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Superoxide Formation from Aqueous Reactions of Biogenic Secondary Organic Aerosols
JINLAI WEI, Ting Fang, Cynthia Wong, Pascale Lakey, Sergey Nizkorodov, Manabu Shiraiwa, University of California, Irvine
Abstract Number: 45
Working Group: Aerosol Chemistry
Abstract
Biogenic secondary organic aerosols (SOA) account for a substantial fraction of atmospheric particulate matter, posing significant impacts on air quality, climate and public health. Reactive oxygen species (ROS) including OH, superoxide, and H2O2 play a central role in aqueous-phase processing and health effects of SOA. Recent studies have revealed that biogenic SOA can release ROS in the aqueous phase, but kinetics and reaction mechanisms of superoxide formation is rarely quantified and hardly understood. Here we present simultaneous measurements of hydroxyl radical and superoxide from aqueous reactions of SOA generated by ozonolysis and OH oxidation of biogenic VOCs using electron paramagnetic resonance spectrometry. Kinetic modeling reproduced temporal evolution of OH and superoxide formation by considering decomposition of organic hydroperoxides, OH oxidation of alcohols, and unimolecular decomposition of α-hydroxyperoxyl radicals. SOA generated from ozonolysis tend to contain higher fractions of peroxides leading to a OH-dominated profile with molar yields of up to ~0.1%, while SOA generated from OH photooxidation mainly form with molar yield of 0.1-0.7% depending on precursors. These findings have significant implications on the atmospheric fate and particle-phase reactions of highly oxygenated molecules, affecting their role in particle formation and chemical transformation of organic aerosols. In addition, inhalation and deposition of SOA particles may lead to a substantial release of superoxide in lung lining fluid, which may contribute to oxidative stress in the human respiratory tract.