The @S05487@ @C01124@ per particle (\(\frac{\text{cm}^{2}}{\text{particle}}\)); \[b_{\text{scat}}=n\ \sigma _{\text{scat}}\] where \(n\) is the number concentration of particles (\(\text{particles cm}^{-3}\)) and \(\sigma _{\text{scat}}\) is the @S05487@ cross-section. \(b_{\text{scat}}\), the @S05487@ component of @E02293@ 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 (\(L_{\text{V}}\)): \(L_{\text{V}}=\frac{3.9}{b_{\text{scat}}}\); \(b_{\text{scat}}\) and \(b_{\text{abs}}\) represent the @S05487@ and absorption coefficients per unit length for a light beam (of path length \(L\)) which has a @S05824@ (intensity) \(I_{0}\) incident on a sample of air and \(I\) is the transmitted @S05824@ (intensity), \(\ln (\frac{I_{0}}{I}) = L\ (b_{\text{scat}}+b_{\text{abs}})\).