Sulphur dioxide (SO2) is a colourless gas that is odourless at low concentration but has a pungent smell at very high concentration.
The major source of SO2 is fossil fuel burning at power plants, industrial boilers and vehicular exhaust emission.
SO2 can causes irritation to eyes and nose. It can also cause narrowing of airways which people suffer from asthma and chronic respiratory diseases are more sensitive to than other people.
This gas can be transported over long distance and it contributes to the formation of acid rain, which damages plant and animal life, buildings and electric equipment.