齐齐哈尔市大气细粒子PM_(2.5)单颗粒研究

Investigation and analysis of the individual aerosol particles of PM_(2.5) in the atmosphere of the city of Qiqihaer

为了了解齐齐哈尔市大气细粒子PM2.5单颗粒的形貌、组成及粒度分布特征,选取齐齐哈尔市大学校园和商业市中心两个采样点,针对春季和秋季大气中PM2.5单颗粒,应用场发射扫描电镜(FESEM)和配带X射线能谱的扫描电镜(SEM-EDX)对其微观形貌和元素组成进行了研究。利用图像分析系统对其粒径分布进行统计。结果表明,此地区PM2.5颗粒分为4种类型,即烟尘集合体、飞灰、矿物颗粒和未知颗粒,分别来源于机动车尾气排放、煤炭等燃料燃烧及地壳扬尘。其中春季烟尘集合体数量最多,秋季由于燃煤以飞灰为主。来源于地壳扬尘的矿物颗粒以硅铝酸盐类和碳酸盐类矿物为主。此地区大气中PM2.5颗粒空气动力学直径约90%小于1.0μm,属大气细粒子。其中烟尘集合体平均粒径大于矿物颗粒,飞灰平均粒径最小。

The paper intends to report our statistical research results on the morphology, the elemental composition and the size distribu- tion situation of PM2.5 in the atmosphere of the city of Qiqihaer in ac- cordance with our investigation resuhs in the spring and autumn of this year. For our research goal, we have collected samples of PM2.5 at a university campus and the commercial center of Qiqihaer city. We have also measured and scrutinized the morphology and elemental composition of the individual particles by way of the Electronic Scan- ning Microscopy coupled with the Energy Dispersive X-ray Spectrome- ter （SEM - EDX）. And, then, we have also further analyzed the ob- tained images for their size distribution by means of an image analysis system. It is just based on the morphology and energy spectrum that is mentioned that four types of particles have been identified in this paper as the dominant particles in the PM2.s ： the soot aggregates, the fly ash, the mineral ones and others. The soot aggregates have been identified mainly consisting of C and O, which can be traced to the e- mission of the auto exhausts. The fly ash has usually been found con- sisting of Si, AI and some other minor elements, such as Fe, K, Mg, etc., which can be traced as a result of coal and other fuels＇ combustion. The composition of the mineral fuels has been found pre- dominately particles with alumino-silicates and carbonates. Besides, it can also be found that the calcium feldspar, dolomite, calcite, quartz and hematite are also the constituent elements in mineral or fossil fuels. Needless to say, they could be traced to the flying dust from the earth＇s crust. Generally speaking, more soot aggregates can be found in the spring than in the autumn. However, more fly ash and minerals can be found in the autumn season. More soot aggre- gates can be found in the commercial and repair and other handicraft mending centers in the civilian urban areas than their counterparts in the university campus, because those are places highly polluted and contaminated by the auto exhaust emissions. The electronic image analysis indicate that about 90% of the airborne particles in PM2.5 were smaller than 1.0/zm in diameter, which indicates that they can enter into human lung alveoli. The minimum average particle sizes of the mineral pollutants prove to be slightly larger than the fly ash, soot aggregates, of which the fly ash can be said the smallest ones among all the collected samples of PM2.5.