AAAR 35th Annual Conference October 17 - October 21, 2016 Oregon Convention Center Portland, Oregon, USA
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Linking the Formation of Dimeric Compounds and Organic Peroxides in the alpha-pinene Ozonolysis System
RAN ZHAO, Yuanlong Huang, Christopher Kenseth, Kelvin Bates, Rebecca Schwantes, Paul Wennberg, John Seinfeld, California Institute of Technology
Abstract Number: 126 Working Group: Aerosol Chemistry
Abstract The identity and formation mechanism of high molecular weight organic compounds (e.g. dimers) and organic peroxides (ROOHs) in secondary organic aerosol (SOA) arising from alpha-pinene ozonolysis remain missing aspects to complete our understanding of the alpha-pinene ozonolysis reaction system. Formation of dimers and ROOH have each received much attention separately, but little is known about the links between the two. Certain types of dimers and organic peroxides (e.g. peroxyhemiacetals, diacylperoxides) can be overlapping compounds arising from common formation mechanisms. In this study, we investigate the formation of dimers and ROOHs arising from alpha-pinene ozonolysis using a laminar flow tube reactor, the Caltech Photo-Oxidation Tube (CPOT), as well as the 24 cubic meter Caltech chamber. The CPOT maintains a strict laminar flow and well-controlled temperature/RH conditions, facilitating a systematic investigation of the yields of dimers and ROOHs under a variety of experimental conditions. The chamber experiments represent more ambient-like conditions and provide temporal profiles of dimers and ROOHs. Offline samples are collected from the CPOT and the chamber via filter collection and particle-into-liquid sampling (PILS), respectively. Dimeric compounds in the offline samples are analysed by Ultra Performance Liquid Chromatography Electrospray Ionization Time-of-flight Mass Spectrometry (UPLC/ESI-Q-TOFMS). ROOH concentrations are analyzed by potassium iodide (KI) assay and a high performance liquid chromatography (HPLC) – fluorescence technique. The KI assay determines the total organic peroxides, and the HPLC-fluorescence technique separates and quantifies H$_2O$_2, with the difference of the two techniques representing the ROOH concentrations. The correlations between dimers and ROOHs are evaluated for the first time, and possible formation mechanisms of dimers and ROOHs are discussed based on the observed trends.