北京城区道路灰尘季节性粒度分布及分形特征

对采集的北京城区道路灰尘样品用扫描电镜及X射线能谱进行形貌特征分析,用激光粒度仪进行粒度测定.结果表明:北京城区四季道路灰尘包含矿物颗粒,轮胎磨损颗粒及球型燃烧颗粒,四季道路灰尘粒度分布频率曲线均呈双峰态分布,第一峰值粒径介于256~303μm,第二峰值粒径介于74~88μm.四季道路灰尘粒度分布分形维数为1.7533~2.3137,平均粒径为188.08~200.20μm,分选性差,呈极不对称的极正偏宽峰态到很窄峰态,属砂土.四季道路灰尘均主要是局地灰尘跃移搬运形成,直接通过大气运移沉降的远源灰尘相对较少.平均粒径春季>秋季>夏季≈冬季,分选系数夏季≈秋季>冬季>春季,峰度冬季>秋季>夏季≈春季,偏度无较大区别.春季灰尘可吸入颗粒物最高,并含有可入肺颗粒物,对人体健康和大气环境的危害潜力不容忽视.

Particle size distribution and fractal dimension characteristics of urban road dust in four seasons in Beijing

Road dust samples were collected in 14 representative sampling zones stratified across core urban areas in Beijing. Three types of particles that included aggregated mineral matter, tire wear particles and spherical combustion products were detected with Scanning Electron Microscopy and Energy Dispersive X-ray (SEM-EDS). Bimodal patterns of grain size distributions were observed with Laser Granularity Analyzer. Results of the research showed that bimodal size distribution spectrum ranged from 256 to 303 μm and from 74 to 88 μm, respectively. The fractal dimensions of urban road dust ranged from 1.7533 to 2.3137. The mean particle sizes ranged from 188.08 to 200.20 μm. The poor sorting, the extremely positive skewness and the broad to very narrow kurtosis made urban road dust sand. Saltation and shorter distance suspension actually contribute significantly to the formation of the urban road dust, other transport ways, like long distance suspension, only did a few work. According to the research of road dust in the four seasons, the decreased order of them on mean particle size was spring, autumn, summer, and winter (the last two were similar). The decreased order of sorting coefficient was summer, which was closed to autumn, winter, and spring. When it comes to kurtosis, the decreased order was winter, autumn, summer, and spring, which was also near to summer. The differences of skewness can be ignored. Road dust in spring seemed to have the highest proportions of thoracic, as well as more inhalable and respirable particles, whose potential risk to health and environment should be aware of.