The observational data of acid rain at Lin'an Atmosphere Watch Regional Station( AWRS) for the lal si* years, were used to analyze the characteristics of temporal distribution of pH value of precipitation, acid rain frequency and affecting factors at Lin'an AWRS. In addition, using the Hysplit4. 8 Model and NCEP meteorological reanalysis data of 2008 , the back-trajectory analysis was uaed to confirm the impacts of transputl patterns on the precipitation acidity at Lin'an AWRS. The results show that the monthly pH of the last 6 years was below 4. 5 , which indicates that severe acid rain pollutions occur. The acid rain occurrence frequency reveal* ihft lowest in summer, while the highest in autumn, with annual average pH was less than 5.6 from 1985 to 2009. By the analysis of Daniel tendency statistics, the precipitation at Lin'an AWRS was likely lo decline year by year. Another characteristic was that high wind velocity was favorable to decrease acid rain occurrence frequency. The amount of precipitation had great impact on the pH value of precipitation. The acid raid was significant negative correlation with the SO;concentrations before rainfall occurred. The results of back-trajectories analysis indicate that the north trajectories come from Jiangsu and Shanghai and the trajw.tariM come from the west of Zhejiang play key roles in acid rain occurrence at Lin'an AWRS. Acid rain pollution at Lin'an AWRS had change into sulfuric-nitrous mixed type.%利用临安大气本底站酸雨观测数据,研究临安大气本底站降水pH,酸雨发生频率的时间分布特征、变化趋势及其影响因素;借助后向轨迹分析法分析输送形势对临安大气本底站酸雨的影响.研究表明:最近6年间临安大气本底站降水pH各月均值均小于4.5,均达到强酸雨的程度;临安大气本底站的酸雨发生频率表现为夏季低、秋季高;1985-2009年临安大气本底站降水的年均pH全部达到酸雨程度.根据 Daniel趋势检验,临安大气本底站年均降水pH总体上呈逐年下降的趋势.风速越小,酸雨出现频率就越高;降水pH受降水量的影响较大.临安大气本底站的酸雨与降水前的大气中SO2浓度存在负相关的关系.根据气团的来向与酸雨污染程度的关系分析,临安大气本底站的酸雨污染受到其北部地区和浙西地区的酸雨气体物输送的影响较大.临安大气本底站的酸雨污染特征已由原来的硫酸型转为硫酸型与硝酸型并重.
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