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Pathogens can be collected from air and detected in samples by many methods. However, merely detecting pathogens does not answer whether they can spread disease. To fully assess health risks from exposure to airborne pathogens, the infectivity of those agents must be assessed. Air samplers which operate by growing particles through water vapor condensation and subsequently collecting them into a liquid medium have proven effective at conserving the viability of microorganisms. We present a study that assessed performance improvement of one such sampler, BioSpot-GEM™, gained by augmenting it with an upstream virtual impactor (VI) designed to concentrate particles in aerosols. We demonstrate that such an integrated unit improved the collection of live Escherichia coli by a median Concentration Factor (CF) of 1.59 and increased the recovery of viable human coronavirus OC43 (HCoV OC43) by a median CF of 12.7 as compared to the sampler without the VI. Our results also show that OC43 can be concentrated in this way without significant loss of infectivity. We further present that the small BioSpot-GEM™ bioaerosol sampler can collect live E. coli at an efficiency comparable to the larger BioSpot-VIVAS™ bioaerosol sampler. Our analyses show potential benefits toward improving the collection of viable pathogens from the air using a more portable water-based condensation air sampler while also highlighting challenges associated with using a VI with concentrated bioaerosols. This work can aid further investigation of VI usage to improve the collection of pathogens from air, ultimately to better characterize health risks associated with airborne pathogen exposures. Copyright © 2024 American Association for Aerosol Research [ABSTRACT FROM AUTHOR]

As COVID-19 swept across the globe, increased ventilation and implementation of air cleaning were emphasized by the US CDC and WHO as important strategies to reduce the risk of inhalation exposure to the virus. To assess whether higher ventilation and air cleaning rates lead to lower exposure risk to SARS-CoV-2, 1274 manuscripts published between April 2020 and September 2022 were screened using key words "airborne SARS-CoV-2 or "SARS-CoV-2 aerosol." Ninety-three studies involved air sampling at locations with known sources (hospitals and residences) were selected and associated data were compiled. Two metrics were used to assess exposure risk: SARS-CoV-2 concentration and SARS-CoV-2 detection rate in air samples. Locations were categorized by type (hospital or residence) and proximity to the location housing the isolated/quarantined patient (primary or secondary). The results showed that hospital wards had lower airborne virus concentrations than residential isolation rooms. A negative correlation was found between airborne virus concentrations in primary-occupancy areas and air changes per hour (ACH). In hospital settings, sample positivity rates were significantly reduced in secondary-occupancy areas compared to primary-occupancy areas, but they were similar across sampling locations in residential settings. ACH and sample positivity rates were negatively correlated, though the effect was diminished when ACH values exceeded 8. While limitations associated with diverse sampling protocols exist, data considered by this meta-analysis support the notion that higher ACH may reduce exposure risks to the virus in ambient air. Copyright © 2024 American Association for Aerosol Research [ABSTRACT FROM AUTHOR]

The ability to collect size-fractionated airborne particles that contain viable bacteria and fungi directly into liquid medium while also maintaining their viability is critical for assessing exposure risks. In this study, we present the BioCascade impactor, a novel device designed to collect airborne particles into liquid based on their aerodynamic diameter in three sequential stages (>9.74, 3.94–9.74, and 1.38–3.94 µm when operated at 8.5 L/min). Aerosol samples containing microorganisms—either Saccharomyces kudriavzevii or Micrococcus luteus, were used to evaluate the performance of the BioCascade (BC) paired with either the VIable Virus Aerosol Sampler (VIVAS) or a gelatin filter (GF) as stage 4 to collect particles <1.38 µm. Stages 2 and 3 collected the largest fractions of viable S. kudriavzevii when paired with VIVAS (0.468) and GF (0.519), respectively. Stage 3 collected the largest fraction of viable M. luteus particles in both BC + VIVAS (0.791) and BC + GF (0.950) configurations. The distribution function of viable microorganisms was consistent with the size distributions measured by the Aerodynamic Particle Sizer. Testing with both bioaerosol species confirmed no internal loss and no re-aerosolization occurred within the BC. Irrespective of the bioaerosol tested, stages 1, 3, and 4 maintained ≥ 80% of viability, while stage 2 maintained only 37% and 73% of viable S. kudriavzevii and M. luteus, respectively. The low viability that occurred in stage 2 warrants further investigation. Our work shows that the BC can efficiently size-classify and collect bioaerosols without re-aerosolization and effectively maintain the viability of collected microorganisms. Copyright © 2024 American Association for Aerosol Research [ABSTRACT FROM AUTHOR]

A first-of-its-kind aerosol exposure device for toxicity testing, referred to as the Dosimetric Aerosol in Vitro Inhalation Device (DAVID), was evaluated for its ability to deliver airborne nanoparticles to lung cells grown as air–liquid interface (ALI) cultures. For inhalation studies, ALI lung cell cultures exposed to airborne nanoparticles have more relevancy than the same cells exposed in submerged culture because ALI culture better represents the respiratory physiology and consequently more closely reflect cellular response to aerosol exposure. In DAVID, water condensation grows particles as small as 5 nm to droplets sized >5 µm for inertial deposition at low flow rates. The application of DAVID for nanotoxicity analysis was evaluated by measuring the amount and variability in the deposition of uranine nanoparticles and then assessing the viability of ALI cell cultures exposed to clean-air under the same operational conditions. The results showed a low coefficient of variation, <0.25, at most conditions, and low variability in deposition between the exposure wells, trials, and operational flow rates. At an operational flow rate of 4 LPM (liter per minute), no significant changes in cell viability were observed, and minimal effects observed at 6 LPM. The reliable and gentle deposition mechanism of DAVID makes it advantageous for nanoparticle exposure. Copyright © 2019 American Association for Aerosol Research [ABSTRACT FROM AUTHOR]

Previous studies have shown that bioaerosols can be inactivated in less than a second when exposed to temperatures of hundreds of degrees Celsius in an ultra-high temperature (UHT) process. Here, a new UHT system was developed to make UHT safer and more predictable, in which a heated porous cloth was oriented perpendicularly to the flow direction to produce more uniform flow temperatures. Infrared radiation, which can provide uniform heating for flat surfaces, was used to heat the cloth. Temperature measurements indicated that high temperatures were obtained at the cloth surface and that the downstream flow temperature was more axially uniform than radially/azimuthally uniform. For both Escherichia coli and MS2 virus test bioaerosols, the inactivations were found to be greater than 4.7log for a cloth temperature of about 450°C and residence time of 0.41s. Results from gel electrophoresis showed that infrared–UHT treatment resulted in DNA damages to E. coli. Besides lab testing, the UHT system was found to reduce the concentration of outdoor culturable bacteria by 1–2 orders of magnitude at 210°C and residence time of 0.1s, but was less effective against fungi. On the other hand, SEM imaging and sampling downstream of the cloth revealed that the cloth emitted unidentified particles. The results of the work proved that this IR system – with its perpendicular orientation – can achieve high temperatures and high bioaerosol disinfection, and can be used to better relate temperature to inactivation. Furthermore, the ambient inactivation data, which are not available in literature, allow insights into the real-world applications of an UHT system. [ABSTRACT FROM AUTHOR]

Aerosols generated from the human respiratory tract containing infectious virus can be challenging to measure due to a number of factors that impact the infectivity of the virus they contain. These factors include limitations in the understanding of respiratory aerosol composition, chemical processes that can change the composition and impact infectivity, and the effects of the aerosol collection process. The aerobiological pathway represents a framework to understand how factors influencing these particles can collectively contribute to limitations in the overall understanding of their potential infectiousness. Here, the aerobiological pathway is used to highlight areas of research that could improve the understanding of natural viral particles and their potential hazards. In particular, an improved understanding is required of the chemical and biological composition of the particles and how chemical processes in the aerosol phase can impact the composition. These findings will also be invaluable to improve airborne virus collection and detection. • The aerobiological pathway provides a framework to examine our understanding of viral transmission and measurement. • Improved understanding of airborne respiratory particle composition, and how they change over time, is needed. • Impacts of environment on the composition and stability of respiratory viral aerosol, as a function of size, need more study. • Better characterization of viral aerosol composition can be used to improve our ability to collect intact viral aerosol. [ABSTRACT FROM AUTHOR]

Experimental studies with granular bed filters composed of sized metallic granules have demonstrated their use in aerosol filtration. However, the effectiveness of metallic membrane filters against bioaerosols has not been established. In this work, the filtration efficiency and filter quality of these filters against airborne B. subtilis endospore and MS2 virus were determined as a function of face velocity and loading time. In experiments, a physical removal efficiency greater than 99.9% and a viable removal efficiency greater than 99.999% were observed for both bacterial spore and viral aerosols. A lower face velocity produced both higher collection efficiency and filter quality for virus but was not a statistically significant factor for spore filtration. Although the filter had high filtration efficiency of the test bioaerosols, its high pressure drop resulted in a low filter quality (). Overall, filters with micrometer-sized collectors capture bioaerosols effectively but their applications in aerosol filtration may be limited by their high pressure drop. [ABSTRACT FROM AUTHOR]

• Viable (infectious) SARS-CoV-2 was present in aerosols within the hospital room of COVID-19 patients. • Airborne virus was detected in the absence of healthcare aerosol-generating procedures. • The virus strain detected in the aerosols matched with the virus strain isolated from a patient with acute COVID-19. Because the detection of SARS-CoV-2 RNA in aerosols but failure to isolate viable (infectious) virus are commonly reported, there is substantial controversy whether severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) can be transmitted through aerosols. This conundrum occurs because common air samplers can inactivate virions through their harsh collection processes. We sought to resolve the question whether viable SARS-CoV-2 can occur in aerosols using VIVAS air samplers that operate on a gentle water vapor condensation principle. Air samples collected in the hospital room of two coronavirus disease-2019 (COVID-19) patients, one ready for discharge and the other newly admitted, were subjected to RT-qPCR and virus culture. The genomes of the SARS-CoV-2 collected from the air and isolated in cell culture were sequenced. Viable SARS-CoV-2 was isolated from air samples collected 2 to 4.8 m away from the patients. The genome sequence of the SARS-CoV-2 strain isolated from the material collected by the air samplers was identical to that isolated from the newly admitted patient. Estimates of viable viral concentrations ranged from 6 to 74 TCID 50 units/L of air. Patients with respiratory manifestations of COVID-19 produce aerosols in the absence of aerosol-generating procedures that contain viable SARS-CoV-2, and these aerosols may serve as a source of transmission of the virus. [ABSTRACT FROM AUTHOR]

The size of virus-laden particles determines whether aerosol or droplet transmission is dominant in the airborne transmission of pathogens. Determining dominant transmission pathways is critical to implementing effective exposure risk mitigation strategies. The aerobiology discipline greatly needs an air sampling system that can collect virus-laden airborne particles, separate them by particle diameter, and deliver them directly onto host cells without inactivating virus or killing cells. We report the use of a testing system that combines a BioAerosol Nebulizing Generator (BANG) to aerosolize Human coronavirus (HCoV)-OC43 (OC43) and an integrated air sampling system comprised of a BioCascade impactor (BC) and Viable Virus Aerosol Sampler (VIVAS), together referred to as BC-VIVAS, to deliver the aerosolized virus directly onto Vero E6 cells. Particles were collected into four stages according to their aerodynamic diameter (Stage 1: >9.43 μm, Stage 2: 3.81–9.43 μm, Stage 3: 1.41–3.81 μm and Stage 4: <1.41 μm). OC43 was detected by reverse-transcription quantitative polymerase chain reaction (RT-qPCR) analyses of samples from all BC-VIVAS stages. The calculated OC43 genome equivalent counts per cm3 of air ranged from 0.34 ± 0.09 to 70.28 ± 12.56, with the highest concentrations in stage 3 (1.41–3.81 μm) and stage 4 (<1.41 μm). Virus-induced cytopathic effects appeared only in cells exposed to particles collected in stages 3 and 4, demonstrating the presence of viable OC43 in particles <3.81 μm. This study demonstrates the dual utility of the BC-VIVAS as particle size-fractionating air sampler and a direct exposure system for aerosolized viruses. Such utility may help minimize conventional post-collection sample processing time required to assess the viability of airborne viruses and increase the understanding about transmission pathways for airborne pathogens. • Viable OC43 was present in particles <3.81 μm. • Direct delivery of viable OC43 to host cells through the BC-VIVAS was demonstrated. • Dual utility of BC-VIVAS as an air sampler and exposure system was proven. [ABSTRACT FROM AUTHOR]

Real-time monitoring of dosimetry is critical to mitigating the constraints of offline measurements. To address this need, the use of the Scanning Mobility Particle Sizer (SMPS) to estimate the dose delivered through the Dosimetric Aerosol in Vitro Inhalation Device (DAVID) was assessed. CuO nanoparticles suspended in ethanol at different concentrations (0.01–10 mg/mL) were aerosolized using a Collison nebulizer and diluted with air at a ratio of either 1:3 (setup 1) or 1:18 (setup 2). From the aerosol volume concentrations measured by the SMPS, density of CuO (6.4 g/cm3), collection time (5–30 min), flow rate (0.5 LPM) and deposition area (0.28 cm2), the mass doses (Dose SMPS) were observed to increase exponentially over time and ranged from 0.02 ± 0.001 to 84.75 ± 3.49 μg/cm2. The doses calculated from the Cu concentrations determined by Inductively Coupled Plasma-Optical Emission Spectrometry (ICP-OES) (Dose ICP) also increased exponentially over time (0.01 ± 0.01–97.25 ± 1.30 μg/cm2). Regression analysis between Dose ICP and Dose SMPS showed R2 ≥ 0.90 for 0.1–10 mg/mL. As demonstrated, the SMPS can be used to monitor the delivered dose in real-time, and controlled delivery of mass doses with a 226-fold range can be attained in ≤30 min in DAVID by adjusting the nebulizer concentration, dilution air and time. • Controlled delivery of CuO with mass doses in a 226-fold through DAVID, in ≤30 min. • Reliable dosimetry for non-steady state aerosol generation. • Correlation coefficient between Dose ICP and Dose SMPS ≥ 0.9 for C neb 0.1–10 mg/mL. • The use of SMPS for real-time monitoring of delivered dose was demonstrated. [ABSTRACT FROM AUTHOR]

The chemical characteristics of airborne particulate matter (PM) have been extensively studied; however, little information exists for its biological components (bioaerosol) especially during a haze event in mega cities. Herein, we studied the bioaerosol (fluorescent particle) dynamics on both haze and sunny days in Beijing from Dec. 2013 to March 2014 by employing a widely used real-time bioaerosol sensor-ultraviolet aerodynamic particle spectrometer (UV-APS). Firstly, we studied the fluorescent particle (BioPM) concentration and size distributions during three independent haze and three independent sunny days. Secondly, we investigated BioPM dynamics over a two-week long monitoring period which included consecutive haze days and alternated sunny days. In addition, we analyzed bacterial community structures and endotoxin levels in the air samples using pyrosequencing and Limulus amebocyte lysate (LAL) method, respectively. More than 6-fold higher fluorescent particle concentrations up to 5 × 10 5 /m 3 with peaks at night or early dawn were detected at the time of haze occurrences than those observed on sunny days. When the haze episode progressed for 3–5 days, the BioPM concentrations were observed to decrease to the levels that were typically observed on sunny days. In general, ozone levels were found to be elevated at noon, while BioPM, NO x and relative humidity were reduced. Gene sequence analysis revealed no significant difference in abundances and community structures for top 13 bacterial genera between haze and sunny days, yet about twice higher endotoxin levels (12.4 EU/m 3 ) were detected on haze days than on sunny days. The results here facilitate a better understanding of atmospheric fluorescent particle dynamics including those under haze events. [ABSTRACT FROM AUTHOR]

There is an increasing interest in understanding ambient bioaerosols due to their roles both in health and in climate. Here, we deployed an Ultraviolet Aerodynamic Particle Sizer to monitor viable (fluorescent) bioaerosol concentration levels at city centers (highly polluted) and their corresponding suburbs (near pristine) (total 40 locations) in 11 provinces featuring different climate zones in China between July 16 and 28, 2013. The concentration levels of viable bioaerosol particles (BioPM) of >0.5 µm were measured, and corresponding percentages of BioPM% (biological fraction of total PM) and BioPM% (biological fraction of PM) in particulate matter (PM) and BioPM, respectively, were determined. For some key cities, indoor viable bioaerosol levels were also obtained. In addition, bacterial structures of the air samples collected across these monitoring locations were studied using pyrosequencing. BioPM concentration levels ranged from 2.1 × 10 to 2.4 × 10/m for city centers [BioPM% = 6.4 % (±6.3 %)] and 0.5 × 10 to 4.7 × 10/m for suburbs [BioPM% = 10 % (±8.7 %)]. Distinctive bioaerosol size distribution patterns were observed for different climate zones, e.g., some had fluorescence peaks at 3 µm, while the majority had peaks at 1 µm. Ambient bacterial aerosol community structures were also found different for different geophysical locations. Results suggest that there was a poor overall relationship between PM and BioPM across 40 monitoring locations ( R = 0.081, two-tailed P value = 0.07435). Generally, city centers had higher PM concentrations than suburbs, but not BioPM and BioPM%. Indoor bioaerosol levels were found at least tenfold higher than those corresponding outdoors. Bacillus was observed to dominate the bacterial aerosol community in the air sample. [ABSTRACT FROM AUTHOR]

• Novel system for analyzing airborne particle toxicity, akin to respiratory system. • Demonstrate high deposition and temporal efficiency compared to current systems. • Evidence for welding fume toxicity mitigation using amorphous silica precursor. In assessing the biological impact of airborne particles in vitro , air-liquid interface (ALI) exposure chambers are increasingly preferred over classical submerged exposure techniques, albeit historically limited by their inability to deliver sufficient aerosolized dose. A novel ALI system, the Dosimetric Aerosol in Vitro Inhalation Device (DAVID), bioinspired by the human respiratory system, uses water-based condensation for highly efficient aerosol deposition to ALI cell culture. Here, welding fumes (well-studied and inherently toxic ultrafine particles) were used to assess the ability of DAVID to generate toxicological responses between differing welding conditions. After fume exposure, ALI-cultured cells showed reductions in viability that were both distinct between welding conditions and linearly dose-dependent with respect to exposure time; comparatively, submerged cell cultures ran in parallel did not show these trends across exposure levels. DAVID delivers a substantial dose in minutes (> 100 μg/cm2), making it preferable over previous ALI systems, which require hours of exposure to deliver sufficient dose, and over submerged techniques, which lack comparable physiological relevance. DAVID has the potential to provide the most accurate assessment of in vitro toxicity yet from the perspectives of physiological relevance to the human respiratory system and efficiency in collecting ultrafine aerosol common to hazardous exposure conditions. [ABSTRACT FROM AUTHOR]