Abstract: Continuous observation of PM2.5 was conducted in Taiyuan during high pollution seasons from 17 December 2005 to 28 March 2006. PM2.5 samples were collected using TEOM series 1400a ambient particulate monitor (Rupprecht & Patashnick Co., Inc, USA). The study showed that the concentrations of PM2.5 were high during winter and spring in Taiyuan. The average hourly mass concentration of PM2.5 was 247.6±193.7g/m3, which showed fine particles pollution was serious in Taiyuan. The frequency of hourly averages PM2.5 concentrations less than 400 g/m3 is 84.1%. The PM2.5 concentration has an obvious diurnal variation. The meteorological conditions have significant effects on the ambient concentrations of PM2.5. The wind speed, relative humidity, visibility and atmospheric pressure were major factors that influence the concentration variation of PM2.5. The 3 day air mass backward trajectories were calculated and clustered to analyze transport pathways of the air pollution in Taiyuan. The 3rd cluster trajectory, which moving paths was from the southwest of Taiyuan, had higher average PM2.5 concentration （342.6 g/m3）than other clusters (e.g. 261.1 g/m3 from east, 225.6 g/m3 from northwest). The concentrations of PM2.5 on sandstorm weather are analyzed.

Key words: PM2.5；mass concentration；meteorological conditions；backward trajectories