The influence of multiple light scattering on measurement of particle size distribution by light extinction method

The method of light extinction, based on the Lambert-Beer law, is valid only for the single scattering case theoretically. The multiple scattering effect must be considered when the particle concentration and the particle size are important. In this paper, The Monte Carlo approach and Four-flux model are used to predict the transmittance spectra of water droplets. Different configurations: light-source diameter, Thickness of the medium (or light path), diameter of the round detector, half-angle of aperture of the detector are concerned in numerical simulation. With comparison to the prediction of the Lambert-Beer law, we show that the multiple scattering effect depends not only on the particle concentration, but also on the particle size/light wavelength and the detector's position and size. A reference criterion for the application of Lambert-Beer law will be given in different cases by using a typical inversion technique based on the extinction spectrum.