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Product Formation and Kinetics of Heterogeneous Hydroxyl Radical (OH) Oxidation of IEPOX-Derived SOA
JIN YAN, Yue Zhang, Yuzhi Chen, N. Cazimir Armstrong, Marc Webb, Zhenfa Zhang, Avram Gold, Andrew Lambe, Andrew Ault, Jason Surratt, University of North Carolina at Chapel Hill
Abstract Number: 418
Working Group: Aerosol Chemistry
Abstract
Isoprene is the most abundant non-methane volatile organic compound emitted globally. Isoprene epoxydiols (IEPOX), key photooxidation products of isoprene under low-nitric oxide (NO) conditions, can form secondary organic aerosols (SOA) through acid-enhanced multiphase chemical reactions with inorganic sulfate particles (Sulfinorg). Through converting Sulfinorg to organosulfates (OSs), this reaction changes physicochemical properties (e.g., thickness of organic shell and viscosity) of pre-existing aerosols over time. Our recent study demonstrated that heterogeneous hydroxyl radical (OH) oxidation of the major IEPOX-derived SOA components, 2-methyltetrol sulfates, generates more oxygenated OSs. To accurately describe the evolution of IEPOX-derived SOA in the atmosphere, this study explores the impacts of aerosol acidity and physicochemical properties on the heterogeneous oxidation rate of IEPOX-derived SOA so as to incorporate the results into a chemical kinetic model.
In this study, IEPOX will be reacted with Sulfinorg in a flow tube reactor to form IEPOX-derived SOA with different acidities and physicochemical properties by altering Sulfinorg acidity and its reaction time with IEPOX. The fresh SOA will be subsequently aged in an oxidation flow reactor at varying ambient-relevant OH exposures under low-NO conditions. The aged SOA will be sampled by an online aerosol chemical speciation monitor (ACSM) and collected onto Teflon filters for molecular-level analyses by a recently developed hydrophilic liquid interaction chromatography method interfaced to high-resolution quadrupole time-of-flight mass spectrometry equipped with electrospray ionization (HILIC/ESI-HR-QTOFMS). Measured chemical composition will facilitate developing a kinetic model for the oxidation of fresh IEPOX-derived SOA parameterized by OH exposure and a set of parameters describing properties of IEPOX-derived SOA. To further separate and group oxidation products based on reaction pathways, a positive matrix factorization (PMF) technique will be applied to cross-compare with the kinetic model.