Japan's Environment Ministry found typhoons pick up large quantities of airborne pollutants that cause acid rain as they approach land.
The finding was announced in a report on acid rain delivered at a Meteorological Society of Japan meeting held in Fukuoka, west of Tokyo, the Yomiuri Shimbun reported Wednesday.
A ministry working group analyzed the chemical components in raindrops from Typhoon No. 6, which developed over the Pacific and approached the Ogasawara Islands July 21, coming closest to the islands on July 24.
Their analysis found the concentration of sodium ions, the main component of typhoon rain, had increased until July 24, then declined on July 27 to about a tenth of the maximum recorded density.
However, the amount of sulfate ions increased rapidly to its maximum on July 27. The concentration of the sulfate ions was a fifth that of sodium ions.
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