Acid rain is a global environmental issue because of its trans-boundary impacts on the biogeochemical cycles, its direct adverse effects on ecosystems and indirect effects on human health.  Although rain acidity is historically linked to inorganic acids like H2SO4 and HNO3, a number of studies have shown the importance of the contribution of organic acids, mainly formic, acetic and oxalic acids.  Guizhou province is one of the most serious areas of acid rain in the southwest of China, and has already been suffering from substantial environmental degradation due to air pollution.

 

 

Figure. Seasonal variations of (a) rainfall, volume-weighted average (VWA) concentrations and (b) wet deposition flux of organic acids in precipitation collected at the sampling site (Image by IGCAS)

Prof. LEE Xingqing’s group at Institute of Geochemistry, Chinese Academy of Sciences (IGCAS) has carried out a study on chemical characteristics and sources of organic acids of acid rain in Guizhou region.  They found acidification in rainwater was mainly caused by inorganic pollution in urban and semi-urban sites in Guizhou Province.  However, carboxylic acids significantly affected acidification and the chemical constituents of rainwater in remote and rural sites.  They suggested it is necessary to control emissions of organic acids to reduce the frequency of acid rain, especially in these areas.  In addition, the study reported higher concentrations of the majority of the organic acids during the non-growing season which was not typical of these acids.  The trend was attributed to dilution due to heavy rainfall during the growing season.　 A deposition calculation confirmed higher source strength in the growing season.  Furthermore, the air mass origins had significant influences on the concentrations of organic acids in precipitation.  For the majority of these organic acids, highest concentrations were observed in rain events originating from the Northeastern land in China.

This work was supported by the Knowledge Innovation Program of the Chinese Academy of Sciences (Grant No. KZCX2-YW-306-3) and the National Natural Science Foundation of China (Grant No. 40721002，40573048, 40872212), and more detailed results have been published in Atmos. Environ. 2011, (2) and Chinese Sci Bull, 2011, 56.

(Provided by ZHANG Yanlin)