合肥市酸雨变化特征及其影响因子

Marked changes of acid rain in Hefei and their causes

利用合肥市气象局酸雨监测站1992～2007年资料,分析了该市酸雨年、季变化特征,及其与地面气象条件、地面污染物(SO2、NO2、PM10)浓度的关系;同时,应用轨迹分析和聚类分析的方法研究了酸雨发生率与不同高度输送形势的关系.结果表明,合肥市酸雨发生率秋季最高、夏季最低;年平均降水pH值呈下降趋势,酸雨频率呈增加趋势,尤其是pH值低于4.5的强酸雨在2001年之后出现频率增加显著,与近年来地面SO2浓度的快速增加趋势一致;中度以上强度酸雨出现频率随降水强度的增加呈先增后减的变化特点,中雨和大雨时最高,毛毛雨时最低;地面污染物浓度,尤其是SO2与降水酸度具有显著的相关性,当地面SO2浓度高于40μg.m-3时,酸雨发生率接近90%;轨迹分析结果显示,合肥降雨酸度与输送形势关系密切,酸性降水发生率在低层以偏东北方向的轨迹最高,在中空(1500m)以偏东轨迹和西南轨迹最高,在高空(3000m)以偏西南轨迹最高.

The annual and seasonal characteristics of acid rain in Hefei and their relationships with the surface weather conditions and pollutant concentrations were analyzed using rainwater monitoring data from 1992 to 2007. Back-trajectory and cluster analyses were used to study the relationships between acid rain frequency and transport patterns at different altitudes. The results show that the frequency of acid rain was highest in autumn, and lowest in summer. The annual average pH tended to decrease, and the frequency of acid rain with pH 〈4.5 increased markedly since 2001, accompanied by a rapid increase of ground level SO2 concentration. The frequency of acid rain with pH 〈 5.0 showed a parabolic variation with the increase of precipitation intensity, maximum with moderate （ 10-25 mm·day^-1 ） and heavy rain （25-50 mm·day^-1 ） and minimum at drizzle （ 〈 2 mm·d^-1 ）. Precipitation acidity （pH） displayed obvious positive （negative） correlations with ground level SO2 concentrations. When SO2 concentration was higher than 40 μg·m^-3, the frequency of acid precipitation reached 90%. Precipitation acidity was closely related to the transport pattern. The highest frequency of acid rain was associated with northeasterly （from northeast） trajectory of the lower atmosphere layer （under 1000 m）, easterly and southwesterly trajectory at mid-level （1500 m） and southwesterly trajectory at high level （around 3000 m）.