2011年秋季广州城区大气PM2.5微观形貌和粒度分布

利用高分辨率扫描电镜加能谱仪(SEM-EDX)和图像数据分析技术对2011年秋季广州市中心大气PM2.5的微观形貌和粒度分布特征进行研究,系统获得3种典型颗粒(矿物、烟尘集合体和燃煤飞灰)和其它未知颗粒的数量-粒度分布和体积-粒度分布数据.结果表明,PM2.5颗粒数量-粒度分布峰值落在0.1~0.2μm之间,属于积聚模态中含有气相反应产物的凝结亚模态.3种典型颗粒对PM2.5的数量和体积贡献均为矿物>>烟尘集合体>飞灰.矿物主要分布在0.1~0.3μm范围内,所占数量百分比为41.97%,其中0.1~0.2μm范围内矿物占比高达26.42%,是影响PM2.5颗粒整体分布的主要因素.不同采样时段(上午、下午、晚上)和下雨前后PM2.5颗粒的粒度分布特征基本一致,但晚上和下雨后小于0.1μm的颗粒比例有明显减少趋势.

Microscopic morphology and size distribution of PM2.5 in Guangzhou urban area in fall 2011

Samples of airborne PM2.5 particles were collected during Fall 2011 from Guangzhou urban area. The morphology and size distribution of individual particles were analyzed by a Scanning Electron Microscopy coupled with Energy Dispersive X-ray Spectrometer (SEM-EDX) and Image Analysis System. Based on the morphology, three typical particles (soot aggregates, minerals, and coal fly ash) and other unknown particles in PM2.5 were identified. Results showed that the number-size distribution of PM2.5, peaking in the range of 0.1~0.2 μm, was dominated by the condensing sub-mode within the accumulation mode where gas phase reaction products were distributed. Both number and volume contribution of three typical particles were on the order of mineral >> soot aggregate > fly ash. Minerals were mainly distributed in range of 0.1~0.3 μm with 41.97% in number percentage. The percentage of minerals in range of 0.1~0.2 μm was as high as 26.42% , which was the major factor influencing the overall size distribution of PM2.5. Size distributions of PM2.5particles were fairly similar during different sampling period (morning, afternoon, evening) as well as before and after raining, but the proportions of particles having sizes less than 0.1 μm were significantly decreased in the evening and after raining.