Sulfur dioxide

Sulfur dioxide (SO₂), colorless, poisonous gas that has a sharp smell. It is released naturally in gases emitted during volcanic eruptions. Factories or refineries that burn oil or coal also release sulfur dioxide into the atmosphere, creating the potential for human health problems. Sulfur dioxide in the atmosphere may form acid rain when it dissolves in water droplets. Acid rain is damaging to the environment, killing animals and plants. For this reason, many nations are concerned about how much sulfur dioxide their industries should be allowed to release into the air.

See also: Acid rain.