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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.

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.

You can be exposed to SO2 by breathing it in the air or getting it on your skin. People who live near industrial sources of sulfur dioxide may be exposed to it in the air. You are most likely to be exposed if you work in industries where SO2 is produced, such as copper smelting or power plants, or where it is used in the production of sulfuric acid, paper, food preservatives, or fertilizers. People with malfunctioning appliances or chimneys in their homes may also be exposed to sulfur dioxide.

Most SO2 exposures are caused by people breathing contaminated outdoor air. Therefore, limit your activities outdoors when you know that air pollution levels are high. The EPA and the Wisconsin Department of Natural Resources (DNR) issue air quality alerts for high pollution days. People with existing respiratory difficulties, such as asthma, should pay special attention to these air advisories. Special care should be taken with child asthmatics to limit their outdoor activities during high pollution days.

To reduce the possibility of exposure to sulfur dioxide caused by a source in your home, you can:

  • Use gas appliances with electronic (pilotless) ignition. This will eliminate the continuous low-level pollutants from pilot lights.
  • Use exhaust fans over gas stoves that are vented to the outdoors instead of fans that recirculate the air indoors. Keep the metal mesh filters on your exhaust fans clean (most can be run through the dishwasher).
  • Choose vented appliances whenever possible, and make sure they are vented to the outdoors. Have a trained professional inspect your appliances annually.
  • Never heat your home with a gas range or stove.
  • Do not idle your car in the garage.
  • Do not smoke indoors.

Short-term exposure to high levels of sulfur dioxide can be life-threatening. Generally, exposures can cause a burning sensation in the nose and throat. Also, exposure can cause difficulty breathing, including changes in the body's ability to take a breath or breathe deeply, or take in as much air per breath. Long-term exposure to sulfur dioxide can cause changes in lung function and aggravate existing heart disease.

People with asthma may be sensitive to changes in respiratory effects due to SO2 exposure at even low concentrations. Sulfur dioxide is not classified as a human carcinogen (it has not been shown to cause cancer in humans).

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Last revised June 15, 2022