Sulfur Dioxide (SO₂)

What is SO₂?

Sulfur dioxide is a gas primarily emitted from fossil fuel combustion at power plants and other industrial facilities. It is also emitted from locomotives, ships, and other vehicles and equipment that burn fuel with a high sulfur content.

Sources

The largest source of SO₂ in the atmosphere is the burning of fossil fuels by power plants and other industrial facilities. Smaller sources include industrial processes such as extracting metal from ore, natural sources such as volcanoes, and locomotives, ships, and other vehicles.

Health Effects

Short-term exposure can harm the human respiratory system and make breathing difficult. People with asthma, particularly children, are sensitive to these effects. SO₂ emissions also contribute to the formation of particulate matter pollution and acid rain, which can damage ecosystems.

Protecting Yourself

The most reliable way to reduce your exposure is to monitor the Air Quality Index before spending extended time outdoors. On days when the AQI for SO₂ is elevated, consider moving strenuous exercise indoors and keeping windows closed if outdoor air is worse than indoor air.

Sensitive groups — including children, older adults, and people with asthma or heart disease — should take extra precautions at lower AQI thresholds than the general public. High-quality air purifiers with HEPA and activated carbon filters can significantly reduce indoor concentrations. You can track current SO₂ levels for any US city using the search on this site, which pulls directly from EPA AirNow monitoring stations.