Sinya Seto

Annual and seasonal trends in chemical composition of precipitation in Japan during 1989–1998

Abstract Annual and seasonal trends were discussed for precipitation chemistry in Japan on the basis of a nationwide monitoring network by Japan Environment Agency. For this analysis, 17 sites, selected from the 23 network sites after evaluation of data completeness for the present purpose, were grouped into four areas in terms of the sea which could characterize each area: the Pacific Ocean, the Japan Sea, the Seto Inland Sea and the East China Sea areas. Major ion concentrations at each site were subjected to least-squares multiple regression analysis, and discussion was principally focused on the area-groups. Each area showed significant (p

Precipitation chemistry in Japan 1989–1993

Precipitation chemistry in Japan was discussed on a wet-only sample database obtained in a nationwide survey from April 1989 to March 1993. Wet-only samples were collected at 29 stations over Japan on a biweekly basis. Commonly determined chemical parameters were measured in laboratories. The volume-weighted annual mean pH at each site ranged from 4.50 to 5.83 with a mean of 4.76. Concentration ranges and means (parenthesized) on an equivalent basis for major ions were as follows: nss-SO42−; 5.2–58.9 (38.6), NO3−; 1.8–25.0 (14.1), NH4+; 0.55–29.8 (18.3), nss-Ca2+; 2.0–34.5(14.2), Na+; 6.4–275.3 (49.1), Cl−; 13.7–322.4 (63.5) β eq L−1. Acid-base relationships for Phase-II records were quantitatively discussed in terms of three measures: pH, fractional acidity, and our proposed pAi.

Source Identification of Rural Precipitation Chemistry in Japan

Precipitation chemistry was discussed from the viewpoint of potential sources for four rural sites where wet-only daily-basis measurement data sets were available during the period from April 1996 to March 1997 in Japan. Annual volume-weighted mean concentrations of nss-SO42− and NO3− ranged from 18.0 to 34.6 µeq L−1, and from 9.3 to 23.1 µeq L−1, respectively. The degree of neutralization of input acidity in terms of the concentration ratio, [H+] / ([nss-SO42−] + [NO3−]), ranged from 0.46 to 0.63. This suggests that about half of the input acidity due to H2SO4 and HNO3 was neutralized by NH4+ and nss-Ca2+ to produce the pH values of 4.46 to 4.82 for these sites. Maximum likelihood factor analysis was then performed on the logarithmically transformed daily wet deposition of major ions. Two factors successfully explained a total of about 80% of the variance in the data for each site. Interpreting varimax rotated factor loadings, we could identify two source types: (1) acid source with large loadings on ln(H+), ln(nss-SO42−), ln(NO3−) and ln(NH4+), (2) sea-salt source with large loadings on ln(Na+), ln(Cl−), ln(Mg2+) and ln(K+). The rural wet deposition over Japan appears to have a similar structure in terms of the kinds of sources and their relative location.

Relationship between wet deposition of sulfate and nitrate and rainfall amount in Japan

A regression model of wet deposition on rainfall amount for non-seasalt sulfate (nss-SO42−) and nitrate (NO3−) was applied to a data set obtained through a nationwide survey from April 1989 to March 1993. Wet-only samples on a biweekly basis were collected at 29 sites over Japan. Reparameterized bivariate lognormal distribution was employed to describe the joint distribution of concentration (C) and rainfall amount (R) for each site. Ranges of geometric mean (μD) of biweekly deposition (D = C. R) for each site were 0.54–2.90 meq m−2 for nss-SU42−, and 0.21–1.36 meq m−22 for NO3−; that of biweekly rainfall amount (μR) was 24.1–78.0 mm. Urban or industrialized areas had high values of μD for these ions. Ranges of estimates of the slope of the regression equation of log(D/μD) on log(R/μR), were 0.45–0.99 for nss-SO42−, and 0.35–0.86 for NO3−; thus estimates of the slope for nss-SO42− tend to be larger than those for NO3−. The present analysis, consequently, statistically clarified some differences between the two ions in deposition processes which is understood in the light of current knowledge of atmospheric chemistry.

Automatically Determined pH of Precipitation Samples, Collected by an Automatic Rain-Sensing Sampler and Its Spatial Distribution

Precipitation pH was automatically measured on site for each 0.5 mm-rainfall sample at 29 nationwide stations in Japan in Phase-II of Acid Deposition 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 pH 4.6. There was no pH record less than pH 3.0 which was supposed to affect plant growth. In western Japan and in remote islands in the Sea of Japan, lower pH was observed than in the other regions. Regarding seasonal 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 rainfall 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 samples were compared with those from the manual measurements of biweekly samples, showing that the automatically determined pH was lower than the manually determined one by 0.3 pH unit on average. One of the possible causes of this pH difference is solution of alkali particles in the stored samples.