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SOA Formation in Mixed Oxidant (OH + Cl) Environments
NIRVAN BHATTACHARYYA, Mrinali Modi, Lea Hildebrandt Ruiz, University of Texas at Austin
Abstract Number: 298
Working Group: Aerosol Chemistry
Abstract
Chlorine radicals are part of a complex oxidant mixture in the troposphere. Cl both competes with and produces hydroxyl radicals during oxidation of volatile organic compounds (VOCs). Here we study secondary organic aerosol (SOA) formation from mixed oxidant (Cl + OH) chemistry, using m-xylene as a model VOC. Mixed oxidant environments can be generated several ways, and chemical box modeling showed that ClNO2 experiments form similar amounts of Cl and OH oxidized m-xylene. Environmental chamber experiments were conducted using Cl2, ClNO2, and H2O2 as radical sources for Cl, Cl + OH, and OH oxidation experiments. SOA composition assessed using an iodide mode, chemical ionization mass spectrometer (I- FIGAERO-CIMS) showed clear differences based on radical source. Organochloride formation was observed in Cl experiments, indicating that Cl oxidized later-generation products since Cl + xylene oxidation occurs via hydrogen abstraction, not chlorine addition. SOA formed from ClNO2 and H2O2 radical sources had a smaller average carbon number and was more highly oxidized than SOA formed in Cl2 experiments. SOA yields from the Aerosol Chemical Speciation Monitor (ACSM) were higher for experiments without NOX. The dynamics of these mixed radicals on SOA formation and composition may have a significant impact on outdoor air.