Ion concentration changes observed in drizzling rains

Ion concentrations of NO3− and SO42− in individual rains were observed at Nagagute in the suburbs of Nagoya, Japan, from July 1, 1991 to June 30, 1992. Decreasing concentrations of NO3− and SO42− in rainwater collected during precipitation were frequently observed and this decreasing pattern is expressed by exponential functions. The ion concentration decrease is more influenced by the ion scavenging loss in the precipitation area than the ion supply due to transportation and oxidation processes. Under calm atmospheric conditions, the empirical ion scavenging coefficients were derived from changes in ion concentration in a drizzling rain with a rain intensity of below 15 mm h−1. These coefficients were linearly proportional to the rain intensity. The average empirical scavenging coefficients of NO3− and SO42− were 5.2 × 10−4 and 2.2 × 10−4 s−1, respectively. The coefficient of N03− is 2.5 times more sensitive to the rain intensity than that of SO42−. The NO3− and SO42− concentrations and pH were well simulated in a numerical model containing the obtained empirical scavenging coefficients.