Sensitivity of the polarization ratio method to aerosol concentration

A multiwavelength, multistatic optical scattering instrument is being developed to characterize spherical aerosols. This instrument uses 405 nm (blue), 532 nm (green) and 655 nm (red) diode lasers and two CCD imagers to measure the angular distribution of light scattered from aerosols. The incident light is polarized parallel or perpendicular to the scattering plane; the scattered intensity is measured at backscatter angles ranging from 120° to 170° by CCD imagers. The phase function for each polarization is used to form the polarization ratio, which is used to characterize the aerosols. This method has proven to be a reliable way to characterize spherical aerosols by matching the measured polarization ratio with the polarization ratio calculated by the Mie scattering equations. This method is used to determine the number density, size distribution, and index of refraction of the aerosols. The sensitivity of the polarization ratio to particle concentration is explored using a narrow distribution of one micron polystyrene beads in a chamber. The aerosol concentration is found via an inversion technique that is based on Mie calculations. This study provides the basis for transitioning this instrument to measure multiple particle size ranges and concentrations for common aerosols in an outdoor environment.