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Chlorofluorocarbons and photolytic reactions

Short answer

Chlorofluorocarbons (CFCs) like CCl3F and CCl2F2 are inert refrigerants/propellants. In the stratosphere, UV photolysis cleaves C-Cl bonds: e.g., CCl2F2 + hv -> •CClF2 + Cl•. The released chlorine atoms catalytically destroy ozone: Cl• + O3 -> ClO• + O2; ClO• + O -> Cl• + O2; net O3 + O -> 2O2.

What do you mean by chlorofluorocarbons? Mention their photolytic reactions in the upper atmosphere.

Chlorofluorocarbons

Chlorofluorocarbons (CFCs) are organic compounds containing only carbon, chlorine and fluorine (Freons), for example CCl₃F (CFC-11) and CCl₂F₂ (CFC-12). They are non-toxic, non-flammable and chemically inert in the lower atmosphere, so they were widely used as refrigerants, aerosol propellants, foam-blowing agents and cleaning solvents.

Photolytic reactions in the upper atmosphere

Because CFCs are so stable, they slowly rise to the stratosphere, where strong UV radiation (λ < 220 nm) breaks the C–Cl bond and releases chlorine atoms:

CCl₃F  + hν → •CCl₂F + Cl•
CCl₂F₂ + hν → •CClF₂ + Cl•

The free chlorine atom then destroys ozone in a chain reaction:

Cl• + O₃  → ClO• + O₂
ClO• + O  → Cl• + O₂
-------------------------------
Net:  O₃ + O → 2O₂        (Cl• is regenerated)

A single Cl atom can destroy about 10⁵ ozone molecules before it is removed, for example as HCl (Cl• + CH₄ → HCl + •CH₃) or as chlorine nitrate (ClO• + NO₂ → ClONO₂).

Thus CFCs are the main cause of the thinning of the ozone layer and the ozone hole over Antarctica.

✓ Answer checked by Claude Opus 5.5 (high effort)

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