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Future Concentrations of Atmospheric Chlorine
There is some encouraging news in the long term as can be seen in
Figure 11, which shows the
atmospheric concentration of chlorine from 1960 to the present and projected into the future.
The first strong evidence for the existence of the Antarctic ozone hole was in the 1970's when chlorine concentrations reached about 2 ppb. When the CFCs were implicated as the source of the chlorine leading to ozone destruction, the 1987 Montreal Protocol was adopted. As confirming evidence continued to accumulate, the 1990 and 1992 revisions put increased restrictions on CFC production. The graph shows that with the present restrictions in place, ozone levels may return to 1970 levels by the year 2060. DuPont Chemical which was a major producer of CFCs, and the one that invented them in the first place, was very quick to abandon their production of CFCs (Figure 12). Despite overall progress in reducing ozone-depleting chemicals, year-to-year fluctuations may depart from the long-term trend. The 2006 hole was the largest ever measured. The cause of the large hole in 2006 seems to be related to the very cold temperatures in the South Polar stratosphere.
