The COVID-19 pandemic has contributed to over 1.1 million deaths in the US alone, and the disease is now widespread. Environmental monitoring can provide valuable information on disease prevalence and identities of variants, and is growing in application from sources such as wastewater. However, measurements at the building scale, especially for high-risk populations, are often desired, and wastewater access may be challenging. The goal of this project was to use building dust as a convenient and effective matrix for monitoring SARS-CoV-2 prevalence and variants in a campus community. After a brief pilot phase, vacuumed dust was collected weekly from approximately 50 buildings on the Ohio State University’s campus starting in August 2021. SARS-CoV-2 RNA was quantified and sequenced. Detected concentrations spanned four orders of magnitude with most values typically below 100 copies/mg dust. While the Delta variant was dominant, it was estimated that targeting testing of occupants of buildings with high SARS-CoV-2 dust concentrations could have resulted in 50% improved identifications of buildings with at least one case present compared to random selection. Alpha was the dominant variant detected in early 2021. Delta was the primary variant present from fall of 2021 to January 2022, with an average estimated frequency of 91% (±1.3%). Omicron became the primary variant in January 2022 and was the dominant strain through March with an estimated frequency of 87% (±3.2%). Variants detected in dust correlated with circulation in the surrounding population. Overall, these results demonstrate that dust can be used to track COVID-19 in buildings.

Reducing the concentration of infectious viral aerosols within indoor settings is essential for decreasing infectious risk. Common airborne virus concentration reduction approaches, including outdoor air ventilation, HVAC (heating, ventilation, and air conditioning) system filtration, and in-duct ultraviolet germicidal irradiation are limited by the air exchange rates that can be achieved in a building. Similar to drinking water treatment, directly disinfecting a building’s bulk air with a non-toxic disinfectant is a more effective strategy for reducing airborne infection. Bipolar ionization (BPI) is a currently utilized building bulk-air disinfection technology with the potential to reduce airborne virus concentrations through two proposed mechanisms: facilitating particle agglomeration to increase virus deposition onto surfaces (out of occupant breathing zones), and loss of viral infectivity caused by ion-induced damage to viral surface proteins. We determined BPI-mediated first order inactivation rate coefficients for aerosolized bacteriophage Ф6, a common surrogate organism for SARS-CoV-2. At ~50% relative humidity (RH), when average bipolar ion exposure was increased from a baseline of 10³ ions cm^-3 to experimental conditions of 10⁶ ions cm^-3, the total (0.15 min^-1 to 0.22 min^-1; p<0.01) and infectious (0.31 min^-1 to 0.50 min^-1; p<0.01) Ф6 decay rate coefficients increased. While we observed no difference in total Ф6 decay rates at lower RH values (~26%) (p>0.05) between the two ion concentrations, the inactivation of infectious Ф6 owing to BPI remained significant but lower than the values measured under ~50% RH. At both RH levels, the inactivation attributable to BPI was lower than the inactivation attributable to natural decay.

The potential for masks to act as fomites in the transmission of SARS-CoV-2 has been suggested but not demonstrated experimentally or observationally. In this study, we aerosolized a suspension of SARS-CoV-2 in saliva and used a vacuum pump to pull the aerosol through six different types of masks. SARS-CoV-2 lost all detectable infectivity within 1 hour at 28°C and 80% RH on an N95 and surgical mask, but remained infectious on a polyester mask, two different cotton masks, and a nylon/spandex mask when recovered by elution in a buffer. SARS-CoV-2 RNA remained stable for 1 hour on all masks. We pressed artificial skin against the contaminated masks and detected the transfer of viral RNA but no viable virus to the skin. The potential for masks contaminated with SARS-CoV-2 aerosols to act as fomites appears to be less than indicated by studies involving inocula with very large droplets.

Indoor surfaces play important roles in indoor air quality due to the high surface area to volume ratios in our homes. These films are formed from the deposition of aerosol particles and the sorption of semi-volatile organic compounds and are thus often complex mixtures of organic chemicals. The chemical complexity can expand even further after film formation as the chemicals in the mixture react and age on the surface. The composition of these films will play a role in their behavior indoors, so an improved understanding of the important chemical classes found in these films will help model predictions for partitioning of organic chemicals in indoor air. Important sources for chemicals in these films are food cooking, cleaning, and aerosol particles from wildfires. Food cooking can be a large source for semi-volatile and lower volatility organic chemicals. Cleaning processes can generate aerosol particles and leave behind lower volatility material on indoor surfaces. Depending on the distance of the building from the fire, biomass burning organic aerosol particles (BBOA) can reach indoor spaces at different levels of aging. Here, we investigate the chemical composition of surface films formed during different activities on impermeable surfaces. We also investigate the correlations between this composition, and the composition of size resolved aerosol particles collected at the NIST test house during the CASA field campaign.

Particle deposition in the respiratory tract occurs in different patterns depending on particle characteristics and an individual's respiratory mechanics. In this study, aerosolized CuO nanoparticles (CuONPs) were deposited in four patterns onto A549 cells cultured at the air-liquid interface via the Dosimetric Aerosol in Vitro Inhalation Device (DAVID). ImageJ analysis showed the deposition areas corresponding to spots, ring, rectangle, and circle patterns were ~10, 27, 7 and 68% of the cell culture insert’s area. The doses delivered to the cells were estimated from the mass of Cu quantified by Inductively Coupled Plasma-Optical Emission Spectrometry (ICP-OES) following acid digestion, and the surface area of the cell culture insert (for global dose) or the deposition area corresponding to each pattern (for regional dose). Global doses of ~18±6 to 64±8, 19±3 to 73±10, 11±1 to 43±8 and 10±3 to 38±6 µg/cm² were recorded for spots, ring, rectangle, and circle, respectively, for exposure time of 10-, 20- and 30-min. The percent proliferation of the cells, measured using alamarBlue assay, declined with increasing doses of CuONPs. Correlating the regional dose with the percent proliferation revealed the deposition pattern had an impact on the cellular response, with the rectangular and circular patterns being the most and least toxic, respectively, at the highest regional dose delivered. Correlating the cell proliferation with global doses showed variabilities in proliferation rate, suggesting potential cellular signaling, i.e., communication between cells is response to their environment. The study highlights the importance of deposition pattern in in vitro inhalation toxicology.