中文摘要：

利用离散偶极子近似法和Bruggeman有效介质理论，研究了含有黑碳和硫酸盐两种成分的内混合致密气溶胶粒子在尺度参数变化范围为0.1~25时的光学特性，并通过分析比较两种算法计算光学特性的差别研究了有效介质理论对致密内混合粒子光散射的适用性。对单分散系，有效介质理论在瑞利散射区具有较好的适用性，能较好地被用来近似计算内混合粒子的消光、吸收、散射、后向散射效率因子、不对称因子、消光后向散射比和单次散射反照率，相对偏差皆在7%以内；而有效介质理论在米散射区的适用性较差，相对偏差最大可分别达到25%、88%、66%、5000%、42%、1100%和47%，但当内混合体所含的内核较小（体积比1%以内）时仍可以近似使用。在粒子尺度参数大于4时，有效介质理论基本上会低估散射效率因子，却会高估吸收效率因子和不对称因子。而对多分散系，有效介质理论能近似用来计算各光学参量，相对偏差在9%以内。

英文摘要：

Optical properties of compact internal-mixed aerosol particles composed of black carbon coated with sulfate were carried out utilizing discrete dipole approximation （DDA） and Bruggeman effective medium theory for the size parameters from 0.1 to 25. The validity of effective medium theory（EMT） in the light scattering of compact internal mixture was performed based on the comparison of both methods. For the monodisperse particles, the EMT does an adequate job of simulating the extinction-, absorption-, scattering-, backscattering-efficiency factors, asymmetry parameters, extinction-to-backscatter ratios and single scattering albedos in Rayleigh scattering region with all the relative differences less than 7%.Nevertheless, the EMT does not do an adequate job in the range of Mie scattering except for the cases that the inclusions of the internal mixture are small enough with the volume percentage less than 1%. Usage of the EMT can mainly lead to significant underestimations of the scattering efficiency factors but overestimations of absorption efficiency factors and asymmetry parameters when the size parameters are more than 4. For the polydisperse particles, the EMT does an adequate job for the optical parameters with the relative differences less than 9%.