A 15-year record (2001–2015) of the ratio of nitrate to non-seasalt sulfate in precipitation over East Asia

Abstract

Abstract. Acidifying species in precipitation can cause severe impacts on ecosystem. The chemical concentration of precipitation is directly related to the precipitation amount, so it is partly difficult to identify the long-term variation from precipitation concentration. The ratio of nitrate (NO 3 -) to non-seasalt sulfate (nss-SO 4 2-) concentration in precipitation on an equivalent basis (hereinafter, Ratio) will be a useful index. To identify the long-term record of acidifying species in 15 precipitation over East Asia, where is the highest emission region in the world, we have compiled the ground-based 2-concentration, and hence Ratio in precipitation will be related to these precursors. The anthropogenic NOx and SO 2 emission amount, and NOx/SO 2 emission ratio are analyzed. Further, satellite observations of NO 2 and SO 2 column density to capture the variation in emission was applied. We found that the long-term trend of NO 3 -concentration in precipitation was not related to the variation in NOx emission and the NO 2 column. In comparison, the nss-SO 4 2-concentration in precipitation over China, Korea, and Japan was partly connected to the changes in SO 2 emission from China, but the trends 25were not significant. The long-term trend of Ratio over China, Korea, and Japan were nearly flat during Phase I, increasing significantly during Phase II, and almost flat again during Phase III. These variations of Ratio in East Asia clearly corresponded to the NOx/SO 2 emission ratio and the NO 2 /SO 2 column ratio in China. The first flat trend during Phase I was due to both increases in NOx and SO 2 emissions in China, the significant increasing trend during Phase II was triggered by the increase in NOx emission and decrease in SO 2 emission in China, and the returned flat trend during Phase III was caused 30 by both declines in NOx and SO 2 emissions in China. This suggests that China's emission has a significant impact not only on China but also on downwind precipitation chemistry during the analyzed 15-year period of 2001-2015. In terms of wet depositions, the NO 3 -wet deposition amount over China, Korea, and Japan has not changed dramatically, but the nss-SO 4 2-Atmos. Chem. Phys. Discuss., https://doi