Studies on chemistry and cycles of halogens in the troposphere

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In this program, we conducted several projects. They include (l) measurements of inorganic halogens and their atmospheric behaviors, (2) development of halogen measurement and its application to the atmosphere, (3) atmospheric behaviors of halogenated volatile hydrocarbons, (4) halogenated organics in aerosols and analysis of organic aerosols, (5) carbon isotopic analysis of non-methane hydrocarbons, (6) dynamics and interaction of halogens in air/water interface, and (7) formation mechanism and cycles of biogenic halocarbons.We made a new analytical system to measure hologen gases by using scrubber technique. By using this method, a formation of halogen gases from the sea salt particles was observed. We also observed a decrease in the concentration of Cl^2 and an increase of HCl gas in daytime in the marine atmosphere. A chemical ionization mass spectrometer that was designed for the measurement of Br^2 and Cl^2, has been made in this study. Using this instrument for laboratory experiment, we observed the formation of Br^2 gas on the surface of sea salt particles as a result of Cl uptake. We also confirmed the release of halogen gases from the sea salts by the reaction with ozone. Seawater and air samples collected from the Pacific Ocean were analyzed for holocarbons using a purge and trap GC/mass spectrometry. We found a seasonal change of halogen compounds with maxima in August/September in the western North Pacific. In the marine aerosols, we identified, for the first time, halogenated organic acids and aldehydes, including bromosuccinic and chlorosuccinic acids. The former acid showed higher concentrations in the western North Pacific near Asia continent, whereas the latter increased in the central Pacific. Based on the observations over the Pacific, we proposed a photochemical formation model for the newly rescovered halogenated organic compounds and an evolution model of organic aerosols.