Ozone, O3, in the upper atmosphere absorbs much of the Sun's harmful ultraviolet radiation, which can cause skin cancer and cataracts. Chlorofluorocarbons (CFCs) damage this ozone layer.CFCs are very stable, so they are not broken down in the lower atmosphere. They slowly reach the stratosphere, where ultraviolet light breaks the C-Cl bond by homolytic fission to form chlorine radicals, Cl•.The chlorine radicals catalyse the breakdown of ozone: Cl• + O3 → ClO• + O2, then ClO• + O3 → 2O2 + Cl•. The overall equation is 2O3 → 3O2.
The chlorine radical is regenerated, so one radical can destroy thousands of ozone molecules. Nitrogen monoxide radicals, NO•, from aircraft engines and thunderstorms also catalyse ozone decomposition.Research by chemists showing this damage led to legislation banning CFCs. Chlorine-free alternatives such as HFCs are now used instead.
The chlorine radical is regenerated, so one radical can destroy thousands of ozone molecules. Nitrogen monoxide radicals, NO•, from aircraft engines and thunderstorms also catalyse ozone decomposition.Research by chemists showing this damage led to legislation banning CFCs. Chlorine-free alternatives such as HFCs are now used instead.