Simulated Seasonal Variations in Wet Acid Depositions over East Asia

Abstract

ABSTRACT The air quality modeling system Regional Atmospheric Modeling System–Community Multi-scale Air Quality (RAMS-CMAQ) was applied to analyze temporospatial variations in wet acid deposition over East Asia in 2005, and model results obtained on a monthly basis were evaluated against extensive observations, including precipitation amounts at 704 stations and SO4 2−, NO3 −, and NH4 + concentrations in the atmosphere and rainwater at 18 EANET (the Acid Deposition Monitoring Network in East Asia) stations. The comparison shows that the modeling system can reasonably reproduce seasonal precipitation patterns, especially the extensive area of dry conditions in northeast China and north China and the major precipitation zones. For ambient concentrations and wet depositions, the simulated results are in reasonable agreement (within a factor of 2) with observations in most cases, and the major observed features are mostly well reproduced. The analysis of modeled wet deposition distributions indicates that East Asia experiences noticeable variations in its wet deposition patterns throughout the year. In winter, southern China and the coastal areas of the Japan Sea report higher SO4 2− and NO3 − wet depositions. In spring, elevated SO4 2− and NO3 − wet depositions are found in northeastern China, southern China, and around the Yangtze River. In summer, a remarkable rise in precipitation in northeastern China, the valleys of the Huaihe and Yangtze rivers, Korea, and Japan leads to a noticeable increase in SO4 2− and NO3 − wet depositions, whereas in autumn, higher SO4 2− and NO3 − wet depositions are found around Sichuan Province. Meanwhile, due to the high emission of SO2, high wet depositions of SO4 2− are found throughout the entire year in the area surrounding Sichuan Province. There is a tendency toward decreasing NO3 − concentrations in rainwater from China through Korea to Japan in both observed and simulated results, which is a consequence of the influence of the continental outflow from Eurasia. The same tendency is not found for SO4 2−. IMPLICATIONS Seasonal variations of wet acidic depositions in East Asia were studied using the air quality modeling system RAMS-CMAQ. The simulated results provide information on transport, transformation, and wet deposition patterns of acidic substances over East Asia. This information can assist decision makers in designing emission regulations, especially for areas that have serious problems with acid depositions.