北京市不同天气条件下单颗粒形貌及元素组成特征

使用透射电镜(TEM)对采自北京市2011年3~4月间不同天气条件下的气溶胶样品进行观察,并对比2010年3月沙尘天气和2010年11月18日雾天样品,对可吸入颗粒物PM10的基本形貌、矿物元素组成和硫化特征等做比较分析.结果表明,采样期间PM10主要包括烟尘集合体、飞灰、矿物颗粒、二次反应颗粒等,不同天气条件下颗粒类型并无明显差别.采样期间矿物颗粒以“富Si”颗粒(占总量46%)为主,“富Ca”(总量17%)、“富S”颗粒(总量13%)为次要,“富Fe”(总量7%)及较少“富Na” 颗粒(总量6%)和其他颗粒.沙尘天气中沙尘暴输入大量沙尘颗粒使占颗粒83% 的“富Si”颗粒含量明显高于阴天的36%和雾天的32%.仅在阴天和雾天发现大量“富S”颗粒,其中雾天26%,阴天10.7%,说明这2种天气二次反应强烈,易于生成富S二次颗粒,对颗粒物元素组成产生影响.对所有含S颗粒分析表明,不同天气含S矿物含量差异较大,阴天16%,雾天36%,晴天和沙尘天气则含量很低,说明一定的SO2浓度下,大气湿度越大,硫化现象越明显.雾天颗粒物表面的硫化现象相当严重,在含硫量较高的颗粒中,绝大部分同时含有Ca、Na、Si、Fe等元素,说明大气中含Ca、Na、Si、Fe的碱性矿物对雾水酸性有一定的缓冲作用.

Morphologies and elemental compositions of individual particles under different weather conditions in Beijing

This paper analyzed the morphologies, elemental compositions and sulfuration characteristics of the fine particles collected in Beijing from March to April 2011under different weather conditions by means of Transmission Electron Microscopy (TEM). The fine particles of the dust weather in March 2010and the fog weather samples in November, 2010were also investigated with the same methods. The results showed that particles could be subdivided into 4major morphological categories, including soot aggregates, fly ash, mineral and secondary particles. Particle types have no obvious variation under different weather conditions. According to elemental compositions, mineral particles can be classified into 9categories, namely, “Si-rich” (occupying 46% by number), “Ca-rich” (17%), “S-rich” (13%), “Fe-rich” (7%), “Na-rich” (6%), and other particles including “Ti-rich”, “Al-rich”, “Cl-rich” and “Mg-rich”. The proportion of these different particles in PM10was influenced by weather conditions, with the number percentage of the “Si-rich” particles in dust storm (83%) being obviously higher than those on cloudy day (36%) and foggy day (32%). A higher number of “S-rich” particles were found in the cloudy and foggy days, being 10.7% and 26% respectively, indicating that the cloudy and foggy weather is favorable for secondary reactions and formation of S-rich particles. Sulfuration characteristics analysis of S-containing particles shows that, contain S mineral content differences in different weather, cloudy 16%, fog 36%, and it was barely found in sunny day and dust storm, it shows that at certain SO2concentration, the atmospheric humidity higher, the sulfation is more obvious. The Sulfation on the surface of particles in foggy day is quite serious, in the high sulfur content particles, most also contains Ca, Na, Si and Fe elements, indicating that alkaline mineral in the air which contains Ca, Na, Si and Fe elements have some buffer action to the acid mist.