The characterization of hydrogen ion concentration in sequential cumulative rainwater

From March to June 1996, eight rain events were sampled sequentially on time and volume basis in Uji, Kyoto, Japan. pH was measured by a pH meter. The concentrations (μmol l−1) of chloride ion (Cl−), nitrate ion (NO3−), sulfate ion (SO42−), sodium ion (Na+), ammonium ion (NH4+), potassium ion (K+), calcium ion (Ca2+) and magnesium ion (Mg2+) were measured by ion chromatography. It is found that Cl−, NO3−, SO42−, Na+, NH4+, K+, Ca2+ and Mg2+ concentrations in sequential cumulative rainwater decreased with rain duration. However, hydrogen ion (H+) concentration (derived from pH value) showed approximately an increasing trend with rain duration. The factors influencing H+ concentration as well as the H+ concentration varying pattern for sequential cumulative rainwater were discussed.