Combined Light Extinction and Scattering Measurement for Measuring a Low-Particulate-Mass Concentration with a White Cell-Based Optical System

Abstract

On the basis of a white cell optical system coupled with two wavelengths of 638 and 520 nm, a combined extinction− scattering method was developed to alleviate the effect of particle-size variation on measuring a low particle concentration by light extinction. Due to the chromatic dispersion behavior of the optical lens in the system, the white cell-based optical system was able to provide the extinction signal at a wavelength of 638 nm as well as the forward scattering-light signal at a wavelength of 520 nm. These performances were validated by the real-time responses of the optical signals to the experimentally measured particle concentration in optical measurements with a polydispersed silica aerosol. Analyzing the real-time response between the extinction signal and the scattering-light signal, an excellent linear correlation between the extinction-to-scattering ratio and the experimentally measured mass median diameter (MMD) of the aerosol was successfully obtained; on the basis of this correlation, the average particle size in the range of 0.7−1.1 μm was well-predicted from the response of the extinction signal to the scattering-light signal and used to characterize the extinction−mass correlation for concentration measurement. Compared to the empirically calculated concentrations, the size-corrected calculations agreed better with the experimental value. It validated that the size effect in measuring a low particle concentration by light extinction could be decreased with the combined extinction−scattering measurements using the white cell-based optical system.