拉萨市夏季大气降尘单颗粒矿物组成及其形貌特征

Mineral composition and morphology of individual dust fall particulates over Lhasa in summer

应用带能谱的电子扫描电镜(SEM-EDX)对拉萨市夏季正常天气下收集的大气自然沉降气溶胶样品进行分析,研究了拉萨市大气降尘矿物组成和各种物相形貌特征信息。拉萨市大气颗粒物含有硅酸盐颗粒、富钙颗粒、富铁颗粒、富碳颗粒(燃煤飞灰颗粒和燃油飞灰颗粒)和植物残体颗粒。根据颗粒物数量统计发现拉萨市大气颗粒物以硅酸盐颗粒为主,富钙颗粒和富铁颗粒次之,需要指出的是以燃油飞灰为主的富碳颗粒已占到一定比重,说明以燃油为主的机动车尾气对拉萨大气污染在加强。研究结果表明,大气降尘矿物成分及其形貌特征可以用作判定污染物来源的重要标志,拉萨大气中颗粒来源的多样性决定了治理措施也应综合进行。

Scanning electron microscopy equipped with energy dispersive X-ray detector （SEM-EDX） was used to study the atmospheric dust fall aerosols collected in Lhasa under the regular meteorological conditions in summer. The results offer the particles size, mineral composition and mineral morphology of the atmospheric dust fall in Lhasa. Morphologic observation of SEM reveals that the dust fails are mainly composed of clay silicate particles in the irregular flaky shape and a certain amount of such anthropologic and biological particles as soot and pollens. On the basis of EDX analyses of 149 particles and by using the developed elemental weight method, the authors classified the particles into six different categories, i.e., atmospheric particles mainly composed of ＂Si-rich＂ particles, ＂Ca-rich＂ particles, ＂Fe-rich＂ particles, ＂C-rich＂ particles （fly ash particles from coal and oil combustion）, ＂K-rich＂ particles and ＂Zr-rich＂ particles. Statistics of the particle quantity show that silicates possess 52.4 % of total particles. The silicate particles in the sample include much more felsic components than mafic （Fe-Mg-rich） particles, and the felsic particles are mainly distributed in four subgroups, namely, ＂quartz group＂, ＂orthoclase group＂, ＂pyrophyllite and montmorillonite group＂ and ＂muscovite and illite group＂, with the marie particles mainly distributed in the ＂biotite and vermiculite group＂. ＂Ca-rich＂ particles were detected in 28.2% of the particles, and most of Ca components are ＂high-Ca＂ particles and exist as calcite （CaCO3）. A study of the mixture state of Ca in atmospheric particles shows that particles with weight ratio of Ca, P（Ca）, greater than 0.1 and 0.02 possess 47.3 % and 86.8 %, respectively, and 26.5 % of the particles are Ca-dominant particles with P （Ca） ≥ 0. 65. Particles with Ca are concentrated in the radius range of 〈 5μm,and most of the Ca is internal mixture in silicate particles. Sufficient attention should be paid to fuel carbonaceous particles from vehicle exhaust in emission reduction and control. The mineral composition and morphology of atmospheric dust fall act as important criteria in identifying pollution sources.