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 (406KB)
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23,841,000 Yen (FY 1998 7,920,000 Yen)
(1) Two major marine-derived halocarbons (methyl iodide and bromoform) were measured in the samples collected over western Pacific, eastern Indian Ocean, and Southern Ocean. They showed completely different latitudinal variations; Methyl iodide was more abundant at lower latitudes supporting its photochemical production in the seawater, and bromoform was abundant at coastal areas and at higher latitudes, suggesting more importance of macroalgae for its emission. (2) Particulate and gaseous bromine were observed over the Pacific for 2 years. It was found that gaseous Br concentration was higher than particulate form and increased up to 50-100 ng/m3 in winter, when a lot of sea salt particles exist in the marine atmosphere. In most case, the gaseous Br concentration was higher in daytime than in nighttime. (3) Laboratory experiments on the heterogeneous reactions of ozone with NaCl, NaBr, and NaI as well as synthetic and natural sea salts have been conducted for the purpose of elucidating the mechanism of halogen release from sea salt in the marine atmosphere. Reaction of ozone with the synthetic and natural sea salt has a large uptake coefficient of ca. 1 x 10-3 and gave Br2 as a product. From this result, it was deduced that this reaction is important as a source of active bromine in the marine boundary layer and bromine atoms is thought to give an significant effect on the ozone budget at lease in the marine boundary layer. (4) The effect of introducing halogen molecules on photochemical ozone concentration in a propene/NO/air/photoirradiation system following the attainment of the maximum ozone concentration was investigated. Although the photochemical ozone was depleted by the presence of halogen molecules, the concentration of halogen molecules injected was too high to explain the ozone depletion in the marine boundary layer.
Tropospheric Ozone, Organic Halogen, Inorganic Halogen, Sea Salt Aerosol, Heterogeneous Reactions