Production and diffusion of nitric oxide

The photochemistry and transport of N and NO are studied by means of a program incorporating molecular and eddy diffusion. The sources considered are ionospheric, and metastable reactants are included in order to match the large observed NO concentrations. With (O2(¹Δ) a satisfactory result can be obtained, but only with a rate coefficient 2 orders of magnitude larger than suggested by Norton found in the laboratory. The N(²D) is also satisfactory, and the required rate coefficients have some laboratory support. The N(²D) is taken to be produced by dissociative recombination of NO+, and the yield is required to be between 0.5 and 0.6; the NO concentrations are very sensitive to the exact value in this range. An important new source of N (assumed to be ground state) is introduced: dissociation of N2 by photoelectrons. The yield of N(²D) in NO+ recombination must then be near unity. A possible consequence is an inverse dependence of D-region electron density on solar activity. It is pointed out that NO is determined by quite different factors during the polar night, and that much larger concentrations are plausible.