Numerical model studies of the effect of injected nitrogen oxides on stratospheric ozone

Abstract

The work reported here has employed one-dimensional models, in which atmospheric transport is represented in combination with chemical kinetic mechanisms, to compute average vertical distributions of the minor constituents of the stratosphere as a function of time. Perturbation experiments simulating the effects of exhaust emissions, particularly nitrogen oxides and water vapour, from supersonic and subsonic aircraft fleets have been performed. The effect on stratospheric ozone of a possible four year variation in tropospheric N 2 O levels from 1966 to 1969 has also been investigated. Inert tracer studies from a three-dimensional tropospheric and stratospheric general circulation model have been used to examine specific limitations of the representation of transport processes in one-dimensional models. The inability of current one-dimensional models to represent counter gradient transport of minor gaseous constituents by the mean global circulation is a serious shortcoming in their use for studies of this type; the importance of mean motions in the general circulation is demonstrated by diagnostic data from a three-dimensional general circulation model, and by reference to the production of nitrogen oxides in thunderstorms. Further subjects studied were the effects on the calculated ozone reductions of using different profiles of vertical eddy diffusivity, diurnal and seasonal time dependence of the solar zenith angle in the photochemistry and temperature dependence of the chemical reaction rates. It was also found that the effects of injections from the supersonic and subsonic fleets were not linearly additive in the one-dimensional diffusive models used in this study. The optimum latitude at which to operate a one-dimensional model is discussed; for injected species with long atmospheric lifetimes a value of 34° is recommended for the Northern Hemisphere.