AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
Abstract View
Chemical Transformation of Isoprene Epoxydiol-Derived Organosulfates through Heterogeneous OH Oxidation: A Source of Inorganic Sulfate?
Hoi Ki Lam, Kai Chung Kwong, Hon Yin Poon, James F. Davies, Zhenfa Zhang, Avram Gold, Jason Surratt, MAN NIN CHAN, The Chinese University of Hong Kong
Abstract Number: 414 Working Group: Aerosol Chemistry
Abstract Multiphase chemistry of epoxydiols formed from isoprene oxidation yields the most abundant organosulfates (i.e., methyltetrol sulfates) detected in atmospheric fine aerosols. This potentially determines the physicochemical properties of fine aerosols in isoprene-rich regions. To date, the transformation of these organosulfates in the atmopsphere remains largely unclear. We investigate the heterogeneous oxidation of aerosols consisting of potassium 3-methyltetrol sulfate ester (C5H11SO7K) by gas-phase hydroxyl radical (OH) through studying the oxidation kinetics and reaction products at a relative humidity (RH) of 70.8%. Real-time molecular composition of the aerosols is obtained by using a Direct Analysis in Real Time (DART) ionization source coupled to a high-resolution mass spectrometer. Aerosol mass spectra only show increases in the intensity of bisulfate ion (HSO4−) after oxidation, suggesting the absence of functionalization processes that is likely attributable to the steric effect of substituted functional groups (e.g. methyl, alcohol and sulfate groups) on peroxy–peroxy radical reactions. Overall, potassium 3-methyltetrol sulfate ester likely decomposes to form volatile fragmentation products and aerosol-phase sulfate radial anion (SO4•−). SO4•− subsequently undergoes intermolecular hydrogen abstraction to form HSO4−. Given the high atmospheric abundance of organosulfates in atmospheric aerosols, further study of the contribution and transformation of organosulfates to inorganic sulfate through chemical reactions (e.g. heterogeneous oxidation, aqueous-phase oxidation and hydrolysis) is desirable.