Chemical Composition and Sources of Rainwater Collected at a Semi-Rural Site in Ya’an, Southwestern China

Abstract

Rain and snow water samples were collected from Sep. 2010 to Jun. 2011 at a semi-rural site in Ya'an, a city located in the rain-belt along the Tibetan Plateau, to characterize the chemical composition and the sources of precipitation. The collected samples were severely acidified with an annual volume-weighted mean (VWM) pH of 4.03 and an annual acid rain frequency of 79%. and were the most abundant ions, followed by Ca 2+ , H + , , Cl − , K + , Na + , F − and Mg 2+ . The acidity of samples was predominantly generated by H 2 SO 4 and HNO 3 , which were neutralized by and Ca 2+ as much as 65%. NH 3 played a major role in neutralizing the acid rain. The average ambient concentration of NH 3 was 174.2 μg/m 3 during sampling periods. Different source apportionment methods, including principle compo-nent analysis (PCA), enrichment factor (EF), correlation and back-trajectory analysis were used to track the sources of rainwater. The methods suggested that the pollutants in rainwater were from both local and long-distance transport (1:2.2), or they were from anthropogenic actions (86.4%), sea salts (8.1%) and crustal (5.5%) respectively. 2 4 SO − 4 NH + 3 NO − 4 NH +