Atmospheric Environmental Impacts of Aerosols in East Asia

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Wet deposition is scavenging process during cloud formation and rainfall and it is one of the most important removal processes of gaseous and particulate pollutants from atmosphere. Object of our research group is to elucidate the rainout and washout mechanisms and to estimate the wet deposition rate in East Asia using statistical trend model for the observed data.1. The fixation techniques of liquid particles such as fog and raindrops and individual analytical technique of fixed liquid droplets were developed to investigate the wet deposition mechanism of aerosols. The raindrop size-dependence of ionic concentration could be successfully determined by this measurement method with good accuracy and precision. The ion concentrations in raindrop strongly depend on the raindrop size. Smaller raindrops collect much more aerosols and gaseous pollutants because of large specific surface and longer holding time in atmosphere.2. Mass balance of chemical species in fog droplets generated at the mountain was investigated to elucidate the rainout mechanisms. Scavenging ratio was closely related to the liquid water contents of fog. Absorbed amount of nitrate/nitric acid and sulfate/sulfur dioxide is about 30% and 4%, respectively. Scavenging ratio of aerosols depends on chemical species with high ratio of calcium, sulfate and natrium ions.3. The isopleth maps of wet deposition of sulfate in Japan were produced based on the measurement from two monitoring networks. Acid-base chemistry of wet deposition in East Asia was investigated based on the measurements of International Monitoring Network in East Asia (EANET). The wet deposition of sulfate is extremely high in comparison with Europe and North America because of the combination of high sulfur concentration and much rain.