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Characterization of Fluorescent Bioaerosols Under Extreme Weather Conditions
DAGEN HUGHES, Chamari Mampage, Lillian Jones, Zehui Liu, Elizabeth Stone, University of Iowa
Abstract Number: 597
Working Group: Bioaerosols
Abstract
Although rainfall washes pollen grains from the atmosphere, rain can also osmotically rupture pollen to produce submicron pollen fragments that may carry allergens. Through a multi-platform field campaign based in Iowa City, IA in the spring of 2019, we combined single-particle fluorescence spectroscopy (WIBS-NEO) with offline measurements of chemical tracers and intact pollen grains to provide the first online characterization of pollen fragments in the atmosphere. Collocated measurements were compared with the WIBS-NEO to characterize the size-dependent fluorescence signal of pollen fragments. A convective thunderstorm during tree pollen season (May 18) increased the submicron fluorescent particle concentration from 0.1 cm-3 to a local maximum of 1.3 cm-3. At their peak, 34% of submicron particles fluoresced compared to only 5% prior to the storm, indicating their enrichment relative to other particle types. These fluorescent particles were identified as pollen fragments using size-resolved mass concentrations of fructose, hourly pollen grain concentrations, and light microscopy. The increase in pollen fragments during the thunderstorm can be explained by the osmotic rupturing of pollen grains in the atmosphere and subsequent transfer to the Earth’s surface by precipitation downdrafts. Though the thunderstorm was brief, the fluorescent signal from pollen fragments remained elevated for more than 11 hours. Pollen fragments were also observed in stratiform precipitation and other convective thunderstorms during the tree and weed pollen seasons. The pollen fragments observed by the WIBS-NEO ranged in optical diameter from 0.5–3.0 µm with the greatest concentrations observed at the lower size limit of the instrument suggesting a high concentration of pollen fragments in particles < 0.5 µm. Understanding the concentrations, properties, and occurrence of pollen fragments in the atmosphere is important because they represent an under-characterized aerosol source and their size affects their atmospheric lifetime, climate-relevant properties, and ability to penetrate into the human respiratory tract.