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，是大气中气态污染物和颗粒物污染物的重要去除过程之一。我们课题组的目标是阐明降雨和冲刷的机制，并利用观测数据的统计趋势模型估计东亚的湿沉积速率。发展了雾和雨滴等液体粒子的固定技术和固定液滴的单独分析技术，以研究气溶胶的湿沉积机理。这种测量方法可以成功地测定离子浓度随雨滴大小的变化规律，具有良好的准确度和精密度。雨滴中的离子浓度强烈依赖于雨滴的大小。雨滴越小，聚集的气溶胶和气态污染物越多，这是因为雨滴的比表面积大，在大气中停留的时间更长。对山上雾滴中化学物质的质量平衡进行了研究，以阐明降雨的机理。清除率与雾的液态水含量密切相关。硝酸盐/硝酸和硫酸盐/二氧化硫的吸入量分别约为30%和4%。气溶胶的清除率取决于钙、硫酸盐和钠离子比例较高的化学物种。根据两个监测网的测量结果，绘制了日本硫酸盐湿沉降等值线图。根据东亚国际监测网(EANET)的观测资料，对东亚湿沉降的酸碱化学进行了研究。与欧洲和北美相比，硫酸盐的湿沉降量极高，这是因为硫磺浓度高和多雨的共同作用。

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.