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Dissertation
Impacts of convective storms on bioaerosol properties
University of Iowa
Doctor of Philosophy (PhD), University of Iowa
Spring 2026
DOI: 10.25820/etd.008413
Abstract
Biological particles suspended in the atmosphere, also known as bioaerosols, include pollen, bacteria, and fungal spores. Bioaerosols affect the climate and public health through properties including size, ice nucleating ability, and allergens and toxins. With a focus on fungal spores, bacteria, and pollen, this thesis advances understanding of how convective storm-generated cold pools and precipitation impact bioaerosol concentrations and size distributions. These bioaerosol properties and their temporal variation are essential to characterize, because they affect particle lifetime, their deposition in the respiratory tract, and their ability to affect cloud microphysics as ice nucleating particles.To characterize convective storm impacts on bioaerosols, samples and data were collected in a semi-arid grassland environment as a part of the BioAerosols and Convective Storms (BACS) field campaigns in May – June of 2022 (BACS-I) and 2023 (BACS-II) at the Central Plains Experimental Range in Northern Colorado. Convective storm impacts on bioaerosol sizes, concentrations, and types were characterized through a combination of highly time resolved online measurements and molecular-level offline analysis. Daily samples were collected for offline analysis of chemical tracers, ice nucleating particles, pollen, and fungal spores. Single particle fluorescence spectroscopy provided minute-averaged concentrations of fluorescent particles as a proxy for bioaerosols.
Storm-generated cold pools and precipitation demonstrated significant impacts on bioaerosol properties at the CPER site. BACS-I had drought-like conditions and higher concentrations of endotoxin from gram-negative bacteria, while BACS-II had near record rainfall and higher concentrations of mannitol, a fungal spore tracer. For both campaigns, most precipitation events increased fungal spores, based on mannitol concentrations, microscope analysis of spores, and fluorescent particles. Storm-generated cold pools typically enhanced bioaerosol concentrations, with stronger cold pools, as indicated by perturbations of temperature, humidity, and wind speed, increasing bioaerosol concentrations more than weaker cold pools. Propagating speeds, a robust measure of cold pool strength, correlated significantly with peak fluorescent particle concentrations across both campaigns, further supporting the connection between cold pool strength and the magnitude of bioaerosol response. Increases in ice nucleating particles at warm temperatures (-15 C) coincided with convective storms and correlated with mannitol (2.5-10 µm), consistent with fungal spore contributions to ice nuclei.
The effects of convective storms on bioaerosol size distributions were examined for cold pools with and without precipitation. The gust front of a dust storm increased total bioaerosols and particulate matter with no observed bioaerosol enrichment in coarse particles (2.5-10 µm), consistent with lofting of surface particles by strong winds. Cold pools without rainfall enriched coarse mode bioaerosols associated with fungal spores through microscopy and fluorescent particle signatures. Rainfall increased bioaerosol concentrations, adding a fine mode (1-2.5 µm) of bioaerosols compared to cold pools with no rain. In gust fronts, and cold pools with and without precipitation, fungal spores were the dominant bioaerosol type by number in coarse particles. The fine and coarse bioaerosols associated with storms are of sufficient size to enter the respiratory tract, with fine particles able to penetrate deeper and having higher deposition probabilities.
This thesis advances our understanding of how convective cold pools and precipitation impact bioaerosols and biological ice nuclei. The outcomes of this research will aid in future work to constrain bioaerosol emissions and transport during convective storms by demonstrating fungal spore concentrations can be significantly enhanced in storm-generated cold pools and precipitation, each with distinct size distributions. Significant differences in fungal spore composition between campaigns also provides insight into the impacts of longer-term meteorological conditions on bioaerosol populations. More accurate representation of bioaerosol concentrations and sizes can help to inform strategies to mitigate harmful bioaerosol exposures for sensitive populations and to assess the impacts of storm-generated bioaerosols on cloud processes.
Details
- Title: Subtitle
- Impacts of convective storms on bioaerosol properties
- Creators
- Teresa K. Feldman
- Contributors
- Elizabeth A. Stone (Advisor)Alexei V. Tivanski (Committee Member)David M. Cwiertny (Committee Member)Scott K. Shaw (Committee Member)
- Resource Type
- Dissertation
- Degree Awarded
- Doctor of Philosophy (PhD), University of Iowa
- Degree in
- Chemistry
- Date degree season
- Spring 2026
- DOI
- 10.25820/etd.008413
- Publisher
- University of Iowa
- Number of pages
- xvii, 130 pages
- Copyright
- Copyright 2026 Teresa K. Feldman
- Grant note
- I would like to thank the National Science Foundation (AGS-2105938 and AGS-2106370), Research for Global and Regional Environmental Research (CGRER), and the Graduate College for funding during my graduate career.
- Language
- English
- Date submitted
- 04/28/2026
- Description illustrations
- illustrations, tables, graphs
- Description bibliographic
- Includes bibliographical references (pages 116-130).
- Public Abstract (ETD)
A thunderstorm looms in the distance, and before it hits, you feel a gust of cold air. Did you know that this cold gust of air can change the particles in the air you breathe? My research examines how thunderstorms change the types, amounts, and sizes of biological particles in the air which may carry allergens and toxins. This thesis analyzes thunderstorms and airborne biological particles including pollen, fungal spores, and bacteria, in a Colorado grassland during the summers of 2022 and 2023. Fungal spores had much higher concentrations than pollen for both summers, while bacteria had higher concentrations in 2022 than 2023. During a dust event in Colorado, a cold pool of air with fierce winds visibly whipped up large amounts of dust and particles and also increased biological particles in the air. Cold pools of air without rain that had large temperature drops and high winds increased biological particles that deposit in the upper airways, while rainfall also increased smaller biological particles that can travel deep into the lungs. Thunderstorms also increased biological particles that can seed ice in clouds, which can affect cloud properties and precipitation. This thesis shows that thunderstorms can increase human health risks and through their impacts on bioaerosols, thunderstorms can potentially affect cloud properties compared to clear weather.
- Academic Unit
- Chemistry
- Record Identifier
- 9985176869502771
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