北京城区大气干沉降的水溶性离子特征

Characteristics of water-soluble ions in dry deposition in urban Beijing

为了解北京城区大气干沉降中水溶性离子的化学组成与时间变化特征,连续进行了4年多的干沉降采样与分析.结果表明,在222个有效干沉降样品中,存在不同程度的阴离子缺失.SO42-与Ca2+分别是含量最丰富的阴、阳离子组分,其次是NO3-和NH4+.SO42-、NO3-和NH4+呈现相似的季节变化特征,即其浓度在夏季最高,冬季最低.干沉降基本呈中性,其pH值月变化幅度小,但季节变化明显,夏季低而春季高.

To understand the chemical composition and temporal variations of precipitation in Beijing,one-week integrated dry deposition samples were collected for more than four years.Among 222 dry deposition samples,there existed more or less anion deficits.SO42-and Ca2＋ were the most abundant anion and cation,followed by NO3-and NH4＋,respectively.SO42-、NO3-and NH4＋ exhibited similar seasonal pattern,with higher and lower concentrations occurring in summer and winter,respectively.Dry deposition samples usually appeared neutral,with narrow variations in their monthly averages but an evident seasonal pattern,i.e.,lower level in summer and higher level in spring.