7.4 The Ozone Layer

Notes

The stratospheric ozone layer absorbs most of the Sun's harmful UV-B radiation. This is the "good" ozone, unlike ground-level ozone, which is a pollutant.

• CFCs (chlorofluorocarbons), once used in refrigerators, air conditioners, and aerosol sprays, release chlorine atoms in the stratosphere. One chlorine atom can destroy thousands of ozone molecules.
• The ozone hole forms over Antarctica each spring. Thinner ozone allows more UV radiation, raising risks of skin cancer, cataracts, and damage to plants and plankton.
• The Montreal Protocol (1987) is an international treaty that phased out CFCs. It is widely seen as one of the most successful environmental agreements, and the ozone layer is slowly recovering.
• Ozone depletion and global warming are different problems, although some CFC replacements are also greenhouse gases.
• Example: wearing sunscreen reduces UV exposure; limiting CFCs reduces UV at the source.