key: cord-1001784-1mfelhic
authors: Redmann, R. K.; Beddingfield, B. J.; Spencer, S.; Chirichella, N. R.; Henley, J.; Hager, W.; ROY, C. J.
title: A Micronized Electrostatic Precipitator Respirator Effectively Removes Ambient SARS-CoV-2 Bioaerosols
date: 2022-01-28
journal: nan
DOI: 10.1101/2022.01.27.22269961
sha: 1d2539d383d2e8193e784e29ab98bc8eda925ea7
doc_id: 1001784
cord_uid: 1mfelhic

Rationale: Inhalation of ambient SARS-CoV-2-containing bioaerosols leads to infection and pandemic airborne transmission in susceptible populations. Filter-based respirators effectively reduce exposure but complicate normal respiration through breathing zone pressure differential and are therefore impractical for long-term use. Objectives: We tested the comparative effectiveness of a prototyped micronized electrostatic precipitator (mEP) to a filter-based respirator (N95) in the removal of viral bioaerosols from a simulated inspired air stream. Methods: Each respirator was tested within a 16-liter environmental chamber housed within a Class III biological safety cabinet within biosafety level 3 containment. SARS-CoV-2 containing bioaerosols were generated into the chamber, drawn by vacuum through each respirator, and physical particle removal and viral genomic RNA were measured distal to the breathing zone of each device. Measurement and Main Results: The mEP respirator removed particles (96.5+/-0.4%) approximating efficiencies of the N95 (96.9+/-0.6%). The mEP respirator similarly decreased SARS-CoV-2 viral RNA (99.792%) when compared to N95 removal (99.942%) as a function of particle removal from the airstream distal to the breathing zone of each respirator. Conclusions: The mEP respirator approximated performance of a filter-based N95 respirator for particle removal and viral RNA as a constituent of the SARS-CoV-2 bioaerosols generated for this evaluation. In practice, the mEP respirator would provide equivalent protection from ambient infectious bioaerosols as the N95 respirator without undue pressure drop to the wearer, thereby facilitating long-term use in an unobstructed breathing configuration.

SARS-CoV-2 is a pathogenic beta-coronavirus that is the source of a current worldwide pandemic [1] . The virus has thus far proved to be highly transmissible and passes easily via respiratory droplet between the shedding infectious to naïve host [2] . The combination of inability to readily kill immunocompetent hosts, but rather use the respiratory system as an efficient vectoring pathway to infect others has made the resultant disease (COVID-19) one of the most prolific in human history, infecting hundreds of millions, and killing >5 million worldwide [3] . There has been a sustained surge in the use of respiratory protection throughout all sectors of society to effectively reduce ambient exposure and avoid infection [4] [5] [6] . The majority of the public currently use facial coverings consisting of cloth or 'surgical' masks, which provide protection only to others proximal to the wearer of the cloth mask [7] [8] [9] . The mechanism of particle collection for cloth masking is through microburst high velocity exhalation of the wearer and subsequent impaction upon inside surface of the mask [10] .

Although essentially no protection from ambient bioaerosols is provided when donning cloth/surgical masks, current public health mandates during the pandemic require the use of cloth/surgical masking by the public to further reduce community disease burden by retarding respiratory transmission at the source generator (the infected wearer). Some among the public and most healthcare professionals have chosen to don filter-based respirators which, unlike cloth masks, provide respiratory protection from ambient bioaerosols through impaction and interception collection on a thermospun/cellulose filter substrate [11] . The most popular of filter-based respirators is the nonoil-95 percent collection (N95) filter-based respirator. For filter respirators to properly function, inspired air is required to pass through the face of the filter respirator and pass through a tortuous matrix of the substrate before reaching the breathing zone of the wearer [12, 13] . Particle collection by the filter respirator is also contingent upon a nearly airtight seal on the face of the wearer [14, 15] . This configuration in properly donned filter respirators produces a significant pressure drop (∼0.27 ΔP cm H 2 0) between ambient air and the breathing zone upon inspiration. While providing sufficient protection against particles of a particular size (>0.3 μm non-oily aerosols), this pressure drop can become noticeable and laborious during longer-term use in otherwise healthy users and may become obstructive in individuals with compromised respiratory systems.

Particle collection by electrostatic precipitation (EP) has been used successfully in industrial applications for decades [16] , although application of the technology for the purposes of personal respiratory protection has historically not been pursued, with few exceptions at harnessing a form of EP on a micronized scale for personal protection [17] [18] [19] [20] . The principle of EP provides for removal of particles from an airstream based upon coronal discharge of electrons onto an opposite charged collection plate. The efficiency by which this mechanism collects airborne particles is correlative to the amount of energy provided to the corona, transit time, distance, and corresponding flow rate of the targeted airstream. Most commercially available ionizer-based devices use a corona discharge emitter creating an excess of ions and electrons interposed into the airflow followed by collector plates separated by a specific distance and electric field density between them. The airborne incidental particles and aerosol acquire a charge and then are deposited upon the collector plate and diverted from its intended path. Most of those designs have unidirectional functionality [17] and often have supportive fans to maintain the desired air flow past the corona discharge and between the collector plates needed to remove the particles . CC-BY-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. (which was not certified by peer review)

The copyright holder for this preprint this version posted January 28, 2022. ; https://doi.org/10.1101/2022.01.27.22269961 doi: medRxiv preprint from the air flow path. In this application, an EP was micronized (mEP) and engineered to collect particles from the uninterrupted respiratory airstreams of the wearer. This design also relies upon natural velocities of normal inspiratory and expiratory flow to generate the airflows required to bring functionality to the device. The resulting mEP respirator functions as an energized particle collector without any appreciable pressure drop between ambient air and the breathing zone of the wearer because the mechanism of particle collection is not filtration, a mechanism which requires wearer inspiratory flow to actively pull and push air through a filter substrate. A prototype of the mEP respirator was engineered to be self-contained and worn in a similar configuration that approximates the face fit and head strapping design of popular filterbased respirators.

In this study, we tested the particle collection efficiencies of the prototyped mEP respirator and compared performance with a N95 filter respirator, and an in-line HEPA cartridge filter. Each of the devices were tested using a modified 16-liter chamber operated in a dynamic configuration within high (BSL-3) biocontainment [21] . An atmosphere of viral bioaerosols were synthetically generated and maintained in the chamber during testing of each device. After fully characterizing the particle concentration, airborne viral titer, and corresponding counts within the ambient environment of the chamber, we measured the collection efficiency of each device. Once configured into the chamber, each respirator was sealed in such a way to only collect airstream contents distal to the inlet face or 'breathing zone' upon inspiration. Total particle counts were performed initially to determine particle reduction from each device.

Thereafter, aerosol samples were collected from the airstream in the same configuration and . CC-BY-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. (which was not certified by peer review)

The copyright holder for this preprint this version posted January 28, 2022. ; https://doi.org/10.1101/2022.01.27.22269961 doi: medRxiv preprint analyzed for culturable virus by TCID 50 and genomic RNA content as a surrogate for viral capture as a constituent of the bioaerosols collected by each respirator.

The prototype device ( Figure 1a ) is designed to fit on the face of the user and is held to the face through the use of strapping on the back of the head. The prototype device was designed to minimize the corona discharge by setting the operational point and controlling such with an embedded CPU control of the emitter voltage (Figure 1b and 1c) so that effective particle reduction can occur within the specified geometry and very little corona discharge, or ozone formation, is encountered. This servomechanism maintains performance at the set point despite ambient temperature, humidity, or site elevation. It is therefore advantageous to maintain control of the ionization process and assure its performance under different circumstances and elevations. The same servomechanisms allow for fine control of ozone (O 3 ) production with or without a catalytic degradation filter.

Testing of the mEP for particle removal Preliminary testing of particle removal capacity of the mEP was performed using aerosolized salt solution at high inlet flow (85 liters per minute (LPM)). Briefly, an aerosol particle generator (Model 8026 Particle Generator, TSI Systems, St. Paul, MN) loaded with . CC-BY-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. (which was not certified by peer review)

The copyright holder for this preprint this version posted January 28, 2022. ; https://doi.org/10.1101/2022.01.27.22269961 doi: medRxiv preprint saline solution was connected to a test chamber via tubing and passed through honeycomb to facilitate laminar flow through the chamber that housed the device and the samplers. A regenerative blower (VFC 080P-5T, Fuji Electric, Edison, NJ) was used to create airflow (85 LPM; 16" H 2 0) through the mEP device while housed in the chamber. Flow through the mEP was monitored during this assessment (SFM3000 Mass Flow Meter, Sensirion AG, Stäfa, Switzerland). Particle counts were measured distal to the inlet of the mEP using an optical particle counter (Model 8525, TSI). Ozone concentration was also measured using an ozone measurement device (FD-90A-O3 Forensics Detectors, Estates, CA). Power requirements to the mEP device during this preliminary assessment were both supplied to the device and measured (using a multimeter) in relation to the active particle removal and ozone measurements. Results showed (Fig. 1d ) that a ~0.35 milliwatts (mw) power selection resulted in a particle collection of ~95%. The results of time series experiments using longer operational durations indicated that particle rejection slightly improved to ~97.5%, suggesting relatively stable particle collection over extended wear times (data not shown). Similarly, O 3 levels generated by the device ( . CC-BY-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

The copyright holder for this preprint this version posted January 28, 2022. ; https://doi.org/10.1101/2022.01.27.22269961 doi: medRxiv preprint

Use of standard mask evaluation methodology (e.g., 42 CFR Part 84) [22] was not feasible to the experimental approach as SARS-CoV-2 aerosolization required additional engineering controls, including housing our configuration within a Class III biological Safety cabinet, for added safety during these studies because of the biologically active nature of the virus and the necessity of biosafety level 3 (BSL-3) containment. Therefore, all SARS-CoV-2 aerosol generation took place inside a 16-liter polycarbonate chamber outfitted with dilution and exhaust tubing and a sampling orifice. The chamber was connected to an automated system (Biaera Technologies, Hagerstown, MD) which controlled dilution, exhaust, sampling, and generator air flows when applicable, and also recorded temperature, relative humidity, and pressure readings. The automated system maintained equal rates of total air flow in and out of the chamber in order to retain equilibrium. Figure 2 illustrates the experimental configuration of the chamber utilizing the mEP respirator and the various sampling strategies implemented within biocontainment. The aerosol generator (Fig. 2 , A) used was the 3-jet (3JC) collision nebulizer.

Samples from the chamber (Fig. 2 , C) were collected using either the APS for particle counting ( Fig. 2 D) or the all glass impinger (Fig. 2 , E) sampler for virus collection. Total air flow in and out of the system was maintained at 16 LPM, with adjustments to the dilution (Fig. 2 B) and exhaust flows (Fig. 2 F) as needed for differing generator and sampling requirements, facilitated through the use of the automated aerosol control system (Biaera).

. CC-BY-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

The copyright holder for this preprint this version posted January 28, 2022. ; https://doi.org/10.1101/2022.01.27.22269961 doi: medRxiv preprint Individual aliquots of a liquid volume (5 ml) of SARS-CoV-2 inoculum and corresponding dilutions were prepared for evaluation of each respirator. Upon performance for each respirator, a liquid aliquot was directly expressed into the precious fluid reservoir for the Collison nebulizer and then actuated and allowed to continuously run for analysis. The experimental configuration was harmonized amongst both respirators and shared similar design and internal volume (Fig. 1) . Flow rates for the configured system was maintained at 16 LPM.

Two aerosol sampling instruments with differing flows were used in each discrete aerosol generation event. For the experiments involving particle counting, the aerodynamic particle sizer which was actively monitored throughout all aerosol generation events. The dynamic flows as described through the evaluation chamber were operated continuously for every evaluation for each respirator. Temperature and humidity were monitored continuously. The prevailing temperature was 20.4±3.6º C and relative humidity 57.6±7.2% across all evaluations.

. CC-BY-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

The copyright holder for this preprint this version posted January 28, 2022. ; Particle characteristics, including particle counts, were determined using an aerodynamic particle sizer (APS Model 3321, TSI Inc., St. Paul, MN). The APS measures the aerodynamic size of particles from 0.5 -20 microns and uses time-of-flight analysis based upon velocity and relative density of interrogated particle stream to determine particle behavior while airborne.

Aerosol is drawn into the APS at a total flow of 5 LPM; 20% of the total flow is dedicated to inlet into the analyzer; 80% is sheath flow. The APS spectrometer uses a double-crest dual laser system and nozzle configuration which reduces the advent of false (e.g., doublet) background counts. Analysis of data from the APS was collected and device software (Aerosol Instrument Manager Version 5.3, TSI Inc., St Paul, MN) was used for initial review of data. The APS device operated on a continual basis once aerosol generation was initiated, and logged data for the duration of each aerosol event. Resulting particle size generated from the Collison nebulizer in this configuration yielded a mass median aerodynamic diameter of 2.1 µm and geometric standard deviation of 1.4.

Virus used for aerosol generation was strain SARS-CoV-2; 2019-nCoV/USA-WA1/2020 (BEI# NR-52281) prepared on subconfluent VeroE6 cells (ATCC# CRL-1586) and confirmed via sequencing. Vero E6 cells were used for live virus titration of sample input and were maintained in DMEM (#11965092, Thermo Scientific, USA) with 10% FBS.

Viral RNA in collected aerosol samples was quantified using RT-qPCR targeting the nucleocapsid (genomic) of SARS-CoV-2. RNA was isolated from aerosol samples using a . CC-BY-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

The copyright holder for this preprint this version posted January 28, 2022. ; https://doi.org/10.1101/2022.01.27.22269961 doi: medRxiv preprint Zymo Quick RNA Viral Kit (#R1035, Zymo, USA), per manufacturer's instructions. RNA was eluted in RNAse free water and was extracted using 100 μL of sample. Isolated RNA was analyzed in a QuantStudio 6 (Thermo Scientific, USA) using TaqPath master mix (Thermo Scientific, USA) and appropriate primers/probes [23] with the following program: 25°C for 2 minutes, 50°C for 15 minutes, 95°C for 2 minutes followed by 40 cycles of 95°C for 3 seconds and 60°C for 30 seconds. Signals were compared to a standard curve generated using in vitro transcribed RNA of each sequence diluted from 10 8 down to 10 copies. Positive controls consisted of SARS-CoV-2 infected VeroE6 cell lysate. Viral copies per sample were calculated by multiplying mean copies per well by amount in the total sample extract.

Median Tissue Culture Infectious Dose (TCID 50 ) was used to quantify replicationcompetent virus in viral stock used to generate the aerosols used in the respirator evaluations.

VeroE6 ells were plated in 48-well tissue culture treated plates to be subconfluent at time of assay. Cells were washed with serum free DMEM and virus from 50 μL of sample was allowed to adsorb onto the cells for 1 hour at 37°C and 5% CO 2 . After adsorption, cells were overlayed with DMEM containing 2% FBS and 1% Anti/Anti (#15240062, Thermo Scientific, USA).

Plates were incubated for 7-10 days before being observed for cytopathic effect (CPE). Any CPE observed relative to control wells was considered positive and used to calculate TCID 50 by the Reed and Muench method.

. CC-BY-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

The copyright holder for this preprint this version posted January 28, 2022. ; https://doi.org/10.1101/2022.01.27.22269961 doi: medRxiv preprint All data from the evaluation studies that included particle counting and viral bioaerosol removal was assessed using Prism 9 (GraphPad Software, San Diego, CA). For both sets of data, a repeated measures ANOVA was performed with Geisser-Greenhouse correction and Tukey's multiple comparisons test. Significance was noted at p<0.05.

Results of the particle counting in the experiments involving viral bioaerosols showed a clear reduction in the number of particles reaching the distal portion of the mask when the powered mEP or N95 respirator was in place (Figure 3) . A HEPA filter was used as a control mechanism to confirm particle counts would essentially zero when positioned to receive inspiratory flow. The mEP performed on approximately an equivalent basis as the N95 respirator, returning an average 96.5% particle removal as compared to the N95 which removed an average of 96.9% of particles at measured air flow velocities. There were no significant difference between the particle removal rates between the mEP and the N95 respirator. There were significant differences when ambient particle concentration was compared to the powered mEP, N95, or HEPA filter values.

The results of the viral bioaerosol evaluation indicated, as observed from the particle removal experiments, the mEP removed most all of the viral RNA from the airstream as measured by RT-PCR analysis of the distally-positioned aerosol sampler (Figure 4 ). When the mEP was de-energized (denoted in the legend as mEP 'OFF'), viral RNA approximated ambient levels expressed in SARS-CoV-2 genome copies/liter aerosol. Interestingly, percentage . CC-BY-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

The copyright holder for this preprint this version posted January 28, 2022. ; https://doi.org/10.1101/2022.01.27.22269961 doi: medRxiv preprint removal, when measured by viral RNA, was remarkably similar between the mEP (99.79%), N95 (99.94%), and the HEPA filter (99.99%).

SARS-CoV-2 is an emergent, highly transmissible coronavirus. It is the etiologic agent for COVID-19, and the source of an ongoing worldwide pandemic. Over 5.4 million people have died worldwide from COVID-19 to date, with more than 847,000 deaths in the United States alone. Infection is associated with highly heterogenous disease sequelae, ranging from completely asymptomatic to severe acute respiratory distress and death. During this pandemic, respiratory protection in the form of facial coverings and, at times, filter-based respirators have been promoted to curb viral transmission and mitigate disease impact. Here, we performed a preliminary evaluation of a respirator that utilizes micronized electrostatic precipitation (mEP) rather than filtration for aerosol particle removal from the breathing zone of the wearer. We demonstrate that the mEP-based respirator in this evaluation effectively removed laboratory generated SARS-CoV-2-laden aerosol particles from an airstream at a rate that approximates filter-based respirators. The mEP respirator achieved equivalent particle reduction without the pressure drop required of filter-based respirators such as the N95. These data underscore the prospect for use of the new technologies that rely upon an alternative mechanism of airborne particle removal from the airstream than substrate-based filtration.

. CC-BY-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

The copyright holder for this preprint this version posted January 28, 2022. ;

In this study we used a mEP respirator specifically designed to remove aerosol particles from the airstream at a rate associated with normal human respiration. The respirator was engineered to remove airstream particles during both inhalation and exhalation, although studies in this evaluation only sampled and measured inspiratory flow. The mEP respirator removed aerosol particles as demonstrated by the reduction of particle counts and the particle counter configured distal to the ambient air inlet and functional mEP within the respirator. The measurement of viral removal as a correlative of the physical particle removal was measured in the liquid impingement samples also collected distal to the respirator inlet and mEP device. The viral concentration of the ambient air surrounding the respirator was also sampled by liquid impingement for the purposes of residual comparison. The viral content of these liquid samples was measured by Median Tissue Culture Infectious Dose (TCID 50 ) and quantitative RT-PCR.

The resulting culturable concentration of SARS-CoV-2 in the ambient air in the exposure chamber averaged 3.4E+3 TCID 50 /liter, or 9.7E+5 genome copies/liter of aerosol. The TCID 50 measurements of all liquid impinger samples distal to the mEP respirator inlet and the N95 respirator were nondetectable. This was due in part to the poor sensitivity of the TCID 50 assay and the use of the cell culture to attempt to quantify low titer virus. Fortunately, all impinger samples were split after collection and processed for analysis of genomic content by RT-PCR.

The results of this sampling showed an approximately equivalent removal of genomic material by the mEP and the N95 respirator under a similar laboratory configuration. Reduction of SARS-CoV-2 genomic content by either method was highly correlative with the physical particle removal resulting from particle counter measurements. Liberated SARS-CoV-2 virions (≈110 nm) are componentry of biological aerosol particles and will not travel in the air alone but as a . CC-BY-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

The copyright holder for this preprint this version posted January 28, 2022. ; https://doi.org/10.1101/2022.01.27.22269961 doi: medRxiv preprint component of a larger particle. In this case, aerosol particles generated in this evaluation were ≈2 μm thus any SARS-CoV-2 virions would have inhabited the particles removed by the mEP.

There are several limitations in the preliminary evaluation study performed on the mEP respirator as the generation of SARS-CoV-2 bioaerosols necessitated the use high containment LPM during the studies. The disparity between the flowrates used in the NIOSH testing and this evaluation can be considered a weakness of the study. Similarly, although the mEP and the N95 respirators were tested under the inspiration configuration (6 LPM either across the filter substrate of the N95 or through the inlet of the mEP), neither respirator was tested for efficacy for particle removal efficacy upon expiration. Although the mEP respirator will theoretically remove particles upon expiration, this evaluation study does not include a demonstration of the technology performing in this manner and should be one of the aspects of future evaluation studies.

. CC-BY-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

The copyright holder for this preprint this version posted January 28, 2022. ; https://doi.org/10.1101/2022.01.27.22269961 doi: medRxiv preprint Viral bioaerosols removed from the inspiratory airstream accumulate on the collector plates of the mEP respirator within the device. There was no analysis to determine the viability of the virus collected on the mEP plates. The particle removal efficacy studies did not include a hygiene protocol to elute collected aerosol particles from the collector plates once removal had taken place. Theoretically a virus captured in this manner (electrostatically) would dehydrate and be rendered inactive, and although this study did not include a laboratory demonstration of this effect, previous studies using electrically-charged surfaces illustrate the capacity for deactivation of virus [24] . Similarly, the mEP respirator required a continuous power source for functionality and performance, and although airflow is not restricted when the mEP unit is not powered, the benefits of particle removal dissipate. When powered, the mEP unit within the respirator generates ozone (O 3 ) as a by-product of coronal discharge of electrons and oxidation of ambient oxygen, with the amount of O 3 generated directly proportional to the mEP power requirements needed to remove particles from the airstream at a desired percentage efficiency.

Ambient O 3 at certain concentrations is theoretically microbicidal, although this effect was not tested as an aspect of this evaluation. O 3 can also be detrimental to human health when inhaled at relatively high concentrations, and the FDA requires O 3 output of indoor medical devices to be no more than 0.05 ppm or 50 μg/Liter air. The National Institute of Occupational Safety and Health (NIOSH) recommends an upper limit of 0.10 ppm (100 μg/Liter air), not to be exceeded at any time during an 8-hour workday. The mEP in this respirator was engineered in a micronized format that provides a high percentage of particle removal at a relatively low power requirement. The preliminary assessment of the mEP using a variety of power requirements showed low O 3 production at the power setting that was used in the viral bioaerosol experiments . CC-BY-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

The copyright holder for this preprint this version posted January 28, 2022. In summary, results of this evaluation demonstrated approximately equivalent performance in particle removal and viral RNA reduction for both respirators. The mEP respirator successfully demonstrated particle removal and viral removal as a constituent of the bioaerosol without pressure drop to the laboratory-simulated user. The mEP respirator, if further developed, could benefit individuals requiring respiratory protection for long periods of time without the necessity of labored breathing through filter substrate when the use of other respiratory protection such as a powered air-purifying respirator (PaPR) or self-contained breathing apparatus (SCBA) is not available or impractical. The mEP respirator could also be used in circumstances where respiratory protection is required for ambulatory or other compromised individuals that may not be physically able to produce the inspiratory flow required to breathe through filter-based respirators. Future evaluations should investigate many of the aspects that were identified limitations of this study, including the effect of O 3 generation upon the efficiency of particle removal, as well as laboratory assessment of the pathogenagnostic mechanism of particle removal for other airborne threats such as influenza.

. CC-BY-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

The copyright holder for this preprint this version posted January 28, 2022. The air supply to the system was maintained at >40 PSIG, and at ~21 PSIG to the nebulizer (A) which generates ~7 LPM at that pressure, and dilution air (B) providing auxillary air flow for mixing at 9 LPM. The 16 L aerosol chamber (C) was operated dynamically with a constant flow of nebulized aerosol particles within the combination flow provided by the nebulizer and dilution air. Each device or filter was housed within the chamber in discrete experiments. An inlet for sampling by the particle counter (D) or AGI aerosol sampler (E) at an exhause flow of either 5 or 6 LPM, respectively, was acutated at separate times and and residual exhaust, or when the sampler was disengaged, provided a complete exhaust flow of 16 LPM (F). The entire system was expertly controlled using the AeroMP automated aerosol exposure system (Biaera).

. CC-BY-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. (which was not certified by peer review)

The copyright holder for this preprint this version posted January 28, 2022. ; https://doi.org/10.1101/2022.01.27.22269961 doi: medRxiv preprint Figure 3 . Particle counts of viral bioaerosols using the evaluation system within biocontainment. Counts from the energized mEP significantly reduced aerosol particles by a mean of 96.5% when compared to ambient (chamber) aerosol content; the N95 filter respirator significantly reduced particles by an approximately equivalent 96.9% when compared to ambient (chamber) particle content. The HEPA filter essentially removed all particles from the airstream. 

The emergence of a novel coronavirus (SARS-CoV-2), their biology and therapeutic options

Evidence of short-range aerosol transmission of SARS-CoV-2 and call for universal airborne precautions for anesthesiologists during the COVID-19 pandemic

The global battle against SARS-CoV-2 and COVID-19

Reducing Aerosol-Related Risk of Transmission in the Era of COVID-19: An Interim Guidance Endorsed by the International Society of Aerosols in Medicine

Medical Masks vs N95 Respirators for Preventing COVID-19 in Health Care Workers A Systematic Review and Meta-Analysis of Randomized Trials. Influenza Other Respir Viruses

Filtration Efficiencies of Nanoscale Aerosol by Cloth Mask Materials Used to Slow the Spread of SARS-CoV-2

Cloth Masks May Prevent Transmission of COVID-19: An Evidence-Based, Risk-Based Approach

Covid-19: Are cloth masks still effective? And other questions answered

Cloth Masks May Prevent Transmission of COVID-19

Influenza virus aerosols in human exhaled breath: particle size, culturability, and effect of surgical masks

Update Alert: Use of N95, Surgical, or Cloth Masks to Prevent COVID-19 in Health Care and Community Settings: Living Practice Points From the American College of Physicians (Version 1)

Advanced testing method to evaluate the performance of respirator filter media

N95 and p100 respirator filter efficiency under high constant and cyclic flow

Safety concerns for facial topography customized 3D-printed N95 filtering face-piece respirator produced for the COVID-19 pandemic: initial step is respiratory fit testing

A novel approach to fit testing the N95 respirator in real time in a clinical setting

The quantitative assay of bacterial aerosols by electrostatic precipitation

Microorganism-ionizing respirator with reduced breathing resistance suitable for removing airborne bacteria

Direct and rapid analysis of ambient air and exhaled air via electrostatic precipitation of aerosols in an atomizer furnace and Zeeman spectrometry

Electrostatic respirator filter media: filter efficiency and most penetrating particle size effects

Deposition and resuspension of selected aerosols particles on electrically charged filter materials for respiratory protective devices

Persistence of Severe Acute Respiratory Syndrome Coronavirus 2 in Aerosol Suspensions

NIOSH publishes respirator final rule. Occup Health Saf

Effective Prophylaxis of COVID-19 in Rhesus Macaques Using a Combination of Two Parenterally-Administered SARS-CoV-2 Neutralizing Antibodies

Electroceutical fabric lowers zeta potential and eradicates coronavirus infectivity upon contact. Sci Rep