三峡库区降水化学组成及时空变化特征

Chemical composition of precipitation and its spatiotemporal variations in the Three Gorges Reservoir Region

对2000—2009年三峡库区巴南、涪陵和万州3个观测点降水的pH、电导率及其主要化学成分的时空变化进行了分析研究.结果表明,巴南、涪陵、万州降水pH平均值分别为5.76、6.03和5.52,平均电导率分别为117.3、72.3和63.1μS.cm-1,降水酸化趋势在逐渐增强,污染程度高于北京、成都、深圳、湖南等地.降水中SO2-4占阴离子总量的77%,NH+4和Ca2+为主要的阳离子.巴南、涪陵、万州3个监测点的[NO-3]/[SO2-4]比值较低,分别为0.125、0.164和0.169,表明降水酸化类型为硫酸型.由于排放与气象条件(包括降雨量等)的季节性变化,各离子组分呈现明显的时空变化特征,总体表现为冬春季降水中离子浓度高于夏秋季,污染程度为巴南>涪陵>万州.

In order to understand the main chemical constituents within precipitations and their spatiotemporal variations in the Three Gorges Reservoir Region,the atmospheric precipitation samples were collected from three stations along the reservoir during 2000 to 2009.pH,conductivity,and ions were analyzed.Average pH values were 5.76,6.03,and 5.52,and average conductivity were 117.3,72.3,and 63.1 μS · cm-1 in Banan,Fuling and Wanzhou,respectively.The rainwater in these districts exhibited a significant acidification trend over the past decade with more serious pollution levels than those in Beijing,Chengdu,Shenzhen,and Hunan.The concentration of SO2-4 accounted for 77% of total anions,while NH＋4 and Ca2＋ were the major cations.The relatively low mass ratio of NO-3 to SO2-4 in the three stations indicated that the type of rain acidity was still dominantly from sulfuric acid.The ionic constituents of precipitation presented clear spatial-temporal variations,due to seasonal variations in emissions and meteorology,including the rainfall intensity.The ion concentrations were higher in winter and spring and lower in summer and autumn.Precipitation pollution in the three stations exhibited a clearly decreasing trend with distance from downtown Chongqing.