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Ozone depletion




AQA Content

use equations, such as the following, to explain how chlorine atoms catalyse decomposition of ozone:
Cl• + O3 → ClO• + O2 and ClO• + O3 → 2O2 + Cl•

Specification Notes

Ozone, formed naturally in the upper atmosphere, is beneficial because it absorbs ultraviolet radiation.
Chlorine atoms are formed in the upper atmosphere when ultraviolet radiation causes C–Cl bonds in chlorofluorocarbons (CFCs) to break.
Chlorine atoms catalyse the decomposition of ozone and contribute to the hole in the ozone layer.
Appreciate that results of research by different groups in the scientific community provided evidence for legislation to ban the use of CFCs as solvents and refrigerants. Chemists have now developed alternative chlorine-free compounds.


The ozone layer can is found within the stratosphere. Ozone absorbs UV-B from the Sun, protecting life on Earth.
Ozone depletion refers to the thinning of the ozone layer in the stratosphere, which occurs as a result of human activity. The main cause of ozone depletion is the release of chemicals known as chlorofluorocarbons (CFCs) which are found in refrigerants, solvents, and aerosol spray cans. These chemicals rise into the stratosphere, where they are broken down by ultraviolet radiation from the Sun. The breakdown of these chemicals releases chlorine and bromine radicals, which then go on to deplete ozone molecules.

The radical formed is extremely reactive, causing the breakdown of ozone:

Notice that a radical is formed each time a radical reacts.

Termination involves the reaction between two radicals

Oxides of nitrogen behave in a similar way.

The Antarctic ozone hole is a particularly severe region of ozone depletion that occurs over Antarctica each spring. This phenomenon was first discovered in the 1980s and is caused by a combination of cold temperatures in the stratosphere and the presence of CFCs and other ozone-depleting substances.

To address ozone depletion, the 1987 Montreal Protocol was established, which aimed to phase out the production and consumption of ozone-depleting substances. As a result of this treaty and its amendments, the production and consumption of CFCs and other ozone-depleting chemicals have been significantly reduced. However, it will take many years for the ozone layer to recover fully, as CFCs and other ozone-depleting substances have long atmospheric lifetimes.

Ozone depletion causes an increase in ultraviolet radiation reaching the earth's surface, which can cause skin cancer, cataracts, and other health problems. It can also damage crops and disrupt marine ecosystems.

Recent reports in 2022 indicate that the ozone layer is showing signs of recovery.


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