Page 12 - Curriculum Visions Dynamic Book

Ozone
Ozone (O3), named for the Greek word for “smell” is a poisonous, colourless and tasteless gas with a distinctive strong smell. Molecules of ozone are probably the source of the smell that can be detected close to working electrical equipment such as motors and TVs. If a vehicle with a catalytic converter is started cold, ozone can be detected in the exhaust fumes.
The ozone layer
Most ozone is found high in the atmosphere, in a region of the stratosphere called the ozone layer. Here ozone performs a vital life-protecting role, absorbing the ultraviolet rays of the Sun that would be harmful to both plants and animal life.
The number of ozone molecules at this level is very small. If brought down to the ground surface they would form a gas layer no more than 3 mm thick. This is why the ozone layer can be so easily disrupted by human activities.
EQUATION: Reaction of CFCs with ozone
 CFC + ultraviolet light ➪ chlorine CFC(g) + UV light ➪ Cl(g)
 Chlorine atom + ozone ➪ chlorine oxide + oxygen Cl(g) + O (g) ➪ ClO(g) + O (g)
 When chlorofluorocarbons (CFCs) reach the stratosphere they are broken down by ultraviolet
solar radiation releasing chlorine atoms. These atoms attack the ozone molecules in the air, but the chain reaction that occurs releases a chlorine atom at the end. Thus a single chlorine atom can survive in the upper atmosphere for four to ten years. During that time it can destroy countless ozone molecules.
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 Chlorine oxide + oxygen atom ➪ chlorine atom + oxygen ClO(g) + O(g) ➪ Cl(g) + O2(g)
+➡+
Ozone (O3) molecules are formed in the upper atmosphere.

Chlorine (Cl) atom released from CFCs and carried into the upper atmosphere by air currents.

This very reactive chlorine atom is called a “free radical”. It can now react with another ozone molecule, causing further destruction of the ozone layer.
+➡+
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