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

Abstract

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 (τ_a440), Angstrom exponent (α_440–870) and water vapor content with the values 0.93, 1.34 and 3.0 cm, respectively. The second highest seasonal average τ_a440 appears in spring with the largest variation of α_440–870 and minimum α_440–870 0.99 due to the impact of coarse particles. The minimum seasonal average τ_a440 (0.44) and water vapor content (0.4 cm) appear in winter. The annual average τ_a440, α_440–870 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).