Sulfur Dioxide

Also known as: SO2, sulfurous anhydride, sulfuroxide, sulfurous oxide, sulfurous acid anhydride


Sulfur dioxide, SO2, is a colorless gas or liquid with a strong, choking odor. It is produced from the burning of fossil fuels (coal and oil) and the smelting of mineral ores (aluminum, copper, zinc, lead, and iron) that contain sulfur. 

Sulfur dioxide dissolves easily in water to form sulfuric acid.  Sulfuric acid is a major component of acid rain. Acid rain can damage forests and crops, change the acidity of soils, and make lakes and streams acidic and unsuitable for fish. Sulfur dioxide also contributes to the decay of building materials and paints, including monuments and statues.

Where is sulfur dioxide found?

Most of the sulfur dioxide released into the environment comes from electric utilities, especially those that burn coal. Some other sources of sulfur dioxide include petroleum refineries, cement manufacturing, paper pulp manufacturing, and metal smelting and processing facilities. Locomotives, large ships, and some non-road diesel equipment currently burn high-sulfur fuel and release sulfur dioxide into the air.  In nature, volcanic eruptions can release sulfur dioxide into the air.

Some dried fruits are preserved using SO2 to prevent discoloration of the fruit. SO2 is also used in bleaching materials and as a fumigant. In homes, sulfur dioxide gas can result from tobacco smoke, improperly or inadequately vented gas appliances (such as stoves, ranges, furnaces, or clothes dryers), gas or kerosene heaters, wood or coal stoves, automobile exhaust from attached garages, and malfunctioning chimneys.

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Last Revised: March 24, 2016