AAAR 36th Annual Conference October 16 - October 20, 2017 Raleigh Convention Center Raleigh, North Carolina, USA
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High Molecular Weight Dimeric Products from α-pinene Oxidation: Molecular Composition, Formation Mechanisms, and Implications for Particle Formation and Growth
YUE ZHAO, Emma L. D'Ambro, Megan McKeown, Jiumeng Liu, John Shilling, Joel A. Thornton, University of Washington, Seattle, WA
Abstract Number: 644 Working Group: Aerosol Chemistry
Abstract Recent studies have shown that high molecular weight dimeric compounds formed from atmospheric oxidation of biogenic emissions constitute a significant source of low-volatility organic compounds in secondary organic aerosol (SOA) and play an important role in particle formation and growth as well as in controlling the volatility of the particles. However, the underlying mechanisms forming these dimeric compounds remain largely unclear. Although plausible mechanisms involving reactions of stabilized Criegee intermediates (SCI), organic peroxy radicals, and monomeric end products either in the gas or particle phase have been proposed, unambiguous elucidation of these formation pathways and their relative importance is still rather limited. Here we present a detailed experimental investigation of ozonolysis of α-pinene both in a flow reactor and in a continuous-flow environmental simulation chamber, with a focus on the formation mechanisms of dimers and their role in the initial stage of SOA formation. A high resolution time-of-flight chemical ionization mass spectrometer (HRToF-CIMS) utilizing iodide-adduct ionization coupled to the Filter Inlet for Gases and Aerosols (FIGAERO) was used for simultaneous measurement of the gas and particle composition. Another iodide-adduct HRToF-CIMS coupled to an orthogonal atmospheric pressure ion-molecule reaction (IMR) chamber was also deployed to measure the molecular composition of dimers in the gas phase with minimum wall losses of these extremely low-volatility species in the sampling inlet and IMR. The effects of water vapor, SCI and OH scavengers, nitric oxide, and ammonium sulfate seed particles on the formation and gas vs. particle phase distribution of dimers are examined. Implications for particle formation and growth are discussed.