A novel light scattering method with size analysis and correction for on-line measurement of particulate matter concentration

Abstract

Based on the difference in particle size sensitivity between forward and backscattering during the measurement of particulate matter (PM) mass concentration using laser angular scattering, a method was proposed to improve its on-line measurement accuracy using three fixed detectors. Experimental and theoretical calculations indicate that the PM mass concentration sensitivity (PMCS) of the particles at the 22.5° detection angle and the asymmetry factor (I_45°/I_135°) are linearly related to the average particle size, and both decrease as the particle size increases. The average particle size obtained from the asymmetry factor was used to correct the PMCS. Compared with the unmodified light scattering method, when the PM mass concentration varies in the range of 1-8 mg⋅m^-3, the average deviation between the light scattering method with particle size correction and the reference is reduced from 191.11 % ± 9.12 % to 8.90 % ± 3.20 %, and the maximum deviation is reduced from 227.04 % to 21.54 %. The effect of particle size on the measurement is reduced by size analysis and correction, and the accuracy of the light scattering method is much improved. Finally, laboratory measurements of the fly ash from coal-fired and biomass-fired power plants were performed.

Keywords: Asymmetry factor; Light scattering; Mass concentration; Particle size.