10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
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Formation of Highly Oxidized Multifunctional Organic Compounds from Chlorine Atom Initiated Oxidation of α-pinene
Yonghong Wang, MATTHIEU RIVA, Xie Hongbin, Liine Heikkinen, Simon Schallhart, Otso Peräkyla, Chao Yan, Markku Kulmala, Mikael Ehn, University of Helsinki
Abstract Number: 615 Working Group: Aerosol Chemistry
Abstract Highly oxygenated molecules (HOMs) from the oxidation of monoterpenes in the atmosphere can irreversibly condense onto particles and contribute to secondary organic aerosol formation. Recently, the formation of nitryl chloride (ClNO2) from heterogeneous reactions, and subsequent photolysis, to produce chlorine atoms is suggested to be extensive not only in coast area, but also in urban region. However, the oxidation of monoterpenes such as α-pinene by chlorine radicals has received very little attention, and the ability of this reaction to form HOMs is completely unstudied. Here, chamber experiments were conducted with a-pinene and chlorine gas under low NO and high NO conditions, respectively. A NO3-based CI-APi-L-TOF was used to measure highly oxidized products. Clear distributions of monomers with 9-10 carbon atoms and dimers with 18-20 carbon atoms were observed under low NO conditions. With increased concentration of NO in the chamber, the formation of dimers was suppressed due to the competing reactions of peroxy radicals with NO. We calculated the HOM yields from chlorine-initiated oxidation of a-pinene under low NO conditions, while the yield at high NO could not be determined because of interference from ozone produced from the NOx, which subsequently reacted with a-pinene. Our study demonstrates that chlorine radical initiated oxidation of a-pinene will produce low volatility organic compounds, such as HOMs, which indicates that autoxidation processes in chlorine radical oxidation of a-pinene can be important. Further analysis will provide insights on the expected importance of the studied reactions in the atmosphere.