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-SO^sub 4^^sup 2-^ and NO^sub 3^^sup -^ ranged from 18.0 to 34.6 µeq L^sup -1^, and from 9.3 to 23.1 µeq L^sup -1^, respectively. The degree of neutralization of input acidity in terms of the concentration ratio, [H^sup +^] / ([nss-SO^sub 4^^sup 2-^] + [NO^sub 3^^sup -^]), ranged from 0.46 to 0.63. This suggests that about half of the input acidity due to H^sub 2^SO^sub 4^ and HNO^sub 3^ was neutralized by NH^sub 4^^sup +^ and nss-Ca^sup 2+^ 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^sup +^), ln(nss-SO^sub 4^^sup 2-^), ln(NO^sub 3^^sup -^) and ln(NH^sub 4^^sup +^), (2) sea-salt source with large loadings on ln(Na^sup +^), ln(Cl^sup -^), ln(Mg^sup 2+^) and ln(K^sup +^). The rural wet deposition over Japan appears to have a similar structure in terms of the kinds of sources and their relative location.[PUBLICATION ABSTRACT]