Environmental Services Program

Sulfur Dioxide

What is Sulfur Dioxide (SO₂)?

Sulfur dioxide (SO₂) is a colorless gas with a pungent odor. It is primarily produced by the combustion of fossil fuels, particularly coal and oil, and from certain industrial processes like refining petroleum and smelting metal ores. It can also be found in volcanic emissions.

How is Sulfur Dioxide Formed or Where is it Found?

Sulfur dioxide is mainly released into the air by:

• Burning fossil fuels: Power plants, industrial facilities, and transportation that burn coal and oil release sulfur dioxide as a byproduct.
• Industrial processes: Petroleum refining and metal ore smelting contribute to sulfur dioxide emissions.
• Volcanic activity: Naturally, sulfur dioxide is emitted from volcanic eruptions.

In the atmosphere, sulfur dioxide can react with other compounds, such as oxygen and water vapor, forming sulfuric acid (H₂SO₄), a key component of acid rain.

Figure 1: Acid Rain Pathway

This image illustrates the pathway for acid rain in our environment: (1) Emissions of SO2 and NOx are released into the air, where (2) the pollutants are transformed into acid particles that may be transported long distances. (3) These acid particles then fall to the Earth as wet and dry deposition (dust, rain, snow, etc.) and (4) may cause harmful effects on soil, forests, streams, and lakes.

Source: Retrieved from Measuring Acid Rain, U.S. EPA, https://www.epa.gov/air-quality/air-animals-and-plants

Health Effects of Sulfur Dioxide

Sulfur dioxide can have significant health impacts, especially for vulnerable groups such as children, the elderly, and those with respiratory or cardiovascular conditions. Short-term exposure to sulfur dioxide can lead to:

• Respiratory symptoms: Coughing, shortness of breath, and throat irritation.
• Exacerbation of asthma and bronchitis: People with pre-existing lung conditions may experience worsened symptoms.
• Increased risk of cardiovascular disease: Long-term exposure may lead to heart issues.

For the LTBB community, individuals who engage in outdoor activities like fishing, hunting, and ceremonies may experience exacerbated symptoms, especially on days with high sulfur dioxide concentrations.

Environmental Effects of Sulfur Dioxide on LTBB Lands

Sulfur dioxide pollution can also have detrimental effects on the environment:

• Acid rain: When sulfur dioxide combines with water vapor in the atmosphere, it forms sulfuric acid, which falls to Earth as acid rain. This can damage forests, wetlands, and crops that are vital to the LTBB community’s traditional activities and sustenance.
• Soil and water quality degradation: Acid rain can lower the pH of soils and water bodies, making it difficult for plants, aquatic life, and fish to thrive.
• Damage to cultural landscapes: Since LTBB community members rely on the health of the land, water, and wildlife for cultural practices and food, the harmful effects of sulfur dioxide can undermine their way of life.

Figure 2: Critical pH Levels for Aquatic Organisms 

The figure illustrates the pH level at which key organisms may be lost as their environment becomes more acidic. The scale ranges from snails and clams at 6 to frogs at 4.

Source: Retrieved from Measuring Acid Rain, U.S. EPA, https://www.epa.gov/air-quality/air-animals-and-plants

APA Reference List

Environmental Protection Agency. (n.d.). Sulfur dioxide basics. United States Environmental Protection Agency. Retrieved April 9, 2025, from https://www.epa.gov/so2-pollution/sulfur-dioxide-basics

U.S. National Park Service. (n.d.). Air quality and pollution: Sulfur dioxide (SO₂). National Park Service. Retrieved April 9, 2025, from https://www.nps.gov/articles/air-quality-sulfur-dioxide.htm

American Lung Association. (2024). Sulfur dioxide and air pollution. Retrieved April 9, 2025, from https://www.lung.org/clean-air/outdoors/what-makes-air-unhealthy/sulfur-dioxide

World Health Organization. (2021). Sulfur dioxide. World Health Organization. Retrieved April 9, 2025, from https://www.who.int/news-room/fact-sheets/detail/sulfur-dioxide

U.S. Department of Health and Human Services. (2019). Health effects of sulfur dioxide exposure. National Institute of Environmental Health Sciences. Retrieved April 9, 2025, from https://www.niehs.nih.gov/health/materials/sulfur_dioxide_508.pdf

Environmental Protection Agency. (2025, May 5). EPA Air, Animals and Plants . https://www.epa.gov/air-quality/air-animals-and-plants