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.

Airborne transmission of infectious (viable) SARS-CoV-2 is increasingly accepted as the primary manner by which the virus is spread from person to person. Risk of exposure to airborne virus is higher in enclosed and poorly ventilated spaces. We present a study focused on air sampling within residences occupied by individuals with COVID-19. Air samplers (BioSpot-VIVAS, VIVAS, and BC-251) were positioned in primary- and secondary-occupancy regions in seven homes. Swab samples were collected from high-touch surfaces. Isolation of SARS-CoV-2 was attempted for samples with virus detectable by RT-qPCR. Viable virus was quantified by plaque assay, and complete virus genome sequences were obtained for selected samples from each sampling day. SARS-CoV-2 was detected in 24 of 125 samples (19.2%) by RT-qPCR and isolated from 14 (11.2%) in cell cultures. It was detected in 80.9% (17/21) and cultured from 61.9% (13/21) of air samples collected using water condensation samplers, compared to swab samples which had a RT-qPCR detection rate of 10.5% (4/38) and virus isolation rate of 2.63% (1/38). No statistically significant differences existed in the likelihood of virus detection by RT-qPCR or amount of infectious virus in the air between areas of primary and secondary occupancy within residences. Our work provides information about the presence of SARS-CoV-2 in the air within homes of individuals with COVID-19. Information herein can help individuals make informed decisions about personal exposure risks when sharing indoor spaces with infected individuals isolating at home and further inform health departments and the public about SARS-CoV-2 exposure risks within residences.

Abstract. Accurate airborne aerosol instrumentation is required to determine the spatial distribution of ambient aerosol particles, particularly when dealing with the complex vertical profiles and horizontal variations of atmospheric aerosols. A versatile water-based condensation particle counter (vWCPC) has been developed to provide aerosol concentration measurements under various environments with the advantage of reducing the health and safety concerns associated with using butanol or other chemicals as the working fluid. However, the airborne deployment of vWCPCs is relatively limited due to the lack of characterization of vWCPC performance at reduced pressures. Given the complex combinations of operating parameters in vWCPCs, modeling studies have advantages in mapping vWCPC performance. In this work, we thoroughly investigated the performance of a laminar-flow vWCPC using COMSOL Multiphysics® simulation coupled with MATLAB™. We compared it against a modified vWCPC (vWCPC model 3789, TSI, Shoreview, MN, USA). Our simulation determined the performance of particle activation and droplet growth in the vWCPC growth tube, including the supersaturation, Dp,kel,0 (smallest size of particle that can be activated), Dp,kel,50 (particle size activated with 50 % efficiency) profile, and final growth particle size Dd under wide operating temperatures, inlet pressures P (30–101 kPa), and growth tube geometry (diameter D and initiator length Lini). The effect of inlet pressure and conditioner temperature on vWCPC 3789 performance was also examined and compared with laboratory experiments. The COMSOL simulation result showed that increasing the temperature difference (ΔT) between conditioner temperature Tcon and initiator Tini will reduce Dp,kel,0 and the cut-off size Dp,kel,50 of the vWCPC. In addition, lowering the temperature midpoint (Tmid=Tcon+Tini2) increases the supersaturation and slightly decreases the Dp,kel. The droplet size at the end of the growth tube is not significantly dependent on raising or lowering the temperature midpoint but significantly decreases at reduced inlet pressure, which indirectly alters the vWCPC empirical cut-off size. Our study shows that the current simulated growth tube geometry (D=6.3 mm and Lini=30 mm) is an optimized choice for current vWCPC flow and temperature settings. The current simulation can more realistically represent the Dp,kel for 7 nm vWCPC and also achieved good agreement with the 2 nm setting. Using the new simulation approach, we provide an optimized operation setting for the 7 nm setting. This study will guide further vWCPC performance optimization for applications requiring precise particle detection and atmospheric aerosol monitoring.

CeO2 and CuO nanoparticles (NPs) are used as additives in petrodiesel to enhance engine performance leading to reduced diesel combustion emissions. Despite their benefits, the additive application poses human health concerns by releasing inhalable NPs into the ambient air. In this study, a bioinspired lung cell exposure system, Dosimetric Aerosol in Vitro Inhalation Device (DAVID), was employed for evaluating the toxicity of aerosolized CeO2 and CuO NPs with a short duration of exposure (≤10 min vs. hours in other systems) and without exerting toxicity from non-NP factors. Human epithelial A549 lung cells were cultured and maintained within DAVID at the air-liquid interface (ALI), onto which aerosolized NPs were deposited, and experiments in submerged cells were used for comparison. Exposure of the cells to the CeO2 NPs did not result in detectable IL-8 release, nor did it produce a significant reduction in cell viability based on lactate dehydrogenase (LDH) assay, with a marginal decrease (10%) at the dose of 388 μg/cm2 (273 cm2/cm2). In contrast, exposure to CuO NPs resulted in a concentration dependent reduction in LDH release based on LDH leakage, with 38% reduction in viability at the highest dose of 52 μg/cm2 (28.3 cm2/cm2). Cells exposed to CuO NPs resulted in a dose dependent cellular membrane toxicity and expressed IL-8 secretion at a global dose five times lower than cells exposed under submerged conditions. However, when comparing the ALI results at the local cellular dose of CuO NPs to the submerged results, the IL-8 secretion was similar. In this study, we demonstrated DAVID as a new exposure tool that helps evaluate aerosol toxicity in simulated lung environment. Our results also highlight the necessity in choosing the right assay endpoints for the given exposure scenario, e.g., LDH for ALI and Deep Blue for submerged conditions for cell viability.

Abstract. Aerosol particle number concentration measurements are a crucial part of aerosol research. Vertical profile measurements and high-altitude/low-pressure performance of the respective instruments become more important for remote sensing validation and a vital tool for the observation of climate variables. This study tests the new, commercially available water condensation particle counter (MAGIC 210-LP) for the deployment at aircraft cruising pressure levels that the European research infrastructure IAGOS (In-service Aircraft for a Global Observing System; http://www.iagos.org, last access: 2 May 2023) is aiming for by operating measurement instrumentation onboard passenger aircraft. We conducted laboratory experiments for conditions to simulate passenger aircraft flight altitude at operation pressure. We demonstrate that this type of water condensation particle counter shows excellent agreement with a butanol-based instrument used in parallel. A Faraday cup aerosol electrometer serves as the reference instrument. Experiments are performed with test aerosol ammonium sulfate and fresh combustion soot at pressure levels ranging from 700 to 200 hPa. For soluble particles like ammonium sulfate, the 50 % detection efficiency cut-off diameter (D50) is around 5 nm and does not differ significantly for all performed experiments. For non-soluble fresh soot particles, the D50 cut-off diameter of approximately 10 nm does not vary substantially as a function of pressure, whereas the 90 % detection efficiency cut-off diameter D90 increases from 19 nm at 700 hPa to 37 nm at 200 hPa. The overall counting efficiency for particles larger than 40 nm reaches 100 % for working pressures of 200 hPa and higher.

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 (DoseSMPS) 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) (DoseICP) also increased exponentially over time (0.01 ± 0.01–97.25 ± 1.30 μg/cm2). Regression analysis between DoseICP and DoseSMPS 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.

This study aimed to provide environmental surveillance data for evaluating the risk of acquiring SARS-CoV-2 in public areas with high foot traffic in a university. Air and surface samples were collected at a university that had the second highest number of COVID-19 cases among public higher education institutions in the U.S. during Fall 2020. A total of 60 samples were collected in 16 sampling events performed during Fall 2020 and Spring 2021. Nearly 9800 students traversed the sites during the study period. SARS-CoV-2 was not detected in any air or surface samples. The university followed CDC guidance, including COVID-19 testing, case investigations, and contact tracing. Students, faculty, and staff were asked to maintain physical distancing and wear face coverings. Although COVID-19 cases were relatively high at the university, the possibility of acquiring SARS-CoV-2 infections at the sites tested was low.

AbstractVentilation is one of the most critical components in a layered approach toward reducing the spread of airborne infectious diseases in indoor spaces. However, building ventilation systems act together with natural ventilation, local filtration systems and other aerosol removal processes to remove infectious aerosols from an occupied space. Airflow-based determinations of ACH do not account for the full range of aerosol removal processes; however understanding the effective aerosol removal rate is critical to providing airborne infection control.In this study, we investigated the relationship between the calculated air change rate of a space (i.e. volumetric airflow based) and the effective air change rate for aerosol particle removal within the breathing zone based on direct measurements of the rate of change in tracer particle concentrations at representative occupant locations in a room. Further, we examined positional effects under well mixed and non-well mixed conditions.Our results demonstrate that tracer particles combined with real-time sensors can be used to make rapid, accurate measurements of the effective air change rate (eACH) for respiratory aerosols within the breathing zone of non-well mixed rooms. We used two experimental test beds for these analyses. First, numerical simulation (computational fluid dynamic simulation, CFD) was conducted to visualize airflow and particle removal paths within a realistic large room. Here, simulated sensors were placed in concentric zones around a nebulizer providing test-particle releases. This CFD model allowed a direct comparison of the differences between eACH and airflow ACH values under varying levels of mixing and airflow, in a fully controlled system.We then recapitulated this system in physical space to validate the CFD results under real-world conditions that include all mechanisms of particle removal that contribute to true aerosol clearance rates, including deposition and leakage. Here, we measured eACH using the decay of DNA tracer aerosols nebulized and monitored in real-time. We find that a standard sampling time of 15 minutes from the end of nebulization is sufficient to produce an accurate eACH value under non-well mixed conditions. The availability of a rapid direct test for eACH will enable empirical optimization of a wide range of ventilation and filtration mechanisms to reach and maintain target aerosol clearance rates that deliver reliable airborne infection control in typical indoor environments.

Abstract. Accurate airborne aerosol instrumentation is required to determine the spatial distribution of ambient aerosol particles, particularly when dealing with the complex vertical profiles and horizontal variations of atmospheric aerosols. A versatile water-based condensation particle counter (vWCPC) has been developed to provide aerosol concentration measurements under various environments with the advantage of reducing the health and safety concerns associated with using butanol or other chemicals as the working fluid. However, the airborne deployment of vWCPCs is relatively limited due to the lack of characterization of vWCPC performance at reduced pressures. Given the complex combinations of operating parameters in vWCPCs, modeling studies have advantages in mapping vWCPC performance. In this work, we thoroughly investigated the performance of a laminar flow vWCPC using COMSOL Multiphysics® simulation coupled with MATLAB. We compared it against a modified commercial vWCPC (vWCPC Model 3789, TSI, Shoreview, MN, USA). Our simulation determined the performance of particle activation and droplet growth in the vWCPC growth tube, including the supersaturation, Dp,kel,0 (smallest size of particle that can be activated), Dp,kel,50 (particle size activated with 50 % efficiency) profile, and final growth particle size Dd under wide operating temperatures, inlet pressures P (0.3–1 atm), and growth tube geometry (diameter D and initiator length Lini). The effect of inlet pressure and conditioner temperature on vWCPC 3789 performance was also examined and compared with laboratory experiments. The COMSOL simulation result showed that increasing the temperature difference (∆ T) between conditioner temperature Tcon and initiator Tini will reduce Dp,kel,0 and the cut-off size Dp,kel,50 of the vWCPC. In addition, lowering the temperature midpoint (Tmid = (Tcon + Tini) / 2) increases the supersaturation and slightly decreases the Dp,kel. The droplet size at the end of the growth tube is not significantly dependent on raising or lowering the temperature midpoint but significantly decreases at reduced inlet pressure, which indirectly alters the vWCPC empirical cut-off size. Our study shows that the current simulated growth tube geometry (D = 6.3 mm and Lini = 30 mm) is an optimized choice for current vWCPC flow and temperature settings. The current simulation can more realistically represent the Dp,kel for 7 nm vWCPC and also achieved a good agreement with the 2 nm setting. Using the new simulation approach, we provide an optimized operation setting for the 7 nm setting. This study will guide further vWCPC performance optimization for applications requiring precise particle detection and atmospheric aerosol monitoring.