A study of radiative properties of fractal soot aggregates using the superposition T-matrix method
✍ Scribed by Li Liu; Michael I. Mishchenko; W. Patrick Arnott
- Publisher
- Elsevier Science
- Year
- 2008
- Tongue
- English
- Weight
- 876 KB
- Volume
- 109
- Category
- Article
- ISSN
- 0022-4073
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✦ Synopsis
We employ the numerically exact superposition T-matrix method to perform extensive computations of scattering and absorption properties of soot aggregates with varying state of compactness and size. The fractal dimension, D f , is used to quantify the geometrical mass dispersion of the clusters. The optical properties of soot aggregates for a given fractal dimension are complex functions of the refractive index of the material m, the number of monomers N S , and the monomer radius a. It is shown that for smaller values of a, the absorption cross section tends to be relatively constant when D f o2 but increases rapidly when D f 42. However, a systematic reduction in light absorption with D f is observed for clusters with sufficiently large N S , m, and a. The scattering cross section and single-scattering albedo increase monotonically as fractals evolve from chain-like to more densely packed morphologies, which is a strong manifestation of the increasing importance of scattering interaction among spherules. Overall, the results for soot fractals differ profoundly from those calculated for the respective volume-equivalent soot spheres as well as for the respective external mixtures of soot monomers under the assumption that there are no electromagnetic interactions between the monomers. The climate-research implications of our results are discussed.