Optical inhomogeneity of dust-like aerosols and its effects on scattering and absorption

Abstract:

The use of the very concept of effective refractive index has been implicit in virtually all computations of electromagnetic scattering by dust-like aerosols since the nanometer-scale heterogeneity of such particles has been essentially ignored. Therefore, the failure of this concept in application to dust-like aerosols would create a highly problematic situation. It is thus imperative to perform a comprehensive analysis of the actual physical origin of the heuristic effective-medium approximations (EMAs) and the range and conditions of their practical applicability.

In this talk, we will identify the true place of the EMAs in the framework of statistical electrodynamics. We will validate the outcome of this analysis by superposition T-matrix computer calculations and will perform a detailed quantitative assessment of the actual accuracy of the EMAs when they are applied to less-than-ideal types of heterogeneity encountered in nature. It is expected that the accuracy of an EMA will depend on many factors:

• on type of mixing;
• on refractive indices and size parameters of the host and the inclusions;
• on number, spatial distribution, and packing density of the inclusions;
• on whether one computes monodisperse or polydisperse optical characteristics;
• on whether one computes only integral radiometric characteristics or also the elements of the scattering matrix; etc.

If so, the actual practical suitability of an EMA will vary widely depending on the specific type of application, e.g., lidar remote sensing, polarimetric remote sensing, radiometric remote sensing, or integral radiation-budget computations.