Nitric Oxide Formation by Meteoroids in the Upper Atmosphere

The process of nitric oxide formation during atmospheric entry of meteoroids is analyzed theoretically. An ablating meteoroid is assumed to be a point source in a uniform flow with a continuum regime evolving in its wake. The amount of nitric oxide produced by high-temperature reactions of air in the continuum regime is calculated by numerical integration of chemical-rate equations. This is accomplished by assuming that flow properties are constant across the reacting region, the radius of the region being determined from considerations of shock-wave formation and molecular diffusion. The results, when summed over the observed mass, velocity, and entry-angle distributions of meteoroids, provide annual global production rates of nitric oxide as a function of altitude. The peak production of nitric oxide is found to occur at altitudes between 9 x 10(exp 4) and 10(exp 5) m, the total annual rate being about 4 x 10(exp 7) kg. The present results suggest that the large concentration of nitric oxide observed below 9.5 x 10(exp 4) m could be attributed to meteoroids instead of photodissociation of nitrogen into metastable, 2D-state atoms, as has been previously hypothesized.