Abstract
Abstract. 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.
Highlights
Acid rain has been one of the most significant environmental problems in China since the late 1970s
What are the causes of this increase and are they related to changes in climatic conditions? In this paper, we report the potential contributions of the summer monsoon and rainfall in the middle and lower Yangtze River regions to precipitation acidity in Central China
We evaluate the influence of variations in emissions on changes in the acidity of precipitation in Central China
Summary
Acid rain has been one of the most significant environmental problems in China since the late 1970s. Rapid economic development and population growth has lead to increases in the emission and subsequent deposition of sulfur, and widespread acid rain was observed in southern and southwestern China between the 1980s and the mid 1990s (Ding et al, 1997, 2004; Wang and Wang, 1995, 1996; Zhao et al, 1988; Huang et al, 1995). Municipal governments attempted to improve air quality in different ways to strengthen the control of the emissions of gaseous pollutants and particulate matter. These efforts had some positive effects in the first few years, rapid economic development and an increased demand for energy have caused further increases in the emissions of SO2 and NO2 over the last decade. A large number of reports (Zhang et al, 2008; Xie et al, 2009; Wang and Xu, 2009; SEPA; Gao et al, 2009; Larssen et al, 2006) reveal that nationwide emissions of SO2 and NO2 have increased significantly since 2000, following the temporary decrease in emissions in the 1990s
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