Whenever wc bum hydrocarbon fuels using air. wc impact the atmosphere and. in some cases, the local air quality. Whatever fuel we burn using air will produce oxides of nitrogen. A concern during the late 1960s was the effect of water vapor from SST engine exhausts on stratospheric ozone levels. It was soon realized, however, that the oxides of nitrogen were much more important (22). This led the Department of Transportation, in 1972. to launch the Gimatic Impact Assessment Program This monumental and highly regarded 7200 page study, comprising the work of over 500 individuals, concluded that a limited fleet of supersonic transports, such as the 30 Concordes and TU-144s then envisioned, posed an insignificant threat to the atmosphere. This study also aided the extraordinary discovery of the reduction of atmospheric ozone by CFC refrigerants (Freon 11 and 12), culminating in ihc Montreal Protocol (1987) which will lead to the eventual elimination of these refrigerants
The oxides of nitrogen catalyticaHy destroy ozone above about 13 kilometers in mid- latitudes; they cataiyiically create ozone below this altitude Aircraft emissions arc the major unnatural source of these oxides in the stratosphere. They are also an important source of them in the upper tn>posphcre. at least of mid-latitudes in the northern hemisphere . Thus it appears that SSTs in the stratosphere may reduce our protection from ultra-violet radiauon by ozone on the one hand At altitudes of 12-14 kilometers (13 kilometers = 42.650 feet), the effect of these oxides on ozone is minor. The calculated ozone column change due to the injection at 20 kilometers of the amount of NO* expected from a full fleet of SSTs was about *12** in 1975. New knowledge changed this to +34 in 1979. Since that lime, increasing knowledge provided a result of -104 in 1988, about double the -54 predicted ozone depletion if CFC releases remained at their 1974 rate (24). Recent results show NO, to be less significant than was once thought, but raise the issue of the effects of engine emissions on stratospheric aerosol surface area. This could also play a role in depleting stratospheric ozone .