北京西北城区与清洁对照点夏季大气PM_(10)的微观特征及粒度分布

Microscopic Characteristics and Size Distribution of Summer PM_(10) in the Air of a Northwestern Urban Site and a Clean Air Site in Beijing

应用高分辨率场发射扫描电镜 (FESEM )和图像分析技术研究了北京西北城区和清洁对照点非取暖期(2 0 0 1年夏季 )大气单个颗粒物的形貌特征以及PM10 和PM2 5的数量 粒度和体积 粒度分布 .研究表明 ,烟尘集合体在 2个采样点都普遍存在 ,具有区域性污染的特征 ;不规则状矿物颗粒物多见于市区PM10 样品中 ,而长条状石膏颗粒多出现在清洁对照点颗粒物样品中 ;在清洁对照点还观察到了生物质颗粒 .PM10 的数量 粒度分布呈双峰分布 ,主峰为 0 2～ 0 5 μm ,次峰为在 1～ 2 5 μm .但PM10 的体积 粒度分布呈单峰分布 ,在 1～ 2 5 μm粒度范围内 .综合分析得出 ,虽然粗颗粒 ,主要是矿物颗粒 ,在数量上对PM10 贡献很小 ,但是对总体积 ,因此对总质量的贡献可能很大 .但在PM2 5中 。

Microscopic characteristics and size distribution of individual particles in the summer (2001) PM 10 collected at a northwestern urban site and a clean air site in Beijing have been investigated using high resolution Field Emission Scanning Electron Microscopy (FESEM) and image analysis technologies. The soot aggregates were observed at both sampling sites, showing a characteristic regional pollution. The irregular mineral particles existed commonly at the urban site but were rarely seen at the clean air site. The elongated gypsums and biological particles were observed only at the clean air site. PM 10 displayed a bimodal number-size distribution, with a higher peak in 0.2～0.5μm range and a lower peak in 1～2.5μm range. In contrast, volume-size distribution of PM 10 exhibited a unimodal pattern with the peak in 1～2.5μm range. The coarse particles, mainly minerals, had a considerable contribution to the PM 10 mass, although they were insignificant in number. In PM 2.5, however, the soot aggregates were dominant both in number and mass.