Aerosol optical depth (AOD) and Ångström exponent of aerosols observed by the Chinese Sun Hazemeter Network from August 2004 to September 2005

Abstract

To reduce uncertainties in the quantitative assessment of aerosol effects on regional climate and environmental changes, extensive measurements of aerosol optical properties were made with handheld Sun photometers in the Chinese Sun Hazemeter Network (CSHNET) starting in August 2004. Regional characteristics of the aerosol optical depth (AOD) at 500 nm and Ångström exponent ( α ) computed using 405, 500, and 650 nm were analyzed for the period of August 2004 to September 2005. The smallest mean AOD (∼0.15) was found in the Tibetan Plateau where α showed the largest range in value (0.06–0.9). The remote northeast corner of China was the next cleanest region with AODs ranging from 0.19 to 0.21 and with the largest α (1.16–1.79), indicating the presence of fine aerosol particles. The forested sites exhibited moderate values of AOD (0.19–0.51) and α (0.97–1.47). A surprising finding was that the AOD measured at a few desert sites in northern China were relatively low, ranging from 0.24 to 0.36, and that α ranged from 0.42 to 0.99, presumably because of several dust‐blowing episodes during the observation period. The AOD observed over agricultural areas ranges from 0.38 to 0.90; α ranges from 0.55 to 1.11. These values do not differ much from those observed at the inland urban and suburban sites where AOD ranges from 0.50 to 0.69 and α ranges from 0.90 to 1.48. Given the geographic heterogeneity and the rapid increase in urbanization in China, much longer and more extensive observations are required.