Kinetic studies of the oxidation pathways of gaseous elemental mercury

Over the last decade our understanding of mercury cycling has dramatically changed. Evidence of rapid atmospheric oxidation has been observed in numerous locations. Observations show that Hg0 can undergo rapid gas-phase oxidation under atmospheric conditions. The mechanism and importance of this transformation is still unclear.;This work determined kinetic rate coefficients for the potentially important mercury reactions. Rate coefficients were determined using a Pulse Laser Photolysis -- Laser Induced Fluorescence (PLP-LIF) technique monitoring one or more of the following species, Hg0, Cl, Br, HgCl, and HgBr. The concentrations of these species were measured by LIF a producing concentration vs. time profiles, from these profiles a rate coefficient for the reaction can be obtained. In this work kinetic rate coefficients for the following reactions were measured. Hg0+Cl+M→HgCl+ M Hg0+Br+M→HgB r+M HgBr+M→Hg0+B r+M HgBr+Br→products HgCl+O2→prod ucts This work was the first direct measurement of a kinetic rate coefficient for these reactions, and the first work which employed one photon LIF to monitor the HgCl and HgBr products.;This work also developed new laser based techniques to detect mercury and its oxidation products for both laboratory and field application. A LIF technique was developed to detect HgCl and HgBr, and a further developed a two photon LIF technique. The two photon LIF technique was used to directly monitor Hg0 atoms, to monitor Hg0 evolving form a gold tube, and to monitor the Hg0 evolving from the thermal decomposition of reactive gaseous mercury collected on a denuder. This work represents significant advances in the development of viable methods the detect mercury and mercury oxidation products for laboratory and field studies, and is the first study to observe clear differences in the characteristic desorption profiles of HgO and HgX2.;This work has broad implications; it enhanced our current knowledge concerning the biogeochemical cycling of mercury, broadened our understanding of the mercury chemistry in high halogen environment, and provided new techniques to use in both field and laboratory studies.