The Peroxy Radical Fates during Heterogeneous Oxidation of Organic Aerosols

WEN ZHANG, Chuanyang Shen, Haofei Zhang, University of California, Riverside

     Abstract Number: 58
     Working Group: Aerosol Chemistry

Abstract
The heterogeneous oxidation of organic aerosols (OA) in the atmosphere can have a great impact on the air quality, climate, and human health. In previous studies of heterogeneous chemistry, flow tube reactors are commonly used as the tool to study the kinetics and aging mechanisms, which create an environment with high OH concentrations ([•OH]) and short reaction time (τ, seconds to a few minutes), to mimic the OH exposure level (= [•OH] × τ) in the real atmosphere. Through these traditional studies, the main heterogeneous mechanisms were found to be peroxy radical (RO2•) centered chemistry including RO2• self-reactions to form an alcohol-carbonyl pair or two alkoxy radicals (RO•). However, it remains unclear whether [•OH] and τ are exchangeable. In this work, we perform •OH-initiated heterogeneous oxidation of OA model systems in a continuous flow stirred tank reactor (CFSTR) to bring the OA heterogeneous oxidation from typical laboratory [•OH] much closer to ambient levels. Besides, we also control the gas-phase concentrations of HO2 and NO to study their reactions with RO2• during the heterogeneous oxidation. The aging kinetics of OA systems and their product composition are measured in real time using a thermal desorption chemical ionization mass spectrometer (TD-CIMS) with iodide as the reagent ion. An offline ion mobility spectrometry mass spectrometer (IMS-MS) with electrospray ionization is used for an isomer-resolved characterization of oxidized OA systems. Using this experimental setup and instruments, we can explore new reaction pathways centered on interfacial RO2• and study aerosol heterogeneous kinetics under conditions that are closer to the real atmosphere.