AUTOMATICALLY DETERMINED PH OF PRECIPITATION SAMPLES, COLLECTED BY ANAUTOMATIC RAIN-SENSING SAMPLER AND ITS SPATIAL-DISTRIBUTION

Precipitation pH was automatically measured on site for each 0.5 mm-ra infall sample at 29 nationwide stations in Japan in Phase-IE of Acid D eposition Survey from 1989 FY to 1992 FY by Japan Environment Agency. The mean pH of all of the stations over the entire survey period was p H 4.6. There was no pH record less than pH 3.0 which was supposed to a ffect plant growth. In western Japan and in remote islands in the Sea of Japan, lower pH was observed than in the other regions. Regarding s easonal variations, pH was rather lower in winter and spring. The mean pH of initial 0.5 mm-rainfall was lower than that of the whole rainfa ll at many stations, although it was higher at 8 stations. The monthly means of pH based on the automatic measurements of 0.5 mm-rainfall sa mples were compared with those from the manual measurements of biweekl y samples, showing that the automatically determined pH was lower than the manually determined one by 0.3 pH unit on average. One of the pos sible causes of this pH difference is solution of alkali particles in the stored samples.