We have conducted several numerical 1-D model experiments in an attempt to simulate the behaviour of Antarctic O3 throughout the year and in particular to account for the observed downward trend of O3 in October. The vertical and horizontal transports were parameterized by a vertical velocity formulation. We find that the observed low October O3 can be simulated by an increase in the intensity of the vertical transport in the polar night and early spring or by a delay in the transition from the winter to summer thermal regimes. In addition, the effect of atmospheric transports on the total O3 is shown to be important throughout the year. We speculate that dynamical changes in the winter vortex, possibly caused by stratospheric cooling due to the greenhouse effect, may be even more important than photochemical changes in the striking enhancement of the Antarctic O3 hole.