Wet Deposition of Bioaerosol Tracers

JANESHTA FERNANDO, Teresa Feldman, Chamari Mampage, Claudia Mignani, Marina Nieto-Caballero, Thomas Hill, Brian Heffernan, Christine Neumaier, Tyler Barbero, Charles Davis, Lexi Sherman, Ben Ascher, Jacob Escobedo, Nick Falk, Sean Freeman, Gabrielle Leung, Allie Mazurek, Daniel Veloso-Aguila, Leah Grant, Susan van den Heever, Russell Perkins, Paul DeMott, Sonia Kreidenweis, Elizabeth Stone, University of Iowa

     Abstract Number: 527
     Working Group: Bioaerosols

Abstract
The BioAerosols and Convective Storms (BACS) field campaigns examine the exchange of bioaerosols between the terrestrial biosphere and atmosphere. The objectives of this study are to evaluate bioaerosol wet deposition and the extent of below- and in-cloud scavenging. Chemical tracer analysis provides insight to three classes of bioaerosols: fungal spores by mannitol; gram-negative bacteria by endotoxins; and pollen and plant matter by fructose, glucose, and sucrose. Samples were collected in the Central Plains Experimental Range in Northern Colorado from May-June of 2022 and 2023. In 2022, cumulative precipitation was 10 mm across five rain events during a 26-day campaign period. In contrast, 2023 experienced significantly higher rainfall, with 119 mm accumulated from 21 rain events over a 32-day period. Increased precipitation and ambient fungal spore and mannitol concentrations in 2023 contributed to significantly higher and more variable wet deposition of fungal spores compared to 2022, while carbohydrate wet deposition per rain event remained consistent across both years. Below-cloud scavenging was estimated from bioaerosol tracer concentrations at the surface, using three different assumptions for the vertical profile: vertical distributions were well-mixed, decreased slightly with altitude, and were enhanced in an aerosol layer detected at 120 m above the surface by drones. Upper estimates of below-cloud scavenging consistently accounted for less than 25% of total bioaerosol tracer wet deposition, suggesting that in-cloud scavenging is the dominant process contributing to wet deposition. These results imply a significant fraction of atmospheric bioaerosol aerosol is present in clouds, where they act as cloud condensation nuclei or ice nucleating particles and are subsequently removed through precipitation.