Abstract: A statistic regression approach was introduced to estimate the wavelength index of black carbon and dust particles, and further to separate the contribution of the two types of aerosols to the aerosol light absorption coefficients measured in the spring of 2006 in Beijing urban area. The results show that the wavelength exponent index (a) of black carbon aerosol at Beijing urban site was about -0.92, which was in agreement to the value of (-0.8±0.2) reported in related studies. The decoupling analysis of the measured light absorption coefficients during the three floating dust periods at Beijing in the spring of 2006 (March 25th, March 27th, April 9th) demonstrate that, on average, light absorption caused by dust particles takes up about 32.8% of total light absorption at 520 nm wavelength, and by black carbon aerosol more than 60%, which indicates that the black carbon is still the major contributor of aerosol light absorption in Beijing urban areas even in the floating dust periods.

Key words: dust, black carbon, decoupling of aerosol absorption coefficient, wavelength exponent index