Effects of simulated atmospheric aging on bioaerosol chemistry in the aqueous phase

Despite the growing importance of atmospheric aerosols of biological origin (bioaerosols) with the warming climate, little is known about bioaerosol chemical composition and their atmospheric fate (e.g., photochemical aging). This study uncovers how laboratory-simulated atmospheric aging alters bioaerosol chemical functional groups, and therefore affects their polarity. Lodgepole pine pollen and Spirulina alga bioaerosols, which represent typical bioaerosols, were extracted and exposed to (1) simulated solar radiation, ranging from 300 to 800 nm, and (2) OH radicals formed from hydrogen peroxide through photolysis. The bioaerosol extracts were analyzed by proton nuclear magnetic resonance ( 1 H-NMR) and Fourier-transform infrared (FTIR) spectroscopy before and after aging to determine the chemical transformation that occurred during the two different types of aging. FTIR results indicated an overall increase of polar functional groups’ signal in comparison to non-polar functional groups after light aging. The largest increase for both bioaerosols was the OH/CH ratio, with a 30.9% increase in lodgepole pine pollen and a 27.5% increase in Spirulina . On the other hand, 1 H-NMR results showed no significant changes in the bioaerosol extracts after light aging, whereaus after photooxidative aging with OH radicals, 1 H-NMR analysis shows that the polarity and percent distribution of functional groups of both bioaerosols transformed significantly. The formation of -COOH and -CHO functional groups was observed, with an 11.1% increase in lodgepole pine pollen and a 43.0% increase in Spirulina alga. Additionally, we observed a decrease in aliphatic protons (CH), a decrease in α-carbon protons, and an increase in amide protons, all of which suggest fragmentation of proteins in Spirulina upon exposure to OH radicals. • Aqueous bioaerosol chemistry altered by laboratory light and photooxidative aging • Analysis of fresh and laboratory aged bioaerosol extracts were performed using 1 H-NMR and FTIR spectroscopy • 1 H-NMR and FTIR results show an increase in polarity of bioaerosol extracts after OH radical aging • Formation of -COOH and -CHO functional groups observed after aging