Comparison of Various Mean Field Formulations for Retrieving Refractive Indices of Aerosol Particles Containing Inclusions

Application of effective medium approximation (EMA) methods to two-component systems are presented. Systems studied are composed of water, sulfate, soot, and dust as these are commonly encountered atmospheric aerosol components. Atmospheric models often employ EMAs to include internally mixed aerosols without the computational burden of exact theory. In the current work, several types of mixing rules (Maxwell-Garnet, Bruggeman, and coherent potential approximation) have been applied to various two-component internally mixed particles at 550 nm using volume fractions of the minor component below 0.1. As expected, results show that the formulations tested produce very similar effective refractive indices indicating that electric field interactions between inclusions is negligible at the tested volume fractions. This indicates that the differences in component refractive index has only a minor effect on the validity of the EMA at the tested volume fractions. In all cases considered, the linear average of the refractive indices of the two components provides an upper limit for the EMAs.