黑碳气溶胶辐射强迫全球分布的模拟研究

The Study of Global Radiative Forcing due to Black Carbon Aerosol

利用一个改进的辐射传输模式,结合全球气溶胶数据集(GADS),计算晴空条件下冬夏两季黑碳气溶胶的直接辐射强迫在对流层顶和地面的全球分布。计算结果表明,与温室气体引起的整层大气都是正的辐射强迫不同,黑碳气溶胶的辐射强迫在对流层顶为正值,而在地面的辐射强迫却是负值。作者从理论上解释了造成这种结果的原因。对北半球冬季和夏季而言,在对流层顶黑碳气溶胶的全球辐射强迫的平均值分别为0.085W/m2和0.155 W/m2,在地面则分别为-0.37 W/m2和-0.63 W/m2。虽然气溶胶的辐射强迫主要依赖于其本身的光学性质和在大气中的浓度,太阳高度角和地表反照率对黑碳气溶胶的辐射强迫会产生很大的影响。研究指出:黑碳气溶胶在对流层顶正的辐射强迫和在地面负的辐射强迫的绝对值都随太阳天顶角的余弦和地表反照率的增加线性增大;地表反照率对黑碳气溶胶辐射强迫的强度和分布都有重要影响。黑碳气溶胶的辐射强迫分布具有明显的纬度变化特征,冬夏两季的大值区都位于30°N^90°N之间,表明人类活动是造成黑碳气溶胶辐射强迫的主要原因。

Combining the global distributions of black carbon （BC） mass concentration given by GADS （Global Aerosol Data Set）, The direct radiative forcing due to BC have been calculated with an improved radiative transfer model under clear sky in both winter and summer. The results show that the radiative forcing by BC is positive at the tropopause and negative at the surface, which is different from the positive radiative forcing of greenhouse gases through the whole atmosphere. The reason is explained theoretically in this paper. The global mean forcing values are 0. 085 W/m^2 for winter and 0. 155 W/m^2 for summer at the tropopause, while they are -0. 37 W/m^2 for winter and -0.63 W/m^2 for summer at the surface. Although the radiative forcing due to BC is highly dependent on the optical properties of itself and its concentration in the atmosphere, surface albedo and zenith angle also irifluence the forcing greatly. It is pointed out in this work that the absolute values of radiative forcing due to Be at both the tropopause and the surface increase linearly with the cosine of zenith angle and the surface albedo. The distribution of Be radiative forcing relies significantly on the latitude change, its maximum value is located between 30°N and 90°N for both winter and summer, which shows that anthropogenic activities are the main cause for Be radiative forcing.