Transport of Sulfur Oxides over the East Asian Region by the Off-line Coupled Meteorological and Transport Model.

A long-range sulfur transport model consisting of two submodels-a meteorological submodel and a dispersion submodel-has been developed to evaluate the extent of acid deposition in East Asia. The Japan Meteorology Agency's operational weather forecasting model was adopted and improved upon, and employed to predict meteorological variables. A Lagrangian particle method was used as the basis for the dispersion model, and a random walk calculation was used for the diffusion process. Dry deposition, below-cloud scavenging, and chemical transformation processes were also included. A numerical simulation was performed for the transport of sulfur oxides in East Asia in 1985, and the annual deposition was evaluated. The results of the simulation showed that the wet deposition of sulfur oxides originating from the Asian continent was roughly 0.05gS/m2/ year, and the dry deposition 0.02-0.17gS/m2/year. The observed wet deposition was about 1.0gS/m2/year, and although uncertain volcanic influence was included in this observed value, it was about 20 times lower than wet deposition of sulfur values observed in Japan. Calculated wet deposition values at four representative receptors were found to be much lower than observed values. Therefore, it was inferred that the contribution from foreign emission sources was extremely low, on the order of around ten percent. An evaluation of the impact of deposition in Kita-Kyushu (in western Japan) showed that emissions from South Korea, Taiwan and the southeastern region of China affected the Kita-Kyushu values. However, an evaluation of the impact of deposition in Niigata (on the Sea of Japan coast) showed that emissions from China dominated.