Precipitation chemistry data were obtained in Phase-I Study of Acid Precipitation Survey over Japan, 1986 approximately 1988 by Japan Environment Agency. Precipitation was sampled over Japan by filtrating bulk samplers as well as wet/dry samplers. Annual mean pH value at each station ranged from 4.5 to 5.2 with a mean of 4.7. Major ion concentrations averaged over all the samples were as follows; SO42- : 2.64, NO3- : 0.96, Cl- : 3.82, NH4+ : 0.39, Ca2+ : 0.52, Mg2+ : 0.26, K+ : 0.18, and Na+ : 1.97-mu-g/ml. Hydorogen-ion concentration did not vary significantly from site to site compared with those of the other ions. pH value of the rainwater was lower in the western Japan than in the eastern Japan, but the concentrations of the other chemical composition were higher in the eastern Japan. The equivalent concentration ratio of Cl-/Na+ in the rainwater was nearly equal to that of sea water, and those of NO3-/nss-SO42- and NH4+/nss-Ca2+ were 0.35 and 0.96. We interpret that the pH values gradually decreased with an increase in the equivalent concentration of {(NO3- + nss-SO42-}-{(NH4+ + nss-Ca2+)}.
