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Effective medium theories for irregular fluffy structures: aggregation of small particles.
Nikolai V Voshchinnikov1, Gorden Videen, Thomas Henning
1Sobolev Astronomical Institute, St. Petersburg University, St. Petersburg 198504, Russia. nvv@astro.spbu.ru
Applied Optics
|June 16, 2007
Summary
This study explores how particle porosity affects light scattering and extinction. An effective medium theory (EMT) model accurately predicts these optical properties for porous particles with Rayleigh inclusions.
Area of Science:
- Atmospheric optics
- Radiative transfer
- Computational physics
Background:
- Particle porosity significantly influences light scattering and extinction.
- Accurate modeling of porous particles is crucial for understanding atmospheric radiative transfer.
- Existing models often simplify particle structure, necessitating investigations into effective medium approximations.
Purpose of the Study:
- To investigate the extinction efficiencies and scattering properties of porous particles.
- To evaluate the accuracy of an effective medium theory (EMT) model for predicting optical properties of porous particles with Rayleigh inclusions.
- To determine the range of validity for the effective model in describing particle optical properties.
Main Methods:
- Discrete dipole approximation (DDA) calculations for porous pseudospheres with Rayleigh inclusions.
- Application of Lorenz-Mie theory with effective refractive indices derived from EMT (Bruggeman mixing rule).
- Comparison of DDA results with predictions from the effective model for various materials and size parameters.
Main Results:
- The effective model, using Bruggeman-based EMT, shows minimal deviations (approx. 5%) in extinction factor for porosities (P) 0-0.9 and size parameters (x) up to 25.
- Deviations are larger for scattering and absorption efficiencies, but smaller for particle albedo and asymmetry parameter.
- The effective model accurately represents scattered radiation intensity and polarization for fluffy aggregates.
Conclusions:
- Effective medium theories, particularly Bruggeman's rule, provide a simplified yet accurate method for calculating optical properties of porous particles with Rayleigh inclusions.
- The effective model is computationally efficient and applicable to both spherical and nonspherical porous particles.
- This simplification aids in modeling radiative transfer in atmospheres containing complex particulate matter.
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