Comparison of Column-Integrated Aerosol Optical and Physical Properties in an Urban and Suburban Site on the North China Plain

The column-integrated optical properties of aerosol in Beijing and Xianghe, two AErosol RObotic NETwork (AERONET) sites situated on the North China Plain (NCP), are investigated based on Cimel sunphotometer measurements from October 2004 to June 2012. The outstanding feature found is that the seasonal medians of aerosol optical depth (AOD) at the two stations are in good agreement. The correlation coefficients and the absolute differences between AOD at the two stations are larger than 0.84 and less than 0.05, respectively. Good agreement in AOD at these two sites (one urban and the other suburban; 70 km apart) indicates that aerosol pollution in the Greater Beijing area is regional in nature. However, we find significant differences in the absorption Angstrom Exponent (AAE), the real and imaginary part of the refractive index, and thereby the single scattering albedo (SSA), and the difference is seasonally dependent. The feature is found to be more prominent in fall when the fine-mode fraction (FMF) and fine-mode effective radius are significantly different at the two stations, besides the parameters mentioned above. The SSA in Beijing at four wavelengths shows lower values as compared to those in Xianghe, although the difference is not significant in some cases. Significant differences in AAE and fine-mode effective radius indicate that there are differences in aerosol physical and chemical properties in urban and suburban regions on the NCP.