Acids and alkalis
Sulphur dioxide is produced when fuels that contain sulphur compounds burn. It is a gas with a sharp, choking smell. When sulphur dioxide dissolves in water droplets in clouds, it makes the rain more acidic than normal. This is called acid rain.
Remember, acid rain contains other non-metal oxides, e.g., carbon dioxide.
Acid rain reacts with metals and rocks such as limestone. Buildings and statues are damaged as a result. Acid rain damages the waxy layer on the leaves of trees and makes it more difficult for trees to absorb the minerals they need for healthy growth. They may die as a result. Acid rain also makes rivers and lakes too acidic for some aquatic life to survive.
The video below highlights the effects of acid rain in the United Kingdom.
Video: Pollution - acid rain
Sulphur dioxide can be removed from waste gases after combustion of the fuel. This happens in power stations. The sulphur dioxide is treated with powdered limestone to form calcium sulphate. This can be used to make plasterboard for lining interior walls, so turning a harmful product into a useful one.
Sulphur can be removed from fuels at the oil refinery. This makes the fuel more expensive to produce, but it prevents sulphur dioxide being produced. You may have noticed 'low sulphur' petrol and diesel on sale at filling stations.
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