Abstract
The Central Research Institute of Electric Power Industry (CRIEPI) constructed a nationwide monitoring network to survey acidic deposition in Japan in October 1987. Although the monitoring network was closed in September 1996, monitoring at Komae, Tokyo has been continued over than last two decades. On the basis of the monitoring data collected between October 1987 and September 2010, we analyzed (i) long term trend in the chemical composition of precipitation, (ii) effect of precipitation amounts on the seasonal variation of concentrations, and (iii) influence of changes in precursor′s emissions on precipitation quality in the metropolitan area.
The equivalent ratio of non sea-salt sulfate to nitrate in precipitation significantly increased by 88% during the period from 1987 to 1999, suddenly decreased in the summer of 2000, and did not change during the period from 2002 to 2010. The equivalent ratio of sulfate, nitrate, and chloride to total non sea-salt anion were 31: 53: 16 for the end of 1980′s, 48: 44: 8 for the end of 1990′s, and 40: 56: 4 for the end of 2000′s, respectively. There was a strong effect of precipitation amounts on monthly concentrations of sulfate and nitrate in the warm season. Eruption of Miyake-jima volcano impacted concentrations of sulfate and chloride during the period from 2000 to 2001. The decrease in the concentration of chloride was considered to be related the reduction in hydrochloric acid emissions from industrial waste incinerators in the metropolitan area.
