中文摘要：

利用透射电子显微镜（TEM）对北京市区和背景点的细颗粒物（PM2.5）的形貌特征和集聚状态进行分析。结合颗粒物能谱（EDX）和选区电子衍射（SAED）特征，将北京市大气细颗粒物分为烟尘集合体、飞灰、矿物颗粒、硫酸盐和有机颗粒等5种单颗粒类型，并讨论了它们的来源．TEM分析表明，北京市区和背景点大气细颗粒物中不同类型的单颗粒所占比例不同，表明市区和背景点细颗粒物的污染物源有所不同．研究还表明，不同类型的细颗粒之间常常发生聚集．

英文摘要：

This paper analyzed the morphological characteristics and aggregate state of the fine particles collected at the urban and background sites of Beijing by means of Transmission Electron Microscopy （TEM）. Coupled with the characteristics from the energy dispersive X-ray spectrometry （EDX） and Selected Area Electron Diffraction （SAED） analyses, the typical fine particles in Beijing were classified into five categories of single particle types, including soot aggregates, fly ashes, mineral particles, sulfates and organic particles. The possible sources origins of these particles were discussed in more detail. The TEM analyses revealed that the relative proportions of these different types of particles at the urban site were different from those at the background site, indicating that the pollution sources of fine particles were different between the urban and background sites. The TEM images showed that these different types of particles tended to aggregate each other.