A LONG-RANGE TRANSPORT MODEL FOR EAST-ASIA TO ESTIMATE SULFUR DEPOSITION IN JAPAN

A long-range transport model for East Asia was developed to estimate t he sulfur deposition in Japan. The model is a hybrid type that combine s a trajectory model for distant sources with a Eulerian model for nea rby sources. The processes of transport and diffusion, chemical reacti ons, cloud scavenging, transfer of sulfate from cloud water to rainwat er, and dry and wet depositions are considered. The emission distribut ion of sulfur dioxides in East Asia, with approximately 80 km X 80 km resolution, was updated. The emission distribution in Japan on a grid system with resolution in both the horizontal and vertical directions three times higher than that of the grid system for East Asia was also estimated for the Eulerian part of the hybrid model. The important as sumption used in the hybrid model is that substances emitted from dist ant sources are well mixed during the long-range transport and are uni formly distributed in the vertical direction. This assumption was conf irmed from the result of airplane measurements in the area of the sea northwest of Kyushu Island in Japan. The results obtained using the hy brid model were evaluated through comparison with observed data of aci dic deposition. Observations were conducted at 21 stations throughout Japan during one year. The calculated amount of total sulfur depositio n in Japan was 0.43 Tgy(-1) (Tgy(-1) = 10(12) g per year) in sulfur eq uivalents, while the observed amount was 053 Tgy(-1). The long-range t ransport model can predict more than 80% of observed sulfur deposition . The tendency of underprediction could be improved by changing the tr eatment of mass transfer to liquid phases. The sources contributing to the total sulfur deposition in Japan were estimated using the hybrid model. The contributions of Japanese anthropogenic sources. volcanic e ruptions, and Asian continental sources were 40%, 20%, and 40%, respec tively.