Atmospheric Ozone: Possible Impact of Stratospheric Aviation

Models for stratosphere temperature and ozone are developed and shown to give good agreement with observational data. The atmosphere is in local radiative equilibrium at heights above about 35 km, and concentrations of ozone above 28 km can be satisfactorily estimated by models assuming photochemical equilibrium. Nitric oxide, formed by photochemical decomposition of nitrous oxide and ammonia, is an important catalyst for recombination of odd oxygen below 50 km, and is responsible for a reduction, by about a factor of 2, in the computed column density of ozone. Possible consequences of nitric oxide and water vapor, exhausted by stratosphere aircraft, are discussed. It is argued that there should be a significant reduction in the concentration of stratospheric ozone, with a related decrease in stratospheric temperature, if the globally averaged aircraft source of nitric oxide exceeds 2 × 107 molecules cm−2 sec−1, approximately half the natural source of stratospheric nitric oxide. An increase in stratospheric water vapor causes a small increase in the concentration of ozone but cannot compensate for the much larger effects associated with nitric oxide. The more detailed analysis reported here confirms conclusions drawn earlier by Crutzen and Johnston regarding the possible impact of large numbers of supersonic transports. A fleet of 320 Concordes operating for 7 hr a day at 17 km is predicted to lead to a decrease of 1% in the column density of ozone, and similar conclusions presumably apply to the Soviet TU144. Aircraft flying at higher altitudes, with similar exhaust characteristics, would be expected to induce relatively more serious changes in atmospheric ozone.