Scattering and absorption coefficients of aerosols in a semi-arid area in China: Diurnal cycle, seasonal variability and dust events

The authors investigated variations of aerosol scattering and absorptive properties in a semi-arid climate Observatory in the Inner Mongolia of China and factors affecting the variation. They use integrated nephelometer and aethalometer observations collected in 2005 and 2006 at the Silinhot Observatory. The results are as follows. 1) in autumn and winter, the diurnal cycle of scattering coefficient exhibited a clear bi-modal variation, and the scattering coefficient was indicative of the type of sandy weather. 2) The concentration of black carbon (BC) aerosols was much higher in winter than in the other seasons with an evident bimodal diurnal variation. 3) When the wind speed was lower than 3.5 m s^?1, the dilution effect of air evidently influenced the scattering coefficient and BC mass concentration; for the wind speed above 3.5 m s^?1, there appeared to be little correlation between wind speed and scattering coefficient or BC mass concentration. 4) Atmospheric visibility calculated from the aerosol scattering and absorptive coefficients was in good agreement with the direct observation of visibility. 5) Absorption by aerosols accounted for 25% of the total extinction in December.