Study on the behavior of atmospheric radon for clarifying the dispersion of atmospheric pollutants from East Asia region to northwest Pacific Ocean

研究核事故引起的东亚地区大气污染物向西北太平洋的扩散及其在大范围内的扩散是东亚地区一个重要而紧迫的环境问题。氡是一种很好的大气污染物示踪剂。在中国的北京、韩国的首尔和通海、日本的松江、金泽和名古屋以及太平洋的波照间、八丈岛和小笠原等岛建造了一个大气氡监测站网络。从中国到日本和太平洋，大气氡浓度逐渐降低。名古屋和北京的氡浓度有明显的日变化。另一方面，在海上孤岛的氡浓度没有表现出日变化。八丈岛大气氡浓度与元素碳和臭氧浓度随时间变化的趋势和峰值吻合较好。利用东亚地区的大气氡浓度观测资料，建立了一个大气氡长距离输送模式，并对该模式进行了评价。所开发的模式包括一个气象模式（MM5）和大气传输模式。MM5模式能较好地预报湍流扩散率、风场和降水场的三维分布。模拟的大气氡浓度随时间的变化与观测值吻合较好。

The study on the diffusion of atmospheric pollutants from East Asia region to northwest Pacific Ocean and the dispersion over a wide area associated with nuclear accident is an important and urgent environmental problem in East Asia. Radon is a good tracer for atmospheric pollutants. A network of atmospheric radon monitoring stations was constructed at Beijing in China, at Seoul and Tonghae in Korea, at Oki and Hekura islands on the Sea of Japan at Matsue, Kanazawa and Nagoya in Japan and at Hateruma, Hachijojima and Ogasawara islands on the Pacific. The atmospheric radon concentration decreases gradually from China to Japan and on the Pacific. The radon concentrations at Nagoya and Beijing showed clear diurnal variations. On the other hand, the radon concentrations at solitary islands on the sea did not show diurnal variations. The atmospheric radon concentrations at Hachijojima island agreed well with the trend and peak of time variations of the concentrations of elemental carbon and ozone. The long-range atmospheric transport model was developed and evaluated by using atmospheric radon concentrations observed in East Asia region. The developed model consists of a meteorological model (MM5) and an atmospheric transport model. The MM5 could predict the three-dimensional distributions of turbulent diffusivity, winds and precipitation fields. The simulated time variations of atmospheric radon concentration agreed well with the observed variations.