Study Of Acid Deposition And Comparison Of Its Long-range Transport Models In East Asia

Analysis of spatial and temporal distributions of acid deposition in East Asia and gas concentrations in the air in Japan was conducted by using observed data from Acid Deposition Monitoring Network in East Asia (EANET). Possible causes of significant differences between observations and simulations from some MICS-Asia (Model intercomparison Study in Asia) models were explored. The analysis shows that: 1) there is a clear difference in regional characteristics of chemical components of rainfall in East Asia, e.g., concentrations of Na⁺ and Cl^- are highest in Japan sites among all EANET sites whereas those of Ca²+, NO₃^-, NH₄⁺, SO₄²-, Mg²+, K⁺ in Northwest China are very high compared to other regions in East Asia. The acidity of precipitation in Northwest China is dependent significantly on concentrations of Ca²+, NH₄⁺, SO₄²-, and NO₃^-. 2) There are great variations with seasonal changes in chemical components of rainfall in East Asia. In addition to the influence of anthropogenic emissions, seasonal change of climate in East Asia is another main factor. 3) Nitrate concentrations in rainfall are increasing in many sites of East Asia due to economic expansion and urbanization in East Asia. Monthly mean daily concentrations of O₃, SO₂, NO, NO_x, PM10 indicate that: 1) PM10 levels in spring are generally higher than those in other seasons whereas PM10 levels in winter are usually low and show little variation with time. Elevated PM10 concentrations in spring are closely related to long-range transport. 2) Elevated SO₂ concentrations generally occur in summer or spring. 3) NO diurnal cycles are significant at most sites of Japan. 4) Highest ozone concentrations always occur at remote sites inspring and long-range transport contribute much to elevated ozone levels. O₃ diurnal cycles at rural and urban sites are remarkable. Highest ozone concentrations usually occur in summer afternoon and photochemical reactions play an important role in high ozone concentrations at rural sites. Four cases (March, July, December of 2001 and March of 2002) were chosen to reflect seasonal changes and kosa episodes. Comparison of observations and simulations shows that most models well simulate seasonal changes in spatial distributions of dry and wet deposition. Some models indicate large biases from observations. Further studies are needed.