Precipitation samples were collected at sixteen sites in Northeast Asia from June 1995 to February 1997, and were analysed for the anions SO_4^2- NO_3^- and Cl^- and for the cations Na^+, NH_4^+, K^+, Mg^2+ and Ca^2+ in addition to pH and conductivity measurements.
The quality assurance of chemical composition data was checked by considering the ion balance evaluating by │h│ value and the conductivity balance.
The sum of cation concentrations were slightly greater than the sum of anion concentraions. For the anions, SO_4^2- clearly dominates in most of sampling sites whereas Cl^- is more abundant in coast and rural sites in Japan. For the cations, Ca^2+ and NH_4^+ are generally the more abundant ions except when sources of Na^+ exist.
The contribution rate of nss-SO_4^2- and NO_3^- to acidity are about 70% and 10-30%, respectively. The neutralizing capacity by a major neutralizing cations such as NH_4^+ and nss-SO_4^2+ are above 98%(heavy polluted and urban sites in China), above 70%(urban sites in Japan and in Korea, coast sites in China) and above 60%(rural sites in Japan and in Korea), respectively.