Study on optical constants inversion and infrared transmission characteristics of aerosol particles

Based on the experimental infrared spectral transmittances, an inverse model has been developed to determine the optical constants of the aerosol particles (SiO ₂ and Al ₂O ₃). Combined with the Mie theory and Kramers-Kronig (K-K) relations, the complex refractive indices of the SiO ₂ and Al ₂O ₃ particles are retrieved. The effects of the measurement errors on the inverse results are also investigated. With the optical constants inversed from the experiment, the discrete ordinate method (DOM) is used to calculate the infrared transmission characteristics of the aerosol particle cloud. Considering the multi-scattering and self-emission of the particles, the equivalent transmittance ratio (ETR) is suggested to evaluate the infrared transmission characteristics of the aerosol particles. Particular attention is given to analyze the effects of the volume fraction and diameters on infrared transmission characteristics. When the volume fraction is larger than 0.001, the particle diameter has little effect on the infrared transmission characteristics. For the uniform monodisperse particles in the detection waveband range of 3-5 μm and 8-12 μm, there exists a critical diameter where the ETR reaches the minimum value. In addition, the ETR of 3-5 μm is smaller than that of 8-12 μm with the same volume fraction and particle diameter.