AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
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Kinetics and Equilibria for the Multiphase Formation of Hemiacetals and Peroxyhemiacetals
JULIA BAKKER-ARKEMA, Megan Claflin, Paul Ziemann, University of Colorado
Abstract Number: 624 Working Group: Aerosol Chemistry
Abstract Volatile organic compounds (VOCs) are emitted into the atmosphere and subsequently oxidized to form a variety of products containing carbonyl, carboxyl, hydroxyl, and hydroperoxy functional groups, many of which can partition into the particle phase to form secondary organic aerosol (SOA). Studies suggest that these products have the potential to undergo heterogeneous and multiphase reactions, and that these processes can influence the formation, composition, and physical-chemical properties of the aerosol phase. Due to the effects of organic aerosols on climate, air quality, and human health, many explicit chemical mechanisms have been developed to model the gas-phase oxidation of VOCs to form SOA in laboratory studies and in the atmosphere. However, these models largely fail to include the subsequent heterogeneous and multiphase chemistry that can occur within and on the surface of aerosol particles because there is limited experimental data providing the necessary kinetics, equilibria, and ambient concentrations of reactants and catalysts to properly model these reactions. In this work, we investigated two multiphase systems: the reactions of alcohols and carbonyls to generate hemiacetals, and the reactions of hydroperoxides and carbonyls to generate peroxyhemiacetals. Alcohol and hydroperoxide precursors were synthesized in the laboratory with a terminal nitrate group to provide a chromophore. Precursors were subsequently reacted with various carbonyl sources including ketones, aldehydes, and SOA generated in the laboratory from the ozonolysis of alpha-pinene with and without the presence of a catalyst. Reaction mixtures were analyzed by reversed-phase liquid chromatography with UV-Vis detection monitoring at 210 nm, where the terminal nitrate group demonstrates a strong absorbance. Products were collected and identified using electrospray ionization time-of-flight mass spectrometry (ESI-TOFMS). Forward and reverse rate constants and equilibrium constants were determined for each reaction. Together, these results improve our understanding of the heterogeneous and multiphase chemistry that can occur in SOA, and going forward will allow chemical models to more accurately capture SOA formation and composition.