Sulfur Dioxide

Overview
Sulfur dioxide (SO2) is part of a group of highly reactive gases called sulfur oxides. SO2 is a colorless, odorless gas at low concentrations. At high concentrations, SO2 is pungent. For more general information about SO2, please read EPA’s Sulfur Dioxide Information page.

SO2 also contributes to the formation of particle pollution, acid rain (deposition) and regional haze.

Health Concerns
Direct health impact from SO2 pollution is usually near the release point of the source. Currently, evidence links short term exposure to an array of respiratory effects including increased asthma symptoms. Sulfur oxides can react with other compounds in the atmosphere to form small particles that can penetrate deeply into sensitive parts of the lungs and can cause or worsen respiratory disease, such as emphysema and bronchitis, and can aggravate existing heart disease.

Environmental Concerns
As SO2 travels away from its source, atmospheric chemistry converts it into various compounds including ammonium sulfate and sulfuric acid. Ammonium sulfate is a particle pollutant and the largest contributor to visibility-reducing haze in New Hampshire; to learn more about haze. Sulfuric acid is a component of acid deposition, which damages forests, lakes and wetlands.

Sourcesphoto of a smokestack
The main sources of SO2 emissions are from fossil fuel combustion at power plants, refineries, and other industrial facilities. Secondary sources of SO2 emissions include ore smelters and the burning of high sulfur fuel by trains, large ships, and non-road equipment. Please see EPA’s Air Emissions Sources page for more about SO2 sources.

Attainment Status and Trends
Please see Sulfur Dioxide Attainment Status and Trends for more information.