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%. SO42- and NH4+ were the most abundant ions, followed by Ca2+, H+, NO3-, Cl-, K+, Na+, F- and Mg2+. The acidity of samples was predominantly generated by H2SO4 and HNO3, which were neutralized by NH4+ and Ca2+ as much as 65%. NH3 played a major role in neutralizing the acid rain. The average ambient concentration of NH3 was 174.2 μg/m3 during sampling periods. Different source apportionment methods, including principle component 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.
Highlights
Acid rain has received worldwide attention during the past decades for its notably negative effects on aquatic and terrestrial ecosystems
Many studies were conducted on acid rains in south China [4,5,6]
Three principle factors were extracted from primary component analysis
Summary
Acid rain has received worldwide attention during the past decades for its notably negative effects on aquatic and terrestrial ecosystems. Many studies were conducted on acid rains in south China [4,5,6]. South China has been regarded as the third largest acid region in the world following Northeast America and Central Europe [4,7]. In these previous studies, major attentions were paid to urban areas because more anthropogenic pollutants, i.e. SO2 and NOx, are emitted in the industrialized sites. The negative effects of acid rain on rural areas, such as on forests, farmlands and water bodies, are as important as on urban areas, and acid rains in rural areas are usually obvious and caused by a significant influence of long range transport air pollutants [8], the knowledge of acid rains in extensive non-urban areas is still limited
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