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Aqueous Photochemistry of Synthesized Pinene-Derived Carboxylic Acids and Dimer Esters
CHRISTOPHER KENSETH, Yuanlong Huang, Nathan Dalleska, John Seinfeld, California Institute of Technology
Abstract Number: 608
Working Group: Aerosol Chemistry
Abstract
Atmospheric aqueous phases (i.e., cloud, fog, and aerosol liquid water) constitute important reaction media for (photo)chemical processing of water-soluble compounds in secondary organic aerosol (SOA). Monoterpenes (C10H16), emitted in large quantities from terrestrial vegetation (~150 Tg y−1), represent a dominant source of SOA globally. Multifunctional carboxylic acids and dimer esters have been identified as significant components of both laboratory-derived and ambient monoterpene SOA, and are expected to be sufficiently water soluble to undergo aqueous-phase processing. Due to a lack of authentic standards, however, aqueous-phase studies of such compounds have been limited, almost exclusively, to commercial terpenoic acids (e.g., cis-pinonic acid). Here, we investigate the aqueous-phase photooxidation (kinetics, products, and mechanisms) of six recently synthesized, enantiopure, pinene-derived carboxylic acid and dimer ester homologues, at cloudwater-relevant concentrations, using liquid chromatography/negative electrospray ionization mass spectrometry [LC/(−)ESI-MS] together with MS/MS analysis and H/D exchange. Characterization of the OH reactivity of the carboxylic acids and dimer esters, which respectively differ only in the identity of the terminal functional group (i.e., ketone vs. carboxylic acid vs. alcohol), affords detailed insight into the dependence of aqueous-phase photochemical processing on both molecular size and functionality, as well as evaluation of structure-activity relationships (SARs) for aqueous-phase OH oxidation of monoterpene SOA constituents.