Seasonal variation and sources of low molecular weight organic acids in precipitation in the rural area of Anshun

• Published in: Chinese science bulletin 2011-04, Vol.56 (10), p.1005-1010
• Main Authors: Zhang, YanLin, Lee, XinQing, Cao, Fang, Huang, DaiKuan
• Format: Article
• Language: English
• Subjects: acetic acid; acid deposition; acidity; air pollution; anions; anthropogenic activities; chemical composition; Chemistry/Food Science; Earth Sciences; emissions; Engineering; formic acid; Humanities and Social Sciences; ion exchange chromatography; Life Sciences; molecular weight; multidisciplinary; oxalic acid; Physics; rain; rural areas; Science; Science (multidisciplinary); seasonal variation; vegetation; wet deposition; winter; 低分子量有机酸; 农村地区; 化学成分; 季节变化; 安顺; 平均浓度; 污染来源; 降水
• ISSN: 1001-6538; 1861-9541
• DOI: 10.1007/s11434-011-4411-5

Low molecular weight （LMW） organic acids are important and ubiquitous chemical constituents in the atmosphere. A compre- hensive study of the chemical composition of precipitation was carried out from June 2007 to June 2008 at a rural site in Anshun, in the west of Guizhou Province, China. During this period, 118 rainwater samples were collected and the main LMW carboxylic acids were determined using ion chromatography. The average pH of rainwater was 4.89 which is a typical acidic value. The most abundant carboxylic acids were formic acid （volume weight mean concentration： 8.77 μmol L-1） and acetic acid （6.90 μmol L-1）, followed by oxalic acid （2.05 μmol L-1）. The seasonal variation of concentrations and wet deposition fluxes of organic acids indicated that direct vegetation emissions were the main sources of the organic acids. Highest concentrations were observed in winter and were ascribed to the low winter rainfall and the contribution of other air pollution sources northeast of the study area. The ratio of formic and acetic acids in the precipitation （[F/A]r） was proposed as an indicator of pollution source. This suggested that the pollution resulted from direct emissions from natural or anthropogenic sources. Comparison with acid precipitation in other urban and rural areas in Guizhou showed that there was a decreasing contribution of LMW organic acids to free acidity and all anions in rainwater from urban to remote rural areas. Consequently, it is necessary to control emissions of organic acids to reduce the frequency of acid rain, especially in rural and remote areas.