https://doi.org/10.1351/goldbook.S05490
The scattering coefficient per particle ( ); where is the number concentration of particles ( ) and is the scattering cross-section. , the scattering component of extinction due to gas and particles, is measured in the atmosphere using a nephelometer. For a homogeneous atmosphere it is related in theory to the meteorological range ( ): ; and represent the scattering and absorption coefficients per unit length for a light beam (of path length ) which has a spectral radiance (intensity) incident on a sample of air and is the transmitted spectral radiance (intensity), .