A polarization-resolved light scattering method for eliminating the interference of water aerosol in industrial stack PM measurement

Abstract

In this study we report polarization resolved intensity measurements for flyash and water aerosol, respectively, in an industrial stack like environment, for the purpose of developing a methodology for in-situ PM measurements in wet stacks. Flyash and water aerosols up to 4 (Formula presented.) mass concentration were seeded in a lab scale simulated industrial stack operated at velocities up to 15 m/s. Scattering of non-polarized (NP) and horizontally polarized light by these two aerosols were observed at (Formula presented.) back-scatter and (Formula presented.) forward-scatter angles for horizontal and vertical polarization states at the detector. Complete depolarization of horizontally polarized incident light was observed for ash at (Formula presented.) while negligible effects were observed for water. Thus the cross-polarization measurement in this angle, where the scattering energy from the mixed flow could directly represent the flyash concentration, can be the best possible measurement configuration for minimizing the impact of interference from water carryover in industrial emission stacks. Further, the change in depolarization ratio of the mixture (δm) when compared to flyash (δa) alone is proportional to the scattering intensity ratios of ash and water, respectively, and could be used to estimate the individual mass concentrations. With this development, we could propose the design of an instrument that can in-situ correct for errors from counting water droplet, and also enable real time estimation of individual mass concentrations. Copyright © 2020 American Association for Aerosol Research.