Stratospheric ozone depletion : Recent developments

A revised version of the satellite derived TOMS (Total Ozone Mapping Spectrometer) global ozone data base has recently been released (Stolarski et al. 1991) and, for the first time, used to deduce global ozone trends that take into account long term natural ozone fluctuations, such as that due to the 11 year solar cycle. The complete TOMS data record (November 1978 - May 1990) shows that between 65 N and 65 S total ozone has declined by 3.0 1.6% or 0.26 0.14%/year. The most severe ozone losses occur in the stratosphere above Antarctica in spring (30% or greater south of 70 S) and in the northern hemisphere winter centred about 45 N (8 3% loss). The global ozone losses are smaller than, but not significantly different from, those reported in previous assessments, whereas the mid-latitude northern hemispheric losses are larger than previously reported. Chlorine, derived largely from CFCs, has been identified as the cause of the Antarctic ozone depletion, while the mechanism(s) of the additional mid-latitude losses in both hemispheres (particularly the northern hemisphere) remain to be identified. Some, as yet untested, hypotheses that involve heterogeneous chemistry and chlorine based ozone destruction on the stratospheric sulfate aerosol have been put forward.