Effective Photodissociation Cross Sections for Molecular Oxygen and Nitric Oxide in the Schumann-Runge Bands

Abstract

Simple polynomial representations of the altitude and zenith angle dependence of effective photodissociation cross sections for molecular oxygen and nitric oxide in the Schumann-Runge band region are presented. Longward of ∼202 nm, the atmosphere is optically thin and the effective cross sections are well correlated with local temperature. Atmospheric transmission values and O2 and NO photodissociation rates calculated using the parameterized effective cross sections are in good agreement with the results of the high spectral resolution computations of Frederick and Hudson. The effective cross section approach allows the use of different solar spectra and avoids the assumption of previous work that ray paths at different solar zenith angles, but with the same O2 absorbing column, have the same opacity and dissociation rates. The errors resulting from this assumption can exceed 20% at optical depths greater than 2.