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Inorganic compound, heavy, colourless, poisonous gas (SO). It has a pungent, irritating odour (the smell of a just-struck match). It occurs in volcanic gases and dissolved in the waters of some warm springs. Huge quantities are made industrially for use as a bleach, as a reducing agent, and as sulfites, which are food preservatives. It is a precursor of the trioxide (SO), used to make sulfuric acid. Sulfur dioxide is formed when sulfur-containing fuels are burned; in the atmosphere it can combine with water vapour to form sulfuric acid, a major component of acid rain.
This entry comes from Encyclopædia Britannica Concise. For the full entry on sulfur dioxide, visit Britannica.com.