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

The opacity of a black smoke (an aerosol of carbon spheres) is calculated from the Mie theory for several lognormal particle distributions. Calculations are presented at a wavelength of 0.55 Am for particle geometric mean diameters in the 10(-3)-1-microm 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 (m(2)) near 0.7, typical of carbon, the smoke opacity is only weakly dependent on the real part of the particle refractive index.