Concentrated and Viable: Improved Bioaerosol Sampling via Virtual Impactor Enhanced Water Condensation Collection

DREW JONES, Emily Kraus, Kristin Rugh, Mark Hernandez, Marina Nieto-Caballero, Sonia Kreidenweis, Shantanu Jathar, Colorado State University

     Abstract Number: 549
     Working Group: Bioaerosols

Abstract
Water condensation-based air samplers can collect bioaerosols with high efficiency while avoiding issues with filter-based sampling, for example desiccation and the need for subsequent extraction from the filter before analysis. However, direct comparison between the methods is complicated by a magnitude or more difference in sampling flowrates. Virtual impactors can concentrate the sampled air, permitting condensation-based sampling at greater equivalent flowrates for particle sizes above the virtual impactor’s cut-point. A virtual impactor was designed based on the work of Romay et al. (2002), using a single multi-nozzle opposing jet layout. The virtual impactor’s 50% cut-point and concentration factor were characterized with non-biological aerosols. The virtual impactor was integrated with a water condensation-based sampler, the Aerosol Devices BioSpot GEM. The bioaerosol collection performance of the combined concentrator/sampler was then compared with unmodified samplers in chamber studies using both gram-negative and gram-positive aerosolized bacteria in separate trials. Further field testing was carried out in Fort Collins, CO in the Summer of 2025. The total amount of genetic material collected by each sampler was quantified using qPCR. PMA-qPCR was utilized to measure cell membrane damage. Microscopy using live-dead staining was also used to gain insights about sampler consistency. The virtual impactor was demonstrated to be capable of concentrating the sampled bioaerosols without significantly affecting the bioaerosol sample integrity. The implication of this research is the availability of a different method of bioaerosol sampling where low ambient concentrations would have previously required the use of higher flowrate filter-based samplers.