Observation of High SO2 Concentrations and Low-pH Acid Rain Caused by Sulfur Oxides from Miyake-jima Volcano.
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概要
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Since the eruption of Miyake-jima in July 2000, steep increases in the concentration of sulfur dioxide in the atmosphere and in the acidity of depositions have been observed in the Kanto region. We investigated the influences of volcanic emissions on atmospheric depositions and on concentrations of sulfur dioxide in the atmosphere. Observation of atmospheric deposition was conducted with bulk samplers at 5 sampling sites in Saitama prefecture, from April 1999 through March 2001. From August 2000 through October 2000, big increases in atmospheric sulfur dioxide concentrations were observed over large areas of the Kanto region. The decreased pH and the increased amounts of non-sea-salt SO<SUB>4</SUB><SUP>2-</SUP> in atmospheric depositions collected from August 2000 through October 2000 compared with those collected from August 1999 through October 1999 indicated an increased contribution of sulfur oxides to the depositions as well as to atmospheric sulfur dioxide concentrations. From September 2000 through the beginning of October 2000, we studied air mass trajectories and variations in concentrations of ionic species in each millimeter of precipitation, measured using an Automatic Acid Rain Collection and an Ion Chromatographic Analysis system installed at Kisai. When the air mass traveled from Miyake-jima to Kisai, we observed a decrease in pH and an increase in sulfate concentrations in the precipitation. Sulfate accounted for as much as 90% of the anions in the precipitation. It was apparent that sulfur oxides originating from Miyake-jima contributed to the precipitation at Kisai, about 220 km from the volcano, because the degrees of pH decrease and sulfate concentration increase in the precipitation changed rapidly in response to changes in air mass direction. The concentrations of atmospheric sulfur dioxide at Kisai accompanying rain depended on atmospheric stability and precipitation initiated washout processes during the transportation route from Miyake-jima, when volcanic gas traveled at high altitudes under stable conditions and volcanic gas traveled at low altitudes under the influence of a strong downward flow, respectively.
- 社団法人 大気環境学会の論文
社団法人 大気環境学会 | 論文
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