The ozone budget in the stratosphere: Results of a one-dimensional photochemical model

Abstract

The ozone concentration in the stratosphere results from the combined action of various catalytic cycles involving nitrogen oxides, HO x and Cl x radicals, as well as from transport processes. The results of our one-dimensional model allow the relative efficiency o those cycles to be evaluated as a function of altitude. To take into account the chemical couplings between stratospheric species, a self-consistent scheme is used to determine the budget of O x NO x Cl x and HO x species. Furthermore, the concept of chemical relaxation time is developed for ozone and the other species. It leads to a better understanding of the role of “temporary reservoir” species in the stratospheric photochemistry. It is found that, in the upper stratosphere, the ozone budget can be established in a straightforward manner, whereas in the lower stratosphere, chemical couplings are more complex and transport processes increasingly important. Due to the oversimplified transport parametrization used in this model, results for this region of the atmosphere must be viewed with caution. The model evaluations of the impact of chlorofluorocarbon release and nitrous oxide and methane increase on the ozone layer are also presented. These results can be interpreted in terms of perturbation to the budget of O x NO x Cl x and HO x species. Nevertheless model predictions should be taken with caution because large uncertainties still remain in some key reaction rates and in the behaviour of most of the source gases. In addition, inadequacies in the model formulation are difficult to assess and contribute to the overall uncertainty.