Antarctic Ozone Depletion and Potential Effects on the Global Ozone Budget

Abstract

In addition to the dramatic reductions in polar ozone observed in the springtime Antarctic stratosphere during the past decade, data from the Total Ozone Mapping Spectrometer (TOMS) instrument also provide evidence of a reduction in total columnar ozone extending into middle latitudes of the Southern Hemisphere (e.g. Watson et al., 1988). It has been suggested that dilution of the mid-lat1tude air by export of ozone-poor air from polar regions following breakup of the vortex would create a deficit which might persist for a long period because of the slow chemical replacement time (months to a year in the lower stratosphere) for ozone (e.g. Sze et al., 1989). If the deficit is maintained until the next springtime depletion episode, the effect might be cumulative, with a permanent reduction in the global ozone budget and, hence, a possible explanation for the mid-latitude reductions of ozone seen in the TOMS data. A study of the so-called “dilution effect” has been conducted using a three-dimensional chemistry/transport model. The results of the model simulations reveal a small, but significant, residual deficit in the total ozone in the Southern Hemisphere 1 year following the formation of an ozone hole in the polar regions. The results are supportive of the dilution concept being a possible explanation for the Southern Hemisphere mid-latitude changes in the TOMS data over the past decade. However, the conclusions must be qualified by noting that other factors which influence the ozone distribution have not been taken into account in this study.