Chlorine, catalytic cycles that destroy

Perfluorinated ethers and perfluorinated tertiary amines do not contribute to the formation of ground level ozone and are exempt from VOC regulations (32). The commercial compounds discussed above have an ozone depletion potential of zero because they do not contain either chlorine or bromine which take part in catalytic cycles that destroy stratospheric ozone (33). 

The involvement of reactive nitrogen, reactive hydrogen, and reactive chlorine in catalytic cycles that destroy ozone has been known for about 20 years. These cycles have the form... 

Stratospheric ozone depletion is one of the best-established phenomena arising from anthropogenic influence on the global environment. As chlorofluorocarbons and other chlorinated and brominated substances are emitted into the atmosphere, those that are not subject to attack in the troposphere may reach the stratosphere where UV radiation breaks the molecules apart, releasing their halogen atoms. These halogen atoms initiate catalytic cycles that destroy stratospheric ozone one chlorine atom can destroy as many as 100,000 ozone molecules before finally being removed from the stratosphere. 

The chlorofluorocarbon effect on the ozone layer illustrates another chemical concern—the special problem that can arise when materials released into the environment are able to act as catalysts. If every chlorine atom generated in the upper atmosphere simply destroyed one ozone molecule, the effect would be minimal. But chemists have elucidated the catalytic cycle by which each chlorine atom destroys thousands of ozone molecules. It is particularly important for chemists to study and understand which substances can have such catalytic effects— and to learn how to prevent the release of such substances into the environment. 

Given that the bottleneck establishing the rate of chlorine-induced ozone destruction is, to first order, the concentration of the rate limiting chlorine free radical in the dominant catalytic cycle destroying odd oxygen, it is essential to establish the propensity of the stratosphere for partitioning total chlorine into the rate limiting radical form. This ratio of CIO to total chlorine as a function of altitude is a quantity of first order importance. 

Fluorine chemistry in the stratosphere has also been considered and attention has been drawn to the atmospheric chemistry of the FOx radicals. The compounds with O-F bonds have gained interest in connection with the ozone depletion problem. It has been suggested that FO and F02 radicals formed in the atmospheric degradation of hydrofluorocarbons (HFCs) could destroy ozone in chain reaction processes. Experimental studies of this hypothesis led to the conclusion that catalytic cycles involving F, FO, and F02 are irrelevant with respect to the chlorine cycle.8 However, kinetic investigations of the reactions of fluorine atoms with 02 and NOx provide useful information on the fluorine chemistry in the polluted atmosphere. 

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