In the stratosphere, anthropogenic chlorine, mostly from chlorofluorocarbons is released as atomic chlorine (a radical) and becomes involved in a chemical cycle that destroys stratospheric ozone:

CF₂Cl₂ + hv ---> Cl + CF₂Cl (this reaction produces chlorine radicals and the other chlorine atom is ultimately also freed for O₃ destruction)

catalytic cycle:

Cl + O₃ ---> ClO + O₂ (chlorine reacts with ozone to form chlorine monoxide)

O₃ + hv ---> O + O₂ (ozone is also photolyzed to produce atomic oxygen)

ClO + O ---> Cl + O₂ (chlorine radicals are reformed)

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NET: 2O₃ -> 3O₂ (the result is conversion of ozone to molecular oxygen)

Atmospheric data have recently shown that the systematic banning of anthropogenic chlorine-containing compounds, CFCs such as Freon-11 and Freon-12, beginning with the Montreal Protocol in 1986, have stopped the degradation of stratospheric ozone, and a healing of this important atmospheric component is underway. And although recent estimates put the return to pre-damage stratospheric levels (< 1979) as being achieved by about 2050, the use of cheap air conditioning systems (using banned CFCs or replacement HCFCs that have otherwise been phased out) in developing countries like India and China may push that "cured" date back by decades.