A comprehensive study on the chemical compositions of rainwater was carried out from June 2007 to December 2008 in Guiyang, a city located on the acid rain control zone of southwest China. All samples were analyzed for pH, major anions (F-, Cl-, NO (3) (-) , SO (4) (2-) ), major cations (K+, Na+, Ca2+, Mg2+, NH (4) (+) ), Sr2+ and Sr isotope. The pH increase is due to the result of neutralization caused by the alkaline dust which contain large amount of CaCO3. It was observed that Ca2+ was the most abundant cation with a volume-weighted mean (VWM) value of 217.6 mu eq/L (52.7-1928 mu eq/L), accounting for 66% (39%-88%) of the total cations. SO (4) (2-) was the most abundant anion with VWM value of 237.8 mu eq/L (49.6-1643 mu eq/L). SO (4) (2-) and NO (3) (-) were dominant among the anions, accounting for 66%-97% of the total measured anions. The Sr concentrations vary from 0.01 to 0.92 mu mol/L, and strontium isotopic ratios vary in the range of 0.707684-0.710094, with an average of 0.708092. The elements ratios and the Sr-87/Sr-86 ratios showed that the solutes of rainwater mainly come from weathering of carbonate and secondary dust input. Moreover, urbanization results in the calcium-rich dust increased and the high concentrations of alkaline ions (mainly Ca2+) have played an important role to neutralize the acidity of rainwater, leading to the increase of arithmetic pH mean value by 0.5 units since 2002. It is worth noting that the emission of SO2 and NOx from the automobile exhaust is increasing and is becoming another important precursor of acid rain now.

Publication name	JOURNAL OF ATMOSPHERIC CHEMISTRY　Volume: 68 　Issue: 2 　Pages: 139-155　 Published: JUN 2011
Author(s)	Han, Guilin; Wu, Qixin; Tang, Yang
Corresponding author	HAN Guilin  hanguilin@vip.skleg.cn  Chinese Acad Sci, Inst Geochem, State Key Lab Environm Geochem, Guiyang 550002, Peoples R China

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