随机分布烟尘团簇粒子辐射特性研究

A study of radiative properties of randomly distributed soot aggregates

基于分形理论,采用蒙特卡罗方法对随机分布的烟尘团簇粒子结构进行了仿真模拟,利用离散偶极子近似(discrete dipole approximation,DDA)方法研究了随机分布的烟尘团簇粒子的辐射特性,分析讨论了分形维数、原始微粒粒径和数量以及复折射率对随机分布烟尘团簇粒子辐射特性的影响.研究表明,在给定分形维数的情况下,烟尘团簇粒子的辐射特性取决于原始微粒粒径、数量及复折射率;原始微粒较小的团簇粒子,当分形维数较小时,吸收截面变化不明显,但当分形维数大于2时,吸收截面骤然增大,然而,对于具有比较大的原始微粒粒径、数量及复折射率的烟尘团簇粒子,吸收截面随着分形维数的增大而单调递减;随着分形维数的增大,团簇粒子的散射截面、消光截面及单次散射反照率均单调递增;从整体上来讲,团簇粒子的辐射特性与等效球形粒子的辐射特性存在着比较大的差别,并且这种差别随着分形维数的增大而减小.该工作对研究气溶胶粒子的辐射及气候效应具有重要的科学价值.

Based on fractal theory,the Monte Carlo method is used to simulate the structures of fractal soot aggegates in random distribution. The radiative properties of randomly distributed soot aggregates are studied using the discrete dipole approximation （DDA）,and the effects of the fractal dimension ,the monomer diameters ,the number of monomers in the soot aggregates and the refractive index on the radiative properties of aggregated soot particles are analyzed. The results show that the radiative properties of randomly distributed soot aggregates of a given fractal dimension are complex functions of the monomer diameters,the number of monomers in the aggregates,and the refractive index. For small values of the monomer diameters,the absorption cross section of soot aggregates tends to be relatively constant when the fractal dimension is small,but increases rapidly when the fractal dimension exceeds two. However,a monotonical reduction in light absorption with the increase of the fractal dimension is observed for soot aggregates with sufficiently large monomer diameters,number of monomers,and refractive index. The scattering cross section ,extinction cross section and single- scattering albedo increase monotonically with the increase of the fractal dimension. In a word,the results for soot aggregates differ profoundly from those calculated for the equivalent spherical particles,and the discrepancies between them change litte with the increase of the fractal dimension. This research is of scientific value in studying the radiative properties of aerosols and their climatic effects.