Impact of Relative Humidity on Chemical Transformations in Biomass Burning Organic Aerosol (BBOA) Particles During Long-term Photolysis-driven Aging
JANIE (YEASEUL) KIM, Willow Hwang, Manjula Canagaratna, Benjamin A. Nault, Anita Avery, Mitchell Alton, Lisa Azzarello, Elise Palombella, Christopher Cappa, Cora Young, Rachel O'Brien, University of Michigan
Abstract Number: 343
Working Group: Aerosol Chemistry
Abstract
Biomass burning organic aerosol (BBOA) particles can travel long distances and eventually arrive in urban areas where they are often deposited on outdoor surfaces. During transport and after deposition, one of the key aging pathways for these aerosols is photolysis-driven aging under sunlight. Throughout this process, the chemical composition of BBOAs can be altered, potentially changing their behavior and interactions with the surrounding environment. Previous studies suggest that water in humid conditions can act as a plasticizer, enhancing molecular mobility and possibly accelerating chemical reactions.
In this study, we conducted controlled long-term photolysis experiments on fresh BBOA samples under both dry and humid conditions. Additionally, we examined the aging of re-atomized water-soluble fractions of BBOA particles to reflect their potential cloud processing during atmospheric transport. Given their hydrophilic properties and increased water uptake in humid environments, these water-soluble fractions may experience distinct photolytic reaction pathways.
To characterize molecular-level changes, we applied complementary analytical techniques, including high-resolution Electrospray Ionization Orbitrap mass spectrometry (ESI-Orbitrap-MS), Aerosol Mass Spectrometry (AMS), and Size Exclusion Chromatography with UV detection (SEC-UV). These methods allowed detailed assessments of functional group alterations, shifts in molecular weight distributions, changes in carbon oxidation states, and variations in light absorption properties.
This work provides new insights into how relative humidity influences the photolysis-driven aging of fresh and water-soluble BBOA particles. By linking environmental conditions to chemical transformation pathways, this study will improve our understanding of how aged BBOA contributes to air quality and climate change during and after long-range transport.