3D Chemical Imaging Reveals Surface and Internal Heterogeneity of Airborne Fungal Spores

ZEZHEN CHENG, Yingxiao Zhang, Gregory W. Vandergrift, Ashfiqur Rahman, Xena Mansoura, Valentina Sola, Tasneem Ahmadullah, Nurun Nahar Lata, Erin Bredeweg, Payton Beeler, Laura Fierce, Darielle Dexheimer, Qi Zhang, Alexander Laskin, Jerome Fast, Fan Mei, Scott Baker, Allison Steiner, Swarup China, Zihua Zhu, Pacific Northwest National Laboratory

     Abstract Number: 287
     Working Group: Bioaerosols

Abstract
Fungal spores are an important component of primary biological aerosol particles, which play important roles in the Earth system. However, there are still limited observations on airborne fungal spores to understand their physicochemical properties. Even fewer are the model simulations to understand their effects on the Earth system. Here, we utilized experimental observation and WRF-Chem simulation to understand the fungal spores' physicochemical properties and their contribution to atmospheric aerosols. We utilized the state-of-the-art Time-of-flight secondary ion mass spectrometry (ToF-SIMS) coupled with the Ar cluster ion sputtering technique to investigate fungal spores' 3D chemical composition. Samples were collected at the Department of Energy's (DOE) Atmospheric Radiation Measurement (ARM) field campaign at the Southern Great Plains (SGP) atmospheric observatory (mega-site, 36.61° N, 97.49° W) on October 14th, 2021. Chemically resolved size distribution shows that more than 25% of coarse particles were biological aerosol particles. ToF-SIMS results reveal that there are two categories of fungal spores. 50% of fungal spores have less Na at the surface, and their cytoplasm is liquid fatty acid (oleic acid and palmitic acid from Triacylglycerol (TAG) fragment signals), which suggests they might be germinating. The fragments from this category of fungal spores might be an important source of airborne fatty acids. Conversely, the rest of the fungal spores have a high Na concentration at the surface, and their cytoplasm is solid or semisolid, suggesting they might be dormant. Moreover, we simulated the fraction of airborne dormant and germination fungal spores at SGP from October 12-15 based on the literature temperature and relative humidity thresholds for surface-deposited fungal spore germination. Results show that there will be consistently higher concentrations of germination fungal spores than dormant ones, which is higher than our observation. This underscores the importance of understanding the environmental conditions for airborne fungal spores to germinate.