Orientation-averaged optical properties of natural aerosol aggregates were analyzed by using discrete dipole approximation (DDA) for the effective radius in the range of 0. 01 to 2 μm with the corresponding size parameter from 0. 1 to 23 for the wavelength of 0. 55 μm. Effects of the composition and morphology on the optical properties were also investigated. The composition show small influence on the extinction-efficiency factor in Mie scattering region, scattering- and backscattering-efficiency factors, and asymmetry factor, but great on the extinction efficiency factor in Rayleigh scattering region and absorption-efficiency factor. The extinction-efficiency factor with the size parameter from 9 to 23 and asymmetry factor with the size parameter below 2. 3 are almost independent of the natural aerosol composition. The extinction-, absorption-, scattering-, and backscattering-efficiency factors with the size parameter below 0. 7 are irrespective of the aggregate morphologly. The intrinsic symmetry and discontinuity of the normal direction of the particle surface have obvious effects on the scattering properties for the size parameter a-bove 4. 6. Furthermore, the scattering phase functions of natural aerosol aggregates are enhanced at the backscattering direction (opposition effect) for large size parameters in the range of Mie scattering.%利用离散偶极子近似法计算分析了随机取向团簇自然气溶胶(包含灰尘和海盐)在等效半径变化范围为0.01～2 μm(波长为0.55 μm时对应尺度参数为0.1～23)时的光学特性.通过考察成分和形状的影响,计算结果表明:成分对团簇自然气溶胶的散射、后向散射效率因子,不对称因子,以及米散射区范围内的消光效率因子的影响均较小,其中对尺度参数为9～23时的消光效率因子和尺度参数小于2.3时的不对称因子几乎没有影响；成分对瑞利散射区范围内的消光效率因子及吸收效率因子的影响相对较大.形状对团簇自然气溶胶在尺度参数小于o.7时的消光、吸收、散射效率因子及后向散射效率因子的影响可以不计；当尺度参数大于4.6时,粒子的内在对称性和表面的突变会带来明显的影响.另外,团簇自然气溶胶在米散射区内、尺度参数较大时,散射相函数有明显的后向散射加强效应.
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