Nitrous Oxide: A Natural Source of Stratospheric NO

Abstract

Supersonic transport planes currently under development will cruise in the stratosphere and there is concern about possible environmental effects. In particular, NO emitted by these aircraft may catalytically affect atmospheric ozone. Here we investigate an important natural source of NO, the reaction O(¹D) + N₂O → 2NO, and compare the natural source with estimates for the source due to a fleet of 500 planes cruising for an average of 7 hr a day. The natural and artificial inputs above 15 km are of comparable magnitude. The natural source corresponds to a net production of NO, averaged over the globe, of about 2 × 10⁷ molecules cm⁻² sec⁻¹, and offers a yardstick for judging the possible significance of any artificial input. Additional sources of stratosphere NO, due to downward diffusion from the ionosphere and upward transport from the earth's surface, are discussed but have not been quantitatively estimated at this time.