The Ozone Layer

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Chlorofluorocarbons

Chlorofluorcarbons are compounds that contain chlorine, fluorine and carbon.

They are commonly known as CFC's.

They are often used in aerosols and refrigerators.

Properties of CFC's:

Chemically inert

Low boiling point

Insoluble in water

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Scientists' views on CFC's

Today, CFC's are banned in the UK, although they have not always been.

At first, scientists were enthusiastic about CFC's because of their inertness.

Later it was discovered that the ozone layer was being depleted and that there was a link between this depletion and the use of CFC's

This led to a broad consensus that CFC's should be banned in order to protect the ozone layer.

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How do CFC's damage the ozone layer?

Ozone is a form of oxygen with the formula \(O_3\)

The ozone layer is the part of the stratosphere (upper atmosphere) where ozone is found in the highest concentrations. It absorbs ultraviolet radiation, preventing most of it from reaching the ground.

CFC's are broken down in the stratosphere by ultraviolet light to give highly reactive chlorine atoms known as free radicals.

The ultraviolet light breaks down the carbon-chlorine bond. One electron goes with the chlorine, the other goes with the rest of the molecule. These molecules with unpaired electrons are known as radicals.

\(CCl_3G \rightarrow CCl_2F + \bullet Cl\)

The chlorine free radicals react with ozone but are regenerated after the reaction - meaning they can react several times, damaging a huge numbers of ozone molecules.

CFC's are broken down slowly by the ultraviolet radiation, so they are only slowly removed from the atmosphere. This slow removal, combined with the fact that one chlorine radical can break down many ozone molecules, means that CFC's will continue to harm the environment long after their use has been banned.

CFC's can be replaced with alkanes or hydrocarbons - these will not damage the ozone.

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Why is the Ozone so important?

Ultraviolet light is found naturally in sunlight. We cannot see or feel it, but it causes our skin to turn darker.

The ozone layer is the part of the stratosphere where ozone is found in highest concentrations.

Ozone absorbs ultraviolet radiation, preventing most of it from reaching the ground.

Depletion of the ozone layer allows more ultraviolet light to reach the Earth's surface.

Excessive amounts of ultraviolet is dangerous for many reasons:

Increased risk of

Sunburn

Skin caner

Cataracts

Accelerated ageing of skin