Aerosol Optical Depth Observed by Chinese Sun Hazemeter Network and Comparison with MODIS Products in Three Typical Cities in China

The CSHNET(Chinese Sun Hazemeter Network) data and MODIS(Moderate Resolution Imaging Spectroradiometer) aerosol products are used to analyze the aerosol optical characteristics in three typical Chinese cities: Beijing, Lanzhou, and Shanghai. The results showed that the annual mean AOD(Aerosol Optical Depth) were 0.41±0.35, 0.55±0.21, 0.55±0.21 in Beijing, Lanzhou, and Shanghai, respectively. The seasonal mean AOD generally exhibited a maximum in summer and aminimum in winter in Beijing but in the opposite trend in Lanzhou and no distinct seasonal cycles in Shanghai. Angstr?m index (α) which conveys aerosol size distributions characteristics were 1.40±0.85, 0.95±0.20, 1.03±0.25 in Beijing, Lanzhou, and Shanghai, respectively, suggesting fine mode particles in Beijing and coarse mode particles in Lanzhou. MODIS AOD reveal satisfactory validations against surface measurements with correlation coefficients 0.91 in Beijng and 0.75 in Shanghai while poor validation is found in Lanzhou with correlation coefficients 0.07. Overestimations of MODIS AOD are noted in Beijing and Shanghai with annual mean 0.52±0.39 and 0.74±0.30 comparing to the underestimation in Lanzhou with annual mean 0.43±0.21. Considering the uncertainty of reflectance result from geographical positions and complicated coverage of urban area, the results are not well enough and the MODIS aerosol products shall be improved in future studies.