北京春季城区与远郊区不同大气粒径颗粒物中水溶性离子的分布特征

Size distributions of water-soluble inorganic ions at urban and rural sites in Beijing during spring

为比较北京城区与远郊区大气颗粒物中水溶性无机离子的组成特征,2012年4月,利用Andersen分级撞击式采样器同时在2个采样点进行大气颗粒物分级采样,样品采用离子色谱分析.结果表明,城区和上甸子大气颗粒物中水溶性无机离子总浓度分别为(83.7±48.9)μg·m-3和(75.5±52.9)μg·m-3,NO-3、SO2-4和NH+4是最主要的水溶性无机离子,分别占总离子浓度的81.2%和84.2%.粒径分布显示,Mg2+和Ca2+在5.8～9.0μm的粒径范围出现峰值,Na+、NH+4、Cl-在0.43～1.1μm和4.7～9.0μm的粒径范围出现双峰,K+、NO-3和SO2-4在0.65～2.1μm的粒径范围出现峰值.后向轨迹簇分析表明,气团来自南方时,城区和上甸子二次离子浓度分别为(92.4±40.0)μg·m-3和(95.0±35.4)μg·m-3,来自其他方向时,分别为(24.0±10.8)μg·m-3和(13.3±10.6)μg·m-3.

In order to investigate the characteristics of water-soluble inorganic ions in particulate matter （PM） at urban and rural sites in Beijing, PM samples were collected with Thermo Scientific Andersen impactors at both sites. The water-soluble inorganic ions were analyzed by IC.The results showed that the concentrations of the total water-soluble inorganic ions at urban and rural sites were （83.7±48.9） μg·m^-3 and （75.5±52.9） μg·m^-3. NO3-, SO42- and NH4＋ were the major ions in particulate matter at both sites, which accounted 81.2% and 84.2% of all the ions. Furthermore, Mg2＋and Ca2＋ were mainly associated with coarse particles with a peak at 5.8—9.0 μm, Na＋, NH4＋and Cl- had a multi-mode distribution, with peaks at 0.43—1.1 μm and 4.7—9.0 μm. K＋, NO3- and SO42- were mainly associated with fine particles with a peak at 0.65—2.1 μm. The backward air mass trajectory analysis suggested that the concentrations of secondary ion were （92.4±40.0） μg·m^-3 and （95.0±35.4） μg·m^-3 when the air mass came from the south, and （24.0±10.8） μg·m^-3 and （13.3±10.6） μg·m^-3 when the air mass came from the other directions at urban and rural sites.