Ozone depletion over antarctica

Abstract

In the decade following the warning given by Professor Rowland and Dr. Molina, of the threat to the ozone layer from halocarbons, very significant advances were made in elucidating the processes which control the abundance and distribution of stratospheric ozone. Laboratory measurements of rate constants and cross sections had provided a firm basis for constructing models of stratospheric chemistry. Satellite instruments were providing for the first time global distributions of many trace constituents. Ground-based and balloon- borne instruments were being developed rapidly, and techniques had been devised for measuring most of the more important minor constituents. It is fair, I think, to say that by 1984 there was more than a hint of complacency amongst workers in this field. Models had produced ozone distributions which were in fair accord with observations, and were predicting only rather slow depletion of ozone in response to the growth in the abundances of halocarbons. The effects were expected to be most pronounced in the upper stratosphere, in the region of photochemical equilibrium - the ozone factory of the world, and from thence to spread slowly along the distribution system - the general circulation of the atmosphere. Figure 1 shows the data presented in Nature (May 1985) - the first unequivocal systematic change in ozone climatology to be reported. When Dr. Watson came to London in September 1985, bringing satellite maps of column ozone over Antartica, constructed from data obtained by NASA's Total Ozone Mapping Spectrometer (TOMS) carried by the Nimbus 7 satellite, it was clear that a serious gap had appeared, not only in the ozone layer, but also in our understanding of the atmosphere. The full implications of the severe seasonal depletion of the ozone layer over Antarctica have yet to be determined. The development of the ozone hole in subsequent years has been widely reported. The depletion seen in 1987 was the most severe to date. Figures 2 and 3 show profiles of the ozone layer over the British Antarctic Survey (BAS) station at Halley Bay on August 15th and October 13th. They were measured using electrochemical balloon-borne sondes, provide by the Chemical Manufacturers' Association. Figure 2 shows that the heart of the ozone layer was destroyed, leaving only the wings of the earlier distribution as two vestigial layers. Between the pressure surfaces of 100 to 50 mbar (altitudes of 14 and 18 km), 97% of the ozone was destroyed.