasing trend (2 percent level, table 3 of Air Quality Trends in Illinois chapter), rather than no trend. In the MetroEast area, only four pollutant/aver- aging time data sets were measured at enough sites to warrant testing for time trend. Only Pb (lead) showed a significant (5 percent) trend toward decreasing concen- trations. After accounting for temperature, Oj showed a decreasing trend at the 6 percent level, but not the 5 percent level. Three of nine datasets tested for time trend in the "remainder" region showed decreasing trends at the 5 percent level or better. The eight noncriteria pollutants were all tested for trend in all four areas mentioned above, except for the MetroEast region, where the data were not adequate to test Cr (chromium) and Ni (nickel). Of the 30 trend tests, 20 showed no significant (5 percent) trend. Over the state as a whole, and in the Chicago area, two species showed significant decreases — SO^^' (sulfaate ion) and As (arsenic). In the MetroEast area, Fe (iron) and Mn (manganese) showed significant increases (the only increasing trends found in this study). In the "remainder" region, SO^^ , As, Cd, and Mn showed significant (5 percent or better) decreases. Comparison of median and maximum pollutant con- centrations within geographic regions, from the yearly box plots in figures 1-30 (Air Quality Trends in Illinois chapter), indicates which geographic areas of the state experienced the highest concentrations of air pollutants. Chicago generally had higher median regional values of annual mean NO^' (nitrate ion), and annual mean and 24-hour Cr. It also experienced higher median annual mean Ni and the highest individual 24-hour Ni concentrations. On the other hand, the Chicago area generally experienced lower concentrations of 3-hour and 24-hour SOj than the rest of the state. The MetroEast area generally experienced higher con- centrations than the rest of the state for annual mean Pb, annual mean TSP (total suspended particulate mat- ter), and both 24-hour and annual mean As, Cd, Fe, and Mn. The Chicago and MetroEast areas experienced higher concentrations than the rest of the state for 1-hour maximum Oj and annual mean SO,. The analyses of spatial distribution of pollutant con- centrations in the Chicago area showed that only one location stands out for its high concentrations of multi- ple pollutants. This is the industrial area of southeast Chicago around Lake Calumet. This area has persistent, relatively high annual mean or 24-hour concentrations, or both, of SO^' , Fe, Mn, and Pb, and possibly Cd, Cr, and Mn. The evidence for the latter three is somewhat weaker than for the others, however. Other locations in the Chicago area appeared to have persistent high concentrations of only one or two pollutants. Atmospheric Deposition Atmospheric deposition is an ensemble of environmen- tal processes by which airborne pollutants from various sources are delivered to receptor systems at the earth's surface. Among the six natural environmental receptors treated by the Critical Trends project, atmospheric deposition is considered for two, forest ecosystems and lakes and impoundments, because research has shown possible damage to these receptors from certain kinds and amounts of atmospheric deposition. The character- AIR RESOURCES: VOLUME SUMMARY istics of atmospheric deposition in Illinois, and how it varies across the state and throughout the year are described in this chapter. Where there are data suffi- cient for an analysis, changes over several years are calculated and trends are inferred, if these changes are significant. Also shown are maps of deposition loadings, which together with the concentration data provide information necessary for assessments of the exposure of Illinois' natural environment to atmo- spheric deposition. While an explicit description of the source-receptor relationships for major pollutants, such as sulfur dioxide (SO^) and nitrogen oxides (NO^), is not considered, the sources of these pollutants in Illinois and surrounding states are compared to their occurrence in atmospheric deposition. Finally, additional work is discussed that is needed to improve our assessment of atmospheric deposition in Illinois and over Lake Michigan. Atmospheric deposition includes gases and aerosols that are solid, liquid, or mixed phase. It includes both primary pollutants, which retain their chemical identity between source and receptor, and secondary pollutants, which undergo transformation during transport in the atmosphere. Deposition of pollutants from the atmo- sphere is a continuous process, though there are large temporal variations in the deposition rate or flux. These variations relate to the kind of deposition that is occur- ring and to surface and atmospheric conditions. There are two kinds of atmospheric deposition, wet and dry. Wet deposition is defined as the delivery of pollutants to the surface by precipitation. Dry deposition is the delivery of gases and aerosols to the surface by mass transfer processes other than precipitation. In principle, dry deposition occurs continuously, while wet deposition occurs episodically, e.g., when it rains. Wet deposition is measured by chemically analyzing precipitation. For this project, wet deposition data from the national network, the National Atmospheric Deposition Program/National Trends Network (NADP/ NTN) were used. The NADP/NTN reports the concen- trations of dissolved calcium (Ca^'), magnesium (Mg^'). sodium (Na*), potassium (K*), ammonium (NH/), sulfate (SO^^ ), nitrate (NO, ), chloride (CI), orthophosphate (PO^' ), and free hydrogen ion (H*), measured in pH units. No trace metals or organics are reported by the NADP/NTN. Samples are filtered to remove insoluble materials, so NADP/NTN provides data for the soluble major inorganic ions found in precipitation, those chemicals that result in acidic deposition or "acid rain," which occurs over all of Illinois. Dry deposition includes the mass transfer of pollutants to the surface by a variety of physicochemical pro- cesses: turbulent diffusion, diffusion followed by surface sorption of gases, gravitational settling of large particles, impaction, and interception of solid and liquid particles. Dry deposition fluxes are strongly affected by atmospheric factors, which influence the rate at which pollutants are delivered to a receptor surface; and by surface factors, which influence the efficiency with which pollutants "stick" to a receptor surface. Among the atmospheric factors is wind speed and turbulence, air temperature, solar radiation, and relative humidity. Among the surface factors are roughness, wetness, surface-to-air temperature differ- ence, and type of surface, which includes whether the surface is animate (plant) or inanimate. The relative importance of these factors in determining the dry deposition rate depends also on the physical and chemical nature of the pollutant. For example, factors that affect the mass transfer of carbonaceous soot, an unreactive, insoluble particle, are much differ- ent than the ones affecting nitric acid, a highly reactive, soluble gas. The dry deposition of gases and submi- cron aerosols involves highly complex processes, and direct measurements are intractable on a spatial domain the size and complexity of Illinois. For this reason, an indirect method is applied to infer, rather than measure, dry deposition fluxes. This inferential method employs a conceptual model that estimates an atmosphere-to-surface coupling pa- rameter known as the "deposition velocity" V^. The dry deposition flux is the product of V_, and the measured air concentration of a particular pollutant. Model inputs, including the atmospheric and surface factors discussed earlier, are measured at a network of sites sponsored by the National Oceanic and Atmo- spheric Administration's Atmospheric Turbulence and Diffusion Laboratory (NOAA/ATDD). Land-use and vegetation type and status are also reported at these sites, along with the airborne concentrations of CI, SO^', particulate NOj , nitric acid vapor (HNOj), and SOj. The NOAA/ATDD sampling system is especially designed to exclude large particles, since the inferential method of calculating dry deposition applies specifi- cally to gases and submicron aerosols. The dry deposition of large particles, which have an aerodynamic diameter greater than I micrometer (jim), is typically estimated from an analysis of the mass of a pollutant accumulated on a surrogate surface. To estimate the dry deposition of large particles (i.e., sedimentation or dryfall) for CTAP, data from the AIR RESOURCES: VOLUME SUMMARY NADP/NTN were used. NADP/NTN measures dryfall in samples taken from the same collector used for precipitation. This device, a wet/dry collector, has two identical containers; it discriminates between wet and dry conditions, exposing the wet deposition container during precipitation and the dryfall container at all other times. Dryfall samples are sent for analysis of the same analytes measured in precipitation. Wet deposition in Illinois has been monitored for ten or more years at eight NADP/NTN sites. NADP/NTN reports the concentrations of ten separate chemical pollutants in precipitation. Just five of these are needed to account for about 90 percent of the chemical composition that causes Illinois precipitation to be acidic. They are, in order of importance: sulfate (SO^^ ) > hydrogen ion (H*) > nitrate (NO3 ) > ammonium (NH^*) > calcium (Ca^*). Illinois precipitation is most simply described as a dilute solution of mineral sulfuric and nitric acids, partly neutralized by ammonium and calcium. Based on statistical tests of time series data alone, there is no unambiguous trend that applies to all of the important pollutants causing acid rain in Illinois. Based on a "weight of the evidence" analysis, however, several points can be made about Illinois precipitation chemistry changes during the 1980s: 1 . Sulfate has decreased 2 to 4 percent per year in the southern third of the state, with smaller decreases elsewhere. 2. Calcium decreased by 3 to 7 percent per year, except at Argonne (suburban Chicago), where it remained steady. 3. Nitrogen species, ammonium and nitrate, remained unchanged. 4. pH increased, but the increase is too small and too variable to be quantified. 5. Sulfur dioxide and NO^ emissions have decreased slightly. Dry deposition in Illinois tends to be somewhat higher in the Chicago area, both due to higher airborne concentrations of most pollutants and higher deposition velocities. For sulfate, nitrate, sulfur dioxide, ozone, arsenic, and manganese, the differences are on the order of 10 to 30 percent. For cadmium, chromium, iron, nickel, lead, and total suspended particles, dry deposition in the Chicago area exceeds the rest of the state by 200 to 400 percent, which is primarily caused by the differences in air quality (see Air Quality Trends in Illinois chapter). Temporal trends in dry deposition generally follow air quality trends, although additional variability is introduced into the time series data by interannual variation in deposition velocities. More important for ecological impacts is the seasonal nature of dry deposition loadings, with higher deposition velo- cities for many pollutants occuring during the warm season, when biological impacts may also be the greatest The total deposition of sulfur in the Chicago area is about 15 percent higher than in the rest of the state. For sulfur (sulfate plus sulfur dioxide), the ratio of wet to dry deposition is about 1 part wet to 1.5 parts dry. The deposition of nitrogen in the Chicago area is about 30 percent higher than in the rest of the state. For nitrogen (nitrate plus ammonium plus nitric acid vapor), the ratio of wet to dry deposition is about 1 part wet to 3 parts dry. The spatial and temporal variation information is most useful in describing the coupling of the atmosphere to receptors that are also distributed in space and have temporally-varying sensitivity to the depositing pollutants. Acid deposition to forests for example, is most likely to have an effect during the growing season, and much less likely to be harmful in the dormant season. Toxic deposition to forests, however, may act through a cumulative effect, where the temporal variation is less important to understanding the impact on the receptor system. Acid deposition to Lake Michigan presents a special difficulty in this analysis, since neither wet nor dry deposition is measured over the lake, although the refinement of estimates based on shoreline measure- ments is an ongoing research topic. Agricultural systems have been shown to be relatively insensitive to curtent levels of acid deposition, but the impact of toxic deposition and dry deposition of many pollutants is unknown. Ozone has been demonstrated to have negative impacts on yield and quality of cash crops in several areas of the United States. The role of wet and dry toxics deposition as a contributor to nonpoint source pollution in surface and ground-water supplies for human consumption is also unknown at this time. The impact of atmospheric deposition (acid rain, toxic pollutants, and biological nutrients) to lakes and streams in Illinois (i.e., other than Lake Michigan waters) has not been documented, although consider- ation of the magnitude of deposition for many chemi- cals would indicate that significant impacts are possible. Finally, the impacts of 80^- , SO,, acids, and NO, deposition, both in precipitation and dry deposi- tion, has been demonstrated in recent federally sponsored research in many areas of the United States. Materials impacts in Illinois are as yet unquantified, but they are potentially large. INTRODUCTION INTRODUCTION RELATIONSHIP OF AIR RESOURCES TO CTAP PROJECT GOALS CRITICAL TRENDS ASSESSMENT PROGRAM (CTAP) OVERVIEW Large amounts of money have been and are being spent on pollution control efforts to protect human health and the environment. Although these efforts have had con- siderable benefits, many environmental goals still have not been met nationally and in Illinois. Thus, we may expect that the expenditures for environmental im- provement will continue and perhaps increase. It is incumbent upon state officials and environmental policy makers to use public funds for environmental improvement wisely. To use funds wisely in this con- text means to effect the greatest possible environmental improvement from the available resources. This implies that priorities must be set for the use of public funds for environmental improvement. What criteria should govern the setting of priorities? The U.S. EPA's Sci- ence Advisory Board (1990) stated that "policy affecting the environment must become more integrated and more focused on opportunities for environmental improvement than it has in the past Integration in this case means that government agencies should assess the range of environ- mental problems of concern and then target protective efforts at the problems that seem to be the most serious." The first step in addressing these issues is to assess the state of the environment. By executive order, Illinois' Governor Edgar directed the Department of Energy and Natural Resources (ENR) and the Governor's Science Advisory Committee (GSAC) to "conduct an environmen- tal trends analysis and to report to the public on the state of the Illinois environment." The goals of this effort are: 1) to document techniques for searching, organizing, analyzing, interpreting, and evaluating data for geogra- phic and temporal presentation, 2) to document assessment methodologies for analyz- ing environmental and human health information, 3) to identify critical data gaps, for use in prioritizing future research, 4) to establish an integrated data structure that will pro- vide the means to judge trade-offs associated with anti- cipated changes in the state's natural environment or infrastructure, and 5) to produce a final report that documents past conditions and assesses the present status of the Illinois environment. The atmospheric environment is an important compo- nent of the overall environment of the state. Weather and climate affect a broad range of ecosystem and human health issues. For example, temperature and moisture conditions and their seasonal changes deter- mine to a great extent the geographical distribution of plant and animal species. Droughts and floods have great impacts on agriculture and transportation. Simi- larly, extremes of temperature and precipitation and severe weather are major hazards to human health. Exposure to airborne contaminants also has impacts on the environment and human health, as evidenced by the use of human and environmental health as criteria in setting air pollution standards. Cases of injury to plants and human health caused by exfreme concentrations of airbome pollutants are well documented in the bteraturc. Atmospheric deposition of airbome nutrients and contaminants is more important to ecosystem health than human health at current levels. Benefits may be realized from the atmospheric deposition of nutrients to agricultural lands, although excess nufrients in water bodies can lead to problems. Deposition of acidifying substances can lead to acidification of water bodies and ecosystem damage in certain situations. REPORT COMPONENTS AND STRUCTURE An assessment of the status of the atmospheric environ- ment must include statements related to both its physical features (which over the short term we call weather, and over the long term, climate), its chemical composition, primarily as related to the concentrations of pollutants in air and precipitation, and the deposition of airbome materials back to the earth's surface. An assessment of the state of Illinois' atmospheric environ- ment should include representations of both the spatial distributions and the time history of important features of weather and climate, as well as pollutant concentra- tions and deposition. This report is composed of three major sections: Cli- mate Trends in Illinois, Air Quality Trends in Illinois, and Atmospheric Deposition Trends in Illinois. Each presents information on the current status and temporal and spatial trends of important features of the Illinois environment, based on currently available data. CLIMATE TRENDS IN ILLINOIS CLIMATE TRENDS IN ILLINOIS Kenneth E. Kunkel, Wayne M. Wendland, and Stephen J. Vermette Illinois State Water Survey INTRODUCTION This report presents an analysis of climate trends since the late nineteenth century in Illinois. This work was pursued under the Critical Trends Assessment Project (CTAP) of the Illinois Department of Energy and Natural Resources. Weather and climate events have significant impacts on many socioeconomic and environmental aspects of Illinois. Therefore, an anal- ysis of climate trends provides the necessary back- ground for understanding trends in other aspects of the Illinois environment. Significant climate variability can occur at virtually all time scales. Therefore, a variety of climate data and information from Illinois sites are assembled here in order to investigate the temporal variability of various climate parameters. In addition to studying statewide changes in annual temperature, precipitation, and other climate parameters since the turn of the century, changes by month and by season and in the frequency of extreme events will be investigated over the period of record. CAUSES OF CLIMATE Climate is a description of the overall character of daily weather conditions that is manifested from season to season and from year to year. It is the sum of all statistical weather information that describes the average and variability of weather at a given place. Climate does not include information on the weather of a particular day. We investigated changes in the frequency and magni- tude of several climatic parameters. Some of these yield a clear indication of a U-end. For example, all stations indicate a common temperature trend over the past 100 or more years, with associated changes in related climatic parameters such as degree-day totals, cloud cover, frequency of frozen precipitation, etc. It is not yet possible to definitively identify the specific causes of these trends. However, it is useful to discuss in a general way some of the possible causes of climate variability to provide a perspective on the analyses presented in this report. Ultimately, the climate of the earth is driven by energy received from the sun. Although some of that energy is reflected back to space, most of it remains in the atmo- sphere to provide the fuel for global circulation patterns. The single most important variable affecting climate at a particular point is latitude because this affects the total amount and seasonal distribution of solar radiation reaching the surface at that point. The mid-latitude location of Illinois results in a substantial variation in the amount of solar radiation received between winter and summer. Thus, the seasonal vari- ation in climate is relatively large. It is known that variations in the orbit of the earth around the sun result in cyclic variations in solar radiation on time scales of greater than 10,000 years. Many scientists believe this to be a major factor in the periodic occurrences and retreat of ice ages. However, on shorter time scales (100 years or less), it is not known with certainty whether significant variations in solar radiation occur. Measurements of solar radiation are not accurate enough nor of long enough duration to identify significant fluctuations. Another major factor affecting climate is the distribu- tion of continents and oceans. It is known that tempera- ture differences between the ocean surface and the land surface are a major factor in establishing certain circu- lation patterns in the atmosphere. For instance, during the summertime, the Atlantic Ocean is cooler than the North American continent. This results in a pressure difference (high pressure over the ocean, low pressure over the continent) that forces a southerly flow of air over eastern North America, transporting significant moisture from the Gulf of Mexico into Illinois. This gives us our humid summertime climate with generally abundant rainfall. It is known that fluctuations in ocean surface tempera- tures can occur and that these can cause fluctuations in climate that are of significance. The El Niiio phenom- enon is one example, where a warm pool of water develops aperiodically over the eastern equatorial Pacific. This warm pool of water and the associated disruptions in equatorial wind patterns are known to have effects on climate in many other parts of the globe. It is possible, even probable, that fluctuations in ocean surface temperatures in the Pacific and the Atlantic have effects on climates thousands of miles CLIMATE TRENDS IN ILLINOIS away and may be responsible for some significant fluctuations that have occurred in the past. However, it is very difficult to identify such ocean temperature changes as the clear cause of any particular climate fluctuation experienced in Illinois. The radiation balance and energy transfer within the atmosphere are influenced by the composition of the atmosphere. Some constituents of the atmosphere, notably carbon dioxide, methane, chlorofluorocarbons, and water vapor, limit the loss of infrared radiation by the earth to space. These have a net warming effect on surface temperatures. It is well known that the concen- tration of many of these gases are increasing because of human activities, such as the burning of fossil fuels. If all other causes of climate were to remain constant, we would expect that the temperature at the surface of the earth would increase as the concentration of these gases increased. However, it is still too early to ascribe ob- served changes in Illinois climate solely to this cause. Other factors may also play a role in modulating Illinois' climate. For instance, volcanic eruptions can inject large amounts of dust into the earth's strato- sphere. This can decrease the amount of solar radiation reaching the earth's surface for a year or more in some cases. It is likely that past volcanic eruptions have caused significant changes in the earth's climate. For instance, the recent interruption of Mt. Pinatubo is believed to have resulted in a temporary decrease in global surface temperature of PF. In large urban areas such as Chicago, the change from a natural or agricul- tural land surface to large percentages of paved areas and buildings can cause a local change in climate. Urban areas tend to be warmer than nearby rural areas. Since there are multiple factors that can affect Illinois' climate, it is difficult, if not impossible, to cite a specific cause for any particular feature or trend in Illinois' climate. DATA Data from two major categories of climate stations are analyzed in this report. The first category includes the National Weather Service (NWS) First Order Sites (FOS). They provide data from at least hourly measure- ments taken at major airports. The data are derived from continuous observation of cloud cover, visibility, pressure, temperature, dew-point temperature, winds, hydrometeors, and other obstructions to visibility. This very detailed set of observations is archived in digital form for only five sites in Illinois. The second major category of observing sites are those of the NWS Cooperative Observer Network (CON). This network is composed primarily of individual and institutional volunteers who obtain measurements on a daily basis for the NWS. The NWS provides the mea- surement equipment, and for the most part, the observers are not paid. The observations include daily maximum and minimum temperatures, daily precipita- tion, daily snowfall and snow depth, and in a few cases soil temperature and pan evaporation. Although these observations are not as detailed as those for the FOS network (they provide daily rather than hourly observa- tions), the network is much denser and therefore offers a much-used, quality dataset. For this report, 41 CON stations have been selected, each with long-term data extending back to the turn of the century. For purposes of climate applications, the NWS has divided the state into nine regions, known as "climate divisions." They are shown in figure 1. The National Climatic Data Center has developed a special dataset that consists of temperature and precipitation values averaged for all stations, as available in each of these climate divisions. These values are available monthly from 1 895 through the present. Because this is a rela- tively compact dataset and incorporates information for all available stations, these data were used to assess overall trends in precipitation and temperature. Data from individual stations were used to assess trends in more detailed aspects of temperature and precip- itation that are not available by climate divisions. Although climate division values are available for monthly average temperature and monthly total precip- itation, no such data are available on a daily time scale. Therefore, trends in the following climatic elements were assessed from the data from individual stations: Temperature • Monthly maximum and minimum temperatures. • Number of days with daily mean temperature above 50°F. This threshold is examined because the rate of growth and development of com and soybeans becomes significant when the daily mean temperature is above 50"F. • Extreme daily maximum temperature. This is the highest single daily value occurring in a month. • Extreme minimum daily temperature. This is the lowest single daily value occurring in a month. • Number of days with daily minimum temperature above 70°F. This is a somewhat arbitrary threshold that is meant to represent summer nights of abnor- mal warmth. CLIMATE TRENDS IN ILLINOIS Figure 1. Illinois climate divisions, designated by the National Weather Service. CLIMATE TRENDS IN ILLINOIS • Number of days with daily minimum temperature below QPF. This threshold is examined as a repre- sentation of particularly "cold" nights. • Number of days with daily minimum temperature below 32°F. This threshold is examined because the freezing point affects many processes. • Number of days with daily maximum temperature above 86°F. This threshold is examined because the rate of corn and soybean growth and develop- ment typically reach a plateau near this tempera- ture threshold. That is, above this threshold, the rate of crop growth and development no longer increases with rising temperature. • Number of days with daily maximum temperature above 9(yF. This is a somewhat arbitrary thresh- old, representing particularly warm days of dis- comfort to many people. • Number of days with daily maximum temperature above 100°F. This threshold is examined as a representation of the frequency of days of great discomfort to many people. Precipitation • Number of days with precipitation. • Number of days with precipitation of 1 inch or more. This threshold is examined as a somewhat arbitrary representation of rather heavy rain days. • Total monthly snowfall. • Number of days with snowfall. METHODOLOGY - STATISTICAL TECHNIQUES Trends in Means In order to detect potential trends in climate, several variables were subjected to a mathematical process to remove the seasonal cycle in the data. This process was performed on climate division values of monthly temperature and monthly precipitation and on station values of monthly minimum and maximum tempera- tures. Specifically, the data were "standardized" with the following formula: X . = (x - x )/s. where x^ is the value for year i and month j; x! is the average over all years of the values in month j; and s is the corresponding standard deviation for those values. These converted values are referred to as "Standard- ized" temperature and precipitation. They express the values in terms of the number of standard deviations above or below the mean. The climate division time series consisted of 1,164 data values for each element (97 years x 1 2 months). Over- all trends were assessed by subjecting the time series to a linear regression; the statistical significance of the resulting trends was tested using a t-test for signifi- cance of slope of the regression (Draper and Smith, 1981). Trends in individual seasons were also assessed. The meteorological definition of seasons was used: • Winter (December 1 through February 28/29) • Spring (March 1 through May 31) • Summer (June 1 through August 31) • Fall (September 1 through November 30) Seasonal values were obtained by averaging tempera- ture over the three months and totaling precipitation over the three months. Thus, the resulting seasonal time series each consisted of 97 data points. For the time series of individual stations, only 91 years of data were available. For variables involving the number of exceedances in temperature and precipitation and for monthly snowfall totals, the monthly values were summed for each year. The resulting data (91 data points) were subjected to the regression analysis for trend indicated above. The extreme monthly maximum temperatures were ana- lyzed by taking the highest value in each year and subjecting each of the 91 values to the regression anal- ysis for trend. The lowest extreme monthly minimum temperature value for each year was also assessed for trend in this manner. In all of the above regressions, the trends were tested for significance at the 10 percent level using a two- sided t-test. Variance Assessments In addition to testing the time series for trends in the mean, the data were also analyzed for changes in the variability of temperature and precipitation over the period of record. A subjective analysis of the time series suggested that certain periods of time, a decade or more in length, were characterized by significantly less or more variability than the rest of the time series. To assess this, the climate division values of tempera- ture and precipitation were broken into six 15-year segments, beginning in 1901. For each 15-year subset 10 CLIMATE TRENDS IN ILLINOIS of data, the standard deviation of the time series was calculated. The resulting data were plotted and sub- jectively analyzed. Temperature and Precipitation Index An additional objective of this study was to identify certain periods of time characterized by specific cli- mate conditions — in particular, multiyear periods characterized as: • Warm and wet • Warm and dry • Cool and wet • Cool and dry To assess these conditions, two combined temperature/ precipitation indices were defined and calculated as follows: • Index 1 = standardized temperature + standardized precipitation • Index 2 = standardized temperature - standardized precipitation The association between these indices and the above scenarios is: • Warm and wet (large positive values of Index 1 ) • Warm and dry (large positive values of Index 2) • Cold and wet (large negative values of Index 2) • Cold and dry (large negative values of Index 1 ) Modifications to this rather straightforward categoriza- tion scheme were required, as will be explained as part of the section Anomalous Episodes from the Illinois Climate Record. Time series of the index were plotted and examined to identify multiyear periods with the above climate conditions. TRENDS IN PRECIPITATION Trends in Average Precipitation Mean annual statewide precipitation, averaged for all available stations since 1840 is shown in figure 2. The data are considered to well represent statewide condi- tions since about 1890, by which time the annual values were derived from at least 113 stations in the state. The "statewide" totals during the 1880s were based on 1 8 stations; on six or seven stations from 1852 to 1880; and on only one station (Athens, Sang- amon County) ft-om 1840 to 1851. Because of the paucity of data prior to about 1 890, some care must be exercised in its interpretation. If representative, they indicate a slight decline in annual precipitation from the mid- 1 800s to about the turn of the century, with an increase thereafter. However, as shown, the year-to- year variation is the dominant characteristic of statewide precipitation, as with an individual station's record. The statewide mean annual precipitation record based on 150 to 200 sites for each year (figure 3) has varied widely from 25 to 50 inches. (Figure 3 duplicates the more recent portion of figure 2. This time frame facili- tates comparison with other figures in this report, most of which cover the period from 1901 to 1991.) Occa- sionally, consecutive years exhibit similar anomalies, but in the vast majority of cases, one year's precipita- tion is unrelated to that of the next. The statewide average is about 37 inches, with about 5 inches less in northern counties and about 5 inches more in the south. No obvious discontinuity in statewide annual precipita- tion has occurred since 1901. Changnon (1984), in an analysis of data through 1980, also noted that year-to- year variability was the dominant characteristic of the time series. He noted a slight tendency for lower values during the period 1910 to 1940 compared to values both before and after that 30-year period. A close examination of figure 3 does suggest this. In addition, an analysis of trends of individual stations (reported later) also suggests a general upward trend in precipita- tion during this century. However, this trend is weak compared to the short-term variability. The number of days per year with precipitation (averaged for all long-term stations) exhibits a some- what stronger upward trend since 1901 (figure 4) than does annual precipitation. The number of days per year with precipitation appears to have increased by about 10 during the 90 years of record, although variability appears to increase as well. The annual number of days per year with precipitation trended upward with lime at nearly all the 4 1 long-term stations; only Carbondale (Jackson County) and Wal- nut (Bureau County) digressed. Thus, the trend has been rather ubiquitous throughout the state. However, several of these upward trends were rather weak and not statistically significant. The number of days per year with at least 1 inch of precipitation (with a present recurrence frequency of 11 CLIMATE TRENDS IN ILLINOIS O CD O O CJ :Cn ._ ■T- a >- O O e 5 3 O I o s c c 3 •Si to s _oo (uj) uojiBijdpajd 12 CLIMATE TRENDS IN ILLINOIS 60 55 504 45 ^ 40H c '^ 35 o ^ 30 a "<^ 25 >_ CL 20 15- 10 5 W+ 1901 1911 1921 1931 1941 1951 1961 1971 1981 Year 991 Figure 3. Statewide average annual Illinois precipitation composed of available sites, 1901-1991 (inches). 13 CLIMATE TRENDS IN ILLINOIS 150 140- 130- 120- co 110^ £ 1004 o =»*: 90H 80- 70- 60- 50- 1901 19 1 1921 1931 1941 1951 Year 1961 1971 1981 1991 Figure 4. Average annual number of days per year in Illinois with precipitation. 14 CLIMATE TRENDS IN ILLINOIS about once every other month in Illinois) is shown in figure 5. As with the above two precipitation measures, identification of trends is difficult. Nonetheless, a slight decline appears during the first few decades with an increase during recent decades. The days per year with a least 1 inch of precipitation at individual stations in the state all exhibit upward trends, except for White Hall (in Greene County). Changnon (1984) found a general increase in the number of days with rains of 2 inches or more during the warm season. In addition. Huff and Angel (1989) found that the frequency of very heavy rainstorms had increased from the early part of this century to the latter part. To summarize temporal trends in precipitation over the state, magnitude (figure 2) appears to decline from 1840 to about the 1930s, increasing thereafter. The frequency of precipitation events appears to have increased slightly in the 90 years since 1901, paralleling the trend in annual precipitation. Much more significant is the substantial year-to-year variation. Trends significant at the 10 percent level, were identified for 9 to 21 of the 41 sites for the five precipitation parameters. Trends for individual stations are listed in appendix table A. 1 , and a summary is given in table 1. Interestingly, nearly all these trends were positive, except for the number of days with measurable snowfall. Sites in northern and east-central Illinois were somewhat more likely to have experienced significant trends than sites in other parts of the state. Trends in Snowfall Annual snowfall for the state since 1901 (figure 6) shows some rather clear characteristics: 1 . Decline from 1901 to the 1930s. 2. Increase from the 1930s to the 1980s. 3. Decline in the last decade. 4. Continuity from year-to-year over episodes of three to six years. For example, note similar snowfall amounts from 1903-1906, 1919-1923, 1939-1945, 1952-1959. 1961-1965, and 1987-1991. Because the year-to-year variation is so large, five-year r\jnning averages of statewide annual snowfall were calculated (figure 7). This figure exhibits a slight increase with time, but much more apparent is the fluctuating nature, as with annual precipitation. Fluc- tuations in annual snowfall exhibit secular episodes of about 13 years, varying from 7 to 17 years since 1901. In general, years with greater than average snowfall also experienced a greater than average number of days with snowfall (figure 8). A decline in the number of days with snowfall is apparent from the turn of the cen- tury to the early 1930s (coincident with the warming shown in figure 11), with a possible increase thereafter. More prominent than frends are the several years with relatively high frequencies of days with snowfall, notably, 1914, 1924, 1951, 1960, 1977, 1978, and 1980. Of 16 Illinois locations with statistically significant trends in annual snowfall (table A. 1 , p.72), five (four in east-central Illinois) exhibited declines, whereas 1 1 indicated increases in annual snowfall from 1901 to 1991 (table 2). Such differences in trend are not likely within such a relatively small area, emphasizing a problem with snowfall observations, i.e., they are extremely sensitive to the exposure of the site, as well as the method used to determine snowfall (precipitation in a gage, average of several depth measurements, or density of snow cores). Trends in Variability Trends in year-to-year variability in precipitation were examined by separating the precipitation data into 15- year segments, beginning with the period 1901-1915. For each 15-year segment, the interannual standard deviation of precipitation was calculated for each sea- son (figure 9). For the summer, a notable feature is the low variability during the period 1961-1975, as opposed to much higher variability from 1901 to 1945 and 1976 to 1990. Figure 10 shows summer precipitation for this century. The low variability during 1961-1975 is the result of an absence of severe summer droughts during the 1960s and 1970s. More frequent droughts during the period 1976-1990 have made variability similar to that during the earlier part of the century. A period of relatively low variability also occurred during the fall in the 1940s, 1950s, and 1960s. By contrast, the period 1916-1945 was characterized by the highest variability. For the winter season, the first half of the century exhibited very low variability com- pared to the second half The greatest variability was exhibited from 1946 to 1960, virtually opposite to the trends for summer. Finally, during the spring, high variability was experienced between 1916 and 1945, with low values before and after, essentially the same trends as those of fall. 15 CLIMATE TRENDS IN ILLINOIS 20 CO Q O 184 16 14 12- 10- 8- 6 4 2 -TTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTT 1901 1911 1921 1931 rrn rrT'TTrrT'TT'TTTTrrTrTrrTrrTrTTTTrrTrTrrTrrTr 1941 1951 1961 1971 1981 1991 Year Figure 5. Average number of days per year in Illinois with at least 1 inch of precipitation. Table 1. Summary of Precipitation Parameter Trends Precipitation parameter Number of stations Number of stations with statistically significant with statistically significant upward trends downward trends Days with precipitation Days with precipitation >1 inch Total precipitation Total snowfall Days with snowfall 19 8 II 11 10 2 1 5 11 16 CLIMATE TRENDS IN ILLINOIS 1901 1911 1921 1931 1941 1951 1961 1971 1981 1991 Year Figure 6. Average annual snowfall in Illinois (inches). ow: 4S- 40 : 35] g 30] w 2o: 15i in- : : ^ . / \ 1^ p. ^y\ / ^ \^ /^ \ I V \T^ >^ w "^ Y 1 'J. 0- 1 1 1 1 n n 1 j 1 1 1 1 1 1 r 1 1 j 1 1 1 1 1 r 1 r 1 1 1 n u 1 1 li I n run n niTTTTTr 1 1 1 1 1 1 M 1 IiniTITT m 1 II 1 II 1901 1911 1921 1931 1941 1951 1961 1971 1981 1991 Year Figure 7. Running five-year averages of Illinois annual snowfall (inches). 17 CLIMATE TRENDS IN ILLINOIS 30 28 26- 24- 22- 20 CO 18 I 16^ *S 14 1o^ 8 6- 4- 2 rr 1901 1911 1921 1931 1941 1951 1961 1971 1981 1991 Year Figure 8. Statewide average number of days per year in Illinois with snowfall. Table 2. Stations where Annual Snowfall Significantly Increased or Decreased (Linear Regression Analysis), 1901-1991 Decreased Flora Hoopeston Olney Pontiac White Hall Increased Aledo Palestine Anna Pana Dixon Paris Effingham Urbana Griggsville Walnut Marengo Note: Significant at the 10 percent level. 18 CLIMATE TRENDS IN ILLINOIS ft a u Summer + Fall ■-^- Winter A Spring 1901-1915 1931-1945 J 1961-1975 1916-1930 1946-1960 1976-1990 Year Figure 9. Standard deviation of 15-year segments of Illinois statewide precipitation by season, 1901-1915 to 1976-1990. Q) D) CO 0) E o > Q c o ■(5 o 10 8 6 4H 2 -2- .4-1. Jl -6- -8 i| J.JLy -10 'ii I II II I II i i I II II M l II I II 1 1 1 I I 1 1 1 I I II I II 1 1 1 1 1 1 II II 1 1 1 II 1 1 1 II I II [1 1 1 [ II 1901 1911 1921 1931 1941 1951 1961 1971 1981 1991 Year Figure 10. Statewide summer precipitation (inches) for Illinois, 1901-1991, expressed as the deviation from the period average. 19 CLIMATE TRENDS IN ILLINOIS TRENDS IN TEMPERATURE Trends in Average Temperature Changnon (1984) presented an analysis of trends in statewide average annual temperatures for Illinois for the period 1940 to 1980. His analysis is extended here to 1991 and presented in figure 11. The number of observing sites prior to 1 890 is limited, as they were for statewide precipitation. Temperatures in Illinois follow a similar trend to those of the nation, i.e., rather stable temperatures during the first few decades (with a state- wide mean of about 50°F). A warming trend follows until about 1930 (to about SS"?), after which cooling reduces the mean to about 52"? by 1980, with wanning suggested thereafter. Cool temperatures during the first few decades refiect an expression of what has been called the "Little Ice Age" (Lamb, 1966). It is impor- tant to recognize that temperatures cooled substantially from the 1930s to 1980 or after (a similar trend for the Northern Hemisphere), five decades during which carbon dioxide was increasing! Mean annual Illinois maximum and minimum tempera- tures since 1901 (figures 12 and 13, respectively) both exhibit similar trends, i.e., warming of 2 to 3°F from 1901 to the 1930s, followed by an equivalent cooling through about 1980, and the suggestion of warming again during the last few years. These trends are not surprising, since they are found in temperature records from the entire United States, the Northern Hemi- sphere, and the world, although the magnitudes of change decrease with ever-increasing areas of interest (e.g., Wigley and Bamett, 1990). The average maxima and minima exhibit extremes dur- ing the same years, i.e., those much warmer or colder than the long-term average, e.g., 1917, 1921, 1924, 1931, 1978, 1979, etc., throughout the period of record. There is no evidence of periodicities. The interseasonal fluctuations of average statewide sum- mer maxima (figure 14) and those of average statewide winter maxima (figure 15), are quite different from each other. This is not unexpected, since temperature anomalies seldom continue longer than just a few months, and, meteorologically, one would not expect similar temperature characteristics to prevail from one season to another. Similar comments apply to statewide winter and summer minima (not shown), i.e., the interseasonal fluctuations need not parallel each other, and they do not The mean number of days (averaged over all stations) with temperatures above 100"F (figure 16) are indeed few, particularly during the most recent decades, which are exhibiting cooling. Several years, namely 1901, 1913, 1930, 1934, and particularly 1936, ex- hibited high frequencies of such days, all during the first four decades of the record. Years with a high frequency of days with temperature greater than 100"? tended to occur in episodes composed of a few sequential years, e.g., 1913-1914, 1930-1936, 1939-1941, and 1952-1954, all of which represented major droughts! The statewide average number of days per year with maximum temperatures above 86°F (figure 17) exhibits trends similar to those shown in figure 16, although the absolute frequencies are greater. The 1930s experi- enced more days with higher temperatures than any other decade on record. Figures 18 and 19, showing the number of days per year with maximum temperatures below 32° and below 0°F, respectively, exhibit inverse trends to those found in figures 16 and 17. More frequent cooler maxima have occurred since about 1960 than before. This trend suggests that the cooler 1960s, 1970s, and early 1980s comprised more frequent cool days, as opposed to cooler extremes only. Note the relatively high fre- quency of cold maxima in 1912, 1924, and 1936 in both figures 18 and 19. The relatively high frequency of maxima below 32°F in the late 1960s, 1970s, and early 1980s is also seen in the frequency of maxima below 0°F (figure 19). Figure 20 presents the statewide average number of days per year when the minimum temperature ex- ceeded 70°F. Not surprisingly, the trend follows that of average temperature and maximum and minimum temperatures, with increasing frequency from 1901 until the 1930s, a decline thereafter, with a possible increase again during the last few years. It should be noted that the high frequencies of 1913, 1931, 1934, and 1936 have not been equaled in Illinois since. Figure 2 1 shows the statewide average number of days per year when the minimum temperature was below 32"F. A declining trend may be suggested from 1901 to perhaps the mid- 1940s, with either stable frequencies or perhaps a slight increase thereafter. Figure 22 presents the statewide average number of days per year when the minimum temperature was below 0"F. Such frequencies were decidedly minimal during the 1940s and 1950s, which were warm dec- ades. The highest frequency of such days occurred in 1936, 1963, 1977-1979, and 1985. 20 CLIMATE TRENDS IN ILLINOIS » CO Q 0) 0) i_ D) < E o k_ c o (0 ■> CD Q CO (0 Q 0) 0) D) < E o c o ■> Q) Q I w CO Q 0) 0) D) Q) Q -700 1901 1 1 1 1 1 1 1 1 1 I I I 1 II I i I 1 1 1 1 I I 1 1 1 1 1 1 1 II 1 1 1 i 1 1 1 1 1 1 1 1 1 i 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 M 1 1 1 1 1 1 1 1 1 1911 1921 1931 1941 1951 1961 1971 1981 Year 1991 Figure 26. Five-year running averages of statewide mean cooling degree-days for Illinois, presented as deviations from period mean, 1901-1991. 37 CLIMATE TRENDS IN ILLINOIS 3900 3700 3500 P ^ 3300 P 5P3100^ 2 O 2900 2700- 2500 1878 1898 1918 1938 1958 1978 Year Figure 27. Average Illinois annual corn growing degree-days, 1878-1992. 38 CLIMATE TRENDS IN ILLINOIS 230 in >• (0 2, c o w (0 0) CO c 01 150 1901 1911 1921 1931 1941 1951 1961 1971 1981 1991 Year Figure 28. Statewide average length (days) of the growing season for Illinois (defined for both 28"F and 32''F). 1901-1991. 1901 1911 1921 1931 1941 1951 1961 1971 1981 1991 Year Figure 29. Statewide average day (Julian day number) of last spring frost in Illinois (defined for both 28"F and 32''F), 1901-1991. 250 '1 1 1 1 1 [ 1 1 1 1 1 1 m ill I ri 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 11 1 1 1 1 1 1 1 1 1 1 1 1 1 I ll' 1901 1911 1921 1931 1941 1951 1961 1971 1981 1991 Year Figure 30. Statewide average day (Julian day number) of first autumn frost in Illinois (28"F and 32''F), I90I-I99I. 39 CLIMATE TRENDS IN ILLINOIS Table 3. Summary of Growing Season Trends Freeze thresholds Number of stations with trends toward later (longer) freezes (growing season) (statistically significant trends given in parentheses) Number of stations with trends toward earlier (shorter) freezes (growing season) (statistically significant trends given in parentheses) Last spring freeze (threshold = 32°F) Last spring freeze (threshold = 28°F) First fall freeze (threshold = 32^) First fall freeze (threshold = 28°F) Growing Season Length (threshold = 32°F) Growing Season Length (threshold = 28°F) 5(0) 6(0) 24 (10) 24(13) 30(17) 26 (16) 36 (24) 35 (11) 17(5) 17(4) 11(3) 15(4) Table 4. Summary of Trends in Temperature Parameters of 40 Illinois Sites Temperature parameter Number of stations with upward trends (statistically significant number in parentheses) Number of stations with downward trends (statistically significant number in parentheses) Average monthly temperature Average monthly minimum Average monthly maximum Highest temperature of year Lowest temperature of year Days with mean T > 50"F Days with T- max > 86°F Days with T- max > 90°F Days with T- max > 100°F Days with T- max < 0°F Days with T- max < 32°F Days with T- min > 70°F Days with T- min < 0"F Days with T- min < 32^ 16(5) 18(9) 13(3) 2(0) 23(3) 22 (12) 7(0) 2(0) 0(0) 40 (18) 36 (19) 18(7) 38(7) 21(6) 25(9) 23 (10) 26 (12) 39 (27) 18(0) 19(1) 34(18) 39 (29) 41 (21) 1(0) 5(1) 23(4) 3(1) 20(9) 40 CLIMATE TRENDS IN ILLINOIS reflects the high summer temperatures experienced during the 1930s and the relative absence of extreme high temperatures during the last three to four decades. This same feature is also evident in half or more of the sites in the number of days with maximum tempera- tures above 86°?, 90°F, and lOOT. This feature is in general agreement with the general downward trend in average temperature from the 1930s into the 1970s (figure 1 1). Although the average temperature record and the number of "hot" days in the last decade suggest a reversal of this trend, this change has not been of long enough duration or magnitude to overcome the large downward trend in the earlier period. Somewhat surprisingly, the number of days of extreme cold, identified as the number of days with maximum temperatures below OT (figure 19), has exhibited an upward trend at many stations. This was caused by a significant number of extren>ely cold arctic air outbreaks during the last 15 years. These outbreaks have even occurred with some frequency during the 1980s, a per- iod of generally very warm winters. This also reflects the strong influence of the very cold winters in Illinois dur- ing an extended period in the late 1970s and early 1980s. Trends in selected parameters (seasonal average, minimum, and maximum temperature and seasonal precipitation) were also examined by individual seasons. The results of this analysis are given in tables A.5-A.8 (beginning on p.82) for the autumn, winter, spring, and summer seasons, respectively, and summa- rized in table 5. Very few stations show statistically significant seasonal trends in total precipitation. How- ever, a number of stations show downward trends in temperature for autumn. Also, seven to eight stations show downward trends in winter temperature. Trends in spring are weakly positive. Trends in Variability An analysis of the trends in temperature variability are shown in figure 31 by season. For the summer season, the period 1961-1975 was characterized by the lowest variability. Figure 32 shows summer temperatures for this century. The low variability during 1961-1975 was the result of the absence of severe summer heat waves. By contrast, variability was much higher from 1976 through 1990, caused by more frequent summer heat waves. This latter 15-year period was quite similar to the first half of the century. For the fall season, low variability was experienced during 1901-1915 and 1945-1990, while higher variability characterized the years 1931-1945. For winter, 1976 through 1990 exhibited the greatest variability. This was the result of the very cold winters during the late 1970s, contrasted with the mild winters of the middle and late 1980s. The spring season was also characterized by high variability during the period 1976-1990, as was winter. Interestingly, trends of seasonal temperature variability in summer and fall parallel those of precipitation (figure 9), whereas those of winter and spring do not appear to be related. TRENDS IN CLOUD COVER Changnon (1984) presented the number of days per five years with cloudy skies (any cloud type or combi- nation covering 70 percent or more of the sky) at Springfield, St. Louis, and Evansville, IN (figure 33) and Peoria, Moline, and Chicago (figure 34), from 1901 through 1980. All six sites showed a rather steady increase in cloudy days for the period of record, from about 90 days per year for the first few decades of the century, to about 160 days per year after about 1940 and continuing to 1980. Additional data from 1981 through 1990 maintain the higher frequencies (figure 33), except those of Evansville, IN (figure 34). Chang- non (1984) questioned whether the increases might be due to greater frequencies of jet contrails, perhaps instead of or in addition to natural clouds. The question is as yet unanswered. Although Petersen (1990) reported that cloud observing techniques were changed in June 1951 by the National Weather Service, the cloud cover record does not exhi- bit any discontinuity during the period shown. Prior to June 1951, fractional amounts of only two possible cloud layers were observed and therefore recorded, plus the height of the lowest scattered layer. Following 1951, sky cover and cloud height were reported. Whether this procedural change may have biased the record has not been evaluated. Changnon et al. (1980) investigated temporal changes in cloud cover over Illinois from the turn of the century to 1977 (not shown). They demonstrated that the num- ber of cloudy days increased by about 50 percent from the early years (about 1 10 days per year in southern Dli- nois, and 140 days per year in the north) to about 160 days per year in the south, and 180 such days in the north. Petersen (1990) further calculated seasonal solar radia- tion since 1948 at several locations about the Midwest, based upon surface pressure, dew-point temperature, cloud height, and fractional sky cover. The results 41 CLIMATE TRENDS IN ILLINOIS Table 5. Summary of Seasonal Trends in Selected Temperature and Precipitation Parameters (Number of Stations) (Statistically Significant Counts in Parentheses) Season Autumn Winter Spring Summer Average Average minimum Average maximum Total temperature temperature temperature precipitation Trend (°F/decade) CF/decade) CF/decade) (inches/decade) Upward 14(1) 17(6) 10(0) 35(3) Downward 27 (14) 23(11) 30 (14) 6(0) Upward 8(0) 10(0) 9(0) 27(0) Downward 33(7) 31(8) 32(7) 13(0) Upward 26(5) 26(11) 24(1) 35(5) Downward 15(2) 15(2) 17(3) 6(0) Upward 18(5) 20 (13) 13(0) 31(5) Downward 22(9) 21(6) 28 (10) 10(0) ^4 .2 4-) V Q 4J a u g K .^K "N" X *-' V IT A Summer + Fall -^- Winter dk-- Spring 1901-1915 1931-1945 1961-1975 1916-1930 1946-1960 1976-1990 Year Figure 31. Standard deviations of 15-year segments of Illinois statewide average temperature, 1901-1915 to 1976-1990. 42 CLIMATE TRENDS IN ILLINOIS 0) 2 > < E o > Q> Q 2 270- < Q O I 220; % 195- 170 Moline Springfield St. Louis 1901 ' 1911 ' 1921 ' 1931 ' 1941 ' 1951 ' 1961 ' 1971 ' 1981 ' YEARS Figure 38. Average number of days with thunderstorms per five years (plotted on first of the five years) for Moline, Springfield, and St. Louis, MO. 48 CLIMATE TRENDS IN ILLINOIS 120 i2 100- 80- 60 40- 20- O-Mnrl^ illllyJ li ljiiiiiil l ii lliiii i li l jjhi i [ n iiiiiniinnii m innnnnnnniin m inn m i nun ii u niii m ii mim nnni m nnnnnnnn 1845 1865 1885 1905 1925 1945 1965 1985 Year Figure 39. Number of reported tornadoes in Illinois (figure 7 from Wendland and Guinan, 1988), 1845-1990. 49 CLIMATE TRENDS IN ILLINOIS The annual record of the number of days with tornadoes in the state since 1960 (figure 40) exhibits several features: 1 . Annual frequencies hover about a mean of about 1 1 tornado days per year from 1962 to 1971. 2. About 35 tornado days occurred in five consecu- tive years, 1973 through 1977. 3 . About 25 tornado days occurred per year thereafter. As to areas of the state that might seem to "favor" tor- nado activity, raw tornado frequencies clearly peak in those counties with greater population densities (Wend- land and Guinan, 1988). The authors believe, however, that this relationship results merely from the fact that more people are likely to see and report isolated, small- scale events as tornadoes, and does not represent an actual urban enhancement of tornado frequency. Trends in the Frequency of Severe Snowstorms Severe snowstorms in Illinois are defined as those where 6 inches or more snow or freezing precipitation of any intensity falls over at least 10 percent of the area of the state within a 48-hour period. These storms exert tremendous hardship on those within the area of impact in terms of disruption to commerce, communication, comfort, and economics. As opposed to the historical tornado record, that for severe winter storms is believed to be rather well defined since the turn of the century because each such storm generally impacts an area of some 15,000 square miles and would therefore be recorded by observations from 50 or more NWS Coop sites, even in areas of less population density than represented today (Changnon, 1969, 1978). Newspa- pers have proven to be a reliable source for a relatively complete record of severe winter storms, whereas tornadoes are not necessarily so reported, due to their relatively small area of impact (on the order of a few tens of square miles). From the turn of the century to the early 1960s, severe winter storms have occurred about five times per winter (figure 41). After the early 1960s, the frequency has declined to about three such storms per winter. Winters with greatest severe storm frequencies include 191 1-1912 with 12 storms, and 10 each in 1925-1926, 1943-1944, and 1950-1951. There were no severe winter storms in ten of the last 30 winters, including 1961-1962, 1962-1963, 1965-1966, 1967-1968, and 1968-1969, 1970-1971, 1980-1981, 1981-1982, and 1982-1983, and 1991-1992. The record of severe winter storm frequencies in Illinois somewhat parallels that of temperature, sug- gesting increased winter storm frequency with increased mean temperatures. This relationship may be due to a number of factors, including greater moisture supplies during warmer winters, a more northerly storm track during the middle of winter, etc. However, this study did not examine specific factors for this relationship. Trends in Illinois Droughts Drought can be measured by several techniques. In this instance we restrict our discussion to meteorological drought, i.e., a shortfall of precipitation. We present the percentage of the state experiencing 50 percent or less of the 30-year average precipitation during July and August from 1901 through 1991. The second uses the same threshold but for the full growing season, April through August, also from 1901 through 1991. Five of the July- August droughts (figure 42) impacted at least 50 percent of the area of Illinois during the period 1901-1992, notably 1991 (impacting 79 percent of the state), 1930 (70 percent), 1936 (51 percent), 1971 (66 percent), and 1983 (55 percent). The recent 1988 drought impacted only about 30 percent of the state by this criterion. According to the more stringent criterion, 50 percent or less than average precipitation from April through August (figure 43), a somewhat different distribution emerges, with extraordinary droughts in 1914 and 1936 (impacting about 60 percent of the state) and 1988 (54 percent). Neither 1914 nor 1988 were particularly note- worthy according to the different criterion, 50 percent or less precipitation during July and August. However, those years (particularly 1988) were characterized by extraordinary dryness in late spring and early summer. Temporal Changes in Visibility There has been and continues to be concem as to whether the atmosphere is becoming more turbid with time, perhaps due to industrialization, increased plowing and cultivation frequencies etc. Such a change could lead to reduced insolation, and related reduction in surface temperature, atmospheric clarity, and visibility. Although measurements of atmospheric turbidity are not gener- ally available, we use several proxy records, including visibility and finequency of days with smoke or haze. Wendland and Bryson ( 1 970) discussed a simple rela- tionship between mean temperature, carbon dioxide (CO,) concentration, atmospheric turbidity and sun- spots from 1880 to 1960. Using dust concentrations obtained in high snowfields of the Caucasus (Davitaia, SO CLIMATE TRENDS IN ILLINOIS 50 45 40 cd ^30 -d §25 u ^15 10 5 O'TTTfTfTTTTTTTTffTfTTTTTTT 1960 1965 1970 1975 1980 1985 Year Figure 40. Number of tornado days in Illinois per year (Wendland and Guinan, 1988), 1960-1985. 51 CLIMATE TRENDS IN ILLINOIS 'iTTrTTTTrTTTTrTTTTrTTTTrTITTrTTTTTrTTTTrTTTrrTTTTrTTTTrTITTrTl iTTlTllTlTTTTrTriTl llTTriTTTri 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 Year Figure 41. Number of severe winter storms per year in Illinois (defined as an area with at least 6 inches of snow or any amount of glaze within 48 hours, over 10 percent or more of the state), 1900-1992. 52 CLIMATE TRENDS IN ILLINOIS 80 70- <^60 4J "Sso 8,40 o30 u 20- 10- I 1901 1911 1921 1931 1941 1951 Year h 961 1971 1981 ll tT 991 Figure 42. Percent of Illinois impacted by 50 percent or less average precipitation during July-August, 1901-1992. 53 CLIMATE TRENDS IN ILLINOIS 60 50 0) 8,30 2 ^20 10 rlU if II iiT iTllTllllllTTllllllTlTlTTlllTlTlTlTllllTllllTllllllTTlTllTlllTTlllTllTllllTTllTllllTlTTllTl 1901 1911 1921 1931 1941 1951 1961 1971 1981 1991 Year Figure 43. Percent of Illinois impacted by 50 percent or less average precipitation during April-August, 1901-1992. 54 CLIMATE TRENDS IN ILLINOIS 1965) which they suggest reflect integrated hemi- spheric loadings, they demonstrated that global mean temperature changes during those eight decades could be statistically explained by those three parameters. Specifically, the warming from 1 880 through the mid 1900s was primarily related to increases in CO^ concentration, whereas the cooling thereafter was primarily related to the dramatic increase in dust load- ings, noted during the 1940s and 1950s. Atmospheric clarity can be defined and measured several different ways. The concept of visibility, how- ever, is straightforward, the measurement technique has changed little over time, and hence visibility measure- ments of decades ago are generally comparable to those of today. Vinzani & Lamb (1985) showed declin- ing visibility at NWS sites in and around Illinois since 1950. We analyzed hourly observations of visibility since 1948 at Chicago-O'Hare, Moline, and Peoria. Frequencies of occurrences of visibilities in various categories were accumulated for each year. Following Vinzani and Lamb (1985), we estimated the values that were exceeded 60 percent and 90 percent of the hours. Trends in these values are shown in figures 44 and 45. The trends in the 60 percent and 90 percent exceedance values are upward at Chicago, indicating improving visibility. Decreasing trends in the 90 percent value are seen at Moline and Rockford. Decreasing trends in the 60 percent value are seen at Springfield. The increasing visibility at Chicago, in contrast to the negative or insignificant trends at the other sites, may be due to more stringent pollution controls on industry. Using yet another approach, Changnon (1987) showed that the number of smoke and/or haze days at six NWS First Order Stations in and around Illinois showed a dramatic increase from a few tens of days per year prior to the 1930s, to 100 or more days per year thereafter through 1980! We have updated the frequency of smoke and/or haze data through 1990 (figures 46 and 47), and find that the increased frequencies which abruptly began in the 1930s essentially continue to the present, though the highest frequencies at all sites were noted in the 1930s and 1940s. The values of the last few pentads continue at several times greater than pre- 1930 frequencies, but about half the maximum- ever values. ANOMALOUS EPISODES FROM THE ILLINOIS CLIMATE RECORD Global climate models (GCMs) suggest a future warm- ing in Illinois and redistribution of precipitation during the year under greenhouse-induced effects of additional trace gases into the atmosphere. What would the im- pacts of such climate changes be for Illinois? The model outputs provide only average conditions, although state resources vulnerable to climate are often influ- enced by interannual or multiyear anomalies or by several conditions not defined by GCMs. For example, the range of certain species of insects or vegetation in Illinois depends on such conditions as the number of frost-free days, the timing of precipitation events, and changes in diurnal temperature ranges, conditions not available from GCMs. The variability of a potential future climate may also be documented by studying the climates of the past. Identifying extreme seasons or years from the past that lie within the average conditions specified by the GCMs allows one to reconstruct variabilities and use past analogs to estimate future climates. Over the past century, notable months, seasons, and years stand out as having been particularly warm, cold, wet, or dry. Indeed, it is often thecombination of tem- perature and precipitation extremes that stand out and impact Illinois resources. For example, the Dust Bowl years of the 1930s were prominent for their extreme drought and warm temperatures as were the 1988 drought and 1993 floods. To understand how climate has varied over the past century, it is useful to isolate those episodes classified as 1 ) warm and dry, 2) cold and wet, 3) warm and wet, and 4) cold and dry. This characterization is also useful in grappling with the impacts of potential future cli- mates in Illinois. To identify combined temperature and precipitation extremes from the Illinois climate record, individual mean monthly temperature and precipitation values were recorded for each year between 1 895 and 1 99 1 and normalized relative to the 97-year average. The index for temperature is calculated as: I. = (T. T )/T,, where: I, = normalized monthly temperature T = average temperature for month in question T = 97-year monthly mean temperature T^j = 97-year monthly temperature standard deviation For precipitation, the calculation is: I = (P - P ) / P , p ^ I avg' sld 55 CLIMATE TRENDS IN ILLINOIS h — r~I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I r 1950 1955 1960 1965 1970 1975 1980 1985 1990 YEAR Figure 44. Visibility (miles) exceeded 60 percent of the time for Moline, Chicago, and Peoria, 1950-1991. 8 H 7-j O o 6- Q W w 5- w u X " 4- I— ( d S 3- 2 I — I — rn — I — I — I — I — I — I — I — I — I — I — I — I — I — I — I — I — I — I — I — I — I — I — I — I — I — I — I — I — I — I — I — I — I — I — I — I — >" 1950 1955 1960 1965 1970 1975 1980 1985 1990 YEAR Figure 45. Visibility (miles) exceeded 90 percent of the time for Moline, Chicago, and Peoria, 1950-1991. 56 CLIMATE TRENDS IN ILLINOIS 1000 1 1 I 1 1 1 T" 1901 1911 1921 1931 1941 1951 1961 1971 1981 Year -*— Moline Peoria -A- Springfield Figure 46. Number of days per five years when smoke and/or haze was reported at Moline, Peoria, and Springfield (abscissa date in the first year of the five-year periods). 1400 0"H — I — I — r — I — I — I — I — I — I — I — I — I — I — r — I — n 1901 1911 1921 1931 1941 1951 1961 1971 1981 Year Chicago --+— St.Lociis — A - Evansville Figure 47. Number of days per five years when smoke and/or haze was reported at Chicago, St. Louis, and Evansville. 57 CLIMATE TRENDS IN ILLINOIS where: I = normalized monthly precipitation P. = total precipitation for month in question P^^ = 97-year monthly mean precipitation P^^ = 97-year monthly precipitation standard deviation A normalized monthly value near zero indicates a tem- perature or precipitation value similar to that of the 97- year average. Values above zero represent positive deviations (warmer or wetter than the average). Values below zero represent a negative deviation (cooler or drier than the average). The magnitude of the deviation is expressed in standard deviation units, i.e., +1.0 indi- cates that the anomaly is one standard deviation greater than the period average. A seasonal normalized value was calculated for each season. Warm and dry, and cold and wet seasons were distin- guished by subtracting the normalized seasonal precip- itation from normalized temperature: large positive numbers represent the former, and large negative numbers represent the latter. Warm and wet, and cold and dry seasons were distinguished by adding the normalized seasonal precipitation and temperature values: large positive results represent warm and wet seasons, whereas large negative numbers represent cold and dry seasons. When adding the normalized values, results near zero indicate that either temperature or precipitation is greater than the mean by about the same amount that the remaining parameter is less than the mean. When subtracting normalized precipitation from normalized temperature, results near zero indicate near-equal anomalies for each parameter. An inherent problem occurs when interpreting the result of either adding or subtracting normalized values of temperature and precipitation. One relatively large normalized value will dominate the result of either process if the other normalized value is a very small number, i.e., very close to the long-term mean. When results from either addition or subtraction were near zero, they had to be individually studied to determine the significance of the number. In this study, small normalized values, those between -0.25 and +0.25, were set to zero. (Therefore some years in the follow- ing figures exhibit no difference from the long-term mean.) Normalized precipitation and temperature values were added and subtracted to identify warm and dry, cold and wet, warm and wet, and cold and dry statewide conditions for each of four seasons between 1895 and 1991. Statewide Summer Index The combined indices for summer are plotted in figures 48 and 49. They show a high frequency (over three times as likely) of warm and dry, and cold and wet summers, as opposed to summers that were either warm and wet, or cold and dry. In addition, the magni- tude of the latter index is much less than that for warm and dry, and cold and wet summers. As expected in a continental climate, heat waves are more likely to be associated with moisture deficiencies, and cool sum- mers are more likely associated with excess moisture. The combined extremes of warm and dry, and cold and wet summers are more pronounced than warm and wet, and cold and dry summers. A second feature is the persistent nature of the occurrence of warm and dry, and cold and wet summers; i.e., summers of a given character tend to occur in succession. For example, the period between 1899 and 1926 is characterized by a variety of combined temperature and precipitation extremes. The period between 1930 and 1944 is almost exclusively warm and dry, whereas the period from 1961 to 1981 is almost exclusively cold and wet. The period between 1950 and 1959 is characterized by a return to a variety of extremes, as is the period between 1981 and 1991 . All but one of the cold and dry sum- mers occurred prior to 1920. Individual summers that stand out as warm and dry are 1901, 1913, 1914, 1930, 1933, 1936, 1983, 1988, and 1991; whereas cold and wet are 1902, 1907, 1915, 1924, 1958, and 1981; warm and wet are 1980 and 1987; and cold and dry are 1920 and 1976. For the summers with identified extremes, seasonal tempera- ture and precipitation values and deviations from the 97-year average are presented in table 7. Statewide Winter Index The combined indices for the winter months are plotted in figures 50 and 5 1 as a function of time. In contrast to the summer months, warm and dry, and cold and wet winters are less frequent than warm and wet, and cold and dry conditions over the past 97 years. Cold and dry winters were three times more likely than cold and wet winters. The occurrence of cold and wet winters is restricted to the years after 1962, and three out of the four occurred after 1978. Individual winters that stand out as warm and dry are 1921, 1931, 1953, 1954, and 1987; whereas 1979 and 1985 were cold and wet; 1949, 1950, and 1983 were warm and wet; and 1963, 1977, and 1978 were cold and dry. For the win- ters with identified extremes, seasonal temperature and 58 CLIMATE TRENDS IN ILLINOIS -4 1 1 1 1 n 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 i 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 [ i j 1 1 1 1 1 1 1 1 1 N 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 [ i I 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1895 1905 1915 1925 1935 1945 1955 1965 1975 1985 Year Figure 48. Identification of statewide warm and dry, and cold and wet summers (1895-1991). See text for definition of index. Warm and Wet ■a c / l ii i i i iii K i n iii i I I I I I f I MM I I iH iiiii i 1 1 I I I n i l 1 1 lu l l lu ll I I II II I n il 1 1 l i i ii i iiii m i i ii i i i i i n i l l l iii -2 Cold and Dry 'i 1 1 M 1 1 1 1 1 1 1 1 1 1 i 1 1 1 1 1 1 1 [[ 1 1 1 1 1 1 1 1 1 1 1 1 1 1 I J 1 1 1 n i 1 1 1 1 1 1 1 I I 1 1 n I n 1 1 1 1 1 n I I J 1 1 1 n 1 1 1 1 ' 1895 1905 1915 1925 1935 1945 1955 1965 1975 1985 Year Figure 49. Identification of statewide warm and wet, and cold and dry summers (1895-1991). See text for definition of index. 59 CLIMATE TRENDS IN ILLINOIS Table 7. Statewide Summer Seasonal Combined Temperature and Precipitation Extremes Temperature Precipitation Year Fahrenheit Deviation Inches Percent deviation 1901 76.7 1902 71.9 1907 71.9 1913 76.4 1914 76.4 1915 69.3 1920 72.5 1924 71.6 1933 76.0 1936 78.6 1958 71.7 1976 72.3 1980 75.5 1981 73.1 1983 76.6 1988 76.2 +2.8 7.79 70 -2.0 17.49 157 -2.0 15.82 142 +2.5 7.02 63 +2.5 7.58 68 -4.6 17.82 160 -1.4 7.59 68 -2.3 15.54 140 +2.1 6.34 57 +4.7 5.63 50 -2.2 17.44 156 -1.6 8.19 73 +1.6 12.69 114 -0.8 17.75 160 +2.7 8.30 74 +2.3 6.14 55 Note: Deviation and percent deviation calculated from the 97-year statewide summer-season average. 60 CLIMATE TRENDS IN ILLINOIS Warm and Dry X X> C ii iiii i i ii i ii iiiiiiiiiiii I li ii I I I I I I i i iii ii f i iiiiii l — li m i i i iiii iiii i iiiiij n il -2 Cold and Wet -4 1 1 1 1 1 1 1 1 1 1 1 [ I 1 1 1 1 1 1 1 1 1 1 1 1 1 1 ij 1 1 1 1 1 [ 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 [ 1 1 1 1 1 1 1 1 1 1 1 1 1 r 1 1 1 ir' 1895 1905 1915 1925 1935 1945 1955 1965 1975 1985 Year Figure 50. Identification of statewide warm and dry, and cold and wet winters (1895-1991). See text for definition of index. 1895 1905 1915 1925 1935 1945 1955 1965 1975 1985 Year Figure 51. Identification of statewide warm and wet, and cold and dry winters (1895-1991). See text for definition of index. 61 CLIMATE TRENDS IN ILLINOIS precipitation values and deviations from the 97-year average are presented in table 8. Statewide Spring Index The combined index for the spring months are plotted in figures 52 and 53 as a function of time. In contrast to both the summer and winter seasons, springtime combined temperature and precipitation extremes are more equally distributed among the four possible com- binations, reflecting the relatively large day-to-day temperature differences during transition seasons. However, the warm and dry springs were for the most part restricted to the years between the 1920s and 1930s and the late 1980s. The spring climate record also shows active and inac- tive intervals. The period between the 1920s and 1930s experienced numerous deviations from average condi- tions (usually warm and dry, or cold and dry), whereas the late 1940s to the mid-1970s was a somewhat benign period with only minor variations from the 96- year average. Individual springs that stand out as warm and dry are 1930, 1934, 1936, 1986, 1987, and 1988; whereas cold and wet are 1983 and 1984; warm and wet are 1921, 1922, 1945, and 1991; and cold and dry are 1901, 1926, and 1971. For the springs with identi- fied extremes, seasonal temperature and precipitation values and deviations from the 97-year average are presented in table 9. Statewide Autumn Index The combined indices for the autumn months are plotted in figures 54 and 55 as a function of time. Warm and dry autumns have occurred more often than the other three possible combinations, with the largest cluster of occurrences confined to the period between the late 1950s and mid-1960s. A significant warm and dry autumn has not occurred since 1971. The warm and wet autumns are clustered in the period between the early 1920s and the late 1930s. Individual autumns that stand out as warm and dry are 1938, 1939, 1953, 1963, and 1971 ; whereas cold and wet are 1911 and 1926; warm and wet are 1927, 1931, and 1941; and cold and dry are 1917 and 1976. For the autumns with identified extremes, seasonal temperature and precipitation values and deviations from the 97-year average are presented in table 10. Statewide Annual Index While warm and dry, cold and wet, warm and wet, and cold and dry seasons have been identified from Illinois' 97-year climate record, the succession of the seasons and their climate has the ultimate impact. For example, the impact of a warm and dry summer would likely be greater if the previous spring and wintCT were also warm and dry in relation to their respective averages. Thus, efforts to group the climates of consecutive seasons are useful. For example, an examination of calendar years (a grouping of four seasons) identified 1914, 1930, 1934, 1936, 1953, and 1987 as warm and dry; the years 1926, 1950, 1951, and 1972 as cold and wet; the years 1973 and 1983 as warm and wet; and the years 1895, 1917, 1920, and 1976 as cold and dry. The results of several GCMs suggest that the trend of the Illinois climate of the future will be toward warm and dry summers and warm and wet winters. Analog years with similar summer and winter frends are 1930, 1933, and 1983. Regional Index The state of Illinois measures approximately 400 miles north to south, and the climates of northern, central, and southern Illinois are not homogeneous. For exam- ple, a cold and wet summer in northern Illinois may occur in concert with a warm and dry summer in the southern third of the state. The National Weather Service divides Illinois into nine climate regions (see figure 1 , p.9). For this comparison, the northern sector of the state was represented by region 1 , the central district by region 5, and the south by region 9. Warm and dry, cold and wet, warm and wet, and cold and dry seasons were identified in a fashion similar to the statewide calculations. Comparison of the combined index for each of the three regions and the statewide calculation shows general agreement across the region for each of the four seasons. A number of identified years overlap (especially those identified as extreme) and the trends over time are similar to the statewide trends. However, some year-to- year differences occur when an identified season for a particular region is not similarly identified as a statewide occurrence and vice versa. As illustration, warm and dry, cold and wet, warm and wet, and cold and dry summer seasons are identified for each of three regions (figures 56 and 57). CONCLUSIONS Although long-term trends can be identified in various climate parameters, the dominant characteristic of niinois's climate is the presence of large variability on time scales of a few years or less. That is, the magni- tude of long-term trends is in general considerably less 62 CLIMATE TRENDS IN ILLINOIS Table 8. Statewide Winter Seasonal Combined Temperature and Precipitation Extremes Temperature Precipitation Year Fahrenheit Deviation Inches Percent deviation 1921 33.6 1931 33.2 1949 31.0 1950 32.5 1953 33.0 1954 33.4 1963 21.9 1977 20.8 1978 19.6 1979 19.9 1983 33.7 1985 26.1 1987 31.4 +4.9 5.10 79 +4.5 2.47 38 +2.3 11.41 177 +3.8 15.51 240 +4.3 5.48 85 +4.7 5.25 81 -6.8 2.37 37 -7.9 2.95 46 -9.1 4.56 71 -8.8 7.95 123 +5.0 9.01 140 -2.6 8.93 138 +2.7 4.03 62 Note: Deviation and percent deviation alculated from the 97-year statewide winter season average. 63 CLIMATE TRENDS IN ILLINOIS -4 1 1 1 1 1 1 1 1 1 1 1 r 1 1 1 1 1 r 1 1 1 1 1 u M 1 1 1 1 1 1 1 1 1 1 1 1 1 J 1 1 1 1 1 1 1 1 1 1 1 1 1 J 1 1 1 1 1 1 1 r ir 1 1 1 1 1 1 ir 1 1 1 n 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1895 1905 1915 1925 1935 1945 1955 1965 1975 1985 Year Figure 52. Identification of statewide warm and dry, and cold and wet springs (1895-1991). See text for definition of index. 1 1 1 [ 1 1 1 1 1 1 M 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 u 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 i j 1 1 1 1 1 1 1 1 1 1 1 1 1 i 1 1 1 1 1 1 r 1895 1905 1915 1925 1935 1945 1955 1965 1975 1985 Year Figure 53. Identification of statewide warm and wet, and cold and dry springs (I895-I99I). 64 CLIMATE TRENDS IN ILLINOIS Table 9. Statewide Spring Seasonal Temperature and Precipitation Extremes Temperature Fahrenheit Deviation Precipitation Inches Percent deviation Year 1901 1921 1922 1926 1930 1934 1936 1945 1971 1983 1984 1986 1987 1988 1991 Note; Deviation and percent deviation calculated from the 97-year statewide spring season average. 49.4 -2.1 7.07 65 56.0 +4.5 11.97 110 53.6 +2.1 14.97 140 47.8 -3.7 7.93 73 52.4 +0.9 6.07 56 52.0 +0.5 5.16 47 52.7 +1.2 6.01 55 53.6 +2.1 17.32 158 49.6 -1.9 6.27 57 48.8 -2.7 15.08 138 47.3 -4.2 14.13 129 54.6 +3.1 8.01 73 55.3 +3.8 7.14 65 52.2 +0.7 6.91 63 56.0 +4.5 12.34 113 «5 CLIMATE TRENDS IN ILLINOIS Warm and Dry n c i i ii ii ii 11 [I nil I i| — ii i ii i n i l — n i l i i ni i i iiiii i ii i n ii Cold and Wet -4 ' 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 M 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 i 1 1 1 1 1 1 1 1 1 1 1 n 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 M 1 1 1 1895 1905 1915 1925 1935 1945 1955 1965 1975 1985 Year Figure 54. Identification of statewide warm and dry, and cold and wet autumns (1895-1991). See text for definition of index. -4 1 1 1 1 1 1 1 1 11 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 II 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 M 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 M I r 1 1 1 r 1 1 J r I M 1 1 1 1 1 1 1 1 1 1 1 1 n' 1895 1905 1915 1925 1935 1945 1955 1965 1975 1985 Year Figure 55. Identification of statewide warm and wet, and cold and dry autumns (1895-1991). See text for definition of index. 66 CLIMATE TRENDS IN ILLINOIS Table 10. Statewide Autumn Seasonal Temperature and Precipitation Extremes Temperature Precipitation Year Fahrenheit Deviation Inches Percent deviation 1911 1917 1926 1927 1931 1938 1939 1941 1953 1963 1971 1976 Note: Deviation and percent deviation calculated from the 97-year statewide autumn season average. 52.5 -2.0 14.99 166 50.7 -3.8 6.19 68 52.6 -1.9 17.28 191 57.7 +3.2 13.62 150 60.3 +5.8 13.46 149 57.0 +2.5 6.72 74 56.4 +1.9 4.26 47 56.9 +2.4 17.08 189 56.7 +2.2 4.05 45 58.5 44.0 4.66 51 57.9 +3.4 6.66 74 48.6 -5.9 6.05 67 67 CLIMATE TRENDS IN ILLINOIS ' l I I I I 1 1 I I I I I I I I I I I I I I I I I [ I i I I I 1 I I I I I I I I I I I I I I I I I I M i I I M I I I U I I M 1 1 I I I I I I I 11 I N I I 1 1 1 I I 1 1 1 1 1 I I I [ I r 1895 1905 1915 1925 1935 1945 1955 1965 1975 1985 Year -B- Region 1 (north) — ^— Region 5 (central) -^*^ Region 9 (south) Figure 56. Identification of regional (north, central, and south) warm and dry, and cold and wet summers (1895-1991). See text for definition of index. Warm and Wet ■D C Cold and Dry -4 'i 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 11 1 1 1 1 1 n 1 1 1 1 1 1 1 1 M 1 1 N 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 n 1 1 1 1 M 1 1 1 1 [ ir 1 1 1 1 1 1895 1905 1915 1925 1935 1945 1955 1965 1975 1985 Year -e- Region 1 (north) —*— Region 5 (central) -^^ Region 9 (south) Figure 57. Identification of regional (north, central, and south) warm and wet, and cold and dry summers (1895-1991). See text for definition of index. 68 CLIMATE TRENDS IN ILLINOIS than the changes that can occur from one year or a few years to the next. With that being said, however, some identifiable longer-term features can be noted. The most persistent and extreme summertime high temperatures occurred primarily during the 1 930s, the Dust Bowl era. Indeed, average temperatures in Illinois clearly increased by 4 to 5°F from the mid- to late 1800s to the 1930s, and then cooled by about half that amount to the present. AH of the temperature parame- ters assessed herein support those trends, including average temperatures and frequency of days with extreme temperatures, whether warm or cold. These trends are found in records of the continent, the hemisphere, and the world, although the magnitudes of change decrease with increasing areas of integration. During the peak of Illinois temperatures during the 1930s, the frequency and intensity of hot days was unprecedented in Illinois and much of the upper Midwest. The many severe impacts of the heat and dryness of that period are well known. Since then, the frequency and intensity of summertime heat has been substantially less, particularly during the 1960s and 1970s. However, some resurgence of extreme sununer- time heat was noted during the 1980s, with accompa- nying impacts on crop yields. The extent of this trend toward higher frequencies of hot and dry summers cannot be predicted at this time. In general, the frequency of extreme cold events in- creased from 1930 to the present. This upward trend reached its peak in the late 1970s and early 1980s, with an unprecedented string of extremely cold winters. They had major negative impacts on the Illinois econ- omy and environment, affecting transportation, health, energy consumption, etc. During this cooling episode, precipitation may have increased marginally, but the major change in precipitation was the increase in annual snowfall, peaking in the late 1970s. Also nota- ble was the abrupt decline in the annual number of severe winter storms in the state, dropping from an average of five per year prior to about 1980, to about three during recent years. The 1992-1993 winter was perceived by many to be a severe winter, but it was only near-average when compared to the situation of the last two or three decades. Generally benign, moderate summers occurred during the 1960s and 1970s. As noted above, the 1980s were characterized by more frequent hot and dry but quite variable summers, similar to the earlier half of the cen- tury. It should be noted that midwestem agriculture experienced rapid technological advances during this relatively benign period. In addition, virtually all farmers active today have spent their entire careers during that benign period. The severity of the 1988 growing-season drought in Illinois had only been equaled in two other years since the turn of the century. The most recent Illinois drought of equal intensity occurred in 1936, long before virtually all present-day farmers were in the business. The impact of climate variability in the state is exemplified by the cool summer of 1992. Even though overall com yields were the highest ever in the United States, the northemmost 100 miles of the Com Belt accumulated so few GDDs (sixth fewest since 1 878) that the com crop did not mature at its usual rate in that area. Indeed, it was not yet ripe at the time of the first frost in southem Minnesota and Wisconsin, which was within about one week of the long-term average. The degree of cold of the 1 992 summer was also demon- strated by the low total CDDs for the state. Total CDDs in 1992 were the seventh lowest since 1878. This was a boon for the consumer and a bane to the electric utility. The tomado frequency record in Illinois exhibits no trends, rather an average of some 25 tomadoes per year, but varying from 6 to 107 per year! Of interest was the relatively high frequency recorded during the early 1 880s (essentially equal to that of today), even though the tomado record for that time is known to be incomplete. Cloud cover and the frequency of ice/glaze storms have both increased in the state. These changes do not ap- pear to be due to changes in observing procedure, nor are they related to other parameters that might assist in their explanation. It is clear that climate has not been stable in Illinois during the last 150 years, nor should it have been so anticipated. Many of the changes, although abmpt, were of relatively small magnitude. Yet those relatively small-scale changes levied a substantial toll on the inhabitants of the state through discomfort; lost income; increased costs; and impediments to com- merce and agricultural production, in spite of major strides in hybridization and field management prac- tices. Since climate has always changed, it will likely continue to do so. The past gives little hint as to the future direction and magnitude of these changes, but it does suggest limits within which climate may be constrained over the immediate ftiture. The current increase to atmospheric carbon dioxide by the burning of fossil fuels, however, is suspected to change some ti9 CLIMATE TRENDS IN ILLINOIS climate parameters at a faster rate than during the past centuries, thereby possibly rendering past climate a poor tool for evaluating future variability. ACKNOWLEDGMENTS We acknowledge the many hours of programming by Julie Dian, who produced the scores of statistical calcu- lations and figures initially produced for this study. Robin Shealy performed many of the statistical cal- culations. James Angel assisted with the figures, and Jean Dennison managed the manuscript. Folland, C.K., T. Karl, and K.Ya. Vinnikov. 1990. Observed Climate Variations and Change. In J.T. Houghton, G.J. Jenkins, and J.J. Ephraums (eds.). Climate Change: The IPCC Scientific Assessment, Cambridge University Press, Cambridge, pp. 195-238. Huff, F.A., and J.R. Angel. 1989. Frequency Distribu- tion and Hydroclimatic Characteristics of Heavy Rain- storms in Illinois. Illinois State Water Survey Bulletin 70, Champaign. Lamb, H.H. 1966. The Changing Climate. Methune & Co. REFERENCES Changnon, S.A. 1969. Climatology of Severe Winter Storms in Illinois. Illinois State Water Survey Bulletin 53, Champaign. Changnon, S.A. 1978. Record Severe Winter Storms in Illinois, 1977-78. Illinois State Water Survey Report of Investigation 88, Champaign. Changnon, S.A., R.G. Semonin, and W.M. Wendland. 1980. Effect of Contrail Cirrus on Surface Weather Conditions in the Midwest - Phase I. Final report to NSF grant ATM 78-09568. Changnon, S.A. 1984. Climate Fluctuations in Illinois: 1901-1980. Illinois State Water Survey Bulletin 68, Champaign. Changnon, S.A. 1987. Historical Atmospheric Trans- mission Changes and Changes in Midwestern Air Pollution. Bulletin American Meteorological Society, 68(5):477-480. Davitaia, F.F. 1965. Possible Influence of the Atmo- spheric Dust on the Regression of Glaciers and the Warming of Climate. Trans. Soviet Acad. ScL, Geogr. Ser. (2):3-22. Draper, N.R., and H. Smith. 1981. Applied Regression Analysis. John Wiley & Sons, Inc., New York. Petersen, M.S. 1990. Implementation of a Semi-Physical Model for Examining Solar Radiation in the Midwest. Midwestern Climate Center, Illinois State Water Sur- vey Miscellaneous Publication 123, Champaign. Vinzani, P. and P.J. Lamb. 1985. Temporal and Spatial Visibility Variations in the Illinois Vicinity during 1940-1980. Journal of Climate and Applied Meteorol- ogy, 25:435-451. Wendland, W.M. 1990. A History of the Weather Observations in Illinois. Trans., 111. Academy of Sci- ence, S3 {I and2):43-56. Wendland, W.M., and R.A. Bryson. 1970. Atmo- spheric Dustiness, Man, and Climatic Change. Biologi- cal Conservation, 2(2): 125- 128. Wendland, W.M., and P. Guinan. 1988. A Tornado and Severe Windstorm Climatology for Illinois: 1955- 1986. Trans., 111. Academy of Science, 81 (1 and 2): 131-146. Wendland, W.M., and H. Hoffman. 1993. Illinois Tornadoes Prior to 1916. Trans., III. Academy of Science (in press). Wigley, T.M.I, and T.P. Bamett. 1990. Detection of the Greenhouse Effect in the Observations. In T.J. Houghton, G.J. Jenkins, and J.J. Ephraums (eds.), Climate Change, the IPCC Scientific Assessment, Cambridge University Press, Cambridge, pp. 239-255. 70 CLIMATE TRENDS IN ILLINOIS APPENDIX A The following tables present the results of the trend analysis for individual long-term stations. The values given are the magnitude of the trend for those stations where the trend is statistically significant at the 10 percent level. If the trend is not statistically significant, an "NT" is shown. 71 CLIMATE TRENDS IN ILLINOIS Table A.l. Trends in Annual Precipitation Parameters (Asterisk Indicates Trends of Statistical Significance) City Northwest Aledo Dixon 1 NW Galva Mount Carroll Walnut Northeast Aurora Marengo Ottawa 4 SW West La Harpe Monmouth Rushville Central Decatur Lincoln Minonk East Danville Hoopeston Pontiac Urbana West-Southwest Carlinville Greenville 1 E Griggsville Hillsboro Jacksonville Pana White Hall 1 E East-Southeast Charleston Effingham Flora Olney Palestine Paris Waterworks Windsor Total precipitation (inches/decade) 0.11 0.21 0.64* 0.28 27 0.26 0.61* 0.80* 0.37 0.27 0.97* 0.11 0.14 0.55* L12* -0.01 0.27 0.74* 0.02 -0.16 0.16 0.27 0.62* 0.40 -0.14 0.28 0.45 0.58* 0.09 0.15 0.72* -0.28 Number of days with measurable precipitation (days/decade) -0.59 0.93 0.73 1.36* -3.05* 4.12* 0.25 1.87* L54* 0.54 0.58 0.22 0.28 L44* 4.18* 0.63 -0.55 2.32* 1.03* -0.30 2.63* -0.67 -0.60 3.12* L89* -0.49 L84* 1.07 0.83 L85* 4.69* 0.54 Number of days with precipitation > one inch (days/decade) 0.01 0.07 0.35* 0.07 0.03 0.07 0.22* 0.38* 0.14 0.10 0.43* 0.01 0.15 0.17 0.21 -0.07 0.15 0.25* -0.12 0.06 0.03 0.24* 0.37* 0.14 -0.30* 0.14 0.14 0.27* 0.15 0.01 0.10 -0.12 Total Number of Snowfall days with (inches/ measurable decade) snowfall (days/decade) 0.97* 0.16 1.49* 0.73* -0.29 -0.38* 0.52 -0.06 0.70* -0.74* 0.38 -1.23* 1.41* -0.49* 0.40 0.37 -0.10 -0.10 0.36 0.00 0.08 -0.04 -0.08 -0.32 -0.16 -0.23 0.61 0.41* 0.62 0.26 -1.50* 0.23 -0.86* 0.04 0.72* 1.11* 0.04 0.03 -0.37 -0.56* 1.92* 0.83* -0.36 -0.48* 0.41 -0.73* 1.32* 1.07* -0.73* -0.50* 0.20 -0.43* 1.16* 0.47* -0.90* -0.59* -1.06* -0.72* 0.94* 0.62* 2.03* 1.07* 0.08 -0.32 72 Table A. 1. Concluded CLIMATE TRENDS IN ILLINOIS Southwest Anna 1 E Carbondale Du Quoin 4 SE Olive Branch Sparta Southeast Fairfield Harrisburg McLeansboro Mt. Vernon All stations 0.51 -0.68 0.32 0.13 0.20 0.91* -0.06 0.46 0.16 0.35* 2.23* -2.15* 1.18* 2.06* -0.66 4.12* 0.99 2.37* -0.07 1.19* 0.02 0.83* 0.77' 0.27 -0.61 0.66' 0,10 -0.32 -0.10 0.07 0.21 -0.01 0.21 -0.19 0.01 0.25 0.28 0.13 ■0.13 -0.43 -0.26 0.02 0.11 0.17 0.09 0.17 -0.41 0.11 0.37 0.12 73 CLIMATE TRENDS IN ILLINOIS Table A. 2. Trends in Annual Temperature Parameters (Asterisk Indicates Trends of Statistical Signitlcance) City Northwest Aledo Dixon Galva Mount Carroll Walnut Northeast Aurora Marengo Ottawa 4 SW West La Harpe Monmouth Rushville Central Decatur Lincoln Minonk East Danville Hoopeston Pontiac Urbana West-Southwest Carlinville Greenville 1 Griggsville Hillsboro Jacksonville Pana White Hall 1 E East-Southeast Charleston Effingham Flora Olney Palestine Paris Waterworks Windsor Number of days with mean Mean temperature temperature > 5ffF CF/decade) (days/decade) -0.23 -1.24 -0.01 0.52 -0.02 0.37 -0.02 -0.06 -0.29* 09.19 -0.22* -0.89 0.03 0.28 0.53* 2.89* -0.08 0.26 0.06 0.84* 0.07 0.02 -0.29* -0.44 -0.21 0.03 -0.31 -1.35 0.49* 2.68* 0.44* 2.58* -0.25* -0.59 0.06 0.70* -0.09 0.41 -0.11 -2.00 -0.15 -0.68 -0.07 0,11 -0.16* -0.54 0.11 1.25* 0.25* 1.95* 0.33 1.92 0.17 1.70* 0.34 2.76* -0.24 -0.20 -0.15 0,36 0.19* 2.00* 0.02 1.04* Highest daily Lowest daily maximum minimum temperature temperature CF/decade) CF/decade) NT 0,10 NT 0.11 -0.36* 0.32 NT 0.09 -0.29* 0.08 NT -0.15 NT -0.20 -0.31* -0.25 NT 0.17 -0.34* 0.25 NT -0.03 -0.27* -0.01 -0.32* 0.54* -0.53* 0.22 -0.58* -0.04 -0.33* 0.06 -0.40* -0.07 NT 0.40* -0.41* 0.10 NT 0.18 NT 0.04 NT 0.17 -0.36* -0.03 -0.42* 0.17 -0.38* -0.01 -0.35* 0.26 -0.57* -0.04 NT 0.07 -0.45* 0,08 NT -0.10 -0.31* 0.32* -0.34* 0.31 74 CLIMATE TRENDS IN ILLINOIS Table A.2. Concluded Southwest Anna 1 E Carbondale Du Quoin 4 SE Olive Branch Sparta Southeast Fairfield Harrisburg McLeansboro Mt. Vernon All stations 0.09 0.43 1.06* -4.94* 0.19 -0.54 ■0.25* -0.87 0.02 0.90* 0.04 0.93 ■0.34* -0.11 ■0.14* -0.23 ■0.13 -0.31 -0.06 0.26 -0.43* -0.96* -0.29* -0.46* NT 0.52* -0.37* -0.42* -0.41* -0.35* -0.14 0.07 -0.05 -0.07 -0.04 -0.05 -0.10 -0.05 0.20 0.15 75 CLIMATE TRENDS IN ILLINOIS Table A. 3. Trends in Annual Temperature Parameters (Asterisk Indicates Trends of Statistical Significance) Number of days Number of days Number of days Mean with minimum with minimum with minimum minimum temperature temperature temperature temperature > 7(fF < (fF <32°F City (°F/decade) {days/decade) (days/decade) (days/decade) Northwest Aledo -0.17 -0.06 0.14 -0.85* Dixon 1 NW 0.04 0.22 0.66* 0.79 Galva 0.05 0.24 0.44 -0.54 Mount Carroll -0.06 -0.15 0.43 0.73 Walnut -0.32* -0.52* 0.78* 1.23* Northeast Aurora -0.14 -0.01 0.21 -1.10* Marengo -0.18 0.01 0.77* 1.73* Ottawa 4 SW 0.57* 0.78* 0.33 -0.49 West La Harpe -0.13* -0.15 0.43 0.55 Monmouth 0.11 0.20 0.12 -0.83* Rushville -0.04 -0.45 0.28 0.46 Central Decatur -0.22* -0.02 0.18 -1.12* Lincoln -0.10 -0.05 0.23 -1.31* Minonk -0.24 -0.21 0.45 -0.09 East Danville 0.45* -0.02 0.34 1.07 Hoopeston 0.45* 0.41* 0.41 0.72 Pontiac -0.17* -0.32 0.39 0.40 Urbana 0.08 -0.14 -0.04 -0.75* West-Southwest Carlinville 0.06 0,65* 0.03 -1.00* Greenville 1 E 0.01 0.86 -0.74* -2.58* Griggsville -0.13 -0.41 0.14* 0.60 Hillsboro -0.06 -0.23 0.06 -0.16 Jacksonville -0.11* -0.28 0.30 0.57 Pana 0.16* 0.09 0.05 -0.55 White Hall 1 E 0.31* 0.53 0.38 0.57 East-Southeast Charleston 0.39* 0.82* 0.10 0.76 Effingham 0.23 0.27 0.57* 1.20 Flora 0.28 0.24 0.20 0.26 Palestine -0.04 0.60 0.20 -0,50 Olney -0.16 -0.09 0.19 -0.46 Paris Waterworks 0.31* 0.92* 0.20 -1.23* Windsor 0.18* 0.69* 0.00 -1.90* ,76 CLIMATE TRENDS IN ILLINOIS Table A.3. Concluded Southwest Anna 1 E Carbondale Du Quoin 4 SE Olive Branch Sparta Southeast Fairfield Harrisburg McLeansboro Mt. Vernon All stations -0.06 -0.91* -0.10 -0.15* 0.10** 0.13 -0.30* -0.15* -0.22* -0.02 -0.71* -1.93* 0.24 -0.09 1.04* -0.35 -0.45 -0.99* -0.17 0.00 0.08 0.28 0.25 0.28* -0.10 0.19 0.06 0.16 0.84* 0.26 0.61 1.58* -0.14 0.35 -0.76 0.91* 0.41 1.36* 0.78* 0.01 77 CLIMATE TRENDS IN ILLINOIS Table A.4a. Trends in Annual Temperature Parameters (Asterisk Indicates Trends of Statistical Significance) Number of days Number of days Mean with maximum with maximum Number of days maximum temperature temperature with temperatures temperature >86''F >9ff'F >100°F City CF/year) (days/year) (days/year) (days/year) Northwest Aledo -0.11 0.25 -0.20 -0.16 Dixon 1 NW -0.08 -1.07* -0.93* -0.12 Gaiva -0.09 -1.43* -1.43* -0.21* Mount Carroll 0.00 0.03 -04.1 -0.16 Walnut -0.27* -0.61 -1.19* -0.11 Northeast Aurora -0.40* -0.17 -0.60 -0.10 Marengo 0.22 0.87 0.37 -0.07 Ottawa 4 SW 0.40* -0.72 -1.19* -0.34* West La Harpe 0.00 -0.12 -0.94 -0.18 Monmouth 0.01 -0.97 -1.53* -0.23 Rushville 0.17 0.89 0.06 -0.13 Central Decatur -0.37* -0.86 -1.41* -0.26 Lincoln -0.29 -1.54* -1.99* -0.16 Minonk -0.38 -1.07 -1.44* -0.27* East Danville 0.52 -1.19 -2.14* -0.34* Hoopeston 0.44* -0.97 -1.44* -0.22* Pontiac -0.33* -2.34* -2.57* -0.27* Urbana 0.03 0.28 -0.18 -0.03 West-Southwest Carlinville -0.24* -1.24* -1.78* -0.52* Greenville 1 E -0.22 -0.84 -1.32 -0.45 Griggsville -0.23 -1.55* -1.89* -0.24 Hillsboro -1.10 -0.62 -1.29 -0.31 Jacksonville -0.21* -1.84* -1.98* -0.35* Pana 0.01 -1.46* -1.64* -0.23 White Hall 1 E 0.15 -1.16 -1.85* -0.43* 78 CLIMATE TRENDS IN ILLINOIS Table A. 4a. Concluded East-Southeast Charleston Effingham Flora Olney Palestine Paris Waterworks Windsor Southwest Anna 1 E Carbondale Du Quoin 4 SE Olive Branch Sparta Southeast Fairfield Harrisburg McLeansboro Mt. Vernon All stations 0.26 0.20 0.46 -0.30 -0.26* 0.08 -0.13* -0.11 -1.20* -0.29* -0.34* -0.07 -0.19 -0.39* -0.14 -0.05 -0.10 -1.93* -2.31* 0.81 -1.07 -1.08 -1.48* -1.44* -1.63* -4.11* -2.21* -2.45* 0.04 -3.13* -0.70 -1.12 -1.61* -1.10* -2.35* -2.51* -0.14 -1.71* -1.25 -1.54* -2.32* -1.95* -4.68* -2.32* -3.01* -0.73 -3.59* -1.57* -1.51* -1.42* -1.55* -0.40* -0.66* -0.38 -0.41* -0.15 -0.24 -0.37* -0.42* -1.12* -0.36 -0.61* -0.50* -0.52* -0.58* -0.57* -0.20* -0.33* 79 CLIMATE TRENDS IN ILLINOIS Table A.4b. Trends in Annual Temperature Parameters (Asterisk Indicates Trends of Statistical Significance) City Number of days with maximum temperature < (fF Number of days with maximum temperature < 32°F Northwest Aledo Dixon 1 NW Galva Mount Carroll Walnut Northeast Aurora Marengo Ottawa 4 SW West La Harpe Monmouth Rushville Central Decatur Lincoln Minonk East Danville Hoopeston Pontiac Urbana West-Southwest Carlinville Greenville 1 Griggsville Hillsboro Jacksonville Pana White Hall I E East-Southeast Charleston Effingham Flora Olney Palestine Paris Waterworks Windsor 0.02 0.06 0.07* 0.05 0.04 0.03 0.04 0.06* 0.01 0.00 0.01 0.02* 0.01 0.07* 0.02* 0.04* 0.03 0.04* 0.01 -0.01 0.02 0.01* 0.04* 0.02* 0.01 0,03* 0.04* 0.01* 0.01 0.01 0.03* 0.03* 0.38 1.33* 0.62 0.61 0.62 -0.40 -0.48 0.75* 0.39 -0.21 0.47 -0.05 0.53 0.85 0.81* 1.30* 0.87* 0.45 0.67* -1.93* 1.10* 0.12 0.93* 0.59 0.83* 0.45 1.81* 0.65* 0.55 0.69* 0.07 0.76* 80 CLIMATE TRENDS IN ILLINOIS Table A.4b. Concluded Southwest Anna 1 E Carbondale Du Quoin 4 SE Olive Branch Sparta Southeast 0.00 0.01 0.01 0.02* 0.01 0.53* 0.74* 0.56* 0.64* 0.32 Fairfield Harrisburg McLeansboro Mt. Vernon 0.02* 0.00 0.01* 0.07 1.07* 0.32 0.88* 0.51 All stations 0.03* 0.53 81 CLIMATE TRENDS IN ILLINOIS Table A.5. Trends in Autumn Climate Parameters (Asterisk Indicates Trends of Statistical Significance) City Mean temperature CF/decade) Mean minimum temperature CF/decade) Mean maximum temperature CF/decade) Total precipitation (inches/decade) Northwest Aledo Dixon 1 NW Galva Mount Carroll Walnut Northeast Aurora Marengo Ottawa 4 SW West La Harpe Monmouth Rushville Central Decatur Lincoln Minonk East Danville Hoopeston Pontiac Urbana West-Southwest Carlinville Greenville 1 E Griggs ville Hillsboro Jacksonville Pana White Hall 1 E East-Southeast Charleston Effingham Flora Olney Palestine Paris Waterworks Windsor -0.31* -0.22* -0.15* -0.14 -0.19* -0.16 0.02 0.38 -0.16* 0.00 0.14 -0.24 0.27 -0.24 0.11 0.50* -0.17* 0.02 -0.11 0.02 -0.21* -0.14 -0.18* 0.04 0.23 0.44 -0.17* 0.27 0.02 -0.14 0.24 -0.04 -0.27* -0.18 -0.06 -0.18** -0.30* -0.10 -0.27* 0.43* -0.20* 0.06 0.00 -0.16 0.27* -0.23 0.20 0.50* -0.14 0.05 0.05 0.06 -0.19* -0.10 -0.16* 0.11 0.30* 0.51* 0.00 0.24 0.07 -0.04 0.39* 0.17 -0.22 -0.26* -0.23* -0.15 -0.08 -0.50* 0.31 0.47 -0.11 -0.06 0.24 -0.32 0.35 -0.25 0.03 0.29 -0.21* 0.00 -0.28 -O.OI -0.22* -0.27 -0.21* -0.20* 0.12 0.38 -0.35* 0.31 -0.03 -0.25* 0.10 -0.26 -0.04 0.02 0.16 0.04 0.03 0.02 0.12 0.21 0.23 0.02 0.34* -0.06 0.00 0.27* 0.13 0.09 0.07 0.19 0.02 0.12 -0.06 0.09 0.13 0.12 -0.18 0.14 0.06 0.13 0.11 0.12 0.08 0.00 82 CLIMATE TRENDS IN ILLINOIS Table A. 5. Concluded Southwest Anna 1 E Carbondale Du Quoin 4 SE Olive Branch Sparta Southeast Fairfield Harrisburg McLeansboro Mt. Vernon All stations -0.25* -0.80* -0.18* -0.30* -0.03 -0.26 -0.30 -0.16 -0.32* -0.11 -0.17* -0.77* -0.06 -0.15 0.10 -0.04 -0.23 -0.18* -0.46* -0.06 -0.29* -0.82* -0.30* -0.45* -0.15 -0.48* -0.37 -0.15 -0.08 -0.15* 0.02 -0.29 0.23 0.18 0.14 0.25* 0.02 0.16 -0.03 0.10 83 CLIMATE TRENDS IN ILLINOIS Table A.6. Trends in Winter Climate Parameters (Asterisk Indicates Trends of Statistical Significance) Mean Mean minimum Mean maximum Total temperature temperature temperature precipitation City CF/decade) CF/decade) CF/decade) (inches/decade) Northwest Aledo -0.06 0.00 -0.11 -0.02 Dixon 1 NW 0.08 0.03 0.13 0.09 Galva -0.20 -0.14 -0.22 0.08 Mount Carroll -0.02 -0.09 -0.01 0.03 Walnut -0.31* -0.42* -0.21 -0.06 Northeast Aurora -0.16 -0.17 -0.06 0.06 Marengo -0.04 -0.26 0.18 0.05 Ottawa 4 SW 0.10 0.09 0.11 0.05 West La Harpe -0.18 -0.26* -0.10 -0.03 Monmouth 0.06 0.08 0.05 0.07 Rushville -0.20 -0.24* -0.16 0.13 Central Decatur -0.21 -0.18 -0.24 0.04 Lincoln -0.76* -0.65* -0.87* -0.07 Minonk -0.18 -0.15 -0.21 0.15 East Danville -0.06 -0.05 -0.06 0.11 Hoopeston 0.16 0.14 0.18 -0.16 Pontiac -0.43* -0.39* -0.47* -0.12 Urbana -0.09 -0.04 -0.14 O.IO West-Southwest Carlinville -0.16 -0.03 -0.29 0.02 Greenville 1 E 0.37 0.41 0.34 -0.06 Griggsville -0.30* -0.27* -0.34* 0.10 Hillsboro -0.06 -0.12 0.01 0.10 Jacksonville -0.19 -0.20 -0.23 0.07 Pana -0.04 0.01 -0.10 0.16 White Hall 1 E -0.09 -0.11 -0.08 -0.04 East-Southeast Charleston -0.07 -0.06 -0.08 0.05 Effingham -0.09 -0.15 -0.03 0.21 Flora 0.15 0.12 0.19 0.15 Olney -0.13 -0.10 -0.22 0.02 Palestine 0.01 0.05 -0.03 -0.05 Paris Waterworks 0.05 0.11 -0.01 0.17 Windsor -0.15 -0.03 -0.27* 0.01 84 CLIMATE TRENDS IN ILLINOIS Table A. 6. Concluded Southwest Anna 1 E Carbondale Du Quoin 4 SE Olive Branch Sparta Southeast Fairfield Harrisburg McLeansboro Mt. Vemon All stations -0.18 -0.82* -0.25* -0.23 -0.21 -0.10 -0.41* -0.17 -0.08 -0.14 -0.17 -0.84* -0.22 -0.23 -0.12 -0.03 -0.39* -0.22 -0.21 -0.14 -0.14 -0.80* -0.29* -0.22 -0.31 -0.17 -0.43* -0.11 0.10 -0.14 0.14 0.00 0.03 -0.07 -0.03 0.10 -0.13 -0.07 0.05 0.04 85 CLIMATE TRENDS IN ILLINOIS Table A.7. Trends in Spring Climate Parameters (Asterisk Indicates Trends of Statistical Significance) City Northwest Aledo Dixon 1 NW Galva Mount Carroll Walnut Northeast Aurora Marengo Ottawa 4 SW West La Harpe Monmouth Rushville Central Decatur Lincoln Minonk East Danville Hoopeston Pontiac Urbana West-Southwest Carlinville Greenville 1 E Griggsville Hillsboro Jacksonville Pana East-Southeast Charleston Effingham Flora Olney Palestine Paris Waterworks White Hall 1 E Windsor Mean Mean minimum Mean maximum Total temperature temperature temperature precipitation CF/decade) CF/decade) CF/decade) (inches/decade) 0.04 0.05 0.14 0.07 0.06 0.15 -0.12 0.05 0.08 0.12 0.04 0.18 -0.08 -0.04 -0.18 0.12 -0.03 -0.05 -0.01 0.24* 0.03 0.08 -0,06 0.12 0.01 -0.19* 0.21 0.10 0.26* 0.37* 0.16 0.22* 0.01 -0.05 0,07 0.13 0.15 0.17* 0,13 0.15 -0.12 -0.18 -0,06 0.24 0.14 0.11 0.16 0.03 0.30 0.29* 0.31 0.03 -0.20 -0.10 -0.30 0.24 0.12 0,11 0.13 0.14 0.08 0.19* -0.03 -0.03 -0.11 -0.07 -0.16 -0.05 0.19* 0.19* 0,19* 0.05 -0.03 0.08 -0,14 0.03 -0.13 -0.08 -0,18 -0.05 -0.13 -0.09 -0.17 0.08 0.06 0.04 0.08 0.06 -0.09 -0.04 -0.15 0.28* 0.19* 0.21* 0,18 0.11 0.21 0.26* 0,17 -0,01 -0.08 0.00 0.03 0,05 0.26 0.19 0.44 0,16 -0.41* -0.33 -0.49* 0,07 0.24 0,31* 0.07 0,13 0.09 0.19 0.00 0.05 0.21 0.28* 0.13 0.12 0.21* 0.30* 0.16 -0.23 86 CLIMATE TRENDS IN ILLINOIS Table A.7. Concluded Southwest Anna 1 E Carbondale Du Quoin 4 SE Olive Branch Sparta Southeast 0.06 -0.62* 0.12 -0.18 0.23* 0.04 -0.53* 0.15 -0.09 0.23* 0.17 -0.71* 0.09 -0.23* 0.23 0.32 -0.03 0.24 0.10 0.06 Fairfield Harrisburg McLeansboro Mt. Vernon 0.01 0.21 -0.09 -0.02 0.09 0.10 -0.06 -0.13 -0.09 0.24 -0.12 0.08 0.45* 0.27 0.27 0.19* All stations 0.04 0.06 0.02 0.13 87 CLIMATE TRENDS IN ILLINOIS Table A.8. Trends in Summer Climate Parameters (Asterisk Indicates Trends of Statistical Significance) City Mean temperature CF/decade) Mean minimum temperature (°F/decade) Mean maximum temperature CF/decade) Total precipitation (inch es/decade) Northwest Aledo Dixon 1 NW Galva Mount Carroll Walnut Northeast Aurora Marengo Ottawa 4 SW West La Harpe Monmouth Rushville Central Decatur Lincoln Minonk East Danville Hoopeston Pontiac Urbana West-Southwest Carlinville Greenville 1 E Griggsville Hillsboro Jacksonville Pana White Hall 1 E East-Southeast Charleston Effingham Flora Olney Palestine Paris Waterworks Windsor -0.21 0.04 0.18 -0.22 -0.36* -0.27 0.00 0.64* 0.02 0.01 -0.27 -0.53* -0.40* 0.16 0.59* 0.31* -0.29* 0.10 -0.04 -0.55 0.03 -0.15 -0.15* 0.22 0.63* 0.16 0.37 0.49 -0.34 -0.34 0.38* 0.05 -0.17 0.16* 0.29* -0.20 -0,29* -0.12 -0.11 0.78* -0.01 0.12* -0.36* -0.39* -0.14 0.18 0.65* 0.42* -0.07 0.14* 0.15 -0.27 0.04 -0.06 -0.05 0.29 0.75* 0.40* 0.55* 0.39 -0.24 -0.20 0.54* 0.27* -0.24 -0.08 0.-06 -0.09 -0.42* -0.42* 0.02 0.20 0.14 -0.09 -0.18 -0.66* -0.65* 0.15 0.52 0.19 -0.50* 0.07 -0.22 -0.83 -0.22 -0.23 -0.26* 0.15 0.43 -0.08 0.39 0.67 -0.34 -0.42 0.23 -0.17 0.10 0.05 0.22 0.00 0.12 0.11 0.32* 0.22 0.14 0.05 0.16 0.17 0.25 0.03 0.53* 0.01 0.37* 0.40* -0.06 -0.13 0.02 0.03 0.14 0.02 -0.04 0.01 0.01 0.09 -0.06 0.02 0.36* -0.06 88 Table A.8. Concluded CLIMATE TRENDS IN ILLINOIS Southwest Anna 1 E Carbondale Du Quoin 4 SE Olive Branch Sparta Southeast Fairfield Harrisburg McLeansboro Mt. Vernon 0.03 -0.35* -0.18 -0.28* 0.08 -0.03 -0.43* -0.15* -0.10 0.06 -0.20* -0.04 -0.13 0.20* 0.10 -0.35 -0.13* -0.80 -0.19* -0.49* -0.32 -0.44* -0.04 -0.26 -0.51* -0.18 -0.30 0.03 -0.03 -0.14 -0.08 0.03 0.09 -0.11 0.08 -0.04 All stations -0.03 0.06 -0.13 0.08 AIR QUALITY TRENDS IN ILLINOIS AIR QUALITY TRENDS IN ILLINOIS Donald F. Gatz Illinois State Water Survey INTRODUCTION Purpose There are three main purposes for including a compo- nent on air quality in a comprehensive assessment of the Illinois environment. The first purpose is simply to document the current status of Illinois air quality and any recent trends. Specifically, we will look for changes (trends) in pollutant concentrations over time within specific geographic regions, as well as state- wide, and also show spatial variations of pollutant concentrations in the Chicago area, the only area of the state where there are enough sampling sites to permit plots of spatial variability. These analyses will reveal whether concentrations of specific pollutants in Illinois air are getting better, or getting worse, or staying the same. They may also indi- cate which areas of the state experience the highest and lowest pollutant concentrations, and whether such local or regional conditions are improving or worsening. The second purpose is to provide the information necessary for assessments of human and ecosystem exposure to airborne pollutants. These assessments will appear in other reports in this series. The final purpose is to identify gaps and needs in Illinois air quality monitoring and research. be noted that lEPA's main purpose in making these measurements is to monitor compliance, not to document the state's air quality. Thus, to some extent, this examination of EPA data for descriptions of past and current air quality goes beyond the purpose for which the data were originally collected. Consequently, the goal of characterizing air quality over the whole state may not be completely attainable. Pollutants Analyzed The air pollutants to be examined for temporal and spatial trends include, first of all, the seven criteria pollutants, i.e., those for which national or state air quality standards have been set. These include four gaseous pollutants: ozone (Oj), sulfur dioxide (SO^), nitrogen dioxide (NO,), and carbon monoxide (CO). There are also standards for three pollutants that occur as particles: These are lead (Pb); total suspended particulate matter (TSP), for which there is only a state standard; and particulate matter with aerodynamic diameters of 10 micrometers (|im) or less (PMi^,), for which there is only a national standard. In addition, we will examine measured concentrations of several additional pollutants for which standards have not been set. This group includes sulfate and nitrate ions and the metals arsenic (As), cadmium (Cd), chromium (Cr), iron (Fe), manganese (Mn), and nickel (Ni). These pollutants all occur as particles in the atmosphere, and they are measured by chemically analyzing the same filters used to collect the TSP samples. Several additional metals, such as beryllium, copper, selenium, anc^ vanadium, are currently being measured or have been measured in the past by lEPA. These additional metals are not included in this assessment because their concentrations are mostly smaller than the detection limit. Finally, we will summarize occasional (nonroutine) measurements of organic compounds. These measure- ments were made by lEPA or published in the scien- tific literature. Scope This analysis, for the most part, relies on data gener- ated by routine air quality measurements carried out by the Illinois Environmental Protection Agency (lEPA), the state agency charged with monitoring compliance with state and national air quality standards. It should Period of Record The Illinois data to be analyzed represent, at the most, the years between 1978 and 1990. Some pol- lutants were measured only during the later years of this time period. 91 AIR QUALITY TRENDS IN ILLINOIS DATA QUALITY Methods of air pollutant sampling and analysis used by lEPA conform to U.S. EPA standards. However, it should be noted that artifacts can occur on certain types of filters possibly used by lEPA for high volume sam- pling during the data period. Positive sulfate artifacts (formation of sulfate on the filter from gaseous pre- cursors) have been reported (Appel et al., 1984). Both positive and negative (evaporative loss) artifacts can occur for nitrate (ibid.). METHODS Data Source The data used in this report were taken from annual summary reports published by lEPA for the years 1978-1990 (lEPA, 1979-1991). Questionable values were checked with lEPA personnel (Swinford, personal communications, 1992 and 1993) and corrected if necessary. Creation of Computer Files Data were entered by hand into computer spreadsheet and database files from lEPA reports. Sampling site locations were specified by latitude and longitude. Spreadsheet data files were also converted to Geo- graphic Information System (GIS) files using existing data conversion software. Site locations in the Chicago area were verified by comparison of locations plotted on GIS maps against road atlas maps, and corrected when necessary. Statistical Methods Box Plots. Box plots were used to convey information about the distribution of a particular pollutant and its time-averaged concentrations (e.g., annual mean, highest 24-hr average, or highest 1 -hr average) over sampling sites in a specific geographical region for a specific year. For a given year, a box plot shows the 10th, 25th, 50th, 75th, and 90th percentiles, respec- tively, as the low "whisker", the bottom of the "box", the line across the box, the top of the box, and the upper whisker. Individual values outside the 10th and 90th percentiles were also plotted as individual points. Thus, a plot of a series of boxes representing a series of years visually shows how various percentiles of the distribution of pollutant concentration change over time. In addition to showing plots to give a visual im- pression of time trends, we have assessed the statis- tical significance, or lack thereof, of changes in pollutant concentrations over time. Trend Analysis. Time sequences of pollutant con- centrations were tested for statistical significance of time trends over the entire period of record using the nonparametric Spearman Rank Correlation Coefficient as described by Snedecor and Cochran (1980). This is the same trend test used by lEPA to detect the statisti- cal significance of time trends in pollutant concentra- tions. Please note that the critical values of the rank correlation coefficient for significance at various confidence levels given by lEPA (e.g., lEPA, 1991) differ somewhat from critical values given by tables Al l(i) and Al l(ii) in the appendices of Snedecor and Cochran (1980), which were used in this study. The test was applied to the series of medians of the annual distributions over sites within each geographic area. Where significant time trends were found, average an- nual percent changes were calculated by dividing the slope by the concentration computed for 1984 (the mid- dle year of the 1978-1990 series). The 1984 concentra- tion was computed from the linear regression line fitted to the time series of median regional concentrations. Regional Differences. One-way analysis of variance was used to test for differences in mean pollutant concentrations between independent regions; i.e., the Chicago area, the Metro East area, and the remainder of the state. Any data sets that failed the Bartlett's test for homogeneity of variance were also analyzed by the distribution-free Kruskal-Wallace one-way analysis of variance. Differences between individual regions were evaluated from pairwise comparison probabilities computed from the Tukey HSD multiple comparisons procedure. These tests were all carried out using SYSTAT (Wilkinson. 1990). TIME TRENDS IN POLLUTANT CONCENTRATIONS Trends in pollutant concentrations over time are the major emphasis of this part of the Air Resources volume. Table 1 presents computed median pollutant concentra- tions from the distribution of site values for each geographical region and year. Table 2 presents results of statistical tests for significance of time trend for all 92 Table 1. Air Pollutant Concentration Medians, from the Distribution of Individual Sampling Site Values, for Specific Geographic Regions and Years Variable Chicago Metro East Remainder of Year Whole slate area area stale 1978 11.10 10.85 * 12.25 1979 12.10 12.10 ... 16.00 1980 12.75 12.95 — 12.75 1981 16.10 12.65 ... 18.40 1982 13.50 10.40 — 14.50 1983 14.15 14.40 — 12.50 1984 14.00 13.00 — 14.85 1985 9.95 9.65 — 10.30 1986 8.90 8.45 — 11.30 1987 9.75 8.80 ... 11.60 1988 9.30 9.10 — 11.35 1989 8.60 7.30 ... 12.90 1990 9.50 8.90 ... 9.95 1978 7.65 7.15 — . 7.95 1979 8.70 8.60 ... 9.40 1980 7.95 7.35 ... 8.10 1981 9.00 8.80 — 9.50 1982 6.90 6.10 — 7.20 1983 9.30 10.90 — 6.30 1984 8.90 8.90 ... 9.10 1985 6.15 5.55 ... 6.35 1986 5.80 5.45 ... 5.90 1987 5.30 5.30 — 5.30 1988 5.30 5.30 — 5.75 1989 5.10 4.80 ... 7.35 1990 5.30 3.70 ... 5.60 1979 0.430 0.425 0.650 0.340 1980 0.320 0.370 0.390 0.225 1981 0.260 0.285 0.345 0.160 1982 0.290 0.290 0.710 0.160 1983 0.285 0.280 0.400 0.150 1984 0.250 0.240 0.320 0.130 1985 0.150 0.130 0.265 0.070 1986 0.080 0.080 0.220 0.050 1987 0.060 0.060 0.260 0.035 1988 0.050 0.050 0.170 0.020 1989 0.040 0.040 0.165 0.025 1990 0.050 0.055 0.160 0.020 1-hr maximum CO, ppm 8-hr maximum CO, ppm Annual mean Pb, ng/M' Note: * — Insufficient data at enough sampling sites to justify computing a median. 93 AIR QUALITY TRENDS IN ILLINOIS Table I. (Continued) Variable Year Whole state Chicago area Metro East area Remainder of state 1-hr maximum NOj, ppm 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 0.1760 0.1380 0.1480 0.2015 0.1320 0.1320 0.1160 0.1330 0.1060 0.1150 0.1255 0.1125 0.0885 0.2250 0.1460 0.1480 0.2015 0.1320 0.1470 0.1290 0.1340 0.0990 0.1150 0.1290 0,1130 0.0890 24-hr maximum NOj, ppm 1978 1979 1980 1981 1982 1983 1984 198S 1986 1987 1988 1989 1990 0.0970 0.0940 0.0965 0.0740 0.0850 0.0800 0.0570 0.0640 0.0550 0.0590 0.0625 0.0615 0.0480 0.0970 0.0950 0.0965 0.0740 0.0850 0.0900 0.0570 0.0650 0.0560 0.0595 0.0650 0.0630 0.0495 Annual mean NOj, ppm 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 0.0450 0.0510 0.0470 0.0420 0.0385 0.0290 0.0280 0.0270 0.0240 0.0240 0.0230 0.0270 0.0240 0.0450 0.0510 0.0470 0.0420 0.0385 0.0300 0.0290 0.0280 0.0250 0.0260 0.0220 0.0270 0.0250 Note: ' — Insufficient data at enough sampUng sites to justify computing a median. 94 AIR QUALITY TRENDS IN ILLINOIS Table 1. (Continued) Variable Chicago Metro East Remainder of Year Whole state area area state 1978 0.1370 0.1510 0.1710 0.1175 1979 0.1180 0.1215 0.1265 0.1030 1980 0.1210 0.1255 0.1420 0.1050 1981 0.1145 0.1415 0.1230 0.0980 1982 0.1100 0.1170 0.1180 0.0940 1983 0.1370 0.1580 0.1540 0.1065 1984 0.1255 0.1270 0.1380 0.1035 1985 0.1110 0.1145 0.1270 0.1005 1986 0.1110 0.1110 0.1310 0.0985 1987 0.1215 0.1390 0.1260 0.1060 1988 0.1270 0.1275 0.1465 0.1130 1989 0.1100 0.1130 0.1165 0.1030 1990 0.0930 0.0930 0.1180 0.0900 1978 0.1460 0.1125 0.1815 1979 0.1320 0.1310 ... 0.1340 1980 0.1355 0.1450 ... 0.1170 1981 0.1350 0.1150 ... 0.1505 1982 0.1240 0.1160 ... 0.1450 1983 0.0980 0.0900 ... 0.1510 1984 0.1195 0.0955 ... 0.1515 1985 0.1195 0.1090 — 0.1365 1986 0.1210 0.1020 — 0.1990 1987 0.1530 0.1310 — 0.1880 1988 0.1360 0.0880 ... 0.1860 1989 0.1245 0.0870 ... 0.2410 1990 0.1115 0.0660 ... 0.1340 1978 0.0495 0.0435 ... 0.0720 1979 0.0795 0.0820 ... 0.0630 1980 0.0465 0.0400 ... 0.0600 1981 0.0640 0.0650 ... 0.0550 1982 0.0560 0.0615 — 0.0530 1983 0.0420 0.0410 — 0.0645 1984 0.0530 0.0460 ... 0.0670 1985 0.0505 0.0450 ... 0.0690 1986 0.0505 0.0440 ... 0.0850 1987 0.0510 0.0440 ... 0.0565 1988 0.0515 0.0420 ... 0.0850 1989 0.0455 0.0310 — 0.0640 1990 0.0400 0.0260 — 0.0480 1-hr maximum O3, ppm 3-hr maximum SO^, ppm 24-hr maximum SO2, ppm Note: Insufficient data at enough sampling sites to justify computing a median. 95 AIR QUALITY TRENDS IN ILLINOIS Table 1. (Continued) Variable Chicago Metro East Remainder of Year Whole state area area state 1978 0.0090 0.0075 0.0150 1979 0.0120 0.0120 — 0.0110 1980 0.0080 0.0080 ... 0.0095 1981 0.0090 0.0090 ... 0.0075 1982 0.0070 0.0080 — 0.0070 1983 0.0080 0.0090 — 0,0080 1984 0.0080 0,0080 — 0.0080 1985 0.0080 0.0080 ... 0.0085 1986 0.0080 0.0060 ... 0.0085 1987 0.0080 0.0080 ... 0.0090 1988 0.0080 0.0070 — 0.0080 1989 0.0070 0.0070 — 0.0075 1990 0.0070 0.0070 0.0070 1978 189.0 189.0 209.0 183.5 1979 167.5 170.0 217.0 145.0 1980 155.0 156.0 202.0 137.0 1981 161.5 143.5 234.0 163.0 1982 143.5 146.5 166.5 134.5 1983 438.0 495.5 218.0 319.0 1984 139.0 137.0 167.0 139.0 1985 253.0 297.0 179.0 208.0 1986 119.0 123.0 218.0 107.0 1987 141.0 146.0 183.5 131.5 1988 169.0 174.0 188.0 138.0 1989 188.0 188.0 231.0 137.0 1990 220.0 220.0 158.0 237.0 1978 64.0 63.0 85.5 63.0 1979 68.0 68.0 89.5 62.0 1980 68.0 66.0 84.0 65.0 1981 63.0 60.0 84.0 61.0 1982 51.0 52.5 60.0 46.5 1983 53.0 55.0 63.0 50.0 1984 49.0 51.0 63.0 43.0 1985 48.0 50.0 58.5 43.0 1986 48.0 50.0 68.0 44.0 1987 52.0 53.0 76.0 48.0 1988 56.0 60.0 84.0 51.0 1989 70.5 67.0 89.5 50.0 1990 63.0 65.0 78.0 52.0 Annual mean SOj, ppm 24-hr maximum TSP, Mg/M' Annual mean TSP, ng/M' Note: Insufficient data at enough sampling sites to justify computing a median. 96 Table 1. (Continued) AIR QUALITY TRENDS IN ILLINOIS Variable Chicago Metro East Remainder of Year Whole stale area area Slate 1978 5.50 5.50 5.60 5.60 1979 5.40 5.80 5.20 5.20 1980 5.40 4.75 5.50 5.50 1981 5.50 5.80 5.30 5.30 1982 5.15 5.40 4.50 4.50 1983 6.00 6.30 4.90 4.90 1984 5.80 6.00 4.20 4.20 1985 5.00 5.30 3.85 3.85 1986 5.25 5.50 4.10 4.10 1987 5.50 5.50 5.70 5.70 1988 5.30 5.45 4.80 4.80 1989 5.40 5.80 5.05 5.05 1990 4.60 4.80 4.55 4.55 1978 11.90 12.10 13.40 10.50 1979 11.90 11.85 13.50 10.75 1980 12.30 12.55 12.90 11.05 1981 12.00 12.00 12.90 11.60 1982 10.45 10.05 11.55 10.30 1983 12.25 12.20 13.80 10.95 1984 10.80 10.85 11.20 9.10 1985 10.20 10.20 11.65 9.00 1986 10.10 10.05 10.80 8.80 1987 10.20 10.00 14.20 10.00 1988 11.00 10.80 12.10 9.60 1989 10.80 10.50 12.60 9.95 1990 10.70 10.30 12.45 9.50 1978 0.0030 0.0030 0.0080 0.0020 1979 0.0020 0.0020 0.0040 0.0020 1980 0.0020 0.0020 0.0050 0.0020 1981 0.0020 0.0020 0.0040 0.0020 1982 0.0020 0.0015 0.0120 0.0015 1983 0.0020 0.0015 0.0060 0.0015 1984 0.0010 0.0010 0.0080 0.0010 1985 0.0000 0.0000 0.0040 0.0000 1986 0.0010 0.0010 0.0060 0.0000 1987 O.OOIO 0.0010 0.0060 0.0010 1988 0.0020 0.0010 0.0060 0.0010 1989 0.0010 0.0010 0.0040 0.0010 1990 0.0010 0.0010 0.0045 0.0010 Annual mean nitrate, ng/M^ Annual mean sulfate, jig/M' Annual mean As, pg/M' Note: ' — InsufFicient data at enough sampling sites to justify computing a median. 97 AIR QUALITY TRENDS IN ILLINOIS Table 1. (Continued) Variable Chicago Metro East Remainder of Year Whole stale area area state 1978 0.00230 0.00230 0.00760 0.00190 1979 0.00190 0.00175 0.00480 0.00165 1980 0.00070 0.00070 0.00450 0.00045 1981 ... — ... ... 1982 0.00125 0.00055 0.00900 0.00010 1983 0.00040 0.00035 0.00540 0.00015 1984 0.00200 0.00100 0.00500 0.00150 1985 0.00100 0.00000 0.00450 0.00100 1986 0.00300 0.00300 0.00900 0.00100 1987 0.00200 0.00200 0.01000 0.00100 1988 0.00300 0.00300 0.00500 0.00000 1989 0.00000 0.00000 0.00450 0.00000 1990 0.00200 0.00200 0.00400 0.00000 1985 0.0010 0.0010 — 0.0010 1986 0.0095 0.0100 - 0.0035 1987 0.0060 0.0070 ~ 0.0035 1988 0.0050 0.0050 - 0.0040 1989 0.0040 0.0050 - 0.0030 1990 0.0010 0.0040 -- 0.0000 1978 0.850 0.845 1.410 0.740 1979 0.985 0.990 1.785 0.805 1980 0.680 0.710 1.110 0.540 1981 0.605 0.600 1.040 0.580 1982 0.600 0.600 1.365 0.510 1983 0.810 0.810 1.360 0.640 1984 0.690 0.690 1.270 0.500 1985 0.640 0.640 1.435 0.375 1986 0.720 0.720 2.230 0.440 1987 0.840 0.820 2.550 0.530 1988 0.830 0.855 2.700 0.570 1989 1.100 1.245 2.145 0.510 1990 0.980 1.265 2.150 0.600 Annual mean Cd, ng/M-* Annual mean Cr, |ig/M' Annual mean Fe, fig/M^ Note: Insufficient data at enough sampling sites to justify computing a median. 98 AIR QUALITY TRENDS IN ILLINOIS Table 1. (Concluded) Variable Chicago \fetro East Remainder of Year Whole stale area area Slate 1978 0.0435 0.0405 0.1080 0.0590 1979 0.0560 0.0540 0.1330 0.0580 1980 0.0380 0.0355 0.0830 0.0395 1981 0.0380 0.0345 0.0770 0.0410 1982 0.0345 0.0325 0.0850 0.0335 1983 0.0450 0.0460 0.0720 0.0325 1984 0.0430 0.0475 0.0700 0.0320 1985 0.0450 0.0450 0.1040 0.0295 1986 0.0415 0.0420 0.1970 0.0290 1987 0.0430 0.0430 0.2710 0.0370 1988 0.0440 0.0410 0.2760 0.0360 1989 0.0480 0.0480 0.2185 0.0320 1990 0.0470 0.0555 0.2130 0.0360 1984 0.0020 0.0020 .. 0.0030 1985 0.0010 0.0010 - 0.0020 1986 0.0070 0.0070 - 0.0040 1987 0.0050 0.0050 ~ 0.0040 1988 0.0050 0.0070 ~ 0.0030 1989 0.0030 0.0040 ~ 0.0025 1990 0.0030 0.0045 — 0.0020 Annual mean Mn, jig/M^ Annual mean Ni, ng/M' 99 AIR QUALITY TRENDS IN ILLINOIS Table 2. Computed Mean Annual Percent Change in Regional Concentrations, Assuming a Linear Trend. Significance of Time Trend was Based on Spearman Rank Correlation Coefficients. Species CO CO Pb NO2 NO2 NO2 O3* SO2 SO2 SO2 TSP TSP NO3 SO4' As Cd Cr Fe Mn Ni Observation 1-hr maximum 8-hr maximum Aimual mean 1-hr maximum 24-hr maximum Annual mean 1-hr maximum 3-hr maximum 24-hr maximum Annual mean 24-hr maximum Annual Geo mean Annual mean Annual mean Annual mean Annual mean Annual mean Annual mean Annual mean Annual mean Chicago Metro East Remainder Whole state area area of state -3.5" -3.7" -2.7" -4.6- -5.3- ... -3.7- -20.5"' -21.2'" -12.6'" -24.8"' -4.4- -5.5- 5.5- -5.2"' — — -7.1- -6.8"- ... ~ n.s.(D") n.s.(D") n.s n.s. n.s. -3.5"- — n.s. n.s. n.s. — n.s. -2.6"' -5.2* — n.s. n.s. n.s. n.s. n.s. n.s. n.s. n.s. n.s. n.s. n.s. n.s. -2.1* -1.3* -1.6* n.s. -1.4" -8.4'" -11.1- n.s. -9.5"' n.s. n.s. n.s. -12.7" n.s. n.s. ... n.s. n.s. n.s. +6.0" n.s. n.s. n.s. ■HlO.O' -4.4" n.s. n.s. — n.s. Notes: n.s. = not significant. D = downward trend (not quantifiable by method used). Significance levels: ' = 5 percent, " = 1 percent, and "' = 1 percent. — = not enough sites to estimate trends. (When there were not enough Metro East sites for a trend estimate, the Metro East sites are included with the remainder of the state.) * O3 data were tested for time trend both before and after accounting for surface temperature influences. Results in parentheses show trend and significance after accounting for surface temperature. 100 AIR QUALITY TRENDS IN ILLINOIS pollutants examined. Time trends for each pollutant are graphed and the text discusses the results of the related statistical tests in table 2. The graphs show concentra- tions at several percentile points on the distribution of particular pollutant concentration statistics (i.e., annual means or 24-hr maxima) over all sampling sites within a given geographic area for each of a series of years, and how these percentiles of concentration change over the period 1978-1990. The box plot is a convenient graphical device to use for this purpose, because it shows several concentration percentiles simultane- ously. The concentrations plotted in a single graph are averages over a particular time period, such as one hour, 24 hours, or an entire year. For the criteria pollutants, these averaging times correspond to those for which the standards are written for each particular pollutant, so they vary from one pollutant to the next, and a given pollutant may have two or more graphs, corresponding to two or more averaging times. It will become apparent later that the number of sam- pling sites for a given pollutant in any geographical area changed from year to year as new sites were installed or previously used sites were taken out of service. In recent years the number of sampling sites has dropped markedly for most pollutants. This sug- gests an alternative approach to the analysis of time trends: analysis of time trends only at sites with long- term records. This approach was rejected in favor of the analysis of time trends in regional medians because very few sites had long-term records, and such sites could not be inferred to represent broad geographic areas. Data used in the following statistical tests are shown in table 1. Results of the statistical tests for the significance of trends are shown in table 2, and the time sequences of box plots in figures 1-30. Each figure shows results for up to four geographical areas, depending on whether the number of sampling sites in the area was sufficient to justify a separate plot. Each figure shows results for the entire state and the Chicago area, which is the portion of the U.S. EPA's Air Quality Control Region (AQCR) 67 in Illinois. Many figures also show results for the Metro East area on the Illinois side of the Mississippi River across from St. lx)uis. This is the Illinois portion of AQCR 70. The fourth geographic region shown is the remainder of the state, excluding the Chicago area and the Metro East area (if shown separately). If the Metro East area is not shown separately, then the region labeled as "remainder of state" also includes any data from the Metro East area. Criteria Pollutants Carbon Monoxide (CO). Results for CO are shown in table 2 and figures 1 and 2. The table shows trends toward decreasing concentrations significant at the 5 percent level, or better, for both 1-hr (figure 1) and 8-hr (figure 2) maxima during the 1979-1990 period, in all three geographic areas with sufficient data to test. The overall linear trends range from -2.7 percent to -5.3 percent. Figure 1 suggests generally higher and slightly increasing 1 -hr maximum concentrations at all per- centile levels represented by the box plots during the 1978-1984 period, followed by lower and decreasing concentrations from 1985 onward. This pattern appears in all three geographic areas shown in the figure. The 1-hr CO standard, 35 parts per million (ppm), appears not to have been exceeded anywhere in the state during the 1 3 years of record. On the other hand, the 8-hr maximum concentrations of CO (figure 2) exceeded the standard, 9 ppm, repeatedly until very late in the 1979-1990 period. Figure 2 shows a pattern of higher concentrations at all percentiles during the 1978-1984 period, followed by lower and decreasing concentrations from 1985-1990, in all geo- graphic areas. The statistical comparison of CO concentrations between geographical regions found a significant difference (5 percent) between the Chicago area and the remainder of the state for the 1-hr (figure 1), but not for the 8-hr (figure 2) averaging time. For both averaging times, however, it appears that early in the 1979-1990 period the Chicago area contributed the highest individual concentrations, whereas the highest values during the later years of the period came from elsewhere in the state. For both CO averaging times, the number of sampling sites (N) remained relatively constant, with about 1 5 sites in the entire state, 6 to 1 1 sites in the Chicago area, and 6 or 7 sites elsewhere. Lead (Pb). Airborne Pb concentrations decreased dra- matically (figure 3) during the 1979-1990 period, due in part to the phase-out of leaded gasoline, beginning in about 1975 (lEPA, 1991). Table 2 shows decreasing linear trends between -12.6 percent and -24.8 percent per year in the four geographical regions. While the trends are significant at the 1 percent level in all four regions, the rate of decrease in the Metro East area is considerably smaller than the others. Figure 3 graph- ically shows the marked drops in all the concentrations 101 AIR QUALITY TRENDS IN ILLINOIS E Q. Q. c" o c o c o O 35 30 25 20 15 10 5 —I — I — I — I — r Whole state -1 — r O -1 — I — 1 — I — r O . N:16 17 12 15 13 U 13 14 15 12 17 17 16 I I I I I I I I I I I I I T 1 — I r -1 — I — I — I — I — r Chicago area q Q 78 79 80 81 82 83 84 85 86 87 88 89 90 35 E D. Q. c" o c O c o O Note: The national and state primary standards for 1-hr average CO are both 35 ppm. These are not to be exceeded more than once per year. N = number of samples. 30 - 25 20 15 10 5 — 1 — I — I — I — I — I — I — I — I — r Remainder of state Year 78 79 80 81 82 83 84 85 86 87 88 89 90 Figure 1. Trends in 1-hr maximum CO concentrations in Illinois. 78 79 80 81 82 83 84 85 86 87 88 89 90 25 Note: The Federal and State Primary Standards for 8-hr average CO are both 9 ppm. These are not to be exceeded more than once per year. N= number of samples. Year 78 79 80 81 82 83 84 85 86 87 88 89 90 Figure 2. Trends in 8-hr maximum CO concentrations in Illinois. 102 AIR QUALITY TRENDS IN ILLINOIS CO D5 c g i_ -*— ' c Q) O c o O 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0 -| 1 1 1 r O "T — I — I — I — I — r Whole state N:93 101 97 46 46 45 51 39 31 19 15 17 I I I I I I I I I I I 1_ — ; — I — I — I — I — I — I — I — 1 — r- o Metro-East area N:16 15 16 I I L_ 7 7 _l l_ 6 5 4 4 J I I 1_ T 1 1 1 1 1 1 1 1 1 1 1— Chicago area ■^##.ft ^iS. N:52 60 60 35 34 33 37 27 21 11 7 8 I I 1 I 1 I I I I I I 1_ ~i I I I I I I 1 1 I I r Remainder of state N:25 26 21 6 5 5 6 5 4 3 J I I I I I l_ 79 80 81 82 83 84 85 86 87 88 89 90 79 80 81 82 83 84 85 86 87 88 89 90 Year Note: Standards are based on the quarterly arithmetic mean. See text. N = number of samples. Figure 3. Trends in annual mean Pb concentrations in Illinois. E Q. Q. C o ^— • c Q) O c o O 0.40 0.35 0.30 0.25 0.20 0.15 0.10 0.05 0.00 T — r— I — I — r -1 — I — I — I — r Whole state o o ~I I I I p It ■T — I — I — I — I — I — r- Chicago area o o 78 79 80 81 82 83 84 85 86 87 88 89 90 78 79 80 81 82 83 84 85 86 87 88 89 90 Year Note: There are no national or state standards for 1-hr average NO,. Figure 4. Trends in 1-hr maximum NO^ concentrations in Illinois. 103 AIR QUALITY TRENDS IN ILLINOIS 0.30 E Q. 0.25 Q. _ 0?0 C_ n 0.1b m c 0.10 0) o 05 u o ri o.uo T — I — I — I — I — I — 1 — I — I — I — I — I — r Whole state N:43 47 24 23 23 23 23 18 10 9 I I I I I I I I I L -1 — I — I — I — I — 1 — I — I — I — I — I — I — r- Chicago area N:41 42 24 23 23 21 21 17 9 8 13 13 14 I I I r I I f r I I I I I 78 79 80 81 82 83 84 85 86 87 88 89 90 78 79 80 81 82 83 84 85 86 87 88 89 90 Year Note: There are no national or state standards for 24-hr average NOg. N = nunnber of samples. Figure 5. Trends in 24-hr maximum NO concentrations in Illinois. 0.10 g- 0.08 C _0 0.06 ■^ C 0.04 Q) O c O 0.02 0.00 T — I — I — I — I — I — I — I — I — I — I — \ — r- Whole state standard o '-' o 6 N:36 33 21 21 18 21 21 13 10 9 8 14 II I I I I I L. -| — I — I — I — I — I — I — I — I — I — I — I — r- Chlcago area o o O 6 O o N:36 32 21 21 18 19 19 12 9 8 7 13 J I I I I I I I I I I I U 78 79 80 81 82 83 84 85 86 87 88 89 90 78 79 80 81 82 83 84 85 86 87 88 89 90 Year Note; The national and state standards for annual mean NOg are 0.053 ppm. N= number of samples. Figure 6. Trends in annual mean NO concentrations in Illinois. 104 AIR QUALITY TRENDS IN ILLINOIS 0.30 0.25 0.20 0.15 E Q. Q. C g •I—' c 0) o c o O 0.10 0.05 0.00 0.30 0.25 0.20 0.15 0.10 0.05 0.00 T — I — I — I — I — I — I — I — I — I — I — I — r Whole state N:39 43 39 44 38 39 36 39 35 34 37 39 40 I I I I I I I I I I I I l_ -1 — I — I — I — I — I — I — I — I — I — I — I — r- Metro-East area N: 6677777766666 I f r I t I I I I I I I I N:21 24 20 20 18 18 17 20 17 17 18 19 19 J I I I I I I 1 I I I I 1_ -I 1 1 1 1 1 1 1 1 1 1 1 — r- Remainder of state Standard N:12 13 12 15 13 14 12 12 12 11 13 14 15 I I I I 1 I I I I I I I I 78 79 80 81 82 83 84 85 86 87 88 89 90 78 79 80 81 82 83 84 85 86 87 88 89 90 Year Note: The national and state primary standards for 1-hr O3 are 0.12 ppm. N = number of samples. Figure 7. Trends in 1-hr maximum O concentrations in Illinois. E Q. Q. c" g k_ *-« c 0) o c o O "T — 1 — r. — I — ; — I — I — T" Chicago area .Standard 78 79 80 81 82 83 84 85 66 87 88 89 90 - _ 0.7 N:12 18 9 13 14 15 14 14 14 11 11 11 11 1 1 1 I I I 1 I I I I I 1_ Note: There are no national or state primary standards for 3-hr maximum SOj concentration. The secondary national standard for 3-hr maximum SOg concen- tration is 0.5 ppm. N = number of samples. 0.6 0.5 0.4 0.3 0.2 0.1 0.0 "T I I I 1 I I I 1 r Remainder of state IlfiA W y i N:18 17 17 16 17 16 16 16 16 16 17 17 17 I r r I I 1 I I I I t I I Year 78 79 80 81 82 83 84 85 86 87 88 89 90 Figure 8. Trends in 3-hr maximum SO^ concentrations in Illinois. 105 AIR QUALITY TRENDS IN ILLINOIS c CD O c o O T — r — I — I — I — I — I — I — I — I — I — I — I" „ Chicago area / Standard N:44 47 25 13 14 15 14 14 14 11 11 11 11 I I I L. 78 79 80 81 82 83 84 85 86 87 88 89 90o 30 0.25 Note: The national and state primary standards for 24-hr maximum SOg concentration are both 0.14 ppm. N = number of samples. 0.20 0.15 0.10 0.05 0.00 I I I I I r — I — I — I — I — I — 1 — r Remainder of state o o trttl w @ @ N:18 17 17 16 17 16 16 16 16 16 17 17 17 1 I r I I I t I I t t 1 I 78 79 80 81 82 83 84 85 86 87 88 89 90 Year Figure 9. Trends in 24-hr maximum SO^ concentrations in Illinois. E o. a. c o 'To +-» c 0) o c o o 0.05 0.04 0.03 0.02 0.01 0.00 1 — I — I — I — I — r -1 — I — I — I — I — r Whole state N:52 52 39 25 27 29 27 29 27 26 26 27 26 I I I I I I 1 I I I I I L_ T 1 1 1 1 1 1 1 1 1 1 1 I Chicago area / Standard O O O - N:38 36 25 11 11 13 11 13 11 11 11 11 11 r I r I r t r I I 1 r 1 I 78 79 80 81 82 83 84 85 86 87 88 89 90o,o5 0.04 Note: The national and state primary standards for annual arithmetic mean SOg concen- ration are 0.03 ppm. N = number of samples. 0.03 0.02 0.01 0.00 — I — I — I — I — I — I — r Remainder of state N:14 16 14 14 16 16 16 16 16 15 15 16 15 I I I I I I I I I I I I 1_ 78 79 80 81 82 83 84 85 86 87 88 89 90 Year Figure 10. Trends in annual mean SO^ concentrations in Illinois. 106 AIR QUALITY TRENDS IN ILLINOIS c CD O c o o 1200 1000 800 600 400 200 Note: T — I — I — I — I — I — I — I — I — I — I — I — r Metro- East area N:18 20 17 18 16 15 15 16 13 12 8 5 7 r I I I I I I I I I f I I T 1 1 1 1 1 1 — I — I — I — I — I — r Remainder of state 8 p 8 8 ° A iQ i N:44 43 39 34 32 34 33 33 32 30 22 7 7 I r I I I I 1 I I I I I [_ 78 79 80 81 82 83 84 85 86 87 88 89 90 78 79 80 81 82 83 84 85 86 87 88 89 90 Year The state primary standard for 24-hr maximum TSP concentration is 260 /xg/M . N = number of samples. Figure 11. Trends in 24-hr maximum TSP concentrations in Illinois. 300 250 200 150 ■} 100 O) :t 50 c o n CO 300 c o c o O 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0.0 1 1 1 r Whole state Note: Ni measurements began in 1984. Analysis of individual filters for metals began in 1985. There are no national or state standards for Ni. N = number of samples. 1 1 n Chicago area ■1.^^ AUcL N = 29 30 25 Year 84 85 86 87 88 89 90 0.6 1 1 I I II — 1 Remainder of State 0.5 - - 0.4 - - 0.3 - - 0.2 - o 0.1 - 4. -a. ^ ^ ^ _L 1 N = 1 12 11 11 11 9 11 1 1 1 1 1 1 O ^— » c O c o O Figure 29. Trends in 24-hr maximum Ni concentrations in Illinois. 0.040 0.035 0.030 0.025 0.020 0.015 0.010 0.005 0.000 1 : r Whole State ^A X ? i N=15 17 27 17 84 85 86 87 88 89 90 Note: Ni measurements began in 1984. There are no national or state standards for Ni. N = number of samples. 0.040 0.035 0.030 0.025 0.020 0.015 0.010 0.005 0.000 Year Remainder of state ^l^O^i N=11 l_ 12 _l_ Figure 30. Trends in annual mean Ni concentrations in Illinois. _i_ 84 85 86 87 88 89 90 116 AIR QUALITY TRENDS IN ILLINOIS corresponding to the percentiles depicted by the box plots. There has clearly also been a drop in the highest annual Pb concentration in each region, as depicted by the uppermost open circle. This dropoff was quite dramatic in the entire state, where numerous concentrations exceeded 1 microgram per cubic meter (p.g/M') oc- curred between 1979 and 1982, but none thereafter. Comparison of the "whole state" panel with the other three panels clearly shows that high individual concen- trations during the 1979-1982 period occurred in the Metro East area. The marked improvement in maxi- mum and median Metro East airborne Pb concentrations after 1982 is likely to have been strongly influenced by the closure and subsequent cleanup of a secondary lead smelter in Granite City (Cooper and Frazier, 1983). The national and state standard for Pb is a quarterly arithmetic mean of 1 .5 |ig/M'. No violations of this standard have occurred in Illinois since 1982 (ffiPA, 1991). Inspection of figure 3 indicates systematically higher individual Pb concentrations (open circles) in the Metro East area than in the Chicago area or the remain- der of the state, especially during the 1979-1984 per- iod. The statistical test for differences between regional means found only the Metro East Pb concentrations higher than the remainder of the state at the 5 percent level. Median Pb concentrations in the Metro East area were also higher than those in the Chicago area, but the differences were not quite significant at the 5 percent level. As Pb concentrations have decreased, and violations of the standard have dropped to zero, the number of sites measuring airborne Pb concentrations in Illinois has also dropped sharply. Statewide, the number of sam- pling sites with valid annual means decreased from a high of 101 in 1980 to 17 in 1990. In the Chicago area the corresponding numbers are 60 and 8; in the Metro East area, 16 and 4; and in the remainder of the state, 26 and 5. Nitrogen Dioxide (NOj). Concentrations of NO^ decreased substantially in Illinois during the 1980s. Table 2 shows decreasing trends for 1-hr and 24-hr maxima, as well as annual mean NO^ concentrations, both statewide and in the Chicago area. The trends range from 4.4 percent to -7.1 percent per year, and all are significant at the 1 percent level. There were not enough sampling sites in the other areas of the state to justify testing. Box plots for 1-hr maximum, 24-hr maximum, and annual mean NO^ are shown in figures 4-6, respectively. They illustrate the decreases, during the 1979-1990 period, in NO^ concentrations both statewide, and in the Chicago area, over all three averag- ing times. Although only the trend of the median has been tested statistically (table 2), it is apparent that concentrations associated with all the percentiles de- picted by the box plots have decreased. The same is true for the highest individual values each year (plotted as open circles). No national or state standards exist for 1 -hr or 24-hr maximum NO^ concentrations. Numerous concentra- tions above the annual mean NO^ standard (0.053 ppm) occurred in the late 1970s, but none have occurred since 1980. Almost all of the NO^ measurement sites are in the Chicago area, so it is impossible to look for differences in concentrations between geographic regions. The number of sites measuring valid 1-hr NO^ concen- trations has increased recently, both statewide and in the Chicago area, from a low of four sites in the early 1980s to about 15 sites in 1990. The number of sites with valid 24-hr and annual mean NO^ concentrations has decreased from 36-47 sites in the late 1970s to 10- 15 sites in 1990. Ozone (Oj). All pollutants are affected to some extent by weather conditions. Poor dispersion conditions caused by low wind speeds or calm conditions can allow pollutant concentrations to build up in local areas near emission sources, and long-range transport can carry pollutants from their sources for deposit at distant locations. For O^, which is produced in the atmosphere by reactions between hydrocarbons and nitrogen oxides, however, weather conditions — especially tem- perature — affect how much of the pollutant is pro- duced. Thus, it is desirable to remove the effect of weather conditions when looking for trends in O^. We first discuss O, concentrations as observed, and then use a statistical regression approach to look for trends in O3 after the effect of temperature has been removed. Table 2 indicates that no significant trend could be detected in the median of 1 -hr maximum O, concentra- tions in any geographic region of Illinois. The box plots of 1-hr maximum values by geographic area are shown in figure 7. Year-to-year variations are apparent, including higher concentrations statewide and in the Chicago area in 1983 and 1988, when abnormally high temperatures and little rain occurred during the summer 117 AIR QUALITY TRENDS IN ILLINOIS ozone season, but overall the visual impression of no trend toward higher or lower concentrations agrees with table 2. The Chicago and Metro East areas clearly had higher median concentrations during the data period, com- pared to the remainder of the state, and these two urban centers also account for all the the highest individual site values statewide (open circles). The national and state standard for 1-hr maximum O^ concentration is 0.12 ppm. It is apparent that numerous violations of the standard occur most years in Illinois, although only two sites exceeded the standard (one time each) in 1990. Weather conditions over much of Illinois, and especially in the Chicago area, during the summer of 1990 were cooler, cloudier, rainier, and windier than normal (lEPA, 1991). These conditions undoubtedly contributed to the lower O3 concentra- tions observed. The test for differences between regions showed that mean concentrations in the Chicago and Metro East areas were each significantly (5 percent level) greater than that in the remainder of the state. A number of attempts to account for effects of atmo- spheric conditions on O3 concentrations have been published (e.g., Korsog and Wolff, 1991; Shively, 1991). Some of the past work has been quite sophisticated in searching for the best meteorological parameters to use in predicting Oj concentrations, and in the use of sta- tistical methods to characterize the relationship. In contrast, the following attempt to account for the effects of meteorological conditions on O3 in Illinois is relatively simple. It uses only mean surface temperature during the O3 season (April-October) in a regression equation involving a constant, a temperature term, and a time term. The model is: [O3] = Constant + 13, ■ (Tune) + Pj • (Tenperature) (1) where [O3] is ozone concentration, and p, and P^ are coefficients of time and temperature, respectively. The procedure is to evaluate the coefficients of the time and temperature terms using observed O3 and temperature data, and to observe whether the coeffi- cient of the time term is significantly different from zero. If it is, then there is a significant trend with time after the effect of temperature on O^ concentrations has been removed. The model was evaluated for each of the four geographical areas defined above. The O3 data were the medians of the annual disuibution of 1-hr maximum O3 concentrations over all measurement sites in each geographical region. Corresponding April- October mean temperatures were obtained for each region from the Midwestern Climate Information Sys- tem (Kunkel et al., 1990). Time was sequential year number, beginning with 1 in 1978. The regression analyses were carried out using the Multiple General Linear Hypothesis (MGLH) regression routine in the SYSTAT statistical software (Wilkinson, 1990). Results are shown in table 3. The first thing to notice about the results is that the temperature coefficient is positive, indicating a positive correlation between O3 and temperature, as expected, in all four geographical regions. The temperature coef- ficient is significantly different from zero (5 percent level) over the whole state, and also in the "remainder" region, significant at the 10 percent level in the Metro East region, and just barely misses the 10 percent sig- nificance level (P = 0.101 1) in the Chicago area. The coefficient of the time term is negative, indicating a downward trend in concentrations, in all four regions. The downward trend, after accounting for the effects of surface temperature, is significant at the 5 percent level over the whole state and in the Chicago area, and at the 10 percent level in the other two regions. (Note: al- though not shown in table 2, a - 1 .9 percent per year downward linear trend in O, significant at the 10 percent level was detected in the O3 concentrations as observed.) A further indication of the importance of the time term is the improvement in the squared multiple correlation (R^ or the percent of the total variance explained by the regression) as the time term is added to the regression model. The model was evaluated separately without the time term to obtain R^ values with and without the time term in each region. Results are shown in table 4. There is a substantial improvement in the percent variance, explained with the addition of the time term in each region — from 26 to 58 percent for the whole state, from 5 to 46 percent in the Chicago area; from 16 to 42 per- cent in the Metro East area, and from 40 percent to 55 percent in the remainder of the state. The results regarding ozone time trends may be sum- marized as follows. Without accounting for temper- ature effects, no trends were found at a 5 percent significance level, but a 1.7 percent per year downward trend in concenu-ations. significant at the 10 percent level, was detected in the Chicago area (not shown in 118 AIR QUALITY TRENDS IN ILLINOIS Table 3. Results of Regression Analysis To Test Significance of O, Time Trend after Accounting for Effects of Average Surface Temperature Geographic region Whole state Chicago area MetroEast area Remainder of state P Variable' Coefficient (2 -tail) Constant -0.30400 0.0774 Time -0.00177 0.0196 Temperature 0.00565 0.0186 Constant -0.36658 0.2236 Time -0.03108 0.0194 Temperature 0.00707 0.1011 Constant -0.28673 0.2287 Time -0.00212 0.0605 Temperature 0.00548 0.0811 Constant -0.20043 0.0651 Time -0.00073 0.0958 Temperature 0.00401 0.0098 Note: "Temperature = mean surface temperature, April through October, in the region. Table 4. Comparison of R^ Values (Explained Variance) in Regression Equations Evaluated with and without Time Terms Geographic region Whole state Chicago area Metro East area Remainder of state R (without lime) 0.260 0.048 0,165 0.399 R (with time) 0.582 0.464 0.423 0.551 119 AIR QUALITY TRENDS IN ILLINOIS table 3). After accounting roughly for temperature effects, downward trends were detected at the 5 percent level statewide and in the Chicago area, and downward trends significant at the 10 percent level were detected in the other two regions. For evaluating potential effects of ozone on agricultural crops, concentrations in the non- urban "remainder" region would be the most relevant. Sulfur Dioxide (SO^). Table 2 shows downward trends significant at the 1 percent level for 3-hr maximum SO^ in the Chicago area (-3.5 percent per year), and for annual mean SO^ over the whole state (-2.6 percent per year). The table also shows a downward trend signifi- cant at the 5 percent level for annual mean SO^ in the Chicago area (-5.2 percent per year). No trends signif- icant at 5 percent or better were detected for any of the three types of observations in any region of the state; note, however, that the number of observing sites in the Metro East area was insufficient to estimate a trend. Box plots for 3-hr maximum SO^ are shown in figure 8. Any trends are difficult to perceive by the naked eye, despite the highly significant trend detected in the Chicago area (table 2). Comparison of SO^ concentra- tions between regions shows that the highest 3-hr maximum SO^ values observed statewide occurred in areas other than the Chicago area. There is no national or state primary standard for 3-hr maximum SOj. The secondary national standard for 3-hr maximum SO^ is 0.5 ppm. Figure 8 shows that this standard has been exceeded on a few occasions during the 1978-1990 period. The test for differences between regions found concentrations in the Chicago area significantly lower than those in the rest of the state. The number of sampling sites with valid data for 3-hr maximum SO^ has remained very constant during the period. Box plots for 24-hr maximum SO^ are shown in figure 9. No trends are apparent to the naked eye, and no significant trends were detected in table 2. Again, the Chicago area experienced somewhat lower median concentrations than the remainder of the state, which in this case includes the Metro East area. The difference was signif-icant at better than the 1 percent level. The national and state primary standard for 24-hr maximum SOj, 0.14 ppm, has been exceeded a few times state- wide in most years between 1978 and 1990; but only four of these occurred in the Chicago area. Numbers of sites with valid data fell by a factor of about 2 state- wide over the 1978-1990 period. Most of this reduction oc-curred in the Chicago area, which had 47 sites with valid data in 1979, but only 1 1 sites in 1990. Most of this reduction is the result of closing sampling sites, rather than active sites not meeting completeness criteria. Figure 10 shows box plots for annual mean SO^ con- centrations. Decreases in median concentrations statewide are significant at the 1 percent level and in the Chicago area at the 5 percent level (table 2). Regional maximum concentrations (highest open circle) also appear to be on downward trends, at least for the "whole state" and "remainder" regions. There were no significant (5 percent) differences in concen- tration between geographic regions. Numbers of sites with valid data have also decreased over the 1978-1990 period, statewide by about 50 percent, and by about 70 percent in the Chicago area. Particulate Mass (TSP, PM^^. The state standard for particulate mass is written for total suspended particulate matter (TSP), while the national standard is for PM||,, or particulate matter up to 10 |im in aerodynamic diameter. Box plots for 24-hr maximum TSP concentrations are shown in figure 1 1 . Median values have remained relatively constant over the 1978-1990 period with occasional anomaly years such as 1983, when spring dust storms in east central and northeastern Illinois (lEPA, 1984) caused numerous measurements > 500 |j,g/M^ No significant trends in median concentrations were detected (table 2) in any of the four geographic regions for the entire 1978-1990 period, but careful exainination of the individual regional plots suggests a decreasing trend for the first half of the 1980s followed by an increasing trend in the later half, at least in some regions. It is important to know whether these recent concentra- tion increases reflect actual regional environmental conditions, or whether they are an artifact of the year- to-year changes in the measurement network. Numbers of sites with valid samples have dropped sharply in all regions in recent years, and if the sites removed from the network were systematically in cleaner areas (which might be expected), then average concentrations at the remaining sites would be higher. This question could be investigated by comparing records of concentrations at removed sites and at remaining sites. The test for differences between regions found none (5 percent level), but some violations of the standard have occurred each year in all regions. Trends in annual geometric mean TSP concentrations are shown in figure 1 2. No overall significant trends were detected (table 2), but the pattern of decreasing concentrations up to about 1985, followed by increases 120 AIR QUALITY TRENDS IN ILLINOIS through 1989, is clear in all four regions. Again, how- ever, the reality of the increase in the late-1980s is in doubt because the number of sites with valid data declined sharply during the 1986-1990 period. Com- parison of concentrations between regions showed that concentrations in the Metro East area were significantly (1 percent level) higher than those in both the Chicago area and the remainder of the state. In addition, visual examination suggests that the highest individual site values occurred in the Metro East region. The first published data for PM,(, are for 1987 (lEPA, 1988), after the U.S. EPA changed its particulate matter standard from TSP to PM|g, although some measurements were being made in anticipation of the new national standard as early as 1984 (lEPA, 1988). Because data were available for only four years, no evaluation of PM|g trends was included in table 2. However, box plots for 24-hr maximum and annual mean PM^, are shown in figures 13 and 14, respectively. Figure 13 shows a number of violations of the 150 \ig/ M' standard for 24-hr maximum PM^g in both the Chi- cago area and other areas of the state. The number of sampling sites increased in all three geographic areas shown in the figure during the 1987-1990 period. Figure 14 also shows a few concentrations above the 50 Hg/M' standard statewide, none of which occurred in the Chicago area. Statewide, the number of sampling sites collecUng filter samples dropped from > 100 in 1978 to <20 in 1990; the change from 1985 to 1990 was from about 50 sites to <20. In the Chicago area the drop in sites was from >70 in 1978 to 35-40 in 1985 to <10 in 1990. In the Metro East area, there were >15 sites up to 1981 and <5 after 1985. The numbers for the remainder of the state were >25 sites up to 1981 and 4-6 thereafter. Nitrate Ion (NOj). Box plots for 24-hr maximum and annual mean NO^ concentrations are shown in figures 15 and 16, respectively. High year-to-year variability in the median (and other box plot per- centiles) 24-hr maximum NO^ concentrations (figure 15) is apparent, particularly in the Metro East and "remainder" areas, where the plots are based on <10 sites. For annual mean NO^ , the only significant trend (1 per- cent level) was a -2.1 percent per year decreasing trend in the "remainder" region (table 2). Figure 1 6 shows a relatively steady median concentration of about 5 |ig/ M' statewide and in the Chicago area, and somewhat lower concentrations, with more year-to-year variabil- ity in the Metro East and remaining areas of the state. The comparison between regions found the Chicago area concentrations significantly (5 percent or better) higher than those in the Metro East area and the re- mainder of the state. This concludes the presentation of data on the criteria pollutants. There are currently no standards for the remaining pollutants, which all occur as particles in the atmosphere, and are collected on high-volume filters. Filter Analyses: Nitrate, Sulfate, and Metals Through 1984, annual mean concentrations of nitrate, sulfate, and metals were derived from analyses of filters composited monthly. Thus, distributions of annual means are available from 1978-1990, but dis- tributions of 24-hr maximum concentrations are avail- able only after 1985, when measurements of individual 24-hr filters began. Since all of these analyses depend on the collection of filter samples, it is appropriate to discuss changes in the number of valid samples that apply to all of the follow- ing analytes. Of course there are small individual differences between pollutants in the number of valid samples, but the major trends are determined primarily by the number of active sampling sites. Both statewide and in the Chicago area, the varia- bility within individual years, as measured by the interquartile (75th-25th percentile) range, or the height of the "box" in the box plot, appears to have decreased in recent years. Again, however, this oc- curred along with a steep decline in the number of sites with valid data, so the smaller variability may simply reflect the fact that measurements are occur- ring at fewer locations. Sulfate Ion (SO^^). Box plots for 24-hr maximum and annual mean SO^- are shown in figures 17 and 18, respectively. Here also relatively high year-to-year variations in 24-hr maxima occurred, particularly in years or geographic areas with < 1 sites. Table 2 shows that declines in annual mean SO/ con- cenU-ation significant at the 5 percent (whole state and Chicago area) or 2 percent (remainder of the state) levels occurred in all areas other than the Metro East area. The significant linear trends were all between -1.3 and - 1 .6 percent per year. 121 AIR QUALITY TRENDS IN ILLINOIS Concentrations were significantly (1 percent level) higher in the Metro East area than in the Chicago and "remainder" regions of the state. cago area, although the differences were not statisti- cally (5 percent) significant. No significant trends in the median annual mean Cr were detected (table 2). Arsenic (As). Box plots for 24-hr maximum and an- nual mean As are shown in figures 19 and 20, respec- tively. Except for the Metro East area, where median 24-hr maximum concentrations >0.01 fig/M^ occurred in four of the six years of record, the median 24-hr maximum was <0.01 |J.g/M' statewide. One value >0.5 H,g/M' was observed in the Metro East area in 1990. Differences between geographical regions are the most interesting feature of these plots. Comparison of the plots for the various regions shows clearly that the Metro East area accounts for the highest measured values statewide; this is true for both maximum 24-hr concentrations as well as mean annual concentrations. The statistical test for differences between regions was not run on the 24-hr maximum As data because of the relatively few years of data. For annual mean As, the test found that concentrations in the Metro East area were higher than those in the Chicago and "remainder" areas at the 0.1 percent significance level. Table 2 shows declines in As concentrations of -8.4, -11.1, and -9.5 percent per year in the whole state, the Chicago area, and the "remainder" region, respectively. All are significant at the 1 percent level. Cadmium (Cd). Box plots for 24-hr maximum and annual mean Cd are shown in figures 21 and 22, respectively. Again, differences between geographical regions are clear, and again the Metro East area accounts for most of the highest values that were ob- served statewide over both averaging times. The test for regional differences in annual mean concentration confirmed that the highest concentrations occurred in the Metro East area at a significance level of 0.1 per- cent. Table 2 shows that the decline of -12.7 percent per year in annual mean Cd in the "remainder" region was significant at the 2 percent level. Cliromium (Cr). Figures 23 and 24 show box plots of 24-hr maximum and annual mean Cr, respectively. Note that Cr was not measured on filter samples until 1985. The number of sites in the Metro East area was insufficient for a separate plot, so the Metro East sites are included in the "remainder" region. The marked differences between regions that were apparent for As and Cd are smaller or absent here. Rather than the Metro East area having the highest concentrations, Cr appears to be somewhat more prominent in the Chi- Iron (Fe). Box plots for 24-hr maximum and annual mean Fe are shown in figures 25 and 26, respectively. For both averaging periods, it is again clear from the figures that the Metro East area accounts for the highest values statewide. The test for differences between regions confirmed that the highest annual mean Fe concentrations occurred in the Metro East area (0.1 percent level). Moreover, the trend test (table 2) de-tected an upward trend (6.0 percent per year) in the Metro East area, significant at the 2 percent level. While it is true that the two area sampling sites with the lowest annual mean concentrations were closed during the 1985-1990 period (one after 1985, and the other after 1988), this is not the cause of the increasing trend in concentrations. Concentrations at the remain- ing sites also increased during these years. Manganese (Mn). Figures 27 and 28 show box plots for 24-hr maximum and annual mean Mn, respectively. Both the Chicago area and the Metro East area contrib- uted to the highest values over both averaging periods observed statewide, but the Metro East area experi- enced noticeably higher median concentrations (figures 27 and 28). This was confirmed for annual means by the test for differences between regions, which found higher concentrations in the Metro East area compared to the Chicagto and "remainder" areas (0. 1 percent level). As in the case of Fe, the trend test (table 2) detected an increasing trend (10 percent per year), sig- nificant at the 5 percent level, in annual mean Mn in the Metro East area. Also as in the case of Fe, the clos- ing of sampling sites could have had only a minor effect on the increasing Mn concentrations over the 1985-1990 period. Nickel (Ni). Box plots for 24-hr maximum and annual mean Ni are shown in figures 29 and 30, respectively. Ni was not measured on filter samples until 1984. Since the number of sites in the Metro East area was insufficient for a separate plot, the Metro East sites are included in the "remainder" region. For Ni, it appears that the Chicago area contributed most of the highest 24-hr maximum concentrations (figure 29). Comparing annual means between regions, it appears that the Chicago area has recently experienced somewhat higher median concentrations, but the statistical test found no significant (5 percent level) differences. Ap- parently, both regions contribute more or less equally to the highest annual means. The trend test (table 2) 122 AIR QUALITY TRENDS IN ILLINOIS found no significant trends in the median annual mean Ni. creasing somewhat, in agreement with the decreasing trends in concentration seen in table 2. Metal Enrichments, Relative to Soil. Enrichment factors are a common and convenient method of distinguishing between natural and anthropogenic sources of metals in the atmosphere. For many metals the typical natural source examined is crustal or soil aerosols. Enrichment, E, for element X is expressed as a ratio of ratios: E = (X/REL/(X/RE) (2) where RE is a reference element for which the soil or earth's crust is the dominant source in the atmosphere. Enrichments are usually evaluated for measured con- centrations of X in air, using abundances (mass frac- tions) of X and RE in soils from compilations of global mean soil or crustal composition. Figure 3 1 shows element enrichments based on the median statewide annual mean concentrations of As, Cd, Cr, Pb, Mn, and Ni, using Fe as the reference element, for 1978-1990. If the ratio of the subject element to Fe in air is the same as the ratio of the same elements in soil, then the en- richment is 1 .0, and the element X is assumed to come only from the soil. In practice, because of variations in soil composition, elements with enrichments between 1 and 10 are usually assumed to have primarily soil sources. Values of E > 10 are assumed to indicate anthropogenic sources. Using these criteria, figure 3 1 shows that Pb and Cd, with enrichments between 100 and 3000, have primar- ily anthropogenic sources in Illinois. Note that the enrichment of Pb has dropped from 1000-2000 in the early 1980s to 100-200 in recent years as Pb has been removed from automotive fuels. Nevertheless, the concentration of Pb currently in the atmosphere is far in excess of what would be there naturally from soil wind erosion. Sources such as Pb smelters and fly ash from coal burning may now be the major sources of Pb in the atmosphere, although Pb recycled from previ- ously deposited auto exhaust may also be important. Cd also has a high enrichment factor of about 1000, which has remained relatively constant during the 1980s. The absence of a Cd datapoint in 1981 is the result of a one-year hiatus in Cd measurements. Those in 1 983 and 1 989 were caused by median Cd concen- trations of 0.000 jxg/M'. Arsenic enrichments are mostly >10 also, suggesting a mostly anthropogenic source. They appear to be de- Mn enrichments are firmly in the 1-10 range generally ascribed to natural sources, with very little year-to-year variation. The majority of Mn in the Illinois atmo- sphere may well be natural. Mn sources also tend to be Fe sources, however, so the extent to which the refer- ence element Fe is nonnatural, may also hold true for Mn. For example, anthropogenic sources are very likely to be the cause of the significant increase (at the 5 percent level, or better) in concentrations of both Fe and Mn during the 1980s in the Metro East area. The year-to-year variations in Cr and Ni enrichments during the 1985-1990 period are similar to each other, but unlike those of any of the other metals in figure 31. The enrichments are mostly in the 1-10 range, suggest- ing mainly natural sources for these metals, but the sometimes large year-to-year variations suggest that concentrations of both of these metals are enhanced by anthropogenic sources at least during some years. SPATIAL DISTRIBUTIONS OF POLLUTANT CONCENTRATIONS It was a very early goal of this summary of Illinois air quality to draw spatial contours of pollutant concentra- tions on a statewide scale. Examination of the data quickly dashed that early hope, however, as it became clear that sampling sites were concentrated in the two major industrial and population centers, the Chicago and the Metro East areas. The relatively few sampling sites not in these major centers were clustered in smaller cities and the environs of troublesome sources. Data are not available from sparsely populated regions with no major sources. For an agency such as the lEPA with the mission of documenting problems and enforc- ing standards, this sampling strategy is obvious. It does not provide data needed to document statewide air quality, however. For this report, we propose that the data are adequate to show spatial variations in that portion of the state with the highest concentration of sampling sites, the Chicago area. To provide a sense of the temporal changes in Chicago-area spatial patterns, contours have been drawn for 1980, 1985, and 1990, and are pre- sented below. The rapid drop in the number of sam- pling sites, even in the Chicago area, makes the 1990 contours very problematic. The 1990 contours are meant to suggest only the most rudimentary spatial 123 AIR QUALITY TRENDS IN ILLINOIS 10000 1 1000 0) O) c E o c LU 100 r 10 r 0.1 As Mn J I I I I I I I 1 1 1 1 L 78 79 80 81 82 83 84 85 86 87 88 89 90 Year Figure 31. Trends in airborne metal enrichment, relative to soil, in Illinois. 124 AIR QUALITY TRENDS IN ILLINOIS patterns. For most pollutants the data are not adequate to do more. The data and associated discussions for the several pollutants appear in the same order as those of the temporal trends above. Criteria Pollutants CO. Figures 32 and 33 show spatial distributions of 1- hr maximum and 8-hr maximum CO concentrations in the Chicago area in 1980, 1985, and 1990. The low density of sampling sites, and the changes in site loca- tions between years preclude identification of persistent locations of high or low concentrations. In 1980 one sampling site near the lake shore had a 1-hr maximum >20 ppm. In 1985 three sites had 1-hr maxima between 10 and 20 ppm, but there were no measurements >20 ppm. In 1990, only one site recorded a 1-hr maximum >10 ppm. This general decline in concentrations agrees with the significant overall decline in Chicago-area concentrations detected by the trend test (table 2). No violations of the 35 ppm national and state standard for 1-hr maximum CO were observed. Figure 33 shows spatial patterns of 8-hr maximum CO concentrations. Again, temporal changes in the sam- pling network limit discussion mostly to temporal changes in concentrations. In 1980, one lakeshore site exceeded the national and state standard for 8-hr maxi- mum CO (9 ppm), but no violations were observed in the region in 1985 or 1990. A general decline in con- centrations is apparent from 1980 to 1985 to 1990 that agrees with the significant decline detected in the Chicago area from the full 1978-1990 dataset (table 2). Pb. Spatial distributions of annual mean Pb concentra- tions in the Chicago area for 1980, 1985, and 1990 are shown in figure 34. Persistent concentration maxima occurred in the central city and the southeast Chicago industrial area; however, the well-known and very significant decline (table 2) in atmospheric Pb concen- trations during the 1980s is evident here as well. The value of the highest contour line declined from 0.6 |i.g/ M' in 1980 to 0.2 ^g/M' in 1985 and 0.1 ng/M' in 1990. Pb standards are written in terms of mean con- centrations over calendar quarters, which cannot be inferred from the data shown here. See the earlier discussion related to temporal trends. NOj. Spatial patterns of 24-hr maximum and annual mean NO^ in the Chicago area are shown in figures 35 and 36, respectively. In 1980 the highest 24-hr maxima occurred in suburban northwestern (DesPlaines) and southern (Flossmoor) Cook County, with single sites in each area experiencing one or more days with mean concentrations >0.14 ppm. By 1985, the two sites with the highest values in 1980 were no longer active. The data suggest an overall decline in maximum 24-hr con- centrations, with the highest value (0.094 ppm) occur- ring in the city center. The 1990 data show a further overall decline in maximum 24-hr concentrations, with the maximum (0.062 ppm) occurring in a cluster of sampling sites near O'Hare Airport. There are no national or state standards for 24-hr maximum NO^. Figure 36 shows Chicago-area contours of annual mean NOj. Shaded areas in the northwest suburbs (DesPlaines) and the central city exceeded the national and state primary standard (0.053 ppm) in 1980. Although no violations of the standard were observed in 1985 and 1990, the available data suggest that the highest annual mean concentrations still occurred in the central city area near Lake Michigan. The apparent decreasing concentrations agree with the significant trend in Chi- cago area annual mean NO^ discussed earlier (table 2). O3. Figure 37 shows contours of maximum 1-hr O3 concentrations in the Chicago area for 1980, 1985, and 1990. Most of the Chicago area was in violation of the 0.12 ppm standard in 1980, with a conspicuous area of lower values across the middle of Cook County and the city of Chicago. In 1985 the violations of the standard were confined to the northeastern and southeastern portions of Cook County. No violations were observed in 1990; however, there is evidence that this may have occurred because summer weather conditions were relatively unfavorable for O3 formation, as discussed earlier. Table 2 indicates no significant temporal trend in O3 as observed; however, as shown earlier, when surface temperature is accounted for, there is a signifi- cant trend (2 percent level) toward decreasing concen- trations in the Chicago area over the 1978-1990 period. SOj. Figures 38-40 show Chicago-area spatial contours for SO^: 3-hr maximum, 24-hr maximum, and annual mean concentrations, respectively. The contours drawn firom the available data are very difficult to interpret. Overall, 3-hr maximum concentrations were primarily >0.10ppm in 1980 and 1985, and primarily <0.10 in 1990. This apparent trend toward decreasing concentra- tions agrees with the significant trend for the Chicago area detected earlier (table 2). A single high value (0.446 ppm) was observed in the western suburbs (Bedford Park) in 1985. There are no national or state standards for 3-hr maximum SOj. 125 AIR QUALITY TRENDS IN ILLINOIS 10' ■10 1980 DU PAGE 10 WILL Figure 32. Spatial distributions of 1-hr maximum CO (ppm) in the Chicago area for 1980, 1985. and 1990. 1990 126 AIR QUALITY TRENDS IN ILLINOIS 1980 Figure 33. Spatial distributions of 8-hr maximum CO (ppm) in the Chicago area for 1980. 1985, and 1990. The shaded area denotes violation of an air quality standard. 127 AIR QUALITY TRENDS IN ILLINOIS DU PAGE Figure 34. Spatial distributions of annual mean Pb (\iig/M^) in the Chicago area for 1980. 1985. and 1990. WILL 1990 128 AIR QUALITY TRENDS IN ILLINOIS 0.06 0.06 0.06 0.04 Figure 35. Spatial distributions of 24-hr maximum NO (ppm) in the Chicago area for 1980, 1985, and 1990. 129 AIR QUALITY TRENDS IN ILLINOIS 0.03 0.04 1985 0.02 Figure 36. Spatial distributions of annual mean NO^ (ppm) in the Chicago area for 1980, 1985, and 1990. Shaded areas denote violations of an air quality standard. 130 AIR QUALITY TRENDS IN ILLINOIS 0.12 JUG 042. 0.12 0.14 0.10 0.10 DU PAGE COOK V-Jipo.lO 0.085 I 0.08 •0.08 WILL 1990 Figure 37. Spatial distributions of 1-hr maximum O^ (ppm) in the Chicago area for 1980. 1985. and 1990. Shaded areas denote violations of an air quality standard. 131 AIR QUALITY TRENDS IN ILLINOIS DU PAGE 0.084 • 0.052 COOK 0,0?3 0.J73 WILL 1990 Figure 38. Spatial distributions of 3-hr maximum SO2 (ppm) in the Chicago area for 1980, 1985, and 1990. 132 AIR QUALITY TRENDS IN ILLINOIS O.IO^^i^O.H / 0.0*26 Y"'' c / / 0.05 0.023 / .•0.050 0.05 0.05 0.045 0.05 ' "^"f" ^ ' ' 0.055 \ 1980 DU PAGE 0.026 «22 WILL 1° 0.05- •0023 COOK Figure 39. Spatial distributions of 24-hr maximum SO 2 (ppm) in the Chicago area for J 980, 1985, and 1990. The shaded area denotes violation of an air quality standard. 1990 133 AIR QUALITY TRENDS IN ILLINOIS 0.01 0.01 WOIA ^-0.01 .0.01 1985 0.005 0.005 Figure 40. Spatial distributions of annual mean SO 2 (ppm) in the Chicago area for 1980, 1985. and 1990. 134 AIR QUALITY TRENDS IN ILLINOIS Chicago-area spatial contours for 24-hr SO, are shown in figure 39. One site in south-suburban Cook County (Blue Island) exceeded the national and state standard (0.14 ppm) in 1980. Aside from this extreme, concen- trations at most locations were <0.05 ppm. The avail- able data for 1985 and 1990 show maxima in the western suburbs (Bedford Park) in both years, but again most sites experienced 24-hr maximum concentrations <0.05 ppm. There were no violations of the standard in 1985 or 1990. Table 2 shows no significant temporal trends in 24-hr maximum SO^ in the Chicago area. Chicago-area spatial contours for annual mean SO, concentrations are shown in figure 40. The figure shows no strong spatial patterns in any of the three years, but very different patterns of minimal high and low concentrations over the three years. There were no violations of the national and state standard (0.03 ppm) for the annual mean in any of the three years. TSP. Spatial patterns of 24-hr maximum and annual mean TSP in the Chicago area are shown in figures 41 and 42, respectively. The spatial pattern for 1980 shows areas of high concentrations, including viola- tions of the 260 ng/M' standard, in (1) the industrial area of southeastern Chicago, (2) the western suburbs of Cook County (River Forest) and eastern DuPage County (Elmhurst), (3) northwestern Will County (Romeoville, Joliet, and Rockdale), and (4) southwest- em Will County (Braidwood). In 1985 there were widespread violations of the standard, over almost all of Cook County, the southern half of DuPage County, and southwestern Will County On the other hand, there were no violations in the Joliet area. The widespread extent of the violations of the 24-hr standard suggests that a regional weather event might have been respon- sible, and indeed, a dust storm that occurred on May 31, 1985, was the cause of most of the violations (lEPA, 1986). In 1990 the much-reduced sampling network detected only one violation of the standard at Rockdale in Will County. Figure 42 shows the spatial patterns for annual geomet- ric mean TSP. In 1980 maximum concentrations above the national standard (75 |xg/M') occurred in a broad band from the central city area of Chicago to suburban Summit, in the southeast Chicago industrial region, in northeast DuPage County (Bensenville), and in the Joliet area of Will County In 1985, only two sites in the Chicago area violated the standard, one in southeast Chicago and one in west suburban McCook. In 1990 only one site, in downtown Chicago, was in violation; however, the number of sampling sites was down coasiderably. Filter Samples: Nitrate, Sulfate, and Metals There are no standards for the remaining pollutants. NOj'. Spatial patterns of 24-hr maximum and annual mean NO, in the Chicago area are shown in figures 43 and 44, respectively. Data on 24-hr maximum NO,- are not available before 1985. Maximum 24-hr NO, con- centrations are relatively uniform over the area in both 1985 and 1990, varying by a factor of only about 2 from minimum to maximum. Thus, the importance of the locations of relative high and low concentrations is difficult to assess. Figure 44 shows spatial patterns of mean annual NO," in the Chicago area. Again, the values are spatially very uniform. It is interesting to note that in 1980 the Cook County concentrations were generally <5 |ig/M' while those in DuPage and Will Counties were >5 |j,g/ M'; in 1985 the pattern was reversed, although that assessment is based on only four sites outside of Cook County There were too few sites in 1990 to justify any comment on spatial variations. SO^^. Spatial patterns of 24-hr maximum and annual mean S0_,- in the Chicago area are shown in figures 45 and 46, respectively. Interpretation of these patterns is limited by the same factors that affected the NO, data: lack of data for 1980 and a large disparity between the number of sampling sites in 1985 and 1990. Based on only four sampling sites, the data provide a hint that maximum 24-hr concentrations >40 |ig/M^ affected more of the Cook County area in 1990 than in 1985. Further, the southeast Chicago industrial area had maximum concentrations >40 ng/M' in both years. Figure 46 shows Chicago-area spatial patterns of annual mean SO,- . The areas where mean annual SO/" exceeded 1 5 ^ig/M' were scattered throughout Cook County in 1985, but were reduced to one site in 1985, and none at all in 1990. Fe. Spatial distributions of 24-hr maximum and annual mean Fe concentrations in the Chicago area for 1985 and 1990 are shown in figures 47 and 48. In 1985, maximum 24-hr concentrations varied be- tween 1 and 4 |ig/M' over most of the three-county Chicago area, but there was a small area where concentrations exceeded 20 |ig/M' in the southeast Chicago industrial area. In 1990 the typical range was still 1-4 ng/M\ but the high concentrations in southeast Chicago were down considerably. 135 AIR QUALITY TRENDS IN ILLINOIS ;:400 ;60 200 260 00 260 98 200 i' 260 300 '300 •200 260 Figure 41. Spatial distributions of 24-hr maximum TSP i\yg/M^) in the Chicago area for 1980, 1985, and 1990. Shaded areas denote violations of an air quality standard. 136 AIR QUALITY TRENDS IN II I /A/n/g 53 • 4' - 67 6oA 54 • 57» ^ 51 • -75 \ 51 • 56 ^-^ 180. J "» 63 ^l 75 • 66 • tf 198( ) 75 100 75 1985 Figure 42. Spatial distributions of annual geometric mean TSP (ng/M^) in the Chicago area for 1980, 1985. and 1990. Shaded areas denote violations of an air quality standard. 1990 137 AIR QUALITY TRENDS IN ILLINOIS DU PAGE COOK 10 WILL 1990 Figure 43. Spatial distributions of 24-hr maximum NOf (\ig/M^) in the Chicago area for 1985 and 1990. 138 AIR QUALITY TRENDS IN ILLINOIS DU PAGE WILL COOK 1990 Figure 44. Spatial distributions of annual mean NO J- (\ig/M^) in the Chicago area for 1980, 1985, and 1990. 139 AIR QUALITY TRENDS IN ILLINOIS 2- i..„i\/ii\ Figure 45. Spatial distributions of 24-hr maximum SO^ (\ig/M ) in the Chicago area for 1985 and 1990. 140 AIR QUALITY TRENDS IN ILLINOIS Figure 46. Spatial distributions of annual mean so/- (\ig/M^} in the Chicago area for 1980, 1985. and 1990. 141 AIR QUALITY TRENDS IN ILLINOIS Figure 47. Spatial distributions of 24-hr maximum Fe (\ig/M^) in the Chicago area for 1985 and 1990. 142 AIR QUALITY TRENDS IN ILLINOIS 0.5, -0.5 0.5 \ \ \ 0.45 \ \ \ 0.5 1985 Figure 48. Spatial distributions of annual mean Fe (\ig/M^) in the Chicago area for 1980, 1985. and 1990. 143 AIR QUALITY TRENDS IN ILLINOIS Figure 48 shows spatial patterns of mean annual Fe concentrations in the Chicago area. The main feature of the 1980 pattern was a broad area of concentrations >1.0 |ig/M' in central and southeastern Cook County Note, however, the lack of 1980 measurements in the southeast Chicago industrial region, where mean values >3 |ig/M^ were observed in 1985. Most of the few sampling sites remaining in 1990 reported mean Fe concentrations >1.0 |J.g/M', but the southeast Chicago hot spot was gone. Mn. Spatial patterns of 24-hr maximum and annual mean NOj" in the Chicago area are shown in figures 49 and 50, respectively. Notice the similarities be- tween the spatial patterns of Mn (figures 49 and 50) and Fe (figures 47 and 48), especially in 1985. This is not surprising since baseline concentrations are probably the result of wind erosion of soil dust, while local peak concentrations are often associated with industrial activity, especially steel-making. Peak 24- hr maximum concentrations of both Mn and Fe in southeast Chicago decreased by a factor of 4 or 5 from 1985 to 1990. Because of very limited numbers of sampling sites in the Chicago area through 1985, spatial data for the remaining four metals, As, Cd, Cr, and Ni, is limited to 1990 annual means, all presented in figure 51. As. Figure 5 1 shows annual mean concentrations of As at eight sites in the Chicago area. Mean concentrations at six of the eight sites were 0.001 \lgfM\ and the other two were 0.000 p,g/M'. The figure presents only the data. No contours are justified. Cd. The 1990 spatial pattern of Cd in the Chicago area is also shown in figure 51. Annual mean con- centrations were 0.001 or 0.002 H-g/M' at six of the eight sites, with a maximum value (0.008 ^.g/M') in southeast Chicago. Cr. The 1990 spatial pattern of Cr in the Chicago area is also shown in figure 5 1 . Annual means ranged from 0.000 to 0.015 |ig/M'. The maximum concentrations occurred in southeast Chicago and the western suburb of Maywood. Ni. The Chicago-area pattern of mean annual Ni con- centrations for 1990 are also shown in figure 51. There was a broad concentration maximum (>0.(X)5 ^ig/M') over central and southern Cook County, with the high- est value at Maywood. TABULATIONS OF LITERATURE DATA ON OCCASIONAL MEASUREMENTS Some pollutants, including some considered toxic, have not been measured routinely in Illinois for reasons that usually involve the cost of analysis, the ability to detect the extremely low concentrations present in the atmo- sphere, or both. Table 5 summarizes some recent measurements of volatile organic compounds in Illi- nois. Measurements in table 5 were made in Chicago, in the Metro East area, and at a rural agricultural site near Champaign between 1986 and 1990. Sweet and Vermette (1992) found that the concentrations they measured in Illinois urban areas were quite similar to those observed in other urban areas of the United States. Further, the concentrations they observed in an industrial area were quite similar to those seen in other cities without significant industry, which suggests that the major types of sources were widespread small sources, especially related to automotive emission and fuels, rather than large point sources. The available data are not adequate to address the issue of temporal trends, except that there are a few substan- tial differences in mean concentrations between years. With regard to spatial variations, there are compounds for which rural and urban concentrations are similar or different, and some differences in concentration be- tween urban areas. As is true for many atmospheric parameters, concentra- tions of many volatile organic compounds are highly variable both spatially and temporally. These variations depend on sample duration, proximity of sampling to sources, variations in source strength, and especially on weather conditions. Variability between years is seen by comparing the various measured mean concentrations in Chicago. In general, the results of McAlister et al. (1989, 1991) for 1988 and 1990 agree quite well with those of Sweet and Vermette (1992) measured over the 1986-1990 period. However, there are a few exceptions to this rule, notably carbon tetrachloride and tetrachloroethy- lene in 1990, and toluene and meta- plus para-xylene in 1988. The measurements of Wadden et al. (1992) were made in a different Chicago location, near the city cen- ter. There is good agreement between the Wadden et al. measurements and those already mentioned for some com- pounds, such as benzene, but poor agreement for others, such as chloroform and ethylbenzene. In most cases the Wadden et al. values are greater than the others, probably because of spatial variations within the city. 144 AIR QUALITY TRENDS IN ILLINOIS 0J95 0-144 0410* 0090 0^91 1985 ».2% 0,(g7 '«i DU PAGE WILL 1990 COOK Figure 49. Spatial distributions of 24-hr maximum Mn (\ig/M^) in the Chicago area for 1985 and 1990. 145 AIR QUALITY TRENDS IN ILLINOIS Figure 50. Spatial distributions of annual mean Mn ([ig/M^) in the Chicago area for 1980. 1985, and 1990 146 AIR QUALITY TRENDS IN ILLINOIS As o.oo2>— 0.005 0008 0.005 0.01 0.005 Figure 51. Spatial distributions of annual mean As, Cd, Cr, and Ni (\ig/M^) in the Chicago area for 1990. 147 AIR QUALITY TRENDS IN ILLINOIS Table 5. Summary of Measured Concentrations of Some Volatile Organic Compounds in Illinois (N = number of samples) Ref* Years Chicago** Metro East** Bondville ( rural)' »* Compound N Mean SD Max N Mean SD Max N Mean SD Max acetaldehyde 3 1990 28 3.8 9 acetylene 4 1990-91 60 5.2 2.7 13.4 acetone 3 1990 28 7.2 19 acetaldehyde 3 1990 28 3.8 9 benzene 1 2 3 4 1986-90 1988 1990 1990-91 103 34 29 78 4.6 2.8 5.1 7.6 6.6 6.8 54 23 18 38 83 10.6 17.2 102 23 1.3 0.5 2.4 bromodichloromethane 4 1990-91 56 20.7 81.5 582 butane 4 1990-91 71 13.0 29.2 241 i-butane 4 1990-91 64 7.0 12.7 91 carbon tetrachloride 1 3 4 1986-90 1990 1990-91 103 29 63 0.7 2.9 7.4 0.2 9.5 1.7 23 34 83 0.9 0.3 1.7 23 0.8 0.2 1.2 chlorobenzene 1 1986-90 103 0.3 0.2 1.6 83 3.0 6.3 36 23 0.2 0.1 0.5 chloroform 1 4 1986-90 1990-91 103 66 0.3 4.6 0.2 7.2 1.6 40 83 0.5 0.9 6.6 23 0.3 0.1 0.4 cumene 4 1990-91 65 6.4 34.2 277 n-decane 4 1990-91 53 8.6 38.8 282 dibromochloromethane 4 1990-91 63 81.8 189 1025 o-dichlorobenzene 4 1990-91 52 20.4 33.3 150 2-2-dimethyIbutane 4 1990-91 76 4.5 7.6 41 ethane 4 1990-91 60 9.9 5.3 22.8 ethylbenzene 1 2 3 4 1986-90 1988 1990 1990-91 103 34 29 78 1.4 3.0 1.8 8.8 1.2 22.7 7.6 26 6.6 195 83 6.9 17 110 23 0.4 0.3 1.6 ethylene 4 1990-91 60 7.3 3.5 16.7 formaldehyde 3 1990 28 6.0 17 n-heptane 4 1990-91 56 6.4 8.3 45 hexane 4 1990-91 78 9.2 17.9 137 2-methylbutane 4 1990-91 77 16.7 16.8 76 methylene chloride 4 1990-91 65 19.5 34.2 174 2-methylpentane 4 1990-91 77 7.1 8.7 40 3-methylpentane 4 1990-91 77 6.4 6.9 39 n-octane 4 1990-91 39 1.5 1.1 3.7 pentane 4 1990-91 78 8.6 12.4 72 alpha-pinene 4 1990-91 60 0.1 0.2 1.4 n-propylbenzene 4 1990-91 74 8.5 29.1 247 tetrachloroethylene 1 3 4 1986-90 1990 1990-91 103 29 60 1.8 10.7 1.8 1.6 10.7 9.1 41 83 83 1.4 1.3 6.1 23 0.4 0.3 1.2 148 AIR QUALITY TRENDS IN ILLINOIS Table 5. (Concluded) 1 Ref* y^arj Chicago** Metro East** Compound N Mean SD Max N Mean SD Max toluene 1 2 3 1986-90 1988 1990 103 34 29 8.9 61.1 11.8 8.9 56 1284 33 83 8.5 9.3 45 4 1990-91 78 23.5 24.6 131 1,1,1 -trichloroethane 1 1986-90 103 3.3 3.5 25 83 3.9 6.1 31 1 2 1988 34 4.1 23 3 1990 29 8.1 45 4 1990-91 73 17.5 25.3 125 trichloroethylene 1 3 1986-90 1990 103 29 1.0 1.2 1.0 5.9 5.0 83 2.1 5.8 43 4 1990-91 76 3.2 3.2 13.7 1 ,3,5-trimethylbenzene 4 1990-91 77 6.8 24.4 212 m-, p-xylene 1 2 3 1986-90 1988 1990 103 34 29 3.9 20.6 9.8 8.3 22 301 39 83 16 42 312 4 1990-91 78 24.6 86.7 763 o-xylene/styrene 1 1 2 3 1986-90 1988 1990 103 34 29 2.9 3.9 3.7 5.5 44 54 13 83 3.3 8.6 55 i 4 1990-91 78 18.8 79.4 650 BondvHle (rural)** Mean SD Max 23 23 23 23 23 3.0 2.3 1.1 0.6 0.6 0.5 9.5 1.5 1.2 0.8 1.1 0.9 3.9 4.3 Notes: ♦References: 1. Sweet and Vermette (1992). 2. McAlister et al. (1989). 3. McAlister et al. (1991). 4. Wadden et al. (1992). **For Reference 1, sampling was carried out at several sites in southeastern Chicago and several sites in the Metro East area. The compounds reported in Reference 1 were detected in 95 percent of the samples. For References 2 and 3, sampling was carried out at Carver High School in Chicago and Sauget in the Metro East area. Sampling for Reference 4 was carried out near the Chicago city center. The compounds listed in References 2 and 3 were detected in at least 50 percent of the samples. In all cases, for purposes of computing mean values, sample concentrations reported as < the detection limit were assumed to have concentrations of one-half of the detection limit. The rural samples were collected at an agricultural site in Champaign County, 8 km west of Champaign, near Bondville, Illinois. I 149 AIR QUALITY TRENDS IN ILLINOIS Variability between concentrations of organic com- pounds between urban areas occurs for some com- pounds, and not for others. For benzene, chlorobenzene, ethyl benzene, trichloroethylene, and meta- plus para- xylene, mean concentrations show differences ranging from factors of 2 to 10. Note, however, that the variability of the respective concentrations is very high, judging from the standard deviation, so that the differences may not be statistically significant. It is noteworthy that the Metro East concentration was higher for each of these compounds. Urban/rural variability, or to be more precise, the lack of differences in concentration between urban and rural locations, is seen for a few compounds, notably carbon tetrachloride and chloroform (Sweet and Vermette, 1992). Such uniform concentrations are evidence of a well-mixed contaminant with a long atmospheric resi- dence time and few current sources. Carbon tetrachlo- ride is an example of a compound no longer used commercially, so its current sources are very small. However, its residence time in the atmosphere is long, so over time it has become well mixed in the atmo- sphere, and its concentrations are relatively uniform regardless of whether the sampling site is in a rural or urban area (Sweet and Vermette, 1992). DISCUSSION Trends over Time: Increasing, Decreasing, and Level Concentrations Criteria Pollutants. Six pollutant types are included among the criteria pollutants: CO, Pb, NO^, O^, SO^, and particulate matter. Some of these are measured over multiple averaging times, but there is not neces- sarily a standard for every averaging time. For exam- ple, NOj is measured over averaging times of 1 hour, 24 hours, and the calendar year, but there are state and national primary standards only for the annual mean. Particulate matter is measured as TSP, for which there are only state standards (for both annual geometric mean and 24-hr maximum concentrations), and as PM,g, for which there are only national standards (annual arithmetic mean and 24-hr maximum). Thus, for the six pollutant types, measurements have been made for 14 separate pollutant-averaging time combi- nations, 1 1 of which have state or national primary standards. The PM|g measurements have only been made for a few years, not enough to make a trend test meaningful, so of the 14 combinations, only 12 (at the most) have been tested for time trends within individual geographic regions. In some regions there were not enough sites to carry out trend tests. The results of the trend tests within regions are summarized in table 2. For the state as a whole, 12 pollutant/averaging time datasets were tested for time trend. Seven of these (table 2) showed trends toward decreasing concentra- tions significant at the 1 percent or 2 percent level, four had no significant trend (5 percent) (including Oj, before accounting for temperature effects), and none showed increasing trends. After accounting for temperature effects, O^ showed a decreasing trend (2 percent level, table 3), rather than no trend. The same 1 2 kinds of datasets were tested for trend in the Chicago area. Eight of these (table 2) showed decreasing trends at the 5 percent level (all but one of these were at the 1 or 2 percent level). Four showed no significant trend at the 5 percent level, and none showed an increasing trend. After accounting for tem- perature, Oj showed a decreasing trend (2 percent level, table 3), rather than no trend. In the Metro East area, only four pollutant/averaging time datasets were measured at enough sites to warrant testing for time trend. Only Pb showed a decreasing trend ( 1 percent), while three other datasets showed no significant trend (5 percent). After accounting for temperature, Oj showed a decreasing trend at the 6 percent level, but not at the 5 percent level. No sig- nificant (5 percent) increasing trends were found for criteria pollutants. Nine datasets were tested for time trend in the "remain- der" region, four of which included a few sites from the Metro East region when there were insufficient sites for separate tests there. Three of these datasets showed decreasing trends at the 5 percent level (all but one at the 1 percent level), and five datasets showed no sig- nificant (5 percent level) trends. After accounting for temperature, the decreasing trend of O, with time was significant only at the 10 percent level. Again, there were no significant increasing trends. Aside from Pb, the largest decreasing linear trends were found for annual mean NO,, at -7.1 percent per year statewide and -6.8 percent per year in the Chi- cago area. The greatest magnitudes of decreasing linear trends were found for Pb: -12.6 percent per year in the Metro East area, and -20 to -25 percent per year statewide and in the other geographic areas. 150 AIR QUALITY TRENDS IN ILLINOIS Noncriteria Pollutants. Only trends in annual mean concentrations of the noncriteria pollutants measured — NO3 , SO/ , and the six metals (As, Cd, Cr, Fe, Mn, and Ni) — were tested for trend over time. Currently, 24-hr average metal concentrations are also being measured, but their record is too short to permit a meaningful test of time trend. The eight noncriteria pollutants were all tested for trend in all four regions, except for the Metro East region, where the data were not adequate to test Cr and Ni. Of the 30 trend tests, 20 showed no significant (5 percent) trend. Over the state as a whole, and in the Chicago area, two species showed significant decreases: SO/ at the 5 percent level and As at the I percent level. In the Metro East area, Fe and Mn showed significant increases (the only increasing trends found in this study): Fe at the 2 per- cent level, and Mn at the 5 percent level. In the "remain- der" region, SO/ (2 percent). As ( 1 percent), Cd (2 percent), and Mn (5 percent) showed significant decreases. Spatial Trends: Dlinois Hot Spots Comparison of Geographic Regions. Comparison of median and maximum pollutant concentrations within geographic regions, from the yearly box plots in figures 1-30, indicates which geographic areas of the state experienced the highest concentrations of air pollutants. Chicago generally had higher median regional values of annual mean NO^', and of annual mean and 24-hr Cr. It also experienced higher median annual mean Ni and the highest individual 24-hr Ni concentrations. These Cr and Ni results agree with the observations of Sweet and Gatz (1988), based on measurements of fine and coarse particles with dichotomous samplers. On the other hand, the Chicago area generally experienced lower concentrations of 3-hr and 24-hr SOj than the rest of the state. The Metro East area generally experienced higher concentrations than the rest of the state for annual mean Pb, annual mean TSP, and both 24-hr and annual mean As, Cd, Fe, and Mn. Again, the As and Cd results agree with those of Sweet and Gatz (1988), but for Pb and Mn, Sweet and Gatz found higher concentrations in Chicago. tions should be regarded as best guesses, based on available data. But these statements are uncertain as to magnitude of pollutant concentrations as well as to pre- cise location. The available data are not adequate for highly certain conclusions because: I) sampling sites are distributed nonuniformly over the area; 2) the plotted data represent only three years (1980, 1985, and 1990); and 3) numbers of sampling sites, and their locations, have changed from one plotted year to the next, and they have recently dwindled to the extent that the meaning of contours is questionable. Only one locale in the Chicago area stands out for being the location of high concentrations for multiple pollutants: the industrial area of southeast Chicago around Lake Calumet. This area has persistent, rela- tively high concentrations of some metals, in terms of both 24-hr maxima and annual means. The metals with highest 24-hr maxima in the Lake Calumet area were Fe and Mn. There was a persistent peak in 24-hr SO/" in this area as well. Metals with local peaks in annual mean concentrations include Pb, and possibly Cd, Cr, and Mn, although the evidence for the latter three is somewhat weaker. Other locations in the Chicago area appeared as areas of persistent high concentrations of only one or two pollutants. One-hour maximum CO was persistently high along the Lake Michigan shoreline north from downtown Chicago. Annual mean NO^ concentra- tions were also persistently high near the Chicago city center (the Loop). The plotted O, data (figure 37) suggest a possible persistent area of high 1-hr maximum concentrations in northeast Cook County. There is also some weak evidence for relatively high 1-hr maxima of 0^ and annual mean NO,. Southwest suburban Bedford Park had persistently high concen- trations of 3-hr maximum, 24-hr maximum, and annual mean SO^. Finally, various locations in Will County experienced persistently high 24-hr maxi- mum TSP concentrations, perhaps related to wind erosion of agricultural soils. CONCLUSIONS The Chicago and Metro East areas experienced higher concentrations than the rest of the state for 1 -hr max- imum Oj and annual mean SO^. Chicago Area Concentration Contours. Based on the contour plots in figures 32-5 1 , statements about preferred areas of relatively high pollutant concentra- Temporal Trends Criteria Pollutants. Of all the criteria pollutants tested for time trend in any geographic region of the state, results indicated only decreasing trends or no signifi- cant (5 percent) trends. No increasing trends in criteria pollutants were detected. 151 AIR QUALITY TRENDS IN ILLINOIS For the state as a whole, seven of 12 pollutant/averag- ing time datasets tested for time trend showed signifi- cant trends (5 percent level or better) toward decreasing concentrations over the 1978-1990 data period. Pb had the largest decreasing mean linear trend statewide, -20.5 percent per year. After accounting for temperature effects, O3 showed a significant decreasing trend (2 percent level), rather than no trend. In the Chicago area, eight of the 12 datasets showed decreasing trends at the 5 percent level (all but one of these were at the 1 or 2 percent level). Again, Pb had the largest trend, -21.2 percent per year. After account- ing for temperature, O3 showed a decreasing trend (2 percent level, table 3), rather than no trend, in the Chicago area. In the Metro East area, only four pollutant/averaging time datasets were measured at enough sites to warrant testing for time trend. Only Pb showed a significant (5 percent) trend, a trend toward decreasing concentra- tions. The Pb trend was sizable, -12.6 percent per year, but much smaller than the Pb trend observed in all other areas of the state. After accounting for tempera- ture, O3 showed a decreasing trend at the 6 percent level, but not the 5 percent level. Three of nine datasets tested for time trend in the "re- mainder" region showed decreasing trends at the 5 per- cent level or better. Again, Pb had the largest trend, -24.8 percent per year. Noncriteria Pollutants. The eight noncriteria pollut- ants were all tested for trend in all four regions, except for the Metro East region, where the data were not adequate to test Cr and Ni. Of the 30 trend tests, 20 showed no significant (5 percent) trend. Over the state as a whole, and in the Chicago area, two species showed significant decreases — SO^^ and As. In the Metro East area, Fe and Mn showed significant increases (the only increasing trends found in this study). In the "remainder" region, SO^^ , As, Cd, and Mn showed significant (5 percent or better) decreases. Spatial Trends Comparison of median and maximum pollutant con- centrations within geographic regions, from the yearly box plots in figures 1 -30, indicates which geographic areas of the state experienced the highest concentra- tions of air pollutants. Chicago generally had higher median regional values of annual mean NO^ , and of annual mean and 24-hr Cr. It also experienced higher median annual mean Ni and the highest individual 24- hr Ni concentrations. On the other hand, the Chicago area generally experienced lower concentradons of 3-hr and 24-hr SO^ than the rest of the state. The Metro East area generally experienced higher concentrations than the rest of the state for annual mean Pb, annual mean TSP, and both 24-hr and annual mean As, Cd, Fe, and Mn. The Chicago and Metro East areas experienced higher concentrations than the rest of the state for 1-hr maximum O3 and annual mean SO^. Within the Chicago area, only one locafion stands out for its high concentrations of multiple pollutants. This is the industrial area of southeast Chicago around Lake Calumet. This area has persistent, relatively high an- nual mean or 24-hr concentrations, or both, of SO^-', Fe, Mn, and Pb, and possibly Cd, Cr, and Mn. The evidence for the latter three is somewhat weaker than for the others, however. Other locations in the Chicago area appeared as areas of persistent high concentrations of only one or two pollutants. ACKNOWLEDGMENTS Bob Swinford and Dave Kolaz, of the Illinois EPA, were very helpful in providing data, answering ques- tions about the data, and discussing numerous issues. Sherman Bauer entered most of the data into computer files. Peter Scheff and Clyde Sweet provided data on concentrations of organic pollutants. Bob Sinclair pro- vided guidance for conversion of the data to GIS files. Tom Heavisides supplied information on data sources. REFERENCES Appel, B.R., Y. Tokiwa, M.Haik, and E.L. Kothny. 1984. Artifact particulate sulfate and nitrate formation on filter media. Atmospheric Environment, 18(2):409-416. Cooper, J.A., and C.A. Frazier. 1983. Source appor- tionment of TSP and lead in Granite City. Illinois, us- ing chemical mass balance receptor model methods. Final Report, Vols I and II, prepared for the Illinois Environmental Protection Agency by NEA, Inc. Illinois EPA, Springfield, IL. Illinois Environmental Protection Agency. 1979. An- nual Air Quality Report 1978. lEPA, Division of Air Pollution Control, Air Monitoring Section, 2200 Churchill Road, Springfield, IL 62706. 152 AIR QUALITY TRENDS IN ILLINOIS Dlinois Environmental Protection Agency. 1980. 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Office of Air Quality Planning and Stan- dards, U.S. EPA, Research Triangle Park, NC 2771 1, EPA-450/4-89-005. McAlister, R.A., E. Bowles, J. DeGamo, J. Rice, R.F. Jongleux, R.G. Merrill, and J.T. Bursey. 1991. 1990 urban air toxics monitoring program. Office of Air Quality Planning and Standards, U.S. EPA, Research Triangle Park, NC 2771 1, EPA-450/4-9 1-024. Science Advisory Board, U.S. Environmental Protec- tion Agency. 1990. Reducing Risk: Setting Priorities and Environmental Strategies for Environmental Protection. The Report of the Science Advisory Board, Relative Risk Reduction Strategies Cominittee. U.S. EPA, Science Advisory Board, SAB-EC-90-021. Shively, T.S. 1991. An analysis of the trend in ground- level ozone using non-homogeneous Poisson processes. Atmospheric Environment, 25B(3):387-395. Snedecor, G.W., and W.G. Cochran. 1980. Statistical Methods, 7th edition. The Iowa State University Press, Ames, Iowa, p. 192. Sweet, C.W., and S.J. Vermette. 1992. Toxic volatile organic compounds in urban air in Illinois. Environ. Sci. & TechnoL, 26(1), pp. 165-173. Wadden, R.A., P. A. Scheff, J. Lin, H. Lee, C.B. Keil, J. Graf-Teterycz, D. Kenski, J.-Y. Yeng, M. Javor, N. Khalili, and T. Holsen. 1992. Evaluation of two-phase air pollution data for receptor modeling. Paper 92- 104.05, 85th Annual Meeting of the A&WMA, Air & Waste Management Association, Pittsburgh, PA. Wilkinson, L. 1990. SYSTAT: The System for Statistics, SYSTAT, Inc., Evanston, IL. 153 ATMOSPHERIC DEPOSITION TRENDS IN ILLINOIS ATMOSPHERIC DEPOSITION TRENDS IN ILLINOIS Donald A. Dolske and Van C. Bowersox Illinois State Water Survey INTRODUCTION Purpose In the conceptual design of Illinois' Critical Trends Assessment Project or CTAP, (lENR, 1992), atmo- spheric deposition is treated as an environmental process that describes how pollutants from various sources are delivered to receptors. The CTAP plan addresses six natural environmental receptors: (1) forests, (2) agroecosystems, (3) streams and rivers, (4) lakes and impoundments, (5) prairies and savannas, and (6) wetlands. Among these, atmospheric deposition is considered for forest ecosystems and lakes and im- poundments, because research has shown possible damage to these receptors from certain kinds and amounts of atmospheric deposition. For example, the recently completed National Acid Precipitation Assess- ment Program reported evidence that acidic deposition, along with other stresses, affects some high-elevation spruce forests in the eastern United States (Shriner et al., 1990). Long-term changes in low-elevation forests may be possible as well. This section describes the characteristics of atmo- spheric deposition in Illinois, which pollutants have the highest concentrations, and how the concentrations vary across the state and throughout the year. Where there are data sufficient for an analysis, changes over several years are calculated and trends are inferred, if these changes are significant. Also shown are maps of deposition fluxes, which together with the concentra- tion data provide information necessary for assessments of the exposure of Illinois' natural environment to atmospheric deposition. While an explicit description of the source-receptor relationships for major pollut- ants, such as sulfur dioxide or SO^ and nitrogen oxides or NO , is not considered in this section, the sources of these pollutants in Illinois and surrounding states are compared to their occurrence in atmospheric deposi- tion. Finally, additional work is discussed that is necessary to improve our assessment of atmospheric deposition in Illinois and over Lake Michigan. Scope Atmospheric deposition includes gases and aerosols (solid, liquid, or mixed phase). It includes primary pollutants, which retain their chemical identity between source and receptor; and it includes secondary pollut- ants, which undergo physical or chemical transforma- tion during transport in the atmosphere. Calcium is an important chemical element in Illinois atmospheric deposition. As a primary pollutant, calcium is found in dust particles that become airborne during automobile traffic on unpaved roads (Barnard et al., 1986). Dust particles are relatively large (diameter >1 micrometer or p.m); and because of their size and density, the primary mechanism for their removal from the atmo- sphere is gravitational settling, a form of atmospheric deposition. Sulfate is a secondary pollutant in the Illinois atmosphere, because it is emitted mostly as a gas, SOj, when fossil fuels are burned. In the air it is transformed into relatively small sulfate aerosols (diameter < 1 |im), which are removed by deposition processes other than gravitational settling. Deposition of pollutants from the atmosphere is a continuous process, though there are large temporal variations in the deposition rate or flux. These varia- tions relate to the kind of deposition that is occurring and to surface and atmospheric conditions. There are two kinds of atmospheric deposition, wet and dry. Wet deposition is defined as the delivery of pollutants to the surface by precipitation. Dry deposition is the delivery of gases and aerosols to the surface by mass transfer processes other than precipitation. By "surface," here, is meant soil or rock or water bodies or crops or forests or whatever man-made structures cover these natural surfaces (e.g., buildings, monuments, highways, park- ing lots). In principle, dry deposition occurs continu- ously, while wet deposition occurs episodically, e.g., when it rains. Wet deposition includes precipitation-bome pollutants, such as dissolved gases, dissolved particles, insoluble particles, and dissolved materials that are leached from the chemical matrix of particles that do not dissolve in precipitation. An example of this latter type of wet deposition is the potassium that rainwater leaches from soil particles, even though the solid soil particles do not themselves dissolve. Precipitation-borne pollutants can be organic or inorganic. Wet deposition is measured by chemically analyzing precipitation. To measure the chemistry in samples of precipitation collected sepa- rately from dry deposition requires a device that opens only during precipitation. Such a device, a wet-only 155 ATMOSPHERIC DEPOSITION TRENDS IN ILLINOIS deposition collector, involves some compromise, since dry deposition occurs continuously even during precip- itation. Under most conditions and for most chemicals, however, this compromise is inconsequential, since the total, wet plus dry, deposition during precipitation is dominated by the wet part (wet > 10 x dry). An example of an exception to this statement would be rain that occurs during blowing dust, when the chemi- cal deposition from the falling dust dominates that from the rain. For this project, wet deposition data from the national network, the National Atmospheric Deposition Pro- gram/National Trends Network (NADP/NTN) were used. The NADP/NTN reports the concentrations of dissolved calcium or Ca**, magnesium or Mg"^, sodium or Na*, potassium or K*, ammonium or NH/, sulfate or SO^=, nitrate or NO3 , chloride or CI , orthophosphate or PO^^ , and free hydrogen ion or H*, measured in pH units. No trace metals or organic compounds are measured by the NADP/NTN. Samples are filtered to remove insoluble materials, so the NADP/NTN pro- vides data for the soluble major inorganic ions found in precipitation, i.e., for those chemicals that result in acidic deposition or "acid rain," which occurs over all of Illinois. Dry deposition includes the mass transfer of pollutants to the surface by a variety of physicochemical pro- cesses: turbulent diffusion, diffusion followed by surface sorption of gases, gravitational settling of large particles, impaction, and interception of solid and liquid particles. Dew, fog, and mist are examples of liquid particles that are considered dry, not wet, depo- sition, because the mass transfer to the surface is by interception, not precipitation. Dry deposition fluxes are strongly affected by atmo- spheric factors, which influence the rate at which pollutants are delivered to a receptor surface, and by surface factors, which influence the efficiency with which pollutants "stick" to a receptor surface. Among the atmospheric factors are wind speed and turbulence, air temperature, solar radiation, and relative humidity. Among the surface factors are roughness, wetness, surface-to-air temperature difference, and type of sur- face, which includes whether the surface is animate (plant) or inanimate. The relative importance of these factors in determining the dry deposition rate also depends on the physical and chemical nature of the pollutant. For example, factors that affect the mass transfer of carbonaceous soot, an unreactive, insoluble particle, are much different than the ones affecting nitric acid, a highly reactive, soluble gas. The dry deposition of gases and submicron aerosols involves highly complex processes for which direct measurements are intractable on a spatial domain of the size and complexity of Illinois. Thus, an indirect method was applied to infer, rather than measure, dry deposition fluxes. This inferential method employs a conceptual model. This computerized model esti- mates an atmosphere-to-surface coupling parameter known as the deposition velocity, V^. The dry deposition flux is the product of V^ and the measured air concentration of a particular pollutant. Model inputs include the atmospheric and surface factors discussed earlier. These are measured at a network of sites sponsored by the National Oceanic and Atmo- spheric Administration's Atmospheric Turbulence and Diffusion Division (NOAA/ATDD). Land use and vegetation type and status are also reported at these sites, along with the airborne concentrations of CI", S0^=, particulate NO3 , nitric acid vapor or HNO3, and SOj. The NOAA/ATDD sampling system is especially designed to exclude large particles, since the inferential method of calculating dry deposition applies specifically to gases and sub- micron aerosols. The dry deposition of large particles, which have an aerodynamic diameter > 1 |im, is typically estimated from an analysis of the mass of a pollutant accumulated on a surrogate surface (Dolske and Gatz, 1984). The term "surrogate surface" is used, because it is impracti- cal to measure dry deposition on every animate (plant) and inanimate surface, and so a substitute surface is selected. Since the physical process that dominates large particle dry deposition is gravitational settling, the surrogate surface must receive and retain large particles in a manner equivalent to soils, rocks, streams, building surfaces, plant surfaces, etc. In prin- ciple, there is no universal surrogate for surfaces with such diverse characteristics. To estimate the dry deposition of large particles, (i.e., sedimentation or dry fall) for the CTAP, data from the NADP/NTN were used. The NADP/NTN measures dryfall in separate samples collected by the sampler also used for precipitation. This device, a wet/dry collector, has two identical containers; it dis- criminates between wet and dry conditions, exposing the wet deposition container during precipitation and the dryfall container at all other times. Dryfall samples are sent for analysis of the same analytes measured in precipitation. Evaluations of dry deposition monitoring methods (Hicks et al., 1986) have raised objections to this 156 ATMOSPHERIC DEPOSITION TRENDS IN ILLINOIS method for monitoring dry deposition. One objection is that contamination by foreign matter (plant parts, insects, bird feces, etc.) compromises sample integrity. A second objection is that gaseous and fine-particle deposition are poorly characterized. For this study, however, the data were screened to minimize the effect of sample contamination from foreign matter. As to the second objection, the data were used only for dryfall or sedimentation estimates, not for the deposition of gases and submicron aerosols. DATA SOURCES Wet Deposition Data for assessing the precipitation quality and wet deposition fluxes for Illinois' CTAP were taken from the NADP/NTN. This network began operations at 20 sites in 1978 and today operates at nearly 200 U.S. locations, with a site in American Samoa and one in Puerto Rico. Sites were chosen according to network design criteria (Robertson and Wilson, 1985), and equipment was installed to minimize sampling artifacts from local point and area sources (Bigelow, 1984). Based on these criteria, data from network sites are expected to be representative of the region where the sites are located. Using a wet/dry collector of a specified type, one-week, wet-only, deposition samples are collected on Tuesday morn- ings in the NADP/NTN (Bigelow and Dossett, 1988). All samples are sent to a single Central Analytical Laboratory (CAL), located at the Illinois State Water Survey. At the CAL, approved standard procedures are followed for sample analysis (Peden et al., 1986) and data validation (Bowersox, 1984). Table 1 lists the locations, site types, and periods of operation of NADP/NTN sites in Illinois. Seven sites are currently active in the state; the site near Salem (IL47) was closed in 1988 and moved to Stephen Forbes State Park, near Omega (IL99), in 1989. Figure I shows the locations of NADP/NTN sites in and around Illinois. Data from outside the state are included with Illinois data during all spatial objective analyses of precipitation quality and deposition flux fields. This approach precludes "edge effects" from extrapolation of the data, by providing in-state and out-of-state observations that can be used to interpo- late data fields out to and beyond state borders. Edge effects can produce spurious results in objective analysis schemes. Dry Deposition Each of the NOAA/ATDD sites, Argonne, IL19, and Bondville, ILll (see figure I for locations), was deliberately co-located with an existing NADP/NTN site. The objective of the NOAA/ATDD program is to develop and verify models for estimating dry deposi- tion from easily measured surface conditions, micro- meteorological parameters, and air quality data (Hicks et al., 1991). Weekly average air concentration data and a site-specific deposition velocity, V^, are used to calculate dry deposition amounts for certain gases and ions associated with small particles. Surface conditions include local topography, land use, and vegetation type and status. Each of these surface factors contributes to V^ at varying length scales, and these factors vary only slowly over time. Micrometeorological parameters (wind speed and direction and their fluctuations, tem- perature, humidity, solar radiation, surface wetness, and precipitation rate) are monitored continuously and digitally recorded every 15 minutes. All of these factors are input variables for a computer model that provides a set of V^ values for a predeter- mined time period (usually weekly). Each V^ in the set is specific to the chemical species and to the gas or particle size range in which that species is found in the atmosphere. The weekly-average airborne concen- trations of particulate CI , S0^=, and NOj , and of gases, HNOj and SO^, are reported for each site. The sampling system excludes large particles, since the inferential method of calculating dry deposition applies specifi- cally to gases and submicron aerosol-associated materials. The weekly accumulated flux of each chemical is then calculated as the product of the average concentration and the appropriate V^. These calculated results are periodically compared with directly measured dry deposition data at the NOAA/ATDD sites (Meyers et al., 1991), so that the model can be calibrated and revised as needed. The current version of the NOAA/ ATDD model produces dry deposition estimates that generally agree within 10 to 20 percent of the directly measured values. Further model calculations are used to "scale up" to larger areas and longer time scales. In addition to the NOAA/ATDD data, longer term (annual) and wider area concentration data for other chemical species in Illinois' atmosphere were provided through the CTAP (see Air Quality Trends in Illinois chapter). For each of these chemicals (arsenic or As. cadmium or Cd, chromium or Cr, iron or Fe, manga- nese or Mn, nickel or Ni, nitrogen dioxide or NOj, NOj . ozone or O,, lead or Pb, SO^, and SO/, as well 157 ATMOSPHERIC DEPOSITION TRENDS IN ILLINOIS Table 1. National Atmospheric Deposition Program/National Trends Network Sites in Illinois Site designation Site location Latitude Longitude Elevation (m)** Nearest town Site type Dates of operation Wet deposition Begin End IL 11* IL 18 IL 19* IL35 IL47 1L63 IL 78 IL 99 40°3'I2" 4r50'29" 4r42'4" 37°4236" 38°38'36" 37°26'8" 40°56'0" 38°42'36" 88°22'19" 212 Bondville rural 88''51'4" 265 Shabbona rural 87°59'43" 89°16'8" 229 146 Argonne Carbondale suburban rural 88°58T' 173 Salem suburban 88°40'19" 161 Glendale rural 90°4373" 229 Monmouth rural 88°44'57" 153 Omega rural 27 Feb 79 26 May 81 1 1 Mar 80 31 Jul 79 15 Apr 80 30 Jan 79 8 Jan 85 26 Sep 89 continuing continuing continuing continuing 22 Nov 88 continuing continuing continuing Dryfall deposition Begin End 27 Feb 79 26 May 81 1 Apr 80 20 Jul 79 15 Apr 80 30 Jan 79 none none continuing continuing continuing continuing 22 Nov 88 continuing none none Notes: *Also a NOAA/ATDD dry deposition site where airborne pollutant concentrations and atmospheric and surface factors are measured so that deposition can be inferred. **Elevations are reported in heights above mean sea level. Site Type + NADP/NTN site in IL * NADP/NTN and co-located NOAA site in IL o NADP/NTN site outside IL; used for spatial variation analyses Illinois Site ID 1 1 - Bondville 18 - Shabbona 19 - Argonne 35 - Carbondale 47 - Salem 63 - Glendale 78 - Monmouth 99 - Omega Figure 1. Map of the Illinois region, showing locations of sites providing atmospheric deposition data used in the CTAP. 158 ATMOSPHERIC DEPOSITION TRENDS IN ILLINOIS as total suspended particulate matter or TSP), annual statistics from the Illinois Environmental Protection Agency (lEPA) concentration data were combined with the appropriate NOAA/ATDD V^ to estimate the median and range of dry deposition loadings. Dryfall deposition samples are collected at a subset of NADP/NTN sites, using the "dry side" of the wet/dry collector. There are five dryfall sites in Illinois, listed in table 1. While the wet deposition samples at NADP/ NTN sites are collected weekly, dryfall samples are left to accumulate for eight weeks, and then are sent to the CAL for analysis. At the CAL, 250 milliliters (mL) of deionized water is added to the samples, the mixture is swirled to remove dry deposited matter from all sur- faces, and the samples are allowed to equilibrate over- night. Next, the samples are filtered (0.45 |im pore diameter), handled, and analyzed the same way as rain samples (Peden et al., 1986; Lockard, 1987). Results are reported in mass flux units. DATA ANALYSIS METHODS Data Screening Procedures Data from NADP/NTN collection sites in Illinois and neighboring states were used to assess atmospheric deposition for the CTAP. These data were used only when standard network procedures for field, laboratory, and data management operations were followed. Several documents describe the NADP/NTN quality assurance program (NADP/NTN, 1990), field site sample collection and measurement methods (Bigelow and Dossett, 1 988), analytical laboratory operations (Peden et al., 1986), and data verification and screening procedures (Bowersox, 1984). Adhering to standardized procedures ensures that data comparisons among sites are not biased by differences in equipment or procedures and that comparisons over time at a site are not biased by changes in equipment or procedures. Where NADP/NTN measurements of atmospheric deposition were used for Illinois' CTAP, analyses were based on data that are comparable in space and time. In addition to the selection of samples collected according to standard procedures, all wet deposition data must have been for wet-only precipitation sam- ples, uncontaminated by matter foreign to the forma- tion and occurrence of precipitation. The requirement for wet-only sample collection was described in the introduction of this chapter. An example of foreign matter is a leaf or a bug. A report of foreign matter in a sample, while necessary, is not sufficient for exclusion of a record from the analysis. An objective system for identifying an NADP/NTN sample as "contaminated" requires the co-occurrence of foreign matter and an anomalous chemical composition (Bowersox, 1984). "Contaminated" samples are ex- cluded from the analysis. Finally, to create chemical concentration maps and to calculate interannual trends, the data must satisfy four completeness criteria. Expressed as percentages, these four criteria quantify the fraction of time and the frac- tion of the precipitation amount for which there are valid wet deposition data. In summary, these criteria require that there be: 1 . Precipitation amount measurements for 90 percent or more of the time, 2. Valid chemistry measurements for 75 percent or more of the time, 3. Valid chemistry measurements for 75 percent or more of the measured precipitation, and 4. A ratio of total wet-only sample volumes to total measured precipitation of 75 percent or more, tak- ing data records where both values are available. These same criteria are applied in the publication of the NADP/NTN Annual Data Summary (NADP/NTN, 1991). Wet deposition data that pass these validation tests have an acceptable level of comparability and representativeness for making maps and performing trend analyses for the CTAP. Figure 2 displays the record of when wet deposition measurements were made at each of the Illinois sites. Also displayed are the periods when data passed the validation tests for calculating trends. Whole years of data were used to evaluate the four completeness cri- teria. Consequently, a year either passed or failed the tests and is included or excluded, respectively, from the trends analyses. A meteorological year, 1 December through 30 November (Trenberth, 1983), was used to ensure proportionate representation from each season in each year (i.e., December of year 1 and January and February of year 2 comprise a winter season). For making maps, the completeness criteria were applied to the time period on which the maps were based (multiple meteorological years). Notice in the figure that valid data from the Monmouth site (IL78) began in 1986. Given the importance of the data from this site in defining east/west gradients in several of the chemical species, it was decided that concentration 159 ATMOSPHERIC DEPOSITION TRENDS IN ILLINOIS 19 18 78 CO UJ CO 11 CO o z =j 99 47 35 63 ^ ^ WET DEPO & DRYFALL WET DEPO, DRYFALL & V. WET DEPO ONLY WET DEPO TRENDS :^^^^^SS^^^ ^>^^^^S^^^:^^^^:^^^^:^^^^^S^ ____Ji 1979 1981 1983 1985 1987 YEAR 1989 1991 Figure 2. Record of wet and dry deposition measurements at Illinois sites (see figure I for site locations). Wet deposition (WET DEPO) and dryfall measurements are from NADP/NTN sites. Deposition velocity, V^ measurements are from NOAA/ATDD sites. Valid data for long-term trends (WET DEPO TRENDS) are also indicated. 160 ATMOSPHERIC DEPOSITION TRENDS IN ILLINOIS maps would be based on valid data beginning in 1985 and ending in 1990. During this period the Salem site (IL47) terminated operations and was replaced by the Omega site (IL99), with a one-year (1989) hiatus. In the interest of having maximum spatial coverage, valid data from these two nearby sites were pooled in mak- ing concentration maps. With only a year of valid data at the Omega site, no statistical tests were done to evaluate whether these two data sets were from the same population and could be pooled without introduc- ing a bias. This should be done when more data are available for future analyses. Figure 2 also displays when and where dryfall (i.e., dry bucket) measurements are made at Illinois sites (see also figure 1 and table 1). Unlike NADP/NTN wet deposition data, dryfall data are not routinely screened to ensure samples that are dry-only and uncontam- inated. Gatz et al. (1988) examined dry bucket data from the entire NADP/NTN to develop criteria that could be applied to remove unrepresentative contami- nated samples from the data. Their approach was to examine the distribution of ionic concentrations, while applying ever more stringent screening criteria, thus eliminating more and more data. Samples were removed in groups, first due to sample collection and handling errors (i.e., nonstandard procedures), and successively due to contaminants: water, bird drop- pings, plant or insect debris, and other contaminants. Screening to the level where samples with visible contaminants were removed resulted in a clear and statistically significant break in the NH/, K*, and PO^' distributions; this level sharply reduced a positive bias in these constituents. Even H* and SO.^ showed some effects from removal of these samples, though not as marked. For these reasons, dryfall data from Illinois sites were screened to this level for this report. Recall from previous sections that the NADP/NTN dry bucket sampling protocol is to collect an eight-week integrated sample from the "dry side" of a wet/dry collector. This results in either six or seven samples per year. Removing samples to the screening level described above, leaves from two to six samples per year at each of the five Illinois sites. With so few samples in a year, all of the data from each site were pooled to examine spatial patterns in dryfall deposition, but the calculation of interannual trends at a single site was impractical. The dry deposition of gases and submicron aerosols in Illinois is inferred from measurements at two NOAA/ ATDD sites (Argonne and Bondville), shown in figure I and listed in table I . Figure 2 shows the period of operation of these two stations. As previously de- scribed, data from the NOAA/ ATDD sites include the chemistry of weekly-integrated air samples and 15- minute-average micrometeorological measurements, digitally recorded. These are input variables to a model that infers dry deposition fluxes. These data are screened for completeness by verifying that all micrometeoro- logical measurements are continuous during a period for which V^ is computed. Airborne concentrations also must be available for this period. This requires uninter- rupted field equipment operations and complete laboratory analyses for each weekly period. Quality assurance practices (Hicks et al., 1991) help to ensure accurate and complete data from NOAA/ATDD sites. These include: 1 . Weekly site operator verification of instrumental performance, 2. Monthly air quality system checks with field and procedural blanks, 3. Quarterly flow rate calibrations, and 4. Semiannual calibration of the entire system by NOAA/ATDD personnel. Finally, the NOAA/ATDD model occasionally is tested and verified against direct measurements of dry depo- sition at "core" sites in the network. Argonne is one of these sites. The Bondville site is a so-called "satellite" site, where identical methods and instrumentation are used, but no on-site model verification is done. For this report, 45-51 weekly, quality-assured, data. points per site per year were available to calculate dry deposi- tion fluxes, for an overall completeness better than 90 percent. Annual median values from the lEPA concentration data were used (see Air Quality Trends in Illinois chapter) with distribution statistics from the NOAA/ATDD V, results to calculate statewide deposition estimates. Deposition amounts are re- ported only for those years in which sufficient data were available from both data sets to calculate an- nual statistics. Finally, annual estimates of total atmospheric deposi- tion were computed for 1985-1990 for those chemical species (calcium, sulfur, and nitrogen) for which all the various components of wet and dry deposition were available, according to each of the above criteria. The total deposition values were based on summation of annual means of NOAA/ATDD V, values for fine particles and ga.ses, the lEPA concentration data for sulfate, sulfur dioxide, and nitrate, the NOAA/ATDD nitric acid concentration data, and NADP/NTN dryfall and wet deposition data. 161 ATMOSPHERIC DEPOSITION TRENDS IN ILLINOIS Statistical Analyses Ion concentrations in valid wet-only deposition sam- ples from NADP/NTN sites were used to characterize Illinois precipitation chemistry. An approach used by Semonin and Bowersox (1983) to identify the ions that dominate the stoichiometry of precipitation was ap- plied to Illinois data. Briefly, ions were ranked in order of their average concentrations and the subset that comprised about 90 percent of the total ion strength was selected. This subset was used to calculate a charge balance for individual samples and to assess whether the distribution of charge balances was near zero. Zero is expected, if all ions are measured with zero bias and precision, which requires perfect mea- surements. In practice, ion balances are positive and negative due to noise, or imprecision, in every measurement; and so the distribution of ion balances clusters around zero. When the distribution of ion balances for the subset was within the distribution for all measured ions, the process of adding ions to the subset was stopped. This subset was assumed to be characteristic of Dlinois precipitation. The distributions of ions that "characterize" Illinois precipitation are summarized by site and by year in this chapter. Ion concentration distributions are presented in notched box-and-whisker plots, as in figure 3. A com- mercial software package on a personal computer created these plots by ranking the data in ascending order from minimum to maximum. The middle half of the data, defined as the 25th to the 75th percentile, is enclosed in a box. In figure 3 this box begins at 0.23, the 25th percentile, and ends at 0.61, the 75th percen- tile. The box width is proportional to the square root of the number of observations (N) in the data set it repre- sents. Side-by-side boxes are scaled accordingly, so that the reader can distinguish how much data is represented by each box relative to its neighbors. One generally puts more confidence in large rather than small data sets, because they are less likely to change significantly when new data are added, i.e., results are generally more robust as N grows. Along the sides of the box in figure 3 is a V-shaped notch with a horizontal line in its middle. This line marks the median, at ~ 0.36 in figure 3, which is the value in the ranked data with as many observations above as below it. Notches are drawn according to formula ( 1 ) and approximate a 95 percent confidence interval around the median (AXUM, 1992). Notches are drawn at the median ± ( 1 .57 * height of boxVN) ( 1 ) "Informally interpreted, if the notches for two boxes don't overlap, it is evidence that the medians are different" (AXUM, 1992). To facihtate the comparison of medians, a shaded band that fills the notch for a pre- selected reference site was added to some figures, e.g., figure 7. Vertical lines, or whiskers, are located above and below the box and these mark the highest and lowest 25 percent of data, respectively. Short horizon- tal tick marks have been added to the whiskers to mark the location of the 10th and 90th percentiles. In figure 3 the 90th percentile occurs at 0.88 and the 10th percen- tile at 0.17. Altogether, the notched box-and-whisker plots mark the location of the minimum and the 10th, 25th, 50th (median), 75th, and 90th percentiles, and the maximum. Statistical distributions of pollutant concentrations in Illinois precipitation are presented as notched box-and- whisker plots in figures 7-12. All valid data from each site are summarized in these figures. Sites are shown in order from north on the left to south on the right (see table 1 and figure 1 for site names and locations). The number of valid data points (N) for each site varies and depends mostly on the duration of sampling at each site (figure 2). For each site in these figures, N is 450 (IL190); 402 (IL18); 245 (IL78); 497 (ILl 1); 77 (IL99); 293 (IL47); 483 (IL35); and 502 (IL63). All of the basic statistical analyses used to analyze dry deposition estimate distributions to arrive at means, medians, standard error, and ranges were computed using SYSTAT 5.0 routines (Wilkinson, 1990). The development of variables used to generate combined data, e.g., dry deposition = V * concentration and total deposition = wet + dry (gas) + dry (aerosol) -i- dryfall was done using either SYSTAT data management utilities or BASIC programs written specifically for each task. All graphical displays of the dry deposition data, including box plots, bar graphs, stacked bars, and scatterplots, were generated on an ARES 486-66 PC using SYGRAPH 1.0 and SIGMAPLOT 5.0 (Jandel, 1992). SYGRAPH 1.0 was used to prepare the total deposition plots, which were overlaid on a State of Illinois map. 162 ATMOSPHERIC DEPOSITION TRENDS IN ILLINOIS MAXIMUM 90TH PERCENTILE 75TH PERCENTILE TOP OF NOTCH MEDIAN BOTTOM OF NOTCH SHADING BAND 25TH PERCENTILE ■10TH PERCENTILE MINIMUM Figure 3. Example of a notched box-and-whisker plot used to summarize the distributions of ion concentrations in wet deposition. 163 ATMOSPHERIC DEPOSITION TRENDS IN ILLINOIS GIS Use Disclaimer Due to the extremely low spatial density of deposition data, no geographic information system (GIS) cover- ages have been developed for atmospheric deposition. The assignment of wet deposition values to nine cli- mate zones, and dry deposition to the "Chicago area" vs. "Remainder of State" is the best spatial resolution possible with currently available data. Furthermore, for dry deposition in particular, large variations in the rate of deposition can occur for a specific receptor system (lake surface, forest, or agricultural crop) and even elements within a system (for example, various parts of a building exterior within a city). RESULTS Spatial Analysis Wet Deposition. General characteristics of Illinois precipitation chemistry. Wet-only data from the NADP/NTN were used to examine the spatial varia- tions in precipitation-borne pollutant deposition in lUinois. The NADP/NTN reports mass concentrations of ten ions, (Ca^, Mg^, Na\ K% NH/, S0^=, NO,, CI , PO^'", and H*) routinely measured in the filtrate of precipitation collected at network sites. This set of ions includes the major anionic and cationic species that cause acidic precipitation in Illinois and elsewhere. Except for orthophosphate and possibly potassium, each of these ten ions is important in determining the average ionic composition of precipitation somewhere in the United States. In many coastal areas, the proxim- ity of a major source of airborne sea salt results in precipitation having a chemistry dominated by CI", Na*, S0^=, and Mg^ (Junge, 1963). In other areas, the chemical signature of wet deposition reflects the mix of sources that dominates the air quality in the local area. Semonin and Bowersox (1983) used data from North American precipitation chemistry networks to identify these signatures, where possible. In the east- em United States and Canada, four different signatures were reported. One four-ion signature (H*, SO^', NO3 , and NH^*) occurred across a portion of Illinois, although it was determined from a limited set of data, one to two years of data at four sites. Data are now available from eight different locations and for up to 12 years at some of these locations (see figures 1 and 2 and table 1). A procedure similar to the one used by Semonin and Bowersox (1983) was applied to Illinois precipitation data. Volume-weighted average concentrations were calculated for each ion at every site. Site-specific total inorganic ion concentrations were computed by sum- ming up these values at the respective sites. Then, ratios of the average concentrations of each anion and cation to this total inorganic ion concentration were calculated. These ratios are shown as percent of inorganic ions for all eight Illinois sites in figure 4. In this figure, anion and cation percentages are presented in a stacked bar totaling 100 percent for each site. Anion percentages are stacked on the bottom of the figure, beginning with SO^" then NO^ and CI', which is their order of importance. Average orthophosphate concentrations were below the analytical limit of detection and too small to show. Cation percentages are stacked on the top of the figure. Except for firee hydro- gen ion, H*, the order in which cations are stacked is generally from least important (K*) to most important (NH,,*). The H* percentages are shown numerically in the clear bar that separates the anions from the other cations. This arrangement facilitates the comparison of the average precipitation chemistry among sites, and it depicts H* as making up the cations needed to push the total to 100 percent. Indeed, this is what happens chemically in acidic precipitation: the total cation concentration without H* must equal the total anion concentration, and to the extent the cations are defi- cient, H* makes up the difference. Hydrogen ion percentages range from 1 7 percent at the Monmouth site in western Illinois (IL78) to 28 percent in the east-central and south-central parts of the state (Bondville-ILll, Salem-IL47, and Omega-IL99). At all sites, from IL19 in the north to IL63 in the south, there is little variation in the acidic anion contributions of sulfate, nitrate, and chloride. What changes most from site to site is the contribution of basic cations, (NH^*, Ca", Mg", Na*, and K*) that counterbalance or neutra- lize the acidic anions. The cations maximize at Monmouth (IL78), where H* is lowest, and minimize at the Bond- ville (ILl 1), Salem (IL47), and Omega (IL99) sites (see figure 4). At all sites in figure 4, SO^= clearly is the largest contributor to the inorganic ion strength, i.e., the sum of the ion concentrations. Hydrogen ion is the next most important contributor, followed by NO,", NH/, and Ca**. Using volume-weighted average concentrations, these five ions make up 89.4 to 93.1 percent (mean of 90.6 percent) of the inorganic ions in Illinois precipitation. Taking concentrations in individual samples instead of averages, the sulfate concentration is highest in 65 to 82 percent of all Illinois samples. The order of impor- tance of ions in individual samples is the same as for 164 ATMOSPHERIC DEPOSITION TRENDS IN ILLINOIS 100 ^ 80 O O z S 60 o O 40 H Z LIJ o cc S 20 ^ 23 :^ ^ 18 ^ ^ X| 27 ',../-,V-' v.-^r^ \NNH4 ;i£i Ca ^ Mg Na ■ K H ^■^ici ^ N03 ^ S04 Figure 4. Ratios (in percent) of volume-weighted-average anion and cation concentrations to the total measured inorganic ion concentrations at Illinois sites (see figure 1 for site locations). Numbers in the clear stacked bar in the middle are percentages for the hydrogen ion, H*. Average orthophosphate concentrations were below the analytical detection limit and too small to show. 165 ATMOSPHERIC DEPOSITION TRENDS IN ILLINOIS the average concentrations: SO/ > H* > NO, > NH/ > Ca**. Notably, for all but 0.4 percent of the wet deposition samples in Illinois, one of these five ions has the highest concentration. Figure 5 presents the percentage ratios of the sum of these five ions to the sum of all ten ions in individual samples. These ratios are ranked from lowest to highest, and the rankings are depicted in this figure. For individual samples, 90 percent of the ratios are between 82.5 and 96.2 percent, which is consistent with the ratios when average con- centrations are used. A test of whether these five ions are sufficient to char- acterize the stoichiometry of Illinois precipitation is to check for a balance of positive and negative ions. In principle, liquid precipitation is an aqueous solution bearing no net positive or negative charge; thus cation (or positive ion) concentrations must equal anion (or negative ion) concentrations. To the extent that the cations and anions are out of balance, the measured set of ions is incomplete (some have been missed), the measurements are inaccurate (biased and/or imprecise), or a combination of these factors is at play. The charge balance was tested by taking the concentrations of the five largest contributors to the ion strength of individual samples and calculating a quantity labeled "ion percent difference." This quantity was defined by Stensland and Bowersox (1984) as Ion Percent Difference = (anion sum - cation sum)/ (anion sum + cation sum) x 100 percent (2) where (anion sum) is the chemical equivalent, or ionic charge, concentration of SO/ plus NO, and (cation sum) is the concentration of H* plus NH/ plus Ca**. Ion percent differences calculated in this way are summarized in figure 6. For 87.5 percent of the data in this figure, ion percent differences are less than 15 percent. This is consistent with the CAL experience for samples with an ion strength of about 0.2 milliequiva- lents per liter (meq/L) and pH values < 5.0, characteris- tics that are typical of Illinois precipitation. Based on the NADP/NTN Quality Assurance Plan (NADP/NTN, 1990), samples are not even targeted for reanalysis until ion percent differences are 1 5 percent, using the ten-ion set of measurements. A comparison of the original analysis with reanalysis results at the CAL verified that the original analyses were almost always correct, even when ion percent differences were 20 percent (Stensland and Bowersox, 1984). This study reported that 0.2 percent of the original numbers were in error. Thus, the magnitude of ion percent differences with the five-ion set is not markedly higher than for the more complete ten-ion set of measurements. Finally, if analytical imprecision alone is to blame for the ion percent differences from the five-ion set, the number of positive and negative values taken over all samples would be virtually the same. Figure 6 shows a breakdown of the frequency of occurrence of positive and negative differences. Positive differences account for about 60 percent and negative differences for about 40 percent of the cases. This means that a cation deficit is 50 percent more likely to occur than an anion deficit (i.e., 3 cation deficits to every 2 anion deficits). This imbalance could result from an analytical bias or from ions not measured or not considered. Indeed, this im- balance is consistent with the ions not considered in the five-ion set. Looking at the averages in figure 3, Mg", Na*. and K* together exceed CI' at every site. The skewness in the ion balance results in figure 6 reflects the charge imbalance in ions left out of the calculation. It follows from these results that five ions dominate the ion strength of Illinois precipitation: SO/ > H* > NOj' > NH/ > Ca**. While these ions effectively control the solution stoichiometry, there is a small net cation defi- cit from the remaining ions. Illinois precipitation is best characterized as a dilute solution of mineral sulfuric (HjSO^) and nitric (HNO,) acids, partially neutralized by dissolved NH^* and Ca**. The sulfur and nitrogen oxides result almost entirely from the combustion of fossil fuels, while the calcium and ammonium are from terrestrial sources. Since the five ions so dominate the chemistry of Illinois precipitation and since the other measured ions have no deleterious effects at the levels reported, the summary of wet deposition in this chapter focuses on the spatial and temporal distributions of these five ions. Statistical distributions of pollutant concentrations . Precipitation in Illinois has a range of ion strengths from ~ 25 ^eq/L to > 7,000 \ieqfL, a factor of ~ 300 from low to high. Ion strength measures the inorganic pollutant concentration in ion equivalents, so it indi- cates how polluted the rain or snow is. A typical rain sample from an Illinois site might have a pH of 4.4; and if this were entirely due to dilute sulfuric acid, the ion strength would be - 80 |ieq/L. The distributions of total ion strengths of wet deposition samples are shown for each site in figure 7. All of the median concentra- tions (located at the center of the notches in the box plots) are > 80 \ieqfL, which is another indication that Illinois precipitation contains more than sulfuric acid (i.e., more than H* and SO/). It is evident in this figure that more than half of the samples have an ion concen- tration between 100 and 300 |ieq/L. From the results in the previous section, 90 percent of this is due to just five ions. 166 ATMOSPHERIC DEPOSITION TRENDS IN ILLINOIS 100 (0 O + (0 C o o 'E (0 I" S o ^ z o + (D Q. + I 90 80 70 60 50 Percentile Avg ( Range) 98.7 (97.5-98.7) 96.2 (95.5-96.8) 94.7 (94.1-95.6) 92.4(91.4-94.1) 88.4(87.1-91.9) 82.5 (78.9-87.6) 47.3 (47.3-69.2) All Illinois Sites Figure 5. Distribution of the ratios (in percent) of the sum of concentrations of five ions (H* , SO^', NOj, NH/, and Ca**) to the total measured inorganic ion concentrations in individual Illinois samples. The percentage values at seven reference percentiles in the distribution are listed, along with the range of percentages at the eight Illinois sites, when ranked separately (see table 1 for a list of sites). 167 ATMOSPHERIC DEPOSITION TRENDS IN ILLINOIS 10U 1 90 80 — _ z /U — LU CC LU li- 60 — Li. Q 1- 50 — Z III ~ o CC 40 — UJ Q. z 30 — o _ 20 — 10 — ■ >=20 ES 15-19.9 I I 10-14.9 ra 5-9.9 EH 0-4.9 TOTAL POSITIVE NEGATIVE Figure 6. Ion percent differences calculated from the five-ion set (SO/. H* , NO,'. NH/. and Ca**). Differences appear in the five percentage frequency classes shown in the legend. Absolute values of the differences were used in compiling the frequency distributions labeled "TOTAL". Frequency distributions for net "POSITIVE" and "NEGATIVE" differences are also shown. 168 ATMOSPHERIC DEPOSITION TRENDS IN ILLINOIS 19 18 78 11 99 47 55 53 SITE ID Figure 7. Distributions of total inorganic ion concentrations (Total Ion Strength) in Illinois precipitation at NADP/NTN sites (see figure 1 for site locations). Boxes enclose the 25th to the 75th percentiles and the notches mark the median and its 95 percent confidence interval. Box widths are proportional to the square root of the number of observations. Lines (whiskers) extend to the minimum and maximum except where indicated. Horizontal ticks on the whiskers indicate the 10th and 90th percentiles. For comparison, the shaded band marks the location of the notch for ILll. 169 ATMOSPHERIC DEPOSITION TRENDS IN ILLINOIS A shaded band fills the notch (the median and its 95 percent confidence interval) of the box (25th to the 75th percentile) for Bondville (ILll) data in figure 7. Located in rural east-central Illinois, Bondville is roughly halfway between the three northern (IL19, IL18, and IL78) and three southern sampling locations ([L41/99, IL35, and IL63). The location of the notch for a site, either fully above or below this shaded area, indicates that the median pollutant concentration at that site is significantly above or below (respectively) the concentration at Bondville. Only at the Argonne site (IL19) in the Chicago area is the median ion strength significantly above (nearly 10 percent) that at Bond- ville, probably due to the influence of nearby urban sources. Median pollutant concentrations appear to be significantly below the Bondville level at the Mon- mouth site (IL78) in western Illinois and at the Car- bondale site (IL35) in the forested southwestern part of the state. At the remaining sites, median pollutant concentrations, while below the Bondville value, are within the (shaded) confidence interval and are not significantly different than this reference. No north to south gradient is evident in these overall pollutant concentrations, outside of the possible urban influence on Argonne data from the Chicago area. Free acidity, or the concentration of H* in precipitation is measured and reported in pH units; and in Illinois the observed pH range is from 3.10 to 8.45 (0.004 to 794 |ieq/L). Acid rain has been defined as having a pH below 5.6, a value that is based on the free acidity of water in equilibrium with atmospheric carbon dioxide or COj (Barrett and Brodin, 1955). Of Illinois wet deposition samples, 91.3 percent have pH values < 5.6. This 5.6 reference is based on the assumption that, except for CO,, natural pollutants scavenged from the air by precipitation are neither acidic nor basic; i.e., they are neutral. Measurements from remote regions of the world, where natural pollutants dominate anthropo- genic influences, belie this assumption (e.g., Galloway et al., 1982). "No single value for pH or any analyte can be regarded as a worldwide background value;" however, the average pH in humid remote areas is closer to 5.0 than 5.6 (Sisterson et al., 1990). Of Illinois wet deposition samples, 85.6 percent have pH values < 5.0. Taking either of these definitions, 8 to 9 out of every 10 weekly precipitation samples in Illinois can be termed "acidic deposition." Figure 8 plots the distribution of pH measurements at each Illinois NADP/NTN site. The shaded band, filling the notch for the Bondville site (ILl 1 ), once again serves as a basis for comparing data among sites. Bondville pH values at the 10th, 25th, 50th, 75th, and 90th percentiles are the lowest among the sites, and the Bondville median is significantly below the medians at all but the IL63 and IL99 sites. This is consistent with the generally higher SO^" and NO^ measurements at Bondville, shown in figures 9 and 10. At the IL78 site near Monmouth in western Illinois, the median pH is about 4.6 and the middle half of the distribution, the 25th through the 75th percentiles, is almost completely above the middle half of the distribution at Bondville. The free acidity at Monmouth is about half of the Bondville levels, owing to the combined effects of lower SO/ and NO^ and higher Ca"* and NH/. What's more, the spreads in the pH distributions, indicated by the differences in the 10th and 90th percentiles (hori- zontal reference marks on the whiskers in figure 8) are much larger at Monmouth (IL78), Shabbona (ILl 8), and Argonne (ILl 9) than they are at any of the sites in the southern half of the state. The more frequent oc- currence of higher pHs at these sites causes the larger spread, which exceeds a pH unit (> 10-fold difference in H*). Higher pHs occur when higher Ca** or NH^' or both are present to neutralize the SO/ and NO, acid- ity. These conditions occur more often at northern than southern Illinois sites. It is the acidity of precipitation, along with the associ- ated sulfur and nitrogen pollutants, which raises con- cerns about the potential for damage to agroecosystems and to unmanaged systems, such as forests. Nearly all of the reported damage to these ecosystems is the result of a combination of environmental stresses, including acidic deposition (Shriner et al., 1990; Barnard et al., 1990). It is generally not acidic precipitation alone that is the cause of reported damage. Direct damage, though rare, has been reported, however. "Phytotoxic concen- trations of acidic precipitation are generally regarded to lie below pH 3.6" (Shriner et al., 1990). In fllinois, this occurs for 0.6 percent of the weekly wet deposition samples. There are no known reports of direct "acid rain" damage to Illinois crops or forests in the litera- ture, due to these rare, very acidic events. Figures 9 and 10 contain the notched box-and- whisker plots of SO/ and NO, concentrations at Illinois sites. Median SO/ concentrations range from 2.14 to 3.14 mg/L, with an overall median of 2.64 mg/L; and median NO, concentrations range from 1.37 to 1.84 mg/L, with an overall median of 1 .55 mg/L. Sulfate to nitrate mass concentration ratios of - 1 1/2 to 1 are typical of Illinois precipitation. In ion equivalent (or charge) concentration units, this ratio is ~ 2 to 1 , meaning precipitation would have about two units of sulfuric acid for every unit of nitric acid, if both SO/ and NO, were totally unneutralized. Using the shaded 170 ATMOSPHERIC DEPOSITION TRENDS IN ILLINOIS 9 r 8 7 Q. C D 1 — ' r e?__c=hj^^ T g= 19 18 78 11 99 47 35 53 SITE ID Figure 8. Same as figure 7, except for laboratory (CAL) pH measurements. 171 ATMOSPHERIC DEPOSITION TRENDS IN ILLINOIS 24 22 : 20 ^^ 18 - 1 O) 14 E 12 - 10 O 8 ^ 6 4 - L 1 . 1 J • I 1 1 — ' — ii 1 2 1 1 1 1 1 1 I 19 18 78 11 99 47 35 63 SITE ID Figure 9. Same as figure 7, except for sulfate (SO^) mass concentrations in mg/L. Horizontal ticks marking the 10th percentiles on the lower whiskers were too close to the 25th percentiles to show. From left (IL19) to right (IL63) the 10th percentile values are 1.60. 1.25. 1.04. 1.51. 1.03. 1.39, 1.11, and 1.39. respectively. 16 14 -12 0)10 ^ B S 6 I Jr ilX -I r ^ 19 18 78 1 1 99 SITE ID 47 35 63 Figure 10. Same as figure 7, except for nitrate (NOjj mass concentrations in mg/L. Horizontal ticks marking the 10th percentiles on the lower whiskers were too close to the 25th percentiles to show. From left (IL19) to right (IL63) the 10th percentile values are 0.97, 0.79, 0.64. 0.79, 0.58, 0.57, 0.60, and 0.59, respectively. Also the lowest five values at IL35 and the minimum at ILl 1. IL18. IL47. and IL63 were at the analytical limit of detection (0.93 mg/L). 172 ATMOSPHERIC DEPOSITION TRENDS IN ILLINOIS band in the figures as a reference, the similarity in behavior of these two pollutants becomes apparent. While the magnitudes of the respective SO^° and NOj deviations from the reference (i.e., the ILl 1 median with its 95 percent confidence interval) are not identi- cal, IL19 is above ILl 1 and has the overall highest concentrations for both ions. In general, SO^° and NOj concentrations for ILl 8, IL35, IL47, IL63, IL78, and IL99 are below ILl 1; and IL99 data are lowest. Choos- ing reference points other than the median with its confidence interval gives similar results when the two ions are compared; thus covariance is evident in the SO^° and NOj" concentration profiles. To quantify the covariance that appears in figures 9 and 10, correlations for SO/ and NO, concentrations were calculated. Valid samples from all eight Illinois sites were used in the calculations. As a basis for compari- son, correlations among the other three major ions and SO^= and NO^ were included in the analysis. Results are presented in table 2, which lists the correlation coefficients or R- values for the relationships between each ion and the other four ion concentrations in individual precipitation samples. Only linear relation- ships were tried, which means that the magnitude of the R-values indicates the degree to which one concen- tration is proportionate to the other concentration being tested. High positive R-values indicate that as one concentration goes up the other goes up in the same fractional (or proportionate) amount. A value of 1.0 indicates a perfect posiUve correlation. Negative R- values mean that as one ion goes up, the other goes down. It is apparent from the results in table 2 that many of the R-values are > 0.60 and are similar in value, but the S0^° and NO, correlation is best; it has the highest R-value (0.74). Squaring the R-values measures the fraction of ion concentration variance that is accounted for by covariance; and for S0^° and NO^ , R^ in percent is 55. In Illinois precipitation, over half of the variation in SO^° concentrations can be explained by the fact that they track NO^ concentrations, and vice versa. One implication of the correlative behavior of S0^° and NO, in precipitation is that ecosystem exposure to high SO/ is likely to be accompanied by high NO, . Recall from figure 4 and the discussion in the previous section that SO/ and NO, have the highest and third highest average concentrations, respectively, in Illinois precip- itation. Free acidity, H*, has the second highest average concentration. In table 2, the correlations of H* and SO/ (R^ = 38 percent) and H* and NO, (R= = 19 per- cent) are not as high as for several other pollutants, however. Notwithstanding the lower correlations of H' with SO^' or NO, , comparisons of the concentration distributions (i.e., the notched box-and- whisker plots) of these three pollutants in figures 8-10 show that where the notch falls above the shaded band in figure 8, it falls below the band in figures 9 and 10, except for the Argonne (IL19) site. In other words, generally higher pH values at a site and generally lower SO/ and NO, concentrations go together, and vice versa. Where SO^' is high, so too are H* and NO, ; and from the correlation results, when S0^° is high, NO, is more likely than any other ion to be high too. The excep- tional behavior at ILl 9 is another indication of urban Chicago influences on Argonne precipitation. Higher airborne dust levels with higher accompanying Ca** concentrations may be neutralizing the higher SO^° and NO,' in ILl 9 precipitation. Other implications of the correlative behavior of S0^° and NO, in precipitation are that 1 . Precipitation scavenges these two pollutants fi-om the air similarly. 2. The mixing ratio of these pollutants in air varies over a narrow range. 3. Sulfur and nitrogen oxides are emitted ft^om the same sources. 4. A combination of these factors is at work in the atmosphere. Figure 1 1 presents the NH^* concentration distribu- fions in precipitation at Illinois sites. Median concen- trations range from 0.26 to 0.45 mg/L, with an overall median of 0.35 mg/L. Unlike the SO/ distributions, in which all values are above the analyUcal detection limit, and NO, distributions, with only 0.3 percent detection limit values (see figure 10), the frequency of occurrence of detection limits in the NH/ concen- trafions is 3.6 percent. Detection limit values occur at every Illinois site, from a low of 1 .6 percent at Argonne (ILl 9) to a high of 6.0 percent at Carbondale (IL35); and so each of the lower whiskers in figure 1 1 terminates at 0.02 mg/L, the NH/ detection limit. That 28 percent of the concentrations are within a factor of 10 of this detection limit results in greater analytical uncertainty for NH/ (15-17 percent) than for the four other major ions (James, 1992). Sites north (IL19, IL18, and IL78) of Bondville have higher NH/ concentrations than sites to the south (IL99, IL47, IL35, and IL63), although only IL35 is significantly different. This geographical pattern is markedly different than for pH, SO/, or NO, , but is similar to the Ca" pattern in figure 1 2. Of note, too, is that the NH/ concentrations at the Argonne site (IL19) are not the highest, as clearly was the case for SO/ and NO, . 173 ATMOSPHERIC DEPOSITION TRENDS IN ILLINOIS Table 2. Linear Pearson Correlation Coefficients (R Values) and R-squared Values, for the Pairwise Correlations among the Five Major Inorganic Ion Concentrations in Illinois Precipitation (number of observations = 2711; all values significant at better than the .01 percent level except the H* and Ca"^ correlation, which is significant at the 5 percent level) 50/ NO J Ca** NH; H' R R'* R R'* R R'* R R'* R R'- S04' 1.0 1.0 .74 .55 .59 .35 .63 .40 .62 .38 N03 .74 .55 1.0 1.0 .66 .43 .69 .47 .44 .19 Ca** .59 .35 .66 .43 1.0 1.0 .55 .30 -.06 .00 NH/ .63 .40 .69 .47 .55 .30 1.0 1.0 .11 .01 H* .62 .38 .44 .19 -.06 .00 .11 .01 1.0 1.0 Note: ♦Bonferonni-adjusted probabilities (Wilkinson, 1990). 174 ATMOSPHERIC DEPOSITION TRENDS IN ILLINOIS 7 6 MAX= 78.2 E ' ~ ^ 3 X ^ 2 ; 1 . L ' — 3 r- 1 L J , - ; - . ■ 1 1 1 1 1 ^^^ 1 19 18 78 11 99 47 35 63 ( BITE ID Figure 11. Same as figure 7, except for ammonium (NHJ mass concentrations in mg/L. Horizontal ticks marking the 10th percentiles on the lower whiskers were too close to the 25th percentiles and the minimums to show. From left (IL19) to right (IL63) the 10th percentile values are 0.14, 0.16, 0.12, 0.10, 0.07, 0.07, 0.06, and 0.08, respectively. Also all of the minimum values and from 1.6 to 6.0 percent of the other low values in the distribution are the analytical limit of detection (0.02 mg/L). 6 - ^-^ 5 1 - CD 4 - E ^-^ 3 - D ■ a 2 - 1 ■ 1 ir~ 1 i— J 1 — 1 ( ' 1 1 1 ^1 1 - 1 — ' ' — \ — ' 1 — 1 ^ , ,^_^ . . ■, '", ■■! ■, , "" ' 1 ' 1 1 1 1 1 19 18 78 11 99 SITE ID 47 35 63 Figure 12. Same as figure 7, except for calcium (Ca) mass concentrations in mg/L. Horizontal ticks marking the 10th percentiles on the lower whiskers were too close to the 25th percentiles and the minimums to show. From left (IL19) to right (IL63) the 10th percentile values are 0.0997, 0.077. 0.060. 0.058. 0.034. 0.050. 0.050. and 0.053, respectively. Also the lowest three values at IL35 and the minimum at IL19 are the analytical limit of detection (0.009 mg/L). 175 ATMOSPHERIC DEPOSITION TRENDS IN ILLINOIS Ammonium is a nutrient and is one of two nitrogen compounds deposited by precipitation, the other being NO ". In mass concentrations units, NO, and NH/ rank 3 '34 third and fourth in importance in lUinois precipitation, with overall median concentrations of 1.55 and 0.35 mg/L, respectively. In these units, the NO3 median is over four times the NH/ median. To assess the impor- tance of these two pollutants as nutrients deposited on Illinois crops, forests, lakes, and streams, however, it is their nitrogen content that is relevant. As a fraction of the total mass, nitrogen is 22.6 percent of NO3' and 77.6 percent of NH/. Converting the overall median concentrations, above, to nitrogen (N) mass units yields 0.35 and 0.27 mg/L for NO," and NH/, respectively. Expressed this way, the median N from NO^ is just 30 percent more than the median N from NH^*. What's more, NH^* and NO^ have the second highest correla- tion coefficient of all the pollutants reported in table 2. R^ is 0.47, meaning 47 percent of the total variation in these two N compounds in precipitation is accounted for by their covariance. Exposure studies have not shown that crop or forest damage has occurred from the ambient N levels found in wet deposition in the United States (Shriner et al., 1990; Barnard et al., 1990), however, even for the most extreme events. On crops, the N from NO3 and NH/ is likely to enhance growth and productiv- ity. On certain unmanaged high-elevation forests, there is some evidence that the N addition from wet deposition over time may stimulate excess growth, which could predispose trees to winter damage (Shriner et al., 1990). Illinois forests are not exposed to the harsh conditions that sometimes occur at high elevations and are not likely to be affected negatively by N deposition, but this should be assessed. It is not known to what extent wet-deposited N accumulates in Illinois lakes and may contribute to water quality problems and eutrophication. One final observation from figure 1 1 is the lone flier reported at the Shabbona site (IL18). The NH/ in this sample was 78.2 mg/L, more than ten times the second highest value at this site or the maximum at any other site. This same sample appears as the lone flier in figure 7 and is a flier for potassium and orthophos- phate, as well. Although this sample passed all of the screening criteria discussed in the earlier section on screening procedures, it is a clear anomaly. No visible contaminants were reported, but the extreme NH^*, PO/", and K* strongly suggest contamination by ferti- lizer. It has a disproportionately large influence on correlation analyses and so was excluded from the results presented in table 2. The notched box-and-whisker plots for Ca** appear at each of the eight Illinois sites in figure 12. Median Ca** concentrations range from 0.159 to 0.296 mg/L, with an overall median of 0.238 mg/L. A geographic pattern of higher values in northern Illinois than in southern Illinois, described in the discussion on NH^*, is indi- cated in this figure. The highest concentrations occur at the Argonne site (IL19), where Ca" values are 8 to 26 percent above the second highest site values at every reference percentile (minimum, 10th, 25th, 50th, 75th, and 90th) in the distribution except the maximum. Despite the higher concentrations at ILI9, none of the notches appears either completely above or below the shaded band, which means that all of the median con- centrations can be interpreted as being within the 95 percent confidence interval of the Bondville (ILl 1) median. This is consistent with the large relative uncer- tainty or variance in Ca" data. Seventeen percent of all Ca** concentrations are within a factor of ten of 0.009 mg/L, the analytical detection limit; and precision estimates are typically 10 to 16 percent (James, 1992). There are no reports of real or potential ecological damage from Ca"^* in precipitation. It is important in Illinois wet deposition because it is at sufficienUy high concentrations to offset the free acidity effected by SO/ and NO3 . It is the only major ion that has a nega- tive correlation coefficient with H* in table 2, although almost no variance (R^ ~ 0) is explained by this rela- tionship. A study to explain the sharply lower pH (higher H*) in eastern U.S. precipitation in the 1970s, compared with the 1950s, reported that Ca" (and magnesium) decreases, not S0^° and NO3 increases, were the cause (Stensland and Semonin, 1982). High airborne dust levels from widespread droughts in the central United States were cited as the major source of the higher Ca^in the 1950s. Soil aerosols, road dust (Barnard et al., 1986), and construction and demolition activities are important sources of Ca** today. Calcium remains one of five major ions in Illinois precipitation. Overall, figures 9-12 exhibit some features that are common to precipitation chemistry data from all NADP/NTN sites (Knapp et al., 1988). Pollutant concentrations tend to be skewed by a few large outliers. This is evident in the asymmetry of the notched box- and-whisker plots. The upper whiskers (top 25 percent) are often several times longer than the lower whiskers (bottom 25 percent); and the distances from the tick marks al the 90th percentiles and the ends of the whiskers (the top 10 percent) are often several times longer than the distances between the 75th and 90th percentiles. This skewness is typical of many environmental variables, particularly chemical concentrations, which 176 ATMOSPHERIC DEPOSITION TRENDS IN ILLINOIS are bounded by zero but have no upper limit. A log transformation of the data removes a considerable amount of this asymmetry. Indeed, log Ca** concen- trations have a distribution that cannot be distinguished from a normal distribution, which is the classic bell- shaped curve. A statistical test of the hypothesis: log concentration distribution equals normal distribution, was used to make this observation (STATGRAPHICS, 1992; Kolmogrox-Smirrov "goodness-of-fit" test at the one percent confidence level). Applying the same test to log NOj , NH^*, or H' concentrations does not result in normal distributions, i.e., the probability is < one percent that log concentrations have a normal distribu- tion. For H*, this is tantamount to the observation that pH measurements do not have a normal distribution, since pH is proportional to log (H*). Log SO^= concentrations cannot be distinguished from a normal distribution at the one percent confidence level but can at the 10 percent level. Observing that pollutant concentrations in precipitation are skewed (figures 9-12) and knowing how to describe the concentration distributions with mathematical expressions helps effects researched to study and understand the eccosystem response to pollutant experience. What's important is that pollutant concen- trations in Illinois precipitation often range over two or three orders of magnitude, beginning near zero. This means that ecosystems are exposed to many low and moderate concentrations and to a few concentrations that may be 100 to 1000 times higher. In addition, there is a substantial amount of covariance among the ions, which means that these high concentrations tend to occur at the same time. Recall that the frequency of occurrence of pH < 3.6, at which direct damage to some plants has been reported (Shriner et al., 1990), is 0.6 percent in Illinois. For these same samples, S0^° is in the top 1 .3 percent, NO^' is in the top 9.6 percent, and NH^* is in the top 16 percent; Ca** values are low and high. This correlative behavior of precipitation concentrations is quantified in table 2: for SO^'and NOj , R2 is 55 percent; for NH/ and NO;, Ca** and NO, , and NH/ and SO/, R^ is 40 to 47 percent. Among the five major ions, the H* correlations are lowest; however, when H* is correlated with the other ions in a charge balance relationship, R^ improves to 80 percent. This is yet another way to show that Illinois precipitation is a dilute solution of sulfuric and nitric acids, partially neutralized by ammonium and calcium. Dry Deposition. The complex phenomena of pollutant mass transfer by nonprecipitation processes from the atmosphere to receptors at the earth's surface, i.e., dry deposition, are often explained and examined by way of analogy to an electrical circuit. Indeed, such a conceptual model forms the basis for coupling together the computational methods used to arrive at the NOAA/ATDD results for V^ (Hicks et al., 1991). The series resistance model shown in figure 13 (after Davidson, 1 988) considers the airborne concentration of a particular chemical to be analogous to an electrical potential or voltage. The receptor surface is then taken to be a sink, at zero potential, or at the ground state. Pollutant transfer from the atmosphere to the surface actually occurs when particles or gas molecules pass through various layers in the atmosphere and there is a physical or chemical reaction at the surface. Different processes control the rate of transfer in each layer. In the series resistance analogy, this transfer is an electri- cal current that flows through a series of resistors, which control the amount of current that passes. In their simplest form then, the three "resistors" in the series resistance model represent atmospheric pro- cesses. R^ or aerodynamic resistance represents the turbulent processes in the lower levels of the atmo- sphere that mix and deliver airborne materials to thenear surface atmosphere. R^ or boundary-layer resistance represents the effect of the receptor surface on small-scale air turbulence and the rate at which particles and gas molecules can be brought into close enough proximity to the receptor surface to actually react chemically or "stick" physically. R, or surface resistance represents the ability of the surface to retain the materials brought into reactive proximity. A fourth resistor (R or gravitational settling resistance) repre- sents the rate at which particles literally "fall" if they are large or massive enough that gravitational effects dominate the process. As in the analogous electrical circuit, the higher the resistance, the lower the current. The resistance with the highest value becomes the overall rate limiter for the entire process. Mathematical tools that apply to the analyses of electrical circuits apply exactly to this conceptual framework. Additional resistances in series or parallel to the simple three-resistor model can be used to differentiate and examine the effects of addi- tional processes. Large to moderate scale atmospheric processes, and thus daily weather patterns, affect pri- marily R^. The surface type and configuration affect the way a receptor is coupled to the atmosphere, and thus Rj^. Finally, the type of material at the surface, its biological state, composition, physical state, chemical reactivity, and especially wetne,ss, impact R . Overlaying the resistance analogy, and adding additional com- plexity to the deposition rate estimation, is the fact that different pollutants have different resistances. The 177 ATMOSPHERIC DEPOSITION TRENDS IN ILLINOIS Atmosphere Ra Rb Hg Re Ground Notes: R^ = aerodynamic resistance Rj = boundary-layer resistance R = surface resistance c R = gravitational settling resistance Figure 13. Schematic representation of dry deposition processes in the so-called series resistance analogy. 178 ATMOSPHERIC DEPOSITION TRENDS IN ILLINOIS aerodynamic size and solubility of aerosols, and the reactivity of gases with various types of surfaces greatly impact the R values. In a simple series resistance circuit, the overall resistance (R,„,^) is just the sum of the individual elements: R =R + R^ + R lolal a D c This is the basic form of the model for gases and fine aerosol. For these physical forms of pollutants in the atmosphere, gravity has little or no effect on the depo- sition rate, and R has a very large value relative to the other three terms. Where parallel resistances exist in an electrical circuit, R^^^^ is found by inverse summation, so that including all four resistances in the model shown in figure 13 produces the equation: For very large particles, such as aerosol with aerodynamic diameters of several \im, or raindrops whose size is measured in millimeters (mm), R^ becomes a relatively very small number. In this case, the (1/R ) term becomes very large, and the effect of gravity dominates the process. V^ is a conductance, or inverse resistance term, and is calculated simply as v, = i/R.„^ Therefore, many atmospheric and surface parameters are considered to produce a single V^ value, which is specific for the pollutant type and average surface type modeled. The two NOAA/ATDD sites (Bondville and Argonne) were originally selected to represent region- ally typical conditions. The Argonne site is at the southwestern fringe of the Chicago metropolitan area, and is characterized by mixed forest and suburban residential vegetation, with numerous relatively local pollution sources. In contrast, the Bondville site is farmland, rotated annually between soybean and com production, with very few nearby pollution sources. The V^ estimation model takes into account these general site characteristics, as well as day-to-day changes in vegetation status and land use reported by the site operators. In the NOAA/ATDD model, large particles, small particles, ozone, nitric acid, and sulfur dioxide are each treated as a separate case for which V^ values are computed weekly. Finally, this conductivity term is multiplied by the potential term, concentration, and the sampling interval, in units of time (here, one week) to arrive at the dry deposition amount: Deposition = V • concentration • time In the data reported here, this equation was used with appropriate conversion factors to express all dry depo- sition amounts as kilograms of material depositing per year to one hectare of area (kg ha ' yr'). To convert to pounds per year to one acre (lbs ac ' yr ')> multiply the deposition value shown by 1.12. The first step in examining the spatial variation in dry deposition, involves a comparison of the V^ results for the two NOAA/ATDD sites. Figure 14 shows the distri- bution of weekly mean V^ values observed at the two sites during the 1985-1992 period for which data are available. For each of the three pollutants shown (HNOj, SOj, and aerosol), the median V^ at Argonne is somewhat higher than at Bondville due to the site char- acteristics and long-term climatic differences in the two sites. Most important among these factors is the greater roughness scale at Argonne, due to land use and vege- tation type. These factors are expressed primarily in the R^ and R^^ components of the V^ computation. Larger differences are seen in figure 14 between the three pollutant species than between sites.This is due to the R, component, and the differences are caused largely by the varying affinities of the pollutants for surfaces. Aerosol particles may "stick" or "bounce off' surfaces, and R^ is influenced by the physical nature of the surface. SO^ gas is very reactive with surfaces when aqueous films are present to facilitate the chemical reactions that convert SO, to SO = at the surface, so the 2 4 R component for SO^ is strongly controlled by surface wetness. HNO^ is also a gas, but it has a very small R^ value for all surface types, whether wet or dry, and thus HNOj has the largest V^ values overall. Figure 15 is similar to figure 14, but shows the corre- sponding Argonne and Bondville weekly mean air concentration distributions for HNOj, SO^, and SO^' (S0^° is strongly associated with small aerosol, i.e., diameter < 1 n.m). The differences here are attributable to the suburban versus rural nature of the two sites. The SOj concentration at Argonne is somewhat higher, simply due to the higher density of SOj-emitting sources in the Chicago- Joliet region, as compared to the agricultural region around Bondville. SO^' in fine aerosol, by contrast, is largely a secondary pollutant, formed by the reaction of gas phase SOj over time. Thus, SO^° concentrations tend to vary regionally, rather than locally; concentration distribution and the local sources may have somewhat less of a direct impact. HNOj concentrations appear to be quite similar at both sites; the high rate of dry deposition, the reactivity of the gas with aerosol constituents, and the volatile nature of some of the reaction products, preclude generalizations about HNO, distributions. 179 ATMOSPHERIC DEPOSITION TRENDS IN ILLINOIS •*■ ■ -•* * 1 1 Argonne HNO, Bondvitle HNO, Argonne Aerosol Bondville Aerosol Argonne SO, Bondville SO, 1 _| ^ * 1 H 1 1 1 1 1 1 ^ 1 h h 1— 1 1 1 0.0 0.5 1.0 1.5 v., 2.0 cm s 2.5 -1 3.0 3.5 4.0 Figure 14. Comparison of the distributions of weekly mean dry deposition velocities (VJ determined at two Illinois sites (Argonne, IL 19, and Bondville, ILll) over the period 1985-1992. 180 ATMOSPHERIC DEPOSITION TRENDS IN ILLINOIS ^-Q - I'M x- •N Argonne HNO, Bondville HNO, Argonne SO^ Bondville SO« c ** o o ""* I: * *t* 00 O O 1 1 4c «(c:Mc o o (n> ■ Argonne SO, o o Bondville SO, 1 *•* * * =»*D 1 1 1 1 1 6 12 18 24 Concentration, |j.g m^ 30 Figure 15. Comparison of the distributions of weekly mean airborne concentrations of three pollutants /jg m'^) at two Illinois sites (Argonne, IL19, and Bondville, ILl 1) over the period 1985-1992. 181 ATMOSPHERIC DEPOSITION TRENDS IN ILLINOIS Finally, the V^ and concentration data are combined in figure 16. This figure shows the computed dry deposi- tion amounts for the two NOAA/ATDD sites. Dry deposition loading estimates for the period 1984- 1990 were computed using annual median pollutant concentrations from lEPA monitoring data (see Air Quality Trends in Illinois chapter). Separate medians were derived for the Chicago and the "Remainder of State" areas. These concentration values were then combined with V^ statistics based on the model results a from the NOAA/ATDD network data set, to produce the loading estimates shown in figures 17-28. Each figure presents the annual loading values in kg ha' yr' for a particular pollutant, with plot (a) showing the Chicago-area data and plot (b) showing the "Remain- der of State" data. Note that while data were not available for all years of the overall period, the time scale of all plots is constant. For each year, the distribution of NOAA/ATDD weekly mean V_j data was analyzed. The product of the median pollutant concentration (from lEPA measurements) and the annual mean V, value is shown as a horizontal line. a The vertical line represents the loadings at ± one standard deviation in V^. Finally, the triangles pointing up and down indicate the result if the maximum and minimum V^, respectively, are used in the loading calculation. The Argonne NOAA/ATDD site V^ values were used to compute the Chicago- area loadings; Bondville V^ values were used for the "Remainder of State" results. This introduces some additional imprecision in the results, since there exists much variation in land use, topography, and vegetation type in the "Remainder of State" area, while the Bondville V^ values are com- puted for farmland. While modeling tools (Matt and Meyers, 1993) and land-use and vegetation type data (see chapter with GIS data) exist for much finer resolu- tion estimations of V^, development of the calculations was beyond the scope of the current project. From this series of plots (figures 17-28), it is obvious that dry deposition in Illinois tends to be somewhat higher in the Chicago area. This is due to both higher airborne concentrations for most pollutants and higher deposition velocities. For arsenic, manganese, nitrate, ozone, sulfur dioxide, and sulfate (figures 17, 21-24, and 26-27), the differences are on the order of 10 to 30 percent. For cadmium, chromium, iron, nickel, lead, and TSP (figures 18-20, 22, 25, and 28), dry deposition in the Chicago area exceeds the rest of the state by 200 to 400 percent. This is primarily caused by the differ- ences in air quality (see Air Quality Trends in Illinois chapter). Temporal trends in dry deposition generally follow air quality trends, although additional variability is introduced into the time-series data by interannual variation in deposition velocities. Spatial variation in dryfall was examined using the NADP/NTN "dry bucket" data from five Illinois sites for which a long-term record was available (figure 1 and table 1). Figures 29-31 show the distributions of dryfall loading amounts observed in the 8-week integrated samples at the five sites for calcium, ammonium, and sulfate. Dryfall data for other ions (the dryfall samples were analyzed for all of the same ions as the wet deposition samples) is not considered to be a reliable indicator of actual dry deposition rate. This is because the polyethylene bucket, used in the NADP/ NTN wet/dry collector, cannot account for the aerody- namic and chemical reactivity characteristics of natural environmental surfaces. For calcium and the large- particle fraction of ammonium and sulfate, however, there appear to be less significant interfering chemical reactions, and there is a larger R component due to the larger particle sizes associated with these chemicals. Thus, gravitational processes are relatively more important for particles containing calcium and the large-particle fraction of ammonium and sulfate, and the dryfall collector is believed to provide useful data for these species. In figures 29-31, Argonne (IL19) is the leftmost box plot distribution. The other five sites are plotted in roughly north-south order from left to right. Figure 29 shows a slight tendency for calcium to be higher in the southern part of the state. Figure 30 shows that the highest and most variable values for ammonium dryfall occur at Argonne and in northern Illinois. Argonne shows a slightly higher dryfall loading (figure 3 1 ) for sulfate than the rest of the state, where a slight trend to higher values in southern Dlinois is also noticeable. Temporal Trends Wet Deposition. Trends in the chemical composition of Illinois precipitation were assessed by first deter- mining the annual concentration distribution of each ion at each site. Next, the year-to-year changes in concentrations were evaluated by applying a Spear- man rank correlation test to percentile points in the distributions. Three points were chosen, the 25th, 50th, and 75th percentile values. A summary of the test results is shown in table 3. None of the trend estimates were identically zero. A zero trend means that there is no overall direction in the year-to-year concentrations, either up or down. As a result, the changes were labeled as either "up" or "down" in this table. 182 ATMOSPHERIC DEPOSITION TRENDS IN ILLINOIS -t»:m^ * 4»: O O -I * * * o Argonne HNO, ->Uck^ ^ik ik Bondville HNO, 12 18 24 -1 -1 Deposition, kg ha yr Argonne SO^ Bondville SO^ Argonne SO, Bondville SO, I 30 Figure 16. Comparison of the distributions of weekly estimates of annualized dry deposition (kg ha' yr') at two Illinois sites (Argonne, IL19, and Bondville, ILll) over the period 1985-1992. 183 ATMOSPHERIC DEPOSITION TRENDS IN ILLINOIS 0.005 0.004 0.003 :o 0.002 < 0.001 0.000 1 1 1 1 — a. Chicago Loadings I T 1 A A 1 ; 1 1 — A T A A 1 1 1 1 b. Rest of IL Loadings 1 1 1 A ■ 111. r... A T A A 1983 1984 1985 1986 1987 1988 1989 1990 1991 1983 1984 1985 1986 1987 1988 1989 1990 1991 YEAR YEAR Figure 17. Dry deposition loadings of arsenic (kg ha' yr'jfor the Chicago area (a) and the remainder of the State of Illinois (b), from ILEPA annual median concentration and NOAA/ATDD Vj statistics. 1 1 1 1 7 I ■ 1 a. Chicago Loadings V 0.004 >« "a A 'a t 0003 . A . je 1 0.002 a - - - - 3 - " ~ ~ O 0.001 - - 0.000 1 1 1 1 1 i 1 1 1983 1984 1985 1986 1987 1988 1989 1990 1991 1983 1984 1985 1986 1987 1988 1989 1990 1991 YEAR YEAR Figure 18. Dry deposition loadings of cadmium (kg ha' yr') for the Chicago area (a) and the remainder of the State of Illinois (b), from ILEPA annual median concentration and NOAA/ATDD Vj statistics. 184 ATMOSPHERIC DEPOSITION TRENDS IN ILLINOIS 0.010 0.008 0.006 - a c ■■5 s o 0.004 O 0.002 - 0.000 a. Chicago Loadings 1 1 1 1 _ . . ▼ - - - + 1 T 1 » T 1 1 1 1 f 1 1 1 1 1 1 r b. Rest of IL Loadings H ^ T T T + -I i- 1983 1984 1985 1986 1987 1988 1989 1990 1991 1983 1984 1985 1986 1987 1988 1989 1990 1991 YEAR YEAR Figure 19. Dry deposition loadings of chromium (kg ha' yr') for the Chicago area (a) and the remainder of the State of Illinois (b), from ILEPA annual median concentration and NOAA/ATDD Vj statistics. 2.0 X 1.5 'a 1.0 - ■ o 0.5 0.0 1 r 1 1 1 1 I a. Chicago Loadings 4 f A A T (III r r 1 r b. Rest of IL 1 1 1 Loadings - A A T A A T T 1 A A T 1983 1984 1985 1986 1987 1968 1989 1990 1991 1983 1984 19851986 1987 1968 1989 1990 1991 YEAR YEAR Figure 20. Dry deposition loadings of iron (kg ha' yr') for the Chicago area (a) and the remainder of the State of Illinois (b), from ILEPA annual median concentration and NOAA/ATDD V^ statistics. 185 ATMOSPHERIC DEPOSITION TRENDS IN ILLINOIS 0.20 >« 0.15 0.10 0.05 0.00 1 1 1 1 — a. Chicago Loadings 1 T 1 A * : t " 1 1 1 1 — A T I A A t + T T 1983 1984 1985 1986 1987 1988 1989 1990 1991 1983 1984 1985 1986 1987 1988 1989 1990 1991 YEAR YEAR Figure 21. Dry deposition loadings of manganese (kg ha' yf') for the Chicago area (a) and the remainder of the State of Illinois (b), from ILEPA annual median concentration and NOAA/ATDD V^ statistics. 0.020 £ 0.015 0.010 n o ::j 0.005 1 1 1 1 1 1 r a. Chicago Loadings i 0.000 1983 t f - - A i I + I _i i_ 1 1 1 1 b. Rest of IL Loadings I - A A , 4- T A T A t A t 1984 1985 1986 1987 1988 1989 1990 1991 1983 1984 1985 1986 1987 1988 1989 1990 1991 YEAR YEAR Figure 22. Dry deposition loadings of nickel (kg ha' yf'} for the Chicago area (a) and the remainder of the State of Illinois (b), from ILEPA annual median concentration and NOAA/ATDD V^ statistics. 186 ATMOSPHERIC DEPOSITION TRENDS IN ILLINOIS 20 >« 15 a £ a je n 10 c ■o 19 o -1 ■• 5 O z a. Chicago Loadings ! + + + + + + ♦ T T » » -L. _I_ _!_ 1983 1984 1985 1986 1987 1988 1989 1990 1991 1983 1984 1985 1986 1987 1988 1989 1990 1991 YEAR YEAR Figure 23. Dry deposition loadings of nitrate (kg ha' yr'jfor the Chicago area (a) and the remainder of the State of Illinois (b), from ILEPA annual median concentration and NOAA/ATDD V^ statistics. 1.0 > 0.8 - •a • 0.4 o -I e 2 0.2 a. Chicago Loadings . . . : I I I I b. Rest of IL Loadings T r + ± 0.0 1983 1984 1985 1986 1987 1988 1989 1990 1991 1983 1984 1985 1986 1987 1988 1989 1990 1991 YEAR YEAR Figure 24. Dry deposition loadings of ozone (kg ha' yr') for the Chicago area (a) and the remainder of the State of Illinois (b), from ILEPA annual median concentration and NOAA/ATDD V^ statistics. 187 ATMOSPHERIC DEPOSITION TRENDS IN ILLINOIS 0.20 0.00 1983 1984 1985 1986 1987 1988 1989 1990 1991 1983 1984 1985 1986 1987 1988 1989 1990 1991 YEAR YEAR Figure 25. Dry deposition loadings of lead (kg ha' yr') for the Chicago area (a) and the remainder of the State of Illinois (b), from ILEPA annual median concentration and NOAA/ATDD V^ statistics. 30 5 20 O 10 O (0 a. Chicago Loadings JL. 1 1 r b. Rest of IL Loadings » _L 1983 1984 1985 1986 1987 1988 1989 1990 1991 1983 1984 1985 1986 1987 1988 1989 1990 1991 YEAR YEAR Figure 26. Dry deposition loadings of sulfur dioxide (kg ha' yr') for the Chicago area (a) and the remainder of the State of Illinois (b), from ILEPA annual median concentration and NOAA/ATDD Vj statistics. 188 ATMOSPHERIC DEPOSITION TRENDS IN ILLINOIS c n o O M 1 1 1 r b. Rest of IL Loadings H 1983 1984 1985 1986 1987 1988 1989 1990 1991 YEAR 1983 1984 1985 1986 1987 1988 1989 1990 1991 YEAR Figure 27. Dry deposition loadings of sulfate (kg ha' yr') for the Chicago area (a) and the remainder of the State of Illinois (b), from ILEPA annual median concentration and NOAA/ATDD Vj statistics. 100 •D a o _i a. M 1 1 1 1 1 1 1 b. Rest of IL Loadings _ A _ A A A A 1 A - T 1 1 1 r 1 r 1 r ' r 1983 1984 1985 1986 1987 1988 1989 1990 1991 1983 1984 1985 1986 1987 1988 1989 1990 1991 YEAR YEAR Figure 28. Dry deposition loadings ofTSP or mass of aerosol particles (kg ha' yr') for the Chicago area (a) and the remainder of the State of Illinois (b), from ILEPA annual median concentration and NOAA/ATDD Vj statistics. 189 ATMOSPHERIC DEPOSITION TRENDS IN ILLINOIS 15 2 10 it (0 >l a E 3 O O 5 - 1 * * T 1 c 1 1 * T ? ( > IL19 IL18 IL11 IL47 IL35 IL63 Site ID Figure 29. Box plots of the dryfall loadings for calcium (kg ha' yr') measured at six NADP/NTN sites in Illinois (see table 1 for precise sampling intervals included, which vary slightly for each site). 30 n 20 - E .2 10 c o E E < 1 1 II 1 - * * * 1 -■ 1 1 1 1 o o o o o o * * 1 o T T O s riq P^ Q IL19 IL18 IL11 IL47 IL35 IL63 Site ID Figure 30. Box plots of the dryfall loadings for large-particle ammonium (kg ha' yr') measured at six NADP/NTN sites in Illinois (see table I for precise sampling intervals included, which vary slightly for each site). 190 ATMOSPHERIC DEPOSITION TRENDS IN ILLINOIS IL19 IL18 IL11 IL47 IL35 IL63 Site ID Figure 31. Box plots of the dryfall loadings for large-particle sulfate (kg ha' yr') measured at six NADP/NTN sites in Illinois (see table 1 for precise sampling intervals included, which vary slightly for each site). Table 3. Changes in Concentrations of Major Inorganic Ions in Illinois Precipitation Number with significant Ions Ca* NH4* NO,- SO/ pH Number of sites chan ge* Percentile Up Down Up Down 25 1 6 3 50 7 2 75 1 6 2 25 3 4 1 50 3 4 1 75 3 4 25 2 5 50 2 5 1 75 1 6 25 7 3 50 7 75 1 6 1 25 7 50 6 1 75 5 2 Note: ♦Using a Spearman rank correlation test, reject H„ (5 percent level): no change in concentration. 191 ATMOSPHERIC DEPOSITION TRENDS IN ILLINOIS For Ca", results show that the concentrations de- creased at nearly all sites and percentiles. Of the 21 tests (3 percentiles at 7 locations), only 7 were statisti- cally significant at the 5 percent level for NO3 and NH^*: the evidence is weak for a net change in either direction, however. These two pollutants were rela- tively unchanged in precipitation during the last decade. For SO^', the weight of evidence once again shows a downward trend in concentration, although only 4 of 21 tests were significant (at the 5 percent level). And finally, for pH the test results indicate an increase over time. Although none of these tests was significant, the conclusion that pH has risen is consistent, chemically, with the drop in S0^°. Stoichiometrically, the decrease in sulfate was larger than the decrease in calcium, accounting for a net decrease in acidity or a rise in pH. Seasonal variation sin V^, concentration, and deposition at Bondville are shown in figures 32-34. These figures show a LOWESS-fit curve (Cleveland, 1979) through all weekly mean data from the NOAA/ATDD site collected in the period 1985-1992. The results illusti-ate the impact of the cyclic variation in the environment that affects the dry deposition process. In figure 32, the enhancement of the V^ of ozone and SO, in the summer months is obvious, and is largely due to a reduction in R (see figure 9) as biologically active surfaces, i.e., vegetation, and liquid water films proliferate during the growing season. R^ increases, and V^ is thus reduced for these surface-reactive pollutants during the winter season. Fine-particle V^ also shows a tendency for higher warm-season values, but there is a much smaller increase. V^ values for fine particles and HNO3 respond to 1) a decrease in R^, which occurs with the increase in reactive area and roughness of the surface as the vegetation canopy expands, and 2) a decrease in R , which occurs due to and produces increased atmospheric turbulence and instability produced by summer convection. Figure 33 shows the concentration data for fine particulate NOj- and SO^=, and gaseous SOj and HNO3, measured at Bondville, on a corre- sponding annual cycle. A stiong seasonal cycle appears only for SO^". Multiplying the curves of figures 32 and 33 together produces the deposition loading curves of figure 34. When both concentration and V^ have seasonal cycles that are in phase, or peak simulta- neously, then the deposition curve has similar but intensified cycle. This is the case for S0^°, where the fine-particle V^ and the SO/ concentration tend to increase slightiy in the warm season; the SO/ deposi- tion curve then peaks relatively steeply at the same time period. For SO^, only the V^ term has a definite cyclic seasonal trend, but it is nonetheless reflected in the deposition cycle because of its magnitude. Finally, in the case of HNO„ the V^ and concentration curves 3 a are not distinct, but appear to be out of phase, with V^ higher in the summer, and concentration higher in the winter. The resulting deposition curve reveals much variation, but no distinct seasonality. It is important to note from figures 32-34 that simple monitoring of airborne concentration does not necessarily reveal a true picture of the delivery of pollutants to receptors at the surface. The time series of annual distributions of dry deposi- tion loading for several pollutant species, calculated for the Argonne and Bondville NOAA/ATDD sites, is plotted in figures 35 and 36. The box plot for each year indicated shows the distribution of weekly loading estimates, expressed as an annual total in kg ha' yr'. There are no apparent or statistically significant long- term trends for SO,, SO/, HNO3, or NO3 loadings at either site during the 1984-1992 period. However, significant interannual variation exists for dry dejxjsi- tion of each pollutant. These variations tend to follow air quality variations, but not exacUy, due to the independent variations in V^. While slight trends toward decreases in wet deposition have been noted above, and may be attributed to lower emissions of SO^ and SO^° over the 1980s, such a trend is not apparent in the dry deposition data. Figures 12-23 represent additional time-series plots of dry deposition loadings, based on lEPA air quality data. Annual median concentrations for the Chicago area and the "Remain- der of State" area were used in combination with the NOAA/ATDD V^ results to produce the annual deposition estimates. Trends over time in the lEPA air quality data are thus reflected in these figures and are described in detail elsewhere in this report. Total Deposition The wet and dry deposition data compiled throughout this section on atmospheric deposition were combined, where possible, to arrive at estimates of "total atmo- spheric deposition," (figures 37-39). The resultant total deposition estimates should at best be considered very tentative. The uncertainties in each of the values com- bined are relatively large, on the order of tens of per- cent. These uncertainties are compounded when summed into the total deposition estimate. However, these results are a valid statewide estimate, based on real monitoring data, of the magnitude of inputs of several chemicals to the earth's surface. The following data were used to plot the results of total atmospheric deposition for calcium (NADP/NTN wet Ca" + NADP/NTN dryfall Ca**), total nitrogen (NADP/ NTN dryfall NH/ + NOAA/ATDD HNO, + lEPA 192 ATMOSPHERIC DEPOSITION TRENDS IN ILLINOIS Bondville, Illinois: Dry Deposition Velocity 1.0 T 0.8 - « E 0.6 [■ u > 0.2 0.0 T r T r T r 11 12 « 1.0 1 r — 1 r — 1 1 — 1 — r- o 0.8 . - articles, o o ^ 0) - - a. - 1 1 .1 1 1 1 — 1 — — . __ • 0.2 . n rt 1 • 10 11 12 1.0 ^„ 0.8 - S 0.6 - O" 0.4 > 0.2 - 0.0 T r Month Figure 32. Seasonal variations of weekly mean dry deposition velocity, V^ (cm s') for several airborne pollutants calculated from observations at Bondville. Illinois, for the period 1985-1992. 193 ATMOSPHERIC DEPOSITION TRENDS IN ILLINOIS Bondville, Illinois: Concentrations 09 o z X 20 15 10 5 1 1 r -| 1 1 1 1 1 r J I I I I 1 I L 8 9 10 11 12 o (0 10 11 12 Figure 33. Seasonal variations of weekly mean airborne concentration (fig m^)for several airborne pollutants calculated from observations at Bondville, Illinois, for the period 1985-1992. 194 ATMOSPHERIC DEPOSITION TRENDS IN ILLINOIS Bondville, Illinois: Dry Deposition 0.25 0.20 n 0) 0.15 j< >< 0.10 3 U. 0.05 M o z 0.00 T r T r 1 1 1 r 9 10 11 12 10 -[ r T r T r Month Figure 34. Seasonal variations in annualized weekly mean dry deposition loading (kg ha' yf') for several airborne pollutants at Bondville, Illinois, for the period 1985-1992. 195 ATMOSPHERIC DEPOSITION TRENDS IN ILLINOIS Argonne, Illinois: Dry Loadings £ it o Z >• £ o z X 1984. 1985. 1986. 1987. 1988. 1989. 1990. 1991. 1992. 1984. 1985. 1986. 1987. 1988. 1989. 1990. 1991. 1992. 1984. 1985. 1986. 1987. 1988. 1989. 1990. 1991. 1992. 1984. 1985. 1986. 1987. 1988. 1989. 1990. 1991. 1992. Date Figure 35. Annual distributions of dry deposition loading (kg ha' yr'} for several pollutant species, calculated for the Argonne, Illinois NOAA/ATDD site. 196 ATMOSPHERIC DEPOSITION TRENDS IN ILLINOIS Bondville, Illinois: Dry Loadings a O z 2.0 1.5 1.0 0.5 0.0 1 o 1 o 1 1 1 1 1 o 1 o ? 9 i fi i ( 1=^ ^ 4, 4=. ^ o « O z X eg o (0 50 40 30 20 10 h 1985. 1986. 1987. 1988. 1989. 1990. 1991. 1992. 1985. 1986. 1987. 1988. 1989. 1990. 1991. 1992. 1985. 1986. 1987. 1988. 1989. 1990. 1991. 1992. 1 1 1 ~1 .11 1 r ^ 1 P 1 1 1 — 1 — 1 — 1 — 1985. 1986. 1987. 1988. 1989. 1990. 1991. 1992. Date Figure 36. Annual distributions of dry deposition loading (kg ha' yr') for several pollutant species, calculated for the Bondville, Illinois NOAA/ATDD site. 197 ATMOSPHERIC DEPOSITION TRENDS IN ILLINOIS Chicago Area D PraclplUtlofl ■ Drylall Total Atmospheric Deposition - Calcium Figure 37. Annual estimates of total atmospheric deposition (kg ha' yr'jfor calcium for the Chicago area and the remainder of the State of Illinois. 198 ATMOSPHERIC DEPOSITION TRENDS IN ILLINOIS Chicago Area □ Pr*clpltatlon-NH4 □ Prsclpltatlon-N03 a Gat*out-HN03 m Small Pattlcl«-N03 ■ Dry«all-NH4 D Praclpltat! >n-NH4 □ Praclpltatl|in-N03 D Gasaout- B Small Pa^lcla-N03 ■ Dryfall-MH4 Total Atmospheric Deposition - Nitrogen Figure 38. Annual estimates of total atmospheric deposition (kg ha' yr'} for nitrogen for the Chicago area and the remainder of the State of Illinois. 199 ATMOSPHERIC DEPOSITION TRENDS IN ILLINOIS Chicago Area a Prtclpltitlon O G«t*ou« E3 Smill Particle ■ Dryfall Total Atmospheric Deposition - Sulfur Figure 39. Annual estimates of total atmospheric deposition (kg ha' yr') for sulfur for the Chicago area and the remainder of the State of Illinois. 200 ATMOSPHERIC DEPOSITION TRENDS IN ILLINOIS NO3- + NADP/NTN wet NO3 + NADP/NTN wet NH/), and total sulfur (NADP/NTN dryfall SO/ + lEPA SO/ + lEPA SO^ + NADP wet SO/) in figures 37-39, respectively. SUMMARY AND CONCLUSIONS Deposition Trends and Spatial Variation Wet deposition in Illinois has been monitored for ten years or more at eight NADP/NTN sites. The NADP/ NTN reports the concentrations of ten separate chemi- cal pollutants in precipitation, of which just five ac- count for about 90 percent of the chemical composition that causes Illinois precipitation to be acidic. The pollutants in order of importance are: sulfate (SO/) > hydrogen ion (H*) > nitrate (NOj) > ammonium (NH^*) > calcium (Ca**). Illinois precipitation is most simply described as a dilute solution of mineral sulfuric and nitric acids, partly neutralized by ammonium and calcium. Based on statistical tests of time- series data alone, there is no unambiguous trend that applies to all of the important pollutants causing acid rain in Illinois. Based on a "weight of the evidence" analysis, however, sev- eral points can be made about Illinois precipitation chemistry changes during the 1980s: 1 . Sulfate decreased 2 to 4 percent per year in the southern third of the state, with smaller decreases elsewhere. 2. Calcium decreased by 3 to 7 percent per year, ex- cept at Argonne (suburban Chicago), where it re- mained steady. 3. Nitrogen species, ammonium and nitrate, remained unchanged. 4. pH increased slightly, but the increase is too small and too variable to be quantified. 5. Sulfur dioxide and NO emissions decreased slightly. Dry deposition in Illinois tends to be somewhat higher in the Chicago area, due to both higher airborne con- centrations of most pollutants and higher deposition velocities. For sulfate, nitrate, sulfur dioxide, ozone, arsenic, and manganese, the differences are on the order of 10 to 30 percent. For cadmium, chromium, iron, nickel, lead, and TSP, dry deposition in the Chicago area exceeds the remainder of the state by 200 to 4(X) percent; this is caused primarily by the differ- ences in air quality (see Air Quality Trends in Illinois chapter). Temporal trends in dry deposition generally follow air quality trends, although additional variability is introduced into the time-series data by interannual variation in deposition velocities. More important for ecological impacts is the seasonal nature of dry deposi- tion loadings, with higher deposition velocities for many pollutants occurring during the warm season, when biological impacts may also be the greatest. The total deposition of sulfur in the Chicago area is about 15 percent higher than in the rest of the state. For sulfur (sulfate plus sulfur dioxide), the ratio of wet to dry deposition is about 1 part wet to 1 .5 parts dry. The deposition of nitrogen in the Chicago area is about 30 percent higher than in the rest of the state. For nitrogen (nitrate plus ammonium plus nitric acid vapor), the ratio of wet to dry deposition is about one part wet to three parts dry. Deposition to Specific Receptor Systems The spatial and temporal variation information is most useful in describing the coupling of the atmosphere to receptors that are also distributed in space and whose sensitivity varies temporally with the depositing pollutants. Acid deposition to forests for example, is most likely to have an effect during the growing season, and is much less likely to be harmful in the dormant season. Toxic deposition to forests, however, may act through a cumulative effect, in which the temporal variation is less important to understanding the impact on the receptor system. Acid deposition to Lake Michigan presents a special difficulty in this analysis, since neither wet nor dry deposition is measured over the lake. The refinement of estimates based on shoreline measurements is an ongo- ing research topic, however. Other Aspects of Atmospheric Deposition Agricultural systems have been shown to be relatively insensitive to current levels of wet acid deposition, but the impact of toxic deposition and dry deposition of many pollutants is unknown. Ozone has been shown to have negative impacts on yield and quality of cash crops in several areas of the United States. The role of wet and dry toxics deposition as a contributor to nonpoint source pollution in surface and ground-water supplies for human consumption is also unknown at this time. The impact of atmospheric deposition (acid rain, toxic pollutants, and biological nutrients) to lakes and streams in Illinois (i.e., non-Lake Michigan waters) has not been documented, however, consideration of the magnitude of deposition for many chemicals 201 ATMOSPHERIC DEPOSITION TRENDS IN ILLINOIS would indicate that significant impacts are possible. Finally, the impacts of SO^=, SOj, acids, and NOj' deposition on exterior building materials, paints, etc., both in precipitation and dry deposition, have been demonstrated in recent federally sponsored research in many areas of the United States. Materials impacts in Dlinois are as yet unquantified, but are potentially large. Enhancement of Atmospheric Deposition Knowledge Further analyses of the data presented here and addi- tional existing data, which were not accessible in the context of this project, could refine the temporal and spatial resolution of a combined atmospheric deposi- tion database. Recommendations for further work include acquisition of additional extant air quality and precipitation chemistry data, and the development of the NOAA/ATDD model to a high-resolution model specifically for Illinois. ACKNOWLEDGMENTS This work was supported by the Illinois Critical Trends Assessment Project, under the Department of Energy and Natural Resources contract (SENR CTA-2/CRIT TREND) with the Illinois State Water Survey and by the State of Illinois. Data from the National Atmo- spheric Deposition Program/National Trends Network, which supports the ISWS's Central Analytical Labor- atory through a cooperative agreement with Colorado State University's Natural Resource Ecology Labora- tory, were extensively used. The assistance of Rayford P. Hosker, Jr., and Lynn Satterfield in obtaining and formatting the NOAA/ATDD dry deposition data was much ^preciated. 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