Experimental investigation on optical constants of aerosol particles

Based on the experimental infrared spectral transmittances, an inverse model for determining the optical constants of aerosol particles is presented in this paper. Combined with the Mie theory and Kramers–Kronig (K–K) relations, the complex refractive indices of the aerosol particles are retrieved by the spectral transmittance distribution of a cloud of aerosol particles in potassium bromide (KBr) pellets. Particular attention is given to the unique value problems of the complex refractive index. According to calculation and analysis, the uniqueness range of the complex refractive index is obtained. The complex refractive indices of SiO2, Fe2O3, CaSO4, Al2O3 particles or their mixtures with different volume fractions are obtained. At the same time, the retrieved effective refractive indices of mixed particles are compared with those from effective medium theory. Good agreement is obtained between the inverse simulation results and the results from effective medium theory. Finally, the complex refractive index of aerosol particles collected in China is determined by the inverse model used in the present work.