9.2 Reducing Ozone Depletion

Stratospheric Ozone and Its Role

Stratospheric ozone (O3) forms a protective layer that absorbs harmful UV radiation from the sun. Chlorofluorocarbons (CFCs), once used in refrigerants, aerosols, and solvents, rise into the stratosphere where UV light breaks them apart, releasing chlorine atoms that catalytically destroy ozone molecules, thinning the layer over places like Antarctica.

Consequences of Ozone Depletion

A thinner ozone layer lets more UV-B radiation reach Earth's surface, increasing rates of skin cancer, cataracts, and immune suppression in humans, while also harming phytoplankton and crop productivity. The seasonal ozone hole over Antarctica is the most visible symptom of this depletion.

International Action: The Montreal Protocol

The Montreal Protocol (1987) is a landmark international treaty that phased out production and use of ozone-depleting substances (ODS) like CFCs. Nations replaced CFCs with less harmful alternatives (e.g., HFCs). This cooperative effort has led to measurable recovery of the ozone layer, showing how policy can solve global environmental problems.

Key terms

CFCs (Chlorofluorocarbons)

Chemicals once used in refrigerants and aerosols that release chlorine atoms in the stratosphere, destroying ozone.

Stratospheric ozone

A layer of O3 in the stratosphere that absorbs harmful UV radiation, protecting life on Earth.

Ozone hole

A seasonal area of severely thinned ozone, most notably over Antarctica, caused by ODS reactions.

Montreal Protocol

1987 international treaty that phased out production of ozone-depleting substances like CFCs; led to ozone recovery.

Effects of UV-B increase

Higher rates of skin cancer, cataracts, immune suppression, and harm to phytoplankton and crops.

Try an AP-style question

Which international agreement phased out CFCs?

1. The Kyoto Protocol
2. The Paris Agreement
3. The Montreal Protocol
4. CITES