崇明东滩大气湿沉降酸性特征

ACIDITY CHARACTERISTICS OF WET DEPOSITION IN CHONGMING DONGTAN

对崇明东滩湿地的大气湿沉降进行了为期一年的样品采集,对其酸性特征进行了系统分析与讨论.结果表明,大气湿沉降表现出明显的酸性,pH均值为4.85,16.67%的降水达到强酸性,较强酸性的占19.44%;从各月份pH变化来看,9月份pH值相对较低,1月和7月较高,各季节pH值变化规律为秋季<春季<夏季<冬季;降雨pH同降雨量表现出一定的负相关性,同风向表现出显著的正相关,风向变化引起的大气颗粒物含量的差异对湿沉降酸性产生明显影响;湿沉降中主要酸性离子NO3-和SO24-平均含量分别为68μmol.l-1和241μmol.l-1,季节变化均表现为秋季>冬季>夏季≈春季;湿沉降中SO24-和NO3-的当量浓度比均值为15.1,H2SO4对酸雨起决定性贡献作用,燃煤排放是湿沉降呈酸性的最主要原因.

Rainwater samples were collect in Chongming Dongtan,an international important wetland,during one-year period. Characteristics of the acid rain were analyzed in detail.Results showed that the rainwater was acid rain,with an average pH of 4.85. 16.67% of the samples were of strong acidity,and 19.44% of the rainwater exhibited the acidic properties.pH of the rains in September was relatively low,and the values for samples in January and July was elevated.pH of rainwater varied in the ascending order of autumn,spring,summer and winter.There was a positive correlation between pH and wind directions,implying that particle contents in atmosphere could affect the acidity of rainwater.Average levels of NO3^- and SO4^2-,the predominant acidic ions in rains,were 68 mol·l^-1and 241 mol·l^-1 respectively,with the variation in 4 seasons in the order of autumnwintersummer ≈ spring. The mean ratio of SO4^2- to NO3^- equivalent concentrations in rain samples was 15.1,indicating that H2SO4 dominated the acidity of rainwater. It could be concluded that flue gas emitted from coal combustion was the main reason of acid rain in the study area.