Annual Changes in Wet Deposition Fluxes of Trace Metals and Scavenging of Mercury by Precipitation in the Western Tokyo Metropolitan Area

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  • SAKATA Masahiro
    Environmental Science Research Laboratory, Central Research Institute of Electric Power Industry
  • MARUMOTO Kohji
    Environmental Science Research Laboratory, Central Research Institute of Electric Power Industry

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  • 首都圏西部における微量金属の湿性沈着量の経年変化と水銀の降水への取り込み
  • シュトケン セイブ ニ オケル ビリョウ キンゾク ノ シッセイ チンチャクリョウ ノ ケイネン ヘンカ ト スイギン ノ コウスイ エ ノ トリコミ

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Abstract

In this study, we measured the wet deposition fluxes of trace metals such as Hg, Cd, Cu, Mn, Pb and Zn in the western Tokyo metropolitan area (Komae City) from January 2000 to December 2003. Annual wet deposition fluxes of Hg, Cd, Pb and Zn showed a declining trend that corresponds to changes in atmospheric concentration. In particular, for Hg and Pb, a large reduction in wet deposition flux was observed. According to our previous studies, Hg, Cd, Pb and Zn in the atmosphere originate significantly if not predominantly from municipal solid waste (MSW) incinerators located around the study site. It was found that the emissions of Hg and particles from MSW incinerators in the Tokyo area (23 wards) have decreased annually. Thus, the reduction in wet deposition fluxes of trace metals is due to the decrease in their emissions from MSW incinerators by an improved flue gas control system in recent years. Next, we evaluated the contribution of the scavenging of gaseous and particulate Hg by precipitation to the bulk Hg wet deposition flux on the basis of scavenging ratios for trace metals (=concentration in precipitation/concentration in air) . The results indicated that approximately 30-60% of the Hg scavenged by precipitation originated from particulate Hg, which is similar to the contribution from gaseous Hg. This suggests that the scavenging of atmospheric particulate Hg by precipitation plays an important role in Hg wet deposition, along with the scavenging of gaseous elemental Hg by precipitation via its oxidation in the gas and aqueous phases.

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