Abstract:With the analysis on the aerosol scattering coefficient in urban site of Tianjin in September 2006 to February 2007, it is found that there are two peaks for the average diurnal variations of the scattering coefficient of aerosols which can be seen at 06:00 BT and 22:00 BT, with values of 508.5 and 431.4 Mm-1. The scattering coefficient is usually higher in winter than that in autumn. The average scattering coefficients are 588.8 Mm-1 in fog days, 403.7 Mm-1 in haze days, and 172.5 Mm-1 in fine days. Therefore, the average scattering coefficient is the highest in fog days, while the lowest in fine days. The aerosol scattering coefficient varies obviously in gale weather and dust weather. Before wind speed increases the scattering coefficient is higher, and it decreases in gale weather and dust weather. Diurnal change of the PM2.5 mass concentrations accords with the daily change of the scattering coefficient. A good correlation between scattering coefficient and PM2.5 mass concentration can be found with a high coefficient of 0.78.