随机分布黑碳-硅酸盐混合凝聚粒子的消光特性研究

基于分形理论,采用蒙特卡罗方法对随机分布的混合凝聚粒子的空间结构进行了仿真模拟。利用Bruggeman有效介质理论得到了占有不同体积份额黑碳的内混合凝聚粒子的等效复折射率。采用离散偶极子近似方法对随机分布混合凝聚粒子在内外混合状态下的吸收、散射和消光效率因子等消光特性参量进行了数值计算,深入探讨了混合方式、容积含量、入射波长以及基本粒子粒径和数量对混合凝聚粒子消光特性的影响规律。通过将所得数值结果与T矩阵方法的数值结果进行比较发现,两种数值方法计算的结果非常相近。结果表明,随机分布混合凝聚粒子的散射效率因子对混合方式非常敏感,消光效率因子对混合方式较敏感,而吸收效率因子对混合方式不敏感。随着凝聚粒子尺度参数的增大,混合方式对散射和消光效率因子的影响逐渐显著。内外混合方式下,随着黑碳体积比的增大随机分布混合凝聚粒子的吸收、散射和消光效率因子均近似线性增大,并且增大的幅度随着粒子尺度参数的增大而增大。

Extinction Characteristics of Soot-Silicate Mixed Agglomerates in Random Distribution

Based on fractal theory, Monte Carlo method is used to simulate the structures of mixed agglomerates in random distribution. The equivalent complex refractive index of internal mixture of agglomerates containing different volume fractions of black carbon particles is obtained by Bruggeman effective medium theory. The extinction characteristic quantities including the absorption, scattering and extinction efficiency factor of mixed agglomerates in internal and external mixing states are calculated based on the discrete dipole approximation (DDA) method. Meanwhile, the influence of mixture patterns, volume content, solar radiative wavelength, the monomer diameters, and the number of monomers on the radiative properties of mixed agglomerates is mainly discussed. Comparison of the numerical results obtained by the DDA method with T matrix method shows that the numerical results obtained by two numerical methods are very similar. The results show that the scattering efficiency factor is substantially sensitive to mixing patterns, the extinction efficiency factor is weaker, while the absorption efficiency factor is not sensitive. The influence of mixing patterns on the scattering and extinction efficiency factor is becoming more obvious with the increase of the size of mixed agglomerates. The absorption, scattering and extinction efficiency factor of mixed agglomerates in internal and external mixing states increase monotonically with the increasing of the volume fraction of black carbon, and the increase varies with the size parameters of mixed agglomerates.