In this study, we simulated the transport and chemical transformation of air pollutants with a focus on sulfur oxides in the three domains of Asia on different scales, by using the nesting technique of the chemical transport model.
The coarsest, middle and finest domains cover the most part of Asia in 80 km grid, the most part of China in 20 km grid, and Beijing and surroundings in 5 km grids, respectively.
The result of calculating pollutant concentration was compared with the observation by EANET and ACE-Asia.
By the method of process analysis which calculates the contribution of transport and transformation processes, it has showed that most of SO₂ is transformed to SO_4^2- throughout the seasons in southwestern area of China (inland), and that little part of SO₂ emitted from this area is transported out. On the other hand, transformation of SO₂ to SO_4^2- is active in the summer period in eastern area of China (coastal), and most of sulfur oxides are deposited in the area in the summer period, while greater part of sulfur oxides is transported out in the form of SO₂ in the winter period.
From the result of finest domain, the background SO₂ mixing ratio in Beijing transported from the outside of the domain is 5ppb in annual average, and reaches about 30ppb as the maximum of daily averages. In the case of the maximum value it is likely that the background concentration makes achievement of the Chinese environmental standard of SO₂ concentration difficult.