Aerosol absorption optical depth of fine-mode mineral dust in eastern China

The fine-mode aerosol absorption optical depth（AAOD）retrieved from the Aerosol Robotic Network（AERONET）has been used in previous studies to calculate the radiative forcing of black carbon（BC）aerosol,assuming that the absorption by fine-mode aerosols（diameter ≤ 1 μm）is primarily from BC while the absorption by larger particles（diameter 1 μm）is principally from dust.In the present study,the Community Earth System Model was used to simulate and quantify the contribution of fine-mode dust to fine-mode AAOD in eastern China（29–41°N,104–122°E）—an area where concentrations of BC are high.The simulated fine-mode dust concentrations were constrained by observations from nine sites belonging to the Chinese Meteorological Administration Atmosphere Watch Network.Averaged over eastern China,the simulated annual mean fine-mode dust AAOD was 3.6 × 10-3,with the maximum AAOD in spring and the minimum value in winter.The contribution of fine-mode dust to the total fine-mode AAOD（sum of fine-mode dust,BC,and organic carbon）in winter,spring,summer,and autumn was 3.4%,25.2%,12.5%,and 14.9%,respectively,with an annual mean value of 15.1%.The results indicate the importance of removing fine dust AAOD when the AERONET fine-mode AAOD is used for calculating the radiative forcing of BC in eastern China.

由气溶胶自动观测网(AERONET)反演的细模态气溶胶的吸收光学厚度(AAOD)通常被认为是黑碳气溶胶的AAOD,并且通过这种方法得到的黑碳AAOD已经被用在计算黑碳辐射强迫的研究中。但是这种方法是基于如下假设:直径小于1μm的细模态气溶胶和直径大于1μm的粗模态气溶胶对光的吸收主要分别归功于黑碳和沙尘。为了定量描述细模态沙尘气溶胶对全部细模态气溶胶的AAOD的贡献,我们利用地球系统交互模式(CESM)模拟了中国东部(104–122°E,29–41°N)细模态沙尘气溶胶的AAOD。其中,我们根据9个中国气象局大气观测网(CAWNET)站点观测的细模态沙尘地表浓度调整了模拟的细模态沙尘气溶胶的浓度。结果显示,模拟的中国东部年平均细模态沙尘气溶胶的AAOD的值为3.6×10-3,其中AAOD的最大和最小值分别出现在春季和冬季。细模态沙尘气溶胶对总的细模态气溶胶(细模态沙尘、黑碳和有机碳气溶胶的总和)的AAOD的贡献在春季、夏季、秋季和冬季分别为3.4%、25.2%、12.5%和14.9%,其年平均值为15.1%。这些结果显示当利用AERONET反演得到的细模态气溶胶的AAOD来计算中国东部BC气溶胶的辐射强迫时,去除细模态沙尘粒子的影响显得尤为重要。