Impacts of sulfur dioxide from Miyakejima on precipitation chemistry in Japan

Precipitation chemistry data of Japanese Acid Deposition Survey (JADS) by Japan Ministry of the Environment was analyzed to evaluate the influence of SO2 emitted from the volcano of Miyakejima located in the Pacific Ocean 200 km south of Tokyo. Precipitation samples were collected with wet-only samplers on a daily basis at eight sites over Japan. The sampling periods (1997–2005) were divided into three periods in consideration of the start of the eruption, August 2000: 1997–1999 (Period A), 2000–2002 (Period B), 2003–2005 (Period C). The influence was evaluated in terms of the ratio before-to-after the eruption, B/A and C/A. The B/A ratios for mean nss-SO42− concentration ranged from 1.1 to 2.3. The average pH decreased at most sites in Period B. The ratios for annual deposition were the same level as those of the concentration. The influence was also assessed for daily concentration and deposition at Tanzawa and Tsukuba, the two closest sites to Miyakejima. The cumulative frequency distributions of the daily nss-SO42− concentration shifted to higher concentration for both sites in Period B. Daily pH cumulative frequency distributions shifted to lower values at both sites in Period B. The monthly fraction, nss-SO42−/(nss-SO42− + NO3−), increased immediately after the eruption onset. The eruption was found to have influenced concentrations and deposition of nss-SO42− and pH on a national scale, and the sites closest to Miyakejima showed the largest influence.