Chemistry of Secondary Aerosol Formation from Biogenic Hydrocarbons Investigated Using Thermal Desorption Particle Beam Mass Spectrometry

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The objectives of the proposed three-year research program are to investigate the products, kinetics, and mechanisms of secondary aerosol formation from the reactions of selected biogenic hydrocarbons (the monoterpenes b-pinene, limonene, myrcene, and linalool, the sesquiterpene b-caryophyllene, and dimethyl sulfide) with the important atmospheric oxidants OH, O3, and NO3. Reactions will be carried out in an environmental chamber and measurements will include real-time particle analysis using a thermal desorption particle beam mass spectrometer (TDPBMS), gas chromatography-mass spectrometry, and scanning mobility spectrometer. In the TDPBMS, particles in the size range of approximately 0.01-0.5 mm are sampled into a differentially-pumped vacuum chamber, focused into a narrow, low-divergence particle beam using aerodynamic lenses, impacted/vaporized on a heated surface, and the vapor is mass analyzed using a quadrupole mass spectrometer. In addition to the chamber studies, atmospheric particles will be collected from forested and agricultural areas in California and analyzed to determine if organic compounds identified in laboratory reactions are also present in ambient particles. The results of these studies will help to elucidate the fundamental chemical processes involved in atmospheric secondary aerosol formation from biogenic hydrocarbons. The data will help to improve current understanding of the fate of atmospheric organic particles and their potential effects on Earth's radiation balance, atmospheric chemistry and visibility, and human health, and will be useful in determining the atmospheric lifetimes and fates of biogenic organic compounds.