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Pollution responsible for acid rain and acid snow in coastal areas along the Sea of Japan travels via China and the Korean Peninsula during the winter, but comes from other areas in Japan in the summer, an environmental research laboratory in Niigata Prefecture said Friday.

The Niigata Prefectural Research Laboratory for Health and Environment made the findings — the first time in Japan that the movement of acid rain-causing pollution has been researched on a nationwide scale — based on surveys conducted by a national pollution study group.

An official at the laboratory said the analysis may shed light on the different approaches to solving the pollution problem, as it varies with the season.

The national pollution study group, made up of environmental study organizations run by local governments, conducted far-reaching nationwide high-altitude tests for nearly three years.

The group conducted six tests — in June 1995, 1996 and 1997, and in January and February in 1996, 1997 and 1998 — at 60 different locations in Japan. Based on the test results, the laboratory analyzed the possible routes that acid rain-causing substances such as sulfuric acids follow.

Concentrations of ionic sulfate in the atmosphere were particularly high during the January-February period in 11 areas, including the cities of Niigata, Tottori and Kanazawa in Ishikawa Prefecture.

Most of the ionic sulfate is believed to have been carried from inland areas of China, via the Yellow Sea and the Korean Peninsula. Sulfur dioxide emissions in China and South Korea were seen as the likely source of the pollution.

In June, by comparison, high densities of ionic sulfate were found at 20 sites, including Hachinohe in Aomori Prefecture, Maebashi in Gunma Prefecture, and Kochi. Pollution from cities in Japan is believed to be the source.

Sources at the laboratory said joint efforts to work out measures to curtail pollution common to East Asian countries are urgently required, hoping that the results of their research are instrumental to achieve such an end.