我国14个站点降水中甲酸和乙酸浓度及对酸性的贡献

Concentrations and Acidity Contributions of Acetate and Formate in Precipitation at 14 Stations of China

为了较全面地掌握我国大气降水中有机酸含量及其对降水酸性的贡献,于2007年全年在我国14个区域代表性较好的站点采集了降水样品,利用离子交换色谱法分析了样品中的甲酸和乙酸2种重要有机酸的浓度,对所得各站数据进行了统计分析,计算了2种酸的湿沉降通量和对降水酸性的相对贡献.观测到的14个站点甲酸和乙酸平均浓度范围分别为0.96～3.43μmol/L和0～5.13μmol/L,接近国外偏远地区观测结果,也接近我国过去短期观测结果的低端值.比较显示,偏远地区有机酸含量低于城市附近地区.估算的甲酸和乙酸湿沉降通量范围分别为0.38～4.18mmol/(m2.a)和0.06～5.87mmol/(m2.a),南方站点有机酸湿沉降通量大于北方.有机酸对降水酸性的贡献范围是0.02%～51.6%,总平均贡献为2.95%,这一结果表明,虽然我国酸雨主要是硫、氮排放造成的,但有机酸在部分地区及部分时段甚至有很显著的致酸作用,应该成为酸雨观测研究内容之一.

To investigate the concentrations of organic acids in precipitation in China and their contributions to the total acidity of precipitation,samples were taken at 14 stations of regional representativeness in 2007 and analyzed for acetate and formate using ion chromatography. In this paper,data of acetate and formate in precipitation at 14 stations are presented,wet depositions of these organic acids are calculated,and contributions of them to the total free acidity （ TFA ） of precipitation are estimated. Based on the measurements,the mean concentrations of formate at different stations were in the range of 0. 96-3. 43 μmol /L,and those of acetate in the range of 0-5. 13 μmol /L,close to the levels at remote sites in other countries and at the lower ends of concentration ranges from previous measurements in China. Comparisons indicate that the concentrations of the organic acids at remote sites are lower than those at sites in the vicinity of urban areas. The annual wet depositions of formate and acetate were estimated to be in the ranges of 0. 38-4. 18 mmol /（m^2·a） and 0. 06-5. 87 mmol /（m^2·a）,respectively,with larger depositions in southern China and smaller depositions in northern China. The relative contributions of the two organic acids to the TFA of precipitation were estimated to be in the range of 0. 02% -51. 6% ,with an overall average of 2. 95%. This suggests that although acid rain in China is mainly caused by emissions of sulfur and nitrogen oxides,organic acids can significantly contribute to the acidification of precipitation in some regions and during some periods,hence need to be included in observational studies of acid rain.