SO₂ is a highly irritating gas and causes serious respiratory problems, and may cause a fit of coughing.

1. It reacts with water vapour present in the atmosphere to form sulphuric acid. This causes acid rain. Acid rain damages soil [soil become more acidic], plants, and buildings get corroded, especially those made of marble.

In the air, SO₂ is oxidized to SO₃ which is also an irritant.

2SO₂ + O₂ → 2SO₃

SO₃ + H₂O → H₂SO₄

2. Even in very low concentrations, SO₂ causes irritation in the respiratory tract. It causes throat and eye irritation and can also affect the larynx to cause breathlessness.

3. It is extremely harmful to plants. Plants exposed to sulphur dioxide for a prolong time lose colour from their leaves. This condition is known as chlorosis. This is because the formation of chlorophyll is retarded in presence of sulphur dioxide.