4.11

4.11 Understand the biological consequences of pollution of air by sulphur dioxide and carbon monoxide

1) Sulphur dioxide – SO₂ gas

ü  It is released into the atmosphere by combustion of fossil fuels, vehicles and oil/petrol.

ü  SO₂ + H₂O à sulphuric acid

ü  The acid condenses as clouds and rains.

Effects

- Trees/ plants are ‘burned’ by the sulphuric acid (e.g. ends of conifers)

- Acid rain enters the soil and leaches Ca²⁺ and Mg²⁺ out of the soil. This results in yellowing of leaves.

- Acid rain turns into precipitation and enters streams and lakes. This reduces the pH; however, it releases Al³⁺. This affects the fish because aluminium thickens the mucus at the lining of the gills. This reduces the fish’s ability to take oxygen from water.

2) Carbon monoxide – CO gas

It is produced by fossil fuels (coal and gas) burnt with insufficient oxygen. Carbon monoxide combines with haemoglobin inside the red blood cells and forms carbaminohaemoglobin. It prevents RBC from carrying oxygen and reduces oxygen circulation. It is toxic and once the carbaminohaemoglobin is formed, it is difficult to reverse the process.