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 Caand 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 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.

Chemical characteristics of rainwater in Sichuan basin, a case study of Ya’an

“…The potential anthropogenic sources of Cl − include vehicle exhaust, production and application of organochlorine compounds (e.g., dry clean agent), and biomass burning . The high correlation between Cl − and K + (R 2 = 0.80, Table S1) proves that biomass burning was the main source of Cl − , consistent with the previous result in Ya'an reported by Zhao et al (2013). Considered that Ya'an is a semi-rural and less industrialized city, the high contribution of anthropogenic sources (F1) may be attributed to regional and/or long-range transport influences, which will be discussed later.…”

“…Approximately 74 % of pH values of the rainwater samples was <5.6. The frequency of acid rain in Ya'an was in the medium level of south China, where had the range of 71-89 % reported from various studies (Huang et al 2008a(Huang et al , b, 2009(Huang et al , 2010Wang and Han 2011;Zhao et al 2013). Fifteen percent of the events recorded a pH below 4.0, indicating severe acidification caused by strong impact of anthropogenic pollution in this area.…”

“…Our value showed a slightly increase from the VWM of pH 4.03 measured in Ya'an during 2010-2011 . Even though the ranges of pH (3.25-6.86 in the study vs 3.36-6.68 in Zhao et al (2013)) were very close between these two periods, there was an obvious diversity on the frequency of distributions. Up to 68 % of samples was within the range of 3.0-4.5 in 2010-2011, while only 43.5 % in 2013-2014.…”

“…The highest total ionic concentration was accompanied with the lowest rainfall in winter (69 mm), while the lowest one was accompanied with the highest rainfall in summer (961 mm). The remarkable decrease in the event-average ionic concentrations was found when the precipitation amount increased in many other studies (Huang et al 2008a(Huang et al , b, 2009(Huang et al , 2010Zhao et al 2013). In addition, for the crustal species, the long residence time of floating particles in the air during the spring and winter could result in the accumulation of ions, giving rise to high ionic concentrations in rainwater (Chen and Mulder 2007), while wet soils meaning that little surface dust is incorporated into the air during summer and autumn (Huang et al 2008b).…”

Confirming anthropogenic influences on the major organic and inorganic constituents of rainwater in an urban area

“…The dominance of NH 4 NO 3 has also been reported previously (Saxena et al, 1996). The high correlation between SO 2− 4 and NO − 3 suggests a common source origin, due to the co-emission of precursors (SO 2 and NO x ) from the same sources, such as fossil fuel burning, and the similar- = 0.66), suggesting that Ca(NO 3 ) 2 and CaSO 4 are formed from the neutralization reactions of acidity in rainwater (Zhao et al, 2013). Moderate correlation was found between K + and Ca 2+ , indicating a common origin in marine aerosol.…”