A mesospheric source of nitrous oxide

Abstract

In the terrestrial atmosphere, nitrous oxide (N2O) has a major role in the chemistry of ozone. Current atmospheric models assume that N2O is produced only by fixation at the earth's surface and that there are no local sources in the stratosphere or mesosphere. It is pointed out here that a significant in situ N2O source does exist above 20 km due to the excitation of the metastable N2(A 3Sigma u +) state by resonance absorption of solar UV photons that penetrate deeply into the atmosphere through the 1,800-2,200 A O2-O3 window. This source significantly affects the NO altitude distribution in the mesosphere and, in the earth's prebiological atmosphere, made N2O an important stratospheric constituent.