Atmospheric Environmental Impacts of Aerosols in East Asia

湿沉降是云形成和降雨过程中的清除过程，是大气中气体和颗粒污染物的重要清除过程之一。本课题组的目的是利用观测数据的统计趋势模型，阐明东亚地区降水和冲刷机制，并估算湿沉积速率。为了研究气溶胶的湿沉积机理，发展了雾、雨滴等液体颗粒的固定技术和固定液滴的个体分析技术。该测量方法可成功测定雨滴大小对离子浓度的依赖性，具有良好的准确度和精密度。雨滴中的离子浓度与雨滴的大小密切相关。小雨滴由于比表面积大，在大气中停留时间长，因而能收集更多的气溶胶和气态污染物。研究了山区雾滴中化学物质的质量平衡，以阐明降雨机制。清除率与雾中液态水含量密切相关。硝酸盐/硝酸和硫酸盐/二氧化硫的吸收量分别约为30%和4%。气溶胶的清除率取决于具有高钙、硫酸盐和钠离子比率的化学物质。根据两个监测网的测量结果，绘制了日本硫酸盐湿沉积等线图。利用东亚国际监测网（EANET）的观测资料，研究了东亚湿沉积的酸碱化学特征。与欧洲和北美相比，由于高硫浓度和多雨的结合，硫酸盐的湿沉积非常高。

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.