ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-11-1671-2011 Impact of the East Asian summer monsoon on long-term variations in the acidity of summer precipitation in Central China Ge B. Z. 1 4 Wang Z. F. 1 Xu X. B. 2 Tang J. 2 He Y. J. 3 Uno I. 5 Ohara T. 6 State Key Laboratory of Atmospheric Boundary Layer Physics and Atmospheric Chemistry (LAPC), Institute of Atmospheric Physics, Chinese Academy of Science, Beijing 100029, China Key Laboratory for Atmospheric Chemistry, Centre for Atmosphere Watch and Services, Chinese Academy of Meteorological Sciences, China Meteorological Administration, Beijing, China Chinese Research Academy of Environmental Sciences, Beijing, China Graduate University of the Chinese Academy of Sciences, Beijing, 100049, China Research Institute for Applied Mechanics, Kyushu University, Fukuoka, Japan National Institute of Environmental Science, Tsukuba, Japan 21 02 2011 11 4 1671 1684 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys.net/11/1671/2011/acp-11-1671-2011.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/11/1671/2011/acp-11-1671-2011.pdf

The acidity of precipitation has been observed at stations of the Acid Rain Monitoring Network run by the China Meteorological Administration (CMA-ARMN) since 1992. Previous studies have shown that different long-term trends exist in different regions but detailed analysis of the causes of these is lacking. In this paper, we analyze summertime precipitation acidity data from the CMA-ARMN during 1992–2006 using EOFs and show that the summertime pH in China had different trends before and after 2000. The most significant decrease of pH is found in Central China. To investigate the causes of this decrease of pH in summer, we explore the relationship between changes in the pH value, the East Asian summer monsoon index, rainfall data, and pollutants emissions. We find that the East Asian summer monsoon can significantly affect the acidity of summer precipitation in Central China. In strong monsoon years, the pH in Central China is about 0.33 lower than that in weak monsoon years. Chemical transport model simulations using fixed emissions indicate that about 65% of the pH value difference (i.e., 0.22) is related to the summer monsoon, and constitutes 18–36% of the observed pH change (0.6∼1.2) in Central China during 1992–2006. Further studies reveal a relationship between the pH in Central China and the rainfall in the middle and lower reaches of the Yangtze River (MLYR), which can explain about 24% of the variance of pH in Central China. Simulations using an annually varying emission inventory show that at least 60% of the variation in precipitation acidity in Central China can be attributed to changes in pollutant emissions. Therefore, the increase in emissions of acidic species is the most important cause for the observed decrease of pH in Central China, and changes in meteorological factors, such as rainfall and other parameters related to the East Asian summer monsoon, play a less important but still significant role.

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