[Size distribution properties of atmospheric aerosol particles during summer and autumn in Lanzhou]

Atmospheric particle size distributions (size range 0.5-20 microm) were measured using aerodynamic particle sizer (APS-3321) from August 1st to October 31st in Lanzhou. Variations of particle concentrations and properties of volume concentration distributions were analyzed through cluster analysis. The main objective of this study was to identify factors affecting the particle size distributions in Lanzhou. The hourly averaged particle number, surface area and volume concentrations are (108.1 +/- 92.2) cm(-3), (282.9 +/- 267.9) microm2 x cm(-3) and (92.2 +/- 127.3) microm3 x cm(-3), respectively. The number, surface area and volume concentrations of fine particles (0.5-2.5 microm) account for 98.7%, 73.8% and 52.9% of the total particle concentrations in 0.5-20 microm, respectively. The size distribution of number concentrations is unimodal with a peak at accumulation mode. The size distributions of surface area and volume concentrations are bimodal with peaks at accumulation mode and coarse mode, respectively. The size distributions of particle volume concentrations mainly have 7 clusters, indicating the effect of different sources and meteorological conditions. Coarse mode particles are dominant in particle volume size distributions affected by wind-borne dust and on dust days, while that affected by motor vehicle combustion emissions and traffic resuspended dust are characterized by bimodal with peaks at accumulation mode and coarse mode, respectively.