Online Molecular Characterization of Organic Aerosol in Field and Chamber Studies Using a MOVI-CI-HTOF-MS
Joel Thornton | University of Washington |
Category: Aerosol Properties
We report on the continued development and application of a novel approach to the molecular speciation of oxygenated organic compounds in gas and particle phases. A temperature-controlled Micro-Orifice Volatilization Impactor (MOVI) is coupled to a high-resolution time-of-flight mass spectrometer (HTOF-MS) employing a switchable suite of chemical ionization approaches. We demonstrate the capability of the approach to characterize the detailed elemental composition and volatility of a broad class of oxygenated organic compounds using results from both a smog chamber study of alkane oxidation and recent field deployments in Seattle and as part of the Clearflo/Aeroflo project from January–February 2012. In the smog chamber data our approach tracks the successive oxidation of alkanes into highly oxygenated intermediates that are present in both the particle and gas-phases simultaneously. A positive matrix factorization of our high resolution spectra results in a condensed set of factors that illustrate the successive oxidation with time and the time series of which agree remarkably well with an independent PMF analysis of data from the Aerosol Mass Spectrometer. Such highly controlled process studies form the basis for our ongoing interpretation of data obtained as part of the Clearflo/Aeroflo project. We operated the instrument in four different modes: two ionization schemes—carboxylic acid detection using acetate ion chemistry and oxygenated hydrocarbon detection using protonated water clusters—with two different collision-induced ion declustering regimes. These modes, together with the gas and particle separation and the volatility information, are providing an unprecedented characterization of the evolution of organic compounds in aged polluted air. Statistical analyses are ongoing to provide insights into the connections between wintertime VOC processing, SOA, and aerosol optical and physical properties.
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