Atmospheric Processing of Organic Aerosols

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The objective of this project is to conduct laboratory studies of the chemical transformation of organic surfaces that are model systems for particulate organic matter in the troposphere. Organic aerosols play important roles in the troposphere, affecting its oxidative capacity and its radiative balance. Their impacts range from human health effects in urban areas to direct and indirect aerosol forcing related to global climate change. These later effects remain as some of the largest uncertainties in climate change modeling. This project is aimed at providing quantitative information on the oxidative processing of organic particles in various gas phase environments relevant to the atmosphere. The experimental approach to be employed combines various gas-phase and surface analysis techniques such as low and high pressure chemical ionization mass spectrometry, Fourier transform infrared spectroscopy, X-ray photoelectron spectrometry, atomic force microscopy, contact angle goniometry, and the quartz crystal microbalance technique. Prototype organic carbon surfaces and their mixtures will serve as proxies for organic aerosol in the troposphere. Specific projects to be carried out include studies of adsorption and heterogeneous reactions of various inorganic and organic species of atmospheric importance with organic carbon surfaces activated by the reactions of atomic oxygen, hydroxyl radical, atomic chlorine, nitrate radical and ozone. Reactions of oxidized organic carbon surfaces with important inorganic and organic species such as carbon monoxide, nitrogen dioxide, chlorine nitrate, and sulfur dioxide will be studied in the presence of these oxidants using various organic carbon prototypes: aliphatic, aromatic and soot samples and their mixtures. Changes in the chemical composition, morphology and hygroscopicity of organic carbon films will be investigated in the course of their interaction with various gas-phase atmospheric components including atoms and radicals and other labile species. Data on the reactivity of the activated organic carbon surfaces will be useful for atmospheric modeling calculations. This research is expected to contribute to the elucidation of the role of organic particulate matter in free radical chemistry under realistic tropospheric conditions. Furthermore, the research projects will contribute to the training and education of undergraduate, graduate and postdoctoral students in the field of the atmospheric chemistry.