Photochemistry of Atmospheric Bioaerosols

The chemistry and atmospheric fate of biological aerosols (bioaerosols) have been largely unexplored, despite their significant contribution to atmospheric particulate matter and organic carbon. Although bioaerosols are typically larger than anthropogenic aerosols, up to 100 µm, they can be transported over long distances and thus affect cloud physics (CCN, IN) and play a role in atmospheric chemical reactions. Studies have found that bioaerosols are expected to increase in concentration due to rapid climate change. For example, pollen concentrations are anticipated to increase by 21% and the pollen season length to increase by 21 days. Further, increases in instances and intensities of harmful algal blooms are already being observed. Due to the growing importance of bioaerosols in the atmosphere and climate, the goal of this study was to determine the effects of simulated atmospheric aging on bioaerosol functional groups and polarity. Water extracts of bioaerosols, lodgepole pine pollen and spirulina algae, were aged in a Suntest CPS solar simulator for 24 hours, under simulated solar radiation and in the presence of  H₂O₂ to promote oxidation with OH radicals. Proton Nuclear Magnetic Resonance Spectroscopy(¹H-NMR) and Fourier-Transform Infrared Spectroscopy (FTIR) analyses were performed for fresh and aged bioaerosol extracts. FTIR results show an increase in polarity of both bioaerosols after aging with simulated solar radiation, up to 30.9% in pollen and 27.5% in algae, whereas ¹H-NMR results are more complex, and a clear polarity increase was not observed. To our knowledge, this is the first study to analyze the effects of atmospheric aging on the chemistry of bioaerosols.