LIGHT-SCATTERING AND ABSORPTION BY FRACTAL AGGLOMERATES AND COAGULATIONS OF SMOKE AEROSOLS

We used the volume integral equation formulation to calculate the light scattering and absorption of five types of fractal agglomerates with fractal dimensions in the range from 1.7 to 1.9. Results for the absorbed power, absorption, and scattering cross-sections are calculated for three different polarizations of the incident electromagnetic wave with respect to the agglomerates. The obtained results were found to be polarization-dependent with the amount of variation dependent on the frequency of the incident radiation. Furthermore, the obtained scattering and absorption results were compared with those based on the fractal theory, and some differences were observed. Specifically, it is noted that the absorption cross-section of the agglomerates is different from that obtained from multiplying the number of primary particles by the absorption of a single particle. The average difference is approximately 25% at lower frequencies (λ = 10 μm) and is about 15% at higher frequencies (λ=0.5 μm). The maximum difference could be as high as 60% if the orientation of the incident wave with respect to the agglomerates is taken into account. A similar comparison was made for the scattering cross-section. Absorption and scattering calculations were also made over a broad frequency band including the resonant frequencies of the agglomerates. Comments are made regarding the results available from the fractal theory. © 1990 Taylor & Francis Ltd.