Analysis of column-integrated aerosol optical thickness in beijing from aeronet observations

Aerosol Optical Thickness (AOT), water vapor content and derived Angstrom exponent acquired by a CIMEL sun photometer in Beijing are analyzed. Monthly means computed from quality-assured daily means, seasonal trends and inter-annual variations are presented and discussed. Summer has the highest seasonal average AOT at 440 nm (τa440), Angstrom exponent (α440–870) and water vapor content with the values 0.93, 1.34 and 3.0 cm, respectively. The second highest seasonal average τa440 appears in spring with the largest variation of α440–870 and minimum α440–870 0.99 due to the impact of coarse particles. The minimum seasonal average τa440 (0.44) and water vapor content (0.4 cm) appear in winter. The annual average τa440, α440–870 and water vapor content for about 4-year observation period are 0.70, 1.19 and 1.4 cm, respectively. All monthly average Angstrom exponents are within 0.8-1.4, which indicates aerosol in Beijing is a very complex mixture of both fine- and coarse-mode particles (from anthropogenic influence and natural mineral dust).