Washout/rainout classification and precipitation characterization, achievable by 1 mm precipitation observation
摘要
Washout/rainout contributions to sulfate and nitrate in precipitation were studied and estimated based on the precipitation collected with a 1 mm sampling basis. It could be estimated that the washout/rainout contributions to sulfate and nitrate were, for washout, 30–45% and ca. 40% for sulfate and nitrate, respectively; and, for rainout, 55–70% and ca. 60% for sulfate and nitrate, respectively. The 1 mm sampling made it possible to investigate the time series in detail for each individual precipitation. As a consequence, the following points were made clear: (1) the pH value could be correctly identified based on the measured SO42− and NO3− concentrations in precipitation of marine origin, (2) the precipitation in the primary stage of the event was highly neutralized by neutralizing substances accumulated locally around the survey site, (3) sulfate was frequently detected in precipitation with a continent origin, especially in Asian continent-origin precipitation; on the other hand, sulfate was rarely observed in marine-origin precipitation, (4) Asian continent-origin precipitation had measured pH values higher than the calculated pH values from the measured SO42− and NO3− concentrations, (5) the contribution of volcanic gases to lowering the pH value of the precipitation passing over domestic volcanos was implied.