Extinction, Absorption, Scattering, and Backscatter for Aerosolized Bacillus Subtilis Var. Niger Endospores From 3 to 13 um

Abstract : Spectral extinction was measured in situ for aerosolized Bacillus subtilis var. niger (BC) endospores with the use of Fourier-transform infrared (FTIR) spectroscopy from 3.0 to 13.0 micrometers. Corresponding aerosol-size distributions were measured with the use of a commercially available elastic light-scattering probe and verified by direct particle capture and subsequent counting via video microscopy. Aerosol mass density was monitored simultaneously with conventional dosimetry and used to mass-normalize the measured spectral extinction. Mie theory calculations based on measured distributions and available complex indices of refraction agreed well. Also present are resultant Mie calculations for the absorption, total scattering, and backscattering. Included are the real and imaginary components of the complex index of refraction for BC as measured by Milham and Quarry. Both calculated and measured cross sections suggest that for wavelengths longer than 6.0 micrometers, the total extinction is primarily due to absorption. Finally, to offer a comparison, we present measured spectral extinction for three additional aerosols often found in the lower atmosphere, i.e., water fog, diesel soot, and Arizona road dust.