Sulfur Dioxide

Sulfur dioxide

Sulfur dioxide is a pungent, chocking and colourless gas.

Sources of Sulfur dioxide

Natural source – From volcanic eruptions

Man-made source – Combustion of fossil fuels (coal, petroleum, natural gas) in motor engines and industries

Harmful Health Effects of Sulfur dioxides

Irritation of lungs and leads to breathing difficulties.

In more severe cases, lungs inflammation may result

Harmful Environmental Effects of Sulfur dioxides

Gives rise to acid rain

Sulfur dioxide gives rise to acid rain.

Sulfur dioxide is an acidic gas. It dissolves in water to form sulfurous acid.

Chemical equation: SO₂ (g) + H₂O (l) → H₂SO₃ (aq)

Sulfurous acid is then oxidised to sulfuric acid by atmospheric oxygen.

Chemical equation: 2H₂SO₃ (aq)  + O₂ (g) → 2H₂SO₄ (aq)

Unpolluted rainwater has a pH of around 5.6 due to carbon dioxide gas. Carbon dioxide is an acidic gas, which dissolves in rainwater to form weak carbonic acid. This slight acidic is natural and harmless.

However, with the presence of man-made nitrogen dioxide and sulfur dioxide, the pH of rainwater will drop to around 4.

Harmful effects of acid rain

Acid rain reacts with metals and carbonates. It corrodes limestone structures and buildings. It speeds up corrosion of metal structure like bridges and motor vehicles.

Acid rain leaches nutrients from the soil needed by the plants for healthy growth. Plants wither and die. Acid rain react with aluminium hydroxide in the soil to produce Al³⁺ ions, which are toxic to plants.

Acid rain reduces the pH value of lakes and streams, making it too acidic for aquatic life to survive.

Treatment of Sulfur dioxide – Flue Gas Desulfurisation

Waste gases are produced when fossil fuels undergo combustion. Waste gases are called flue gas.

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.