Influence of Refractive Index in Particle Sizing by Light Extinction Spectrum

Light extinction spectrum (LES) is particularly preferred in particle sizing since it is a fast, nonintrusive, and easy-to-realize in situ measurement. The dispersion of particles is often neglected in LES based on particle sizing (LESPS). In this communication, we investigate the effect of the particle refractive index on the extinction properties of particles. We performed a quantitative analysis for the spectral extinction properties of particles with a known size distribution based on two different refractive indices (i.e., the refractive index at a certain wavelength and the dispersive model of refractive index). Our results show that, for water and glass droplets, the biggest difference of extinction values in the two cases is only 0.003 in the visible region; it has no significant influence in LESPS and can be neglected. For tear gas smoke particles, 2-chlorobenzalmalononitrile (CS), the biggest difference is 0.03 in the visible region, and it has great effect on the accuracy of LESPS. Therefore, taking the dispersion of particles into account, the measurement accuracy of particle size distribution and concentration can be improved.