OZONE TREND IN THE NORTHERN-HEMISPHERE - A NUMERICAL STUDY

A two-dimensional model has been used to study the possible effects of heterogeneous chemistry on the ozone concentration in the northern high latitudes. The model uses a diabetic circulation which is consistent with the calculated ozone. The temperature field is prescribed in such a way to realistically reproduce the thermal conditions in the polar lower stratosphere during the winter season. A complete chemical code is included that produces a realistic nitric acid concentration and then the formation of polar stratospheric clouds of nitric acid tri-hydrate particles. NO(x) and ClO(x) families are explicitly predicted as a function of time-dependent N2O, CH4 and CFC mixing ratios from the simulated year 1960 until 2000. The increase of the total chlorine amount in the stratosphere is shown to be a possible explanation for the observed trend of ozone depletion in the high-latitude northern region. The presence of polar stratospheric clouds is found to be important for the seasonal behavior of the ozone secular trend.