Photodissociation of nitric oxide in the middle and upper atmosphere

Abstract

Absorption of solar radiation of wavelengths between 175 to 205 nm plays a fundamental role in the photochemistry of the middle atmosphere. Nitric oxide photodissociates in the δ(0-0) and δ(1-0) bands near 191 and 183 nm, respectively, initiating the primary mechanisms for NO_x removal in the middle atmosphere. The spectrally rich Schumann-Runge (S-R) bands of O₂ are the main source of atmospheric opacity at these wavelengths. A re-evaluation of O₂ absorption has been made based on recent advances in understanding of S-R line shapes, leading to differences with conventional approaches assuming Voigt line profiles in line-by-line calculations of the O₂ cross section. The new results are used to examine the impact of O₂ transmission on the photodissociation of NO in the δ(0,0) and δ(1,0) bands.