Using the data of size resolved aerosol mass concentration and chemical composition obtained at LinAn regional background air pollution monitoring station in Yangtze River delta region of eastern china,the size resolved aerosol effective refractive index was estimated for a summer and winter period.The real part of the estimated effective refractive index ranged from 1.55 to 1.60 if assumed dry aerosols in both summer and winter samples and ranged from 1.44-1.48 in summer samples if liquid water was include in the aerosol mass budget.The imaginary part of refractive index for submicron particles had significantly higher values in winter than in summer,and had much higher values for dry aerosols than if liquid water was included.Based on the estimated aerosol effective refractive index and measured aerosol size distributions,aerosol scattering and absorption coefficients were calculated.The calculated scattering coefficients assuming dry aerosols were 30% ~ 50% lower than those measured using Nephelometer instrument,and the calculated aerosol absorption coefficients were 10% ~ 40% lower than the measured values.When including the liquid water in the aerosol mass budget,the estimated scattering and absorption coefficients were closer to the measured values,but still lower up to 37%.The scattering coefficients increased by a factor of 1.54 after including liquid water content in the aerosol mass,the absorption coefficients increased only 10%,and the single scattering albedo increased 0.04.