Abstract: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.