三峡水库库首地区大气降水化学特征

Chemical characteristics of rainwater collected in the head region of Three Gorges Reservoir

2009年6月-2010年7月对三峡水库库首地区大气降水的水化学特征进行了连续1年的研究，结果表明：三峡库首地区大气降水酸化严重，超过1／3的降水pH值低于4.5．S042和N03为降水中的最主要阴离子，雨量加权平均值分别为161．90，65．24ueq／L，二者分别占无机阴离子总量的66％、27％．ca2＋是最主要的阳离子，离子含量在8．89-932．90ueq／L之间，雨量加权平均浓度为108．34ueq／L，占无机阳离子总量的43％．季节变化分析表明，夏秋季节降水酸化严重，而冬春季节降水酸化不明显．不同季节相对酸度（FA）和中和因子（NF）分析表明，冬春季节的降水酸度主要受ca2＋离子的中和作用控制．主要离子来源分析表明，S042-和N03主要来源于化石燃料燃烧，Na＋、CI主要为海源输入的贡献，而Ca2＋、Mg2＋主要来源于陆壳颗粒物质。

Rainwater samples were collected in the head region of Three Gorges Reservoir from June 2009 to July 2010 and the pH and major ion concentrations were measured. The rain in this region were seriously acidized, more than one third of the rain events＇ pH were lower than 4.5. SO42 and NO3 were the main anions, and their volume-weighted mean were 161.90p.eq/L and 65,241ueq/L, respectively, which account for 66% and 27% of the total measured anions. Ca2＋ was the dominant cation in rainwater with a volume-weighted mean value 108.34ueq/L （8.89-932.901aeq/L）..The seasonal variations of the pH show that the rainwater were more acidized in summer and autumn than those in winter and spring. Results of fractional acidity （FA） and neutralization factors （NF） indicated that the acidity of rainwater in winter and spring were neutralization caused by Ca2＋. Studies of the origins of major ions showed that SO42 and NO3 were from fossil fuels, and Na＋ and CI were from sea sources, while Ca2＋ and Mg2＋ from the terrestrial mineral particles.