Extinction reduction factor f_ext for airglow as a function of airmass (see Eq. (23)) in dex. The factors were calculated for different line-of-sight zenith distances z (in 10° steps) and zenithal optical depths τ₀. For Rayleigh (τ₀ ≤ 0.99) and Mie scattering (τ₀ ≤ 0.05), the values for τ₀ = 0.27 and 0.01 are marked by black “ × ” and green “+” symbols respectively. For z ≤ 60°, these values were used to derive airmass-dependent relations for f_ext. The resulting fits are displayed by blue solid (Rayleigh) and red dashed lines (Mie).