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，是大气中气态和颗粒态污染物的重要清除过程之一。本课题组的研究目的是阐明东亚地区的雨灭和冲刷机制，并利用统计趋势模型对观测数据进行估算。为了研究气溶胶的湿沉降机理，发展了雾、雨滴等液体粒子的固定技术和固定液滴的个体分析技术。该测量方法可以成功地测定离子浓度与雨滴尺寸的关系，具有良好的准确度和精密度。雨滴中离子浓度强烈地依赖于雨滴的大小。较小的雨滴比表面积大，在大气中停留时间长，能收集更多的气溶胶和气态污染物.通过对云雾中化学组分的质量平衡分析，探讨了暴雨过程的物理机制。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钙离子、硫酸根离子和钠离子比例较高的化学物质。3.根据两个监测网的观测资料，绘制了日本硫酸盐湿沉降等值线图。利用东亚国际监测网（EANET）的观测资料，对东亚地区湿沉降的酸碱化学进行了研究。与欧洲和北美相比，硫酸盐的湿沉降非常高，因为硫浓度高和雨水多。

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.