Pollution

Why is combustion bad?

Burning fossil fuels makes carbon dioxide, carbon dioxide can dissolve in water to make an acidic solution.
Rainwater is naturally slightly acidic because of carbon dioxide in the air.
Acid rain has a pH of 5.2 or lower. Sulphur dioxide gas is a major cause of acid rain.

Sulphur Dioxide

Hydrocarbons contain sulphur compounds, when fuels are burnt the sulphur reacts with the oxygen to make sulphur dioxide gas.

It then dissolves in the water in the clouds to make a mixture of acids including sulphurous acid which is turned into sulphuric acid.

Nitrogen Oxides

Nitrogen dioxide also contributes to acid rain

It forms nitric acid when it dissolves in the water in clouds. Nitrogen dioxide is a toxic red-brown gas and it can cause respiratory diseases like bronchitis.

Cars have catalytic converters fitted to turn nitrogen dioxide into harmless nitrogen.

Effects of acid rain

Acid rain can damage crops and other plants. Crops can not grow if the soil is too acidic.
When it makes water in lakes and rivers acidic it can kill fish and stop their eggs from hatching.
Acid rain can damage buildings and increase the effects of weathering.