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Ozone Depletion

Chemistry: AQA A Level, topic 5.3.3

Ozone Depletion

Between 1928 and 1978, halogenoalkanes called chlorofluorocarbons (CFCs) were widely used in industry. These CFCs often escaped into the atmosphere where they depleted the ozone layer.

CFCs and ozone

CFCs and ozone

  • A CFC is a chloroflurocarbon molecule.
  • CFCs only contain carbon, chlorine and fluorine atoms.
  • Ozone has the formula O3.
  • O3 is much less stable than O2.
  • O3 is formed from O2 and UV light.
  • O3 is present in low concentrations.
    • Its highest concentrations are in the ozone layer of the Earth's atmosphere.
Ozone depletion

Ozone depletion

  • Chlorofluorocarbons undergo photolysis in the atmosphere.
  • Photolysis means ‘broken down by light’.
  • This process creates chlorine radicals.
  • Chlorine radicals react with ozone (O3).
Mechanism for ozone depletion

Mechanism for ozone depletion

  • The destruction of ozone is a free radical mechanism.
  • The initiation step is:
  • Cl2→light2Cl∙Cl_2 \xrightarrow[\text{}]{\text{light}} 2Cl\bullet
  • The propagation steps are:
  • Cl∙+O3→ClO∙+O2Cl\bullet + O_3 \rightarrow ClO\bullet + O_2
  • ClO∙+O3→2O2+Cl∙ClO\bullet +O_3 \rightarrow 2O_2 + Cl\bullet
  • The termination step is:
  • 2Cl∙→Cl22Cl\bullet \rightarrow Cl_2
CFC bans

CFC bans

  • CFCs were used in aerosols, as coolants in fridges and as solvents in industry.
  • Scientists collected evidence in the 1970s that they were damaging the ozone layer.
  • This led to bans, beginning with Sweden in 1978, and the development of safer alternatives like hydrofluorocarbons (HFCs) and hydrocarbons.

Test yourself on Ozone Depletion

  • Which of the following areas would contain the highest ozone concentration?

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