コウスイ ニ フクマレル ムキ セイブン ノ カガクテキ トクチョウ ダイ3ホウ

The precipitation samples in Yonezawa city from May 1991 to February 1992 were analyzed concerning pH value, electric conductivity (EC) and concentrations of several major ions. The annual mean pH values of both rainfall and snowfall were 4.9. The pH value (4.9) of rainfall collected in 1990 was higher than the data (4.6) of the western sampling stations from Phase-II Study of Acid Precipitation Survey over Japan by Japan Environmental Agency, and equal to the data (4.9) of Sendai station. It was found that the precipitation collected ih Yonezawa was the cleanest in three cities, Sakata, Yamagata and Yonezawa. The annual means of ion concentration calculated with the amount of precipitation were slightly lower than arithmetric ones. The ratio of [NO3-] to [nss-SO42-] in 1990 increased about 25% on comparing in 1991. This suggests that the ratio of [NOx] to [SO2] is increasing. The pH and EC values of initial rainfall for every 1mm showed that the resulting patterns were classified into two types according to the average wind velocity. The concentrations of phosphate ion in precipitation is 40～50 ng ml-1, and it can be presumed that phosphate ion originate from the non-seasalt materials because concentrations of the phosphate ion are not proportional to those of the saesalt as Na+ or Cl-