Aerosol Absorption Property Over Yuzhong, Northwest China

The influence of aerosol absorption to climate is more complex than green house gas (GHs). Compared with the GHs, aerosols have different sources and form mechanism, the components are more complicated and changeable, so it's difficult to estimate the effect quantitatively. To gain a better understanding of this uncertainty, the aerosol mass absorption efficiency (MAE) is caculated for the first time using the China-U.S. joint dust field experiment data from April to June in 2008 in Zhangye, a upwind city of SACOL(Semi-Arid Climate Observatory and Laboratory), and the result is employed to get the aerosol absorption coefficients(AAC) combining with the black carbon(BC) mass concentration data at SACOL. The specific results are as follow:(1) The daily mean mass concentration is 1568 ngm-3, lower than background site Shang-dian-zi in east China; somehow lower than former research value, indicating the pollution at SACOL is lighter. The mass concentration of BC have remarkable seasonal variation, the maximum arise in winter and the minimum in spring.(2) For the first time the MAE of northwest China is got as 8.61m2g-1, slightly higher than the value 7.5 m2g-1 suggested by Bond and Bergstrom, compared with other research, the result is reasonable.(3) The daily mean AAC is 13.48Mm-1, and also have remarkable seasonal variation. The pollution in winter is dominated by fine particles from coal combustion; during the precipitation period, aerosols are largely swept by the rainfall or snow, the concentration of BC and AAC is lower; during the dust events period, the components of aerosols are complex, in most cases the absorption ability is a joint result of many factors. (4) Via the case study in coal combustion period and dust events period, the aerosols concentration is dominated by horizontal and vertical transport. SACOL lies half way up the mountain, in winter, when the cold front passed through, AAC value decreased because the aerosols were swept by upward vertical transport, it is supported by the high related coefficient(R=-0.88) of upward vertical speed and number concentration; when the dust storm coming, SACOL was also dominated by upward vertical transport, as the upward vertical transport getting weaker, the number concentration getting stronger(R=-0.97), indicating that the aerosols were coming from the sedimentation of dust particles above SACOL.