Opacity of black smoke: calculated variation with particle size and refractive index

Abstract

The opacity of a black smoke (an aerosol of carbon spheres) is calculated from the Mie theory for several log-normal particle distributions. Calculations are presented at a wavelength of 0.55 μm for particle geometric mean diameters in the 10⁻³–1-μm range and geometric mean standard deviations in the 0 (monodisperse) to 0.4 range. For-a given mass concentration the extinction coefficient and, therefore, the opacity can vary by a factor of 2 or more as the size distribution is varied. For absorptive indexes (m₂) near 0.7, typical of carbon, the smoke opacity is only weakly dependent on the real part of the particle refractive index.