Aerosol monitoring at multiple locations in China: contributions of EC and dust to aerosol light absorption

This paper reports on the analysis of 24-h aerosol data measured during 2006, at 14 monitoring sites in China. Measurements included seven-wavelength Aethalometers, thermal/optical reflectance analyses of filter samples and determination of dust aerosols. Black (elemental) carbon (BC, EC) is found to be the principal light-absorbing aerosol over many parts of China; however, the fraction of apparent light absorption attributed to dust varied from 14% in winter, to 11% in spring, to 5% in summer to 9% in autumn. Aerosol light absorption in urban areas was larger than in rural areas by factors of 2.4 in winter, 3.1 in spring and 2.5 in both summer and autumn. These differences may lead to contrasts in radiative, thermal and cloud modification effects between urban and rural areas. Absorption ‘hotspots’ were located in the Sichuan Basin, the provinces south of Beijing, the Pearl Delta River regions and the Guanzhong Plain. The mass absorption coefficient for aerosol BC (σ_BC) based on Aethalometer data is estimated to be 11.7 m² g^-1 at 880 nm wavelength (λ) with inverse (λ^-1) wavelength scaling, whereas the mass absorption coefficient for dust (σ_dust) is 1.3 m² g^-1 on average without significant wavelength dependence.