6.2 Stratospheric ozone

Significant ideas

• Stratospheric ozone is a key component of the atmospheric system because it protects living systems from the negative effects of ultraviolet radiation from the Sun.

• Human activities have disturbed the dynamic equilibrium of stratospheric ozone formation.

• Pollution management strategies are being employed to conserve stratospheric ozone.

Knowledge and understanding

1. Some ultraviolet radiation from the Sun is absorbed by stratospheric ozone causing the ozone molecule to break apart. Under normal conditions the ozone molecule will reform. This ozone destruction and reformation is an example of a dynamic equilibrium.

2. Ozone depleting substances (including halogenated organic gases such as chlorofluorocarbons—CFCs) are used in aerosols, gas-blown plastics, pesticides, flame retardants and refrigerants. Halogen atoms (such as chlorine) from these pollutants increase destruction of ozone in a repetitive cycle, allowing more ultraviolet radiation to reach the Earth.

3. Ultraviolet radiation reaching the surface of the Earth damages human living tissues, increasing the incidence of cataracts, mutation during cell division, skin cancer and other subsequent effects on health.

4. The effects of increased ultraviolet radiation on biological productivity include damage to photosynthetic organisms, especially phytoplankton, which form the basis of aquatic food webs.

5. Pollution management may be achieved by reducing the manufacture and release of ozone-depleting substances. Methods for this reduction include:

   • recycling refrigerants

   • developing alternatives to gas-blown plastics, halogenated pesticides, propellants and aerosols

   • developing non-propellant alternatives.

   • UNEP has had a key role in providing information, and creating and evaluating international agreements, for the protection of stratospheric ozone.

6. An illegal market for ozone-depleting substances persists and requires consistent monitoring.

7. The Montreal Protocol on Substances that Deplete the Ozone Layer (1987) and subsequent updates is an international agreement for the reduction of use of ozone-depleting substances signed under the direction of UNEP. National governments complying with the agreement made national laws and regulations to decrease the consumption and production of halogenated organic gases such as chlorofluorocarbons (CFCs).