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Lifetimes of Chlorine-Containing Compounds
Figure 9 gives the lifetimes of different chlorine-containing
compounds.
Note that the atmospheric lifetimes, range from about 60 to 400 years, with uncertainty levels given in parentheses. Therefore some of the CFCs we release today will be giving up chlorine leading to ozone destruction well beyond the lifetimes of people living today. The halons (fluorocarbons, chlorocarbons, carbon tetrachloride), similarly, have long lifetimes, although not as long as the CFCs. Some uses of the CFCs and halons, such as refrigeration, lubricants, foams and aerosols, are given in the table as well. Manufacture and use of some of the CFCs and halons have been dramatically reduced at least in the US, but not world wide.
It is possible to reduce the adverse effects of CFCs by adding a hydrogen atom to the molecular structure. This makes the molecule somewhat more reactive and less likely to survive long enough to diffuse to the stratosphere. The resulting molecule is called an HCFC or HFC. For example, HFC-134a is a possible replacement for CFC-12, but requires a much more complicated process for production, as is shown in Figure 10.
A recent graph from National Geographic shows trends over the last 20 years in global production and sale ("consumption") of CFCs and atmospheric concentrations of CFCs in Antarctica.
