Photochemistry in the stratosphere—With applications to supersonic transports

Abstract

Two years ago it was pointed out that the oxides of nitrogen from the exhaust gases of 500 American SST would probably reduce the earth's ozone shield by about 20% on an average worldwide basis and up to 50% in zones of high traffic. These calculations depended on extensive assumptions about the natural background of nitrogen oxides in the stratosphere and the expected distribution of exhaust gases from SST. Also, this model involved steady-state photochemistry with explicit neglect of atmospheric motions. Recent studies by many investigators have made some measurements of nitrogen oxides in the stratosphere, calculated the expected distribution of exhaust gases on the basis of an almost-realistic model of three-dimensional motion, calculated the expected reduction of ozone in models that explicitly include one- or two-dimensional motions, and interpreted past historical events as constituting significant injections of nitric oxide into the stratosphere. The model calculations, including atmospheric motions, give a worldwide reduction of ozone by 500 SST between 7 and 28%, and for a 3 to 6 fold “local maximum” between 20 and 50% ozone reduction. Some of these 1973 calculations, including motions, give results comparable to the 1971 steady-state calculations. Recent studies indicate that the nuclear bomb tests of 1952–1962 injected significant quantities of nitric oxide into the stratosphere; the observed increase of ozone in the northern hemisphere during the 1960s may, in part, be the atmosphere returning to normal after the end of large-scale nuclear tests. Also, a recent interpretation of the sunspot modulation of cosmic rays gives a quantitative measure of the response of stratospheric ozone to an injection of nitric oxide; translated into terms of SST, these results indicate that 75 Concordes operating in one flight corridor for 11 months would decrease the local ozone column between 2 and 5%. Some biologists regard even this small reduction of ozone as a matter for serious concern.