Column-integrated aerosol optical properties were derived systematically for the first time from the measurements of a ground-based CIMEL sun photometer in Xian from May to November,2012.Aerosol Optical Depth (AOD),Angstrom exponent,water vapor content and inversed aerosol optical and micro-physical properties,including aerosol volume size distribution,complex refractive indices and single scattering albedo (SSA),were analyzed in this study.Evolution of daily AOD at 440 nm( FTIR Detector PC Ge )was compared with that of 24-hr mean concentrations of PM2.5.Statistics of monthly means calculated from quality-assured daily AOD,Angstrom exponent( FTIR Detector PC Ge )and water vapor content( FTIR Detector PC Ge )were presented and discussed.August showed the highest monthly FTIR Detector PC with the value of 1.13,while the largest monthly FTIR Detector PC (1.30) and FTIRFTIR Detector PC Ge (4.28)appeared both in July.Monthly variations of size distribution were investigated and indicated the domination of coarse mode aerosols in most of the studied months,except July and August,when the contribution of accumulation and coarse mode were fairly comparable.Monthly variability of complex refractive index (including both real and imaginary parts) and single scattering albedo was also studied,along with their wavelength dependence,which implied the variance in aerosol types for different months.Finally,an episode,involving urban and dust aerosols,was analyzed using aerosol retrievals from sun photometer,while MODIS images captured by Aqua satellite and average wind vectors from the NCEP operational global analyses were considered in the case study.