(42a) Photoactivated SOA Formation: Mechanistic Insight from Modeling and Experiments
Reactions in or on aerosol particles involving the participation of light-absorbing organic aerosol species as photoactivators have been suggested as pathways for the photochemical processing of volatile organic species (Yu and Keutsch, 2012; Monge et al., 2012; Aregahegn et al., 2013, Rossignol et al. 2014), leading to the efficient formation of secondary organic aerosol (SOA) material. Additional insight into the mechanisms and kinetics of these processes is required so that we may evaluate their importance on the regional and global scales via atmospheric chemistry modeling. We have used a combination of bulk phase and surface-specific spectroscopy, density functional theory, and box modeling to this end. Bulk flash photolysis kinetics studies, along with the surface-active nature of many likely photoactivator species, show that this chemistry most likely occurs at the gas-aerosol interface. Analysis of published aerosol chamber data using our photochemical box model, GAMMA, shows evidence for SOA formation from glyoxal via photoenhanced fulvic acid and, to a lesser degree, particle-phase products of glyoxal SOA formation. Finally, density functional theory provides insight to candidate photoactivator-VOC pairs, demonstrating the general nature of this phenomenon.