Long term trend of chemical constituents in Tokyo Metropolitan area in Japan

In recent years, acid min has been a social problem all over the world. In Japan, it is also a big problem especially in the metropolitan area. Then, we have measured major ions such as H+, Na+, NH4+, K+ Mg2+, Ca2+, Cl-, NO3- , and SO42- in precipitation and dry deposition samples which had been coll ected at 9 sampling sites at Hiyoshi, Mita, Kashiwa, Shiki, Fujisawa, Yokos uka, Mitaka, Hachiouji, and Ashikaga in Tokyo Metropolitan area for 10 year s since 1990. The average pH of precipitation in their sites was 4.56 (n=19 06). As the results of multiple regression analysis showed that pH of preci pitation was determined by 5 ions such as NH4+, nssCa(2+)(non sea salt calc ium), nssCl(-)(non sea salt chloride), NO3-, nssSO(4)(2-)(non sea salt sulf ate) in the most of the sampling sites. Therefore, it is very important to investigate the behavior of these ions to understand the acidification of r ain in Tokyo Metropolitan area. In this study, a long term trend of each io n concentration in precipitation and wet deposition was also investigated t he base on the data we had observed at 7 sites for 10 years by the statisti cal method.