Abstract:The aerosol optical depth (AODλ= 500nm), Angstr?m wavelength exponent (α) and turbidity coefficient (β) are derived from sun photometer CE318measurements over Beijing from October to December 2010. The results show that, the mean values of AOD, Angstr?m wavelength exponent and turbidity coefficient are 0.5±0.69, 0.95±0.33, 0.24±0.31with coefficients of variation (CV) of 139%, 35% and 132%, respectively. AOD change little in polluted days with a peak at 15:00, but the concentrations of fine particles are relatively high. During polluted days, AOD fluctuate widely without a distinct diurnal variation, and the fine particles are the main components of the air pollutants. In addition, during the non-polluted days, positive and negative correlations are found between α and AOD when α smaller than 0.5and greater than 1.0, respectively. There is no clear correlation between α and AOD during the polluted days, while a decrease trend of α is detected with increase of AOD when α are lager than 1.0. It is indicated that wind speed would not play a critical role in the local changes of aerosol concentrations from similar variations between α and AOD when Vmax4m/s. Wind direction can also have large influence on the relationship between α and AOD, which shows a positive correlation especially for ENE direction. The temperature shift has little effect on variation of α and AOD. AOD increase with relative humidity when α is greater than 0.5though dust aerosols are hydrophobic in this study.