Abstract View
Volatile Organic Acid Formation from the Aqueous and Heterogeneous Oxidation of Isoprene-Derived Organic Aerosol Compounds
James Cope, Karizza Abellar, Kelvin Bates, Xuan Fu, TRAN NGUYEN, University of California, Davis
Abstract Number: 406
Working Group: Aerosol Chemistry
Abstract
Mixing ratios of formic acid (FA) and acetic acid (AA) are often underestimated in atmospheric models, particularly over areas with high biogenic influence. Although FA and AA formation has been suggested from the aging of biogenic organic aerosols, quantitative yields have remained elusive. This presentation discusses the FA and AA yields and formation pathways from the hydroxyl radical (OH) oxidation of major isoprene-derived organic aerosol compounds: 2-methyltetrols (2-MT) and 2-methytriolsulfates (2-MTS). We studied the aqueous OH radical oxidation of 2-MT and 2-MTS in bulk aqueous solution, as well as the heterogeneous OH oxidation of 2-MTS and a lower-volatility analog of 2-MT in suspended aerosol particles mixed with ammonium sulfate. 1H and 13C nuclear magnetic resonance (NMR) spectroscopy, high-performance liquid chromatography coupled with high-resolution mass spectrometry (HPLC-HRMS) were used to quantify organic acid yields. We demonstrate that the photochemical reactions of 2-MT, 2-MTS, and their chemical analogs are strong sources of small acids. Partitioning into the gas phase significantly effects aqueous yields. pH in the bulk aqueous phase, and aerosol water in the suspended particles, also have strong influence on the yields of organic acids. These related aerosol/bulk properties control the dissociation equilibria of organic acids, which affects both partitioning and oxidation chemistry. Kinetics, yields, product distribution, and reaction mechanisms will be discussed.