《攻坚行动方案》实施后北京市PM2.5中微量元素组成特征

文中利用电感耦合等离子质谱仪(ICP-MS)对《攻坚行动方案》实施后北京市环境大气PM2.5中微量元素组成特征进行研究。结果表明，《攻坚行动方案》实施后，北京市PM2.5中微量元素以Zn、Mn、Ba、Pb、Cr、Cu、Ti等7种元素为主，其中元素Zn含量最高。元素Zn、Cd、Tl、Cs、Rb的水溶性组分在总微量元素中占比超过80%，说明这些元素大部分以易溶于水的状态存在于PM2.5中。有趣的是,在PM2.5样品中微量元素的含量(10-6)随着PM2.5污染水平的升高而下降,而质量浓度(ng·m-3)随PM2.5污染水平的升高而升高。这说明单位质量PM2.5中微量元素的含量只与颗粒物的组成成分有关，与颗粒物浓度无关。采样期间PM2.5中的微量元素主要来源于土壤扬尘(48.27%)、燃烧源和工业排放(16.16%)、刹车和轮胎磨损(10.03%)，其次是汽车尾气(5.84%)、建筑扬尘(4.88%)以及其他源(3.68%)。与攻坚行动前相比，PM2.5中微量元素的质量浓度有明显的降低，高污染等级的PM2.5样品中微量元素质量浓度的降幅最为明显，比攻坚行动前下降了80.3%。

Trace element compositions in PM2.5 after the action for comprehensive control of air pollution in Beijing

We investigated by ICP-MS the trace elemental compositions of PM2.5 in Beijing after the implementation of the ‘action plan’ for comprehensive control of air pollution. The results showed that PM2.5 mainly contained 7 trace elements, Zn, Mn, Ba, Pb, Cr, Cu and Ti, with Zn ranked the highest in content. The water-soluble form of Zn, Cd, Tl, Cs or Rb accounted for more than 80% of its total content in PM2.5, revealing that most trace elements occur water-soluble in fine particles. Interestingly, trace elemental contents (10-6) in PM2.5 samples decreased with increasing PM2.5 pollution levels, whereas, mass concentrations (ng·m-3) increased with increasing pollution levels, the same trend as PM2.5 mass concentration. It indicated that the content of trace elements in PM2.5per unit mass is only related to the composition of particles, not the concentration of particles. The trace elements in PM2.5 during the sampling period were mainly from soil dust (48.27%), combustion sources and industrial emissions (16.16%) and vehicle brake and tire wear (10.03%), followed by automobile exhaust (5.84%), construction dust (4.88%) and other sources (3.68%). Compared with the results before the action for comprehensive air pollution control, the mass concentration of trace elements in PM2.5 after the action decreased significantly, with the greatest decrease of 80.3% at high pollution level.