What is Sulfur Dioxide?
Sulfur dioxide (SO₂) is a pungent, choking, and colourless gas.
Sources of Sulfur dioxide
Natural source – From volcanic eruptions
Man-made source – Combustion of fossil fuels (coal, petroleum, natural gas) in power stations, industries, and motor vehicles
Harmful Effects of Sulfur Dioxide
Health Effects
- Irritates the lungs and causes breathing difficulties.
- In severe cases, it can lead to lung inflammation.
Environmental Effects
- Main cause of acid rain.
How Sulfur Dioxide Causes Acid Rain
Sulfur dioxide is an acidic gas. It dissolves in rainwater to form sulfurous acid:
Equation: SO₂(g) + H₂O(l) → H₂SO₃(aq)
Sulfurous acid is then oxidised by atmospheric oxygen to form sulfuric acid:
Equation: 2H₂SO₃(aq) + O₂(g) → 2H₂SO₄(aq)
Unpolluted rainwater has a pH of about 5.6 due to dissolved carbon dioxide. Carbon dioxide is an acidic gas, which dissolves in rainwater to form weak carbonic acid. This slight acidic is natural and harmless.
However, with sulfur dioxide and nitrogen dioxide pollution, the pH can drop to around 4, making the rain significantly more acidic.
Harmful Effects of Acid Rain
Acid rain reacts with metals and carbonates.
- Corrodes limestone structures and buildings. It speeds up corrosion of metal structure like bridges and motor vehicles.
- Leaches essential nutrients from soil, causing plants to wither.
- Reacts with aluminium compounds in soil to release toxic Al³⁺ ions that harm plants.
- Lowers the pH of lakes and rivers, making it difficult for aquatic life to survive.
Treatment of Sulfur Dioxide – Flue Gas Desulfurisation
Flue gases are waste gases produced from burning fossil fuels.
Sulfur dioxide is one of the waste gases from combustion of fossil fuels. The process of removing sulfur dioxide from flue gases is called flue gas desulfurisation.
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