SENSITIVITY OF SUPERSONIC AIRCRAFT MODELING STUDIES TO HNO3 PHOTOLYSIS RATE

In the last few years the possibility of a second generation of supersonic aircraft flying mainly in the stratosphere has been discussed. This, and the increasing number of longhaul subsonic aircraft flying in the lower stratosphere, has caused the issue of possible ozone depletion due to nitrogen oxides emitted in the aircraft exhaust gases to be re-opened. Model calculations have indicated that significant ozone loss could occur if a large, economically viable fleet of supersonic aircraft were to be built. However, the results axe sensitive to a number of assumptions and also to uncertainties in photochemical data. We consider the sensitivity with respect to HNO3 photolysis rates, which axe dependent upon the assumed photochemical data. There is also considerable variability between models in the calculated photolysis rates. If temperature dependent absorption cross sections for HNO3 are used in model simulations of supersonic aircraft exhaust impact, the calculated ozone loss at high latitudes is significantly reduced. and an ozone increase rather than a decrease is calculated for low to mid-latitudes. The result emphasizes our current uncertainty about the impact of future supersonic aircraft on ozone chemistry and, more generally, about processes operating in the lower stratosphere.