Sulfur Dioxide (SO2)
Note: EPA no longer updates this information, but it may be useful as a reference or resource.
Please see www.epa.gov/airtrends for the latest information on Air Quality Trends.
Nature and Sources of the Pollutant: Sulfur dioxide belongs to the family of gases called sulfur oxides (SOx ). These gases are formed when fuel containing sulfur (mainly coal and oil) is burned, and during metal smelting and other industrial processes.
Health and Environmental Effects: The major health concerns associated with exposure to high concentrations of SO2 include effects on breathing, respiratory illness, alterations in pulmonary defenses, and aggravation of existing cardiovascular disease. Children, the elderly, and people with asthma, cardiovascular disease or chronic lung disease (such as bronchitis or emphysema), are most susceptible to adverse health effects associated with exposure to SO2 . EPA's health-based national air quality standard for SO2 is 0.03 ppm (measured on an annual arithmetic mean concentration) and 0.14 ppm (measured over 24 hours). SO2 is a precursor to sulfates, which are associated with acidification of lakes and streams, accelerated corrosion of buildings and monuments, reduced visibility, and adverse health effects.
Trends in SO2 Levels: Between 1986 and 1995, national SO2 concentrations decreased 37 percent and SO2 emissions decreased 18 percent. Between 1994 and 1995, national SO2 concentrations decreased 17 percent and SO2 emissions decreased 13 percent. These significant decreases in concentrations and emissions reflect the success of the first year of the Acid Rain Program. While national SO2 air quality levels have improved, EPA remains concerned about short-term peak SO2 concentrations. As a result, EPA proposed a program for States, industry, and communities to use in evaluating and addressing peak concentrations that could occur near some industrial sources.