Coupling of Gas-Phase Radical Oxidation Chemistry and Organic-Aerosol Formation

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Through laboratory experiments this project will probe complex interactions between gas-phase organic oxidation chemistry and the evolution of organic particulate matter (PM) making use of advanced instruments including (1) a Chemical Ionization Mass Spectrometer (CIMS) designed for flexible, highly sensitive measurement of critical radicals as well as gas-phase organic compounds including organic acids and peroxides and (2) a High-Resolution Time of Flight Aerosol Mass Spectrometer (HR-AMS) to measure the size-dependent non-refractory fraction of particle composition between 50 and 700 nanometer size, explicitly resolving carbon, hydrogen, oxygen and nitrogen in the particles. A portion of the experiments will be "traditional" secondary organic aerosol (SOA) formation from such systems as alpha-pinene plus ozone, but with measurement of peroxides and other reactive oxygen species under a range of conditions. The larger share of experiments will be carried out with several carefully selected sequences of organic precursors designed to model later-generation oxidation products of traditional SOA experiments. Specifically, SOA formation will be initiated from precursors at selected points in a 2-dimensional (2D) space combining volatility and carbon oxidation state to test whether organic aerosol mass yields and properties vary systematically based on location in this space. If SOA properties do organize in this space, that will confirm the utility of this 2D representation as a dramatic simplification for model representations of SOA behavior, and the results of this research will provide essential parameters required to implement this 2D framework in models.Organic aerosols are significant players in both climate and particulate matter health effects. In each case their contributions are among the most uncertain. Consequently, the results of this project will significantly enhance understanding of particulate matter health effects and aerosol-cloud interactions influencing climate. This will inform evolving policy in both areas. The research will be carried out by a postdoctoral associate, a graduate student, and undergraduate students.