AAAR 35th Annual Conference October 17 - October 21, 2016 Oregon Convention Center Portland, Oregon, USA
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Highly Oxidized Multifunctional Compounds in Oxidation of Aromatics; a Step Forward in Understanding Urban SOA
OLGA GARMASH, Matti Rissanen, Oskari Kausiala, Iida Pullinen, Sebstian Schmitt, Thomas F Mentel, Astrid Kiendler-Scharr, Jürgen Wildt, Einhard Kleist, Mikko Sipilä, Markku Kulmala, Mikael Ehn, University of Helsinki
Abstract Number: 404 Working Group: Aerosol Chemistry
Abstract Aromatic compounds are thought to be one of the main precursors of secondary organic aerosol (SOA) in urban areas. In previous studies, discrepancies in SOA yields from oxidation of aromatic compounds have been observed. The aim of this study was to connect the gas-phase chemistry to the formation of SOA from aromatics by measuring the selected oxidation products; more specifically, highly oxidized multifunctional compounds (HOM). Measurements were conducted at the Jülich Plant Atmosphere Chamber (JPAC) where benzene oxidation was studied and in the flow-tube at the University of Helsinki where the formation of HOM in the oxidation of several aromatics (benzene, toluene and naphthalene) was investigated. The gas-phase HOM were detected using a Chemical Ionisation Atmospheric Pressure interface Time-of-Flight mass spectrometer (CI-APi-TOF, Tofwerk AG). In JPAC, aerosol seed experiments were performed where 100nm monodisperse ammonium sulphate (AS) aerosol was added to the chamber. The chemical composition of the particles was measured by a High-Resolution Time-of-Flight Aerosol Mass Spectrometer (HR-TOF-AMS, Aerodyne Inc.). We have identified over 100 different HOM monomers and dimers with more than six oxygen atoms from oxidation of aromatics. The identified HOM were observed for the first time and are not represented by existing chemical oxidation pathways. We determined the HOM molar yield from the benzene-OH reaction to be on the order of 4%, which is similar to that found for alpha-pinene oxidation by ozone. The slight deviation in HOM molar yield as a function of oxidation conditions may explain the SOA yield discrepancies observed in previous studies. In presence of seed particles, rapid decrease of most gas-phase HOM was observed, though some HOM with five oxygen atoms stayed constant, which is indicative of different volatilities of the products.