Sulfur dioxide is a gas composed of one sulfur atom and two oxygen atoms (SO2) in each molecule. The largest source of SO2 in the atmosphere is the burning of fossil fuel that contains sulfur, such as coal or oil, in power plants and other industrial facilities. Other sources of SO2 emissions include industrial processes such as extracting metal from ore, natural sources such as volcanoes, and locomotives, ships, and other vehicles and equipment that burn fuel that contains sulfur.


Like nitrogen dioxide, sulfur dioxide can create secondary pollutants once released into the air. Secondary pollutants formed with sulfur dioxide include sulfate aerosols, particulate matter, and acid rain.

Health Affects of Sulfur Dioxide

Short-term exposures to SO2 can harm the human respiratory system and make breathing difficult. People with asthma, particularly children, are sensitive to these effects of SO2. Also, SO2 reacts in the atmosphere to form other sulfur oxides and then to form particulate matter, which is also harmful when inhaled.

Air Quality Standards and Monitoring

The primary National Ambient Air Quality Standard (NAAQS), based on health effects, for SO2 is 75 parts per billion (ppb) averaged over one hour (99th percentile of 1-hour daily maximum concentrations, averaged over 3 years).

Missouri monitors SO2 concentrations in the air at locations across the state. Sulfur Dioxide is monitored at additional ambient locations by utility and industrial facilities. Monitoring at these industrial facilities follows procedures reviewed by the state, and results are reported to EPA and to the public. Click on the Monitoring tab to learn more about these air monitoring sites. Click on the Data tab to learn more about the data collected from this sites.

More information is available on EPA's Nitrogen Dioxide webpage.


Sulfur Dioxide

EPA not only established a new one-hour standard in 2010, but it also introduced a new form for determining compliance. The new form requires three years of data — the average SO2 concentration from each hour of the year. The department and EPA calculate the design value, using the 99th percentile of one-hour daily maximum concentrations, averaged over three years.

Departmental information about sulfur dioxide (SO2)

  • Description
  • 2010 standard and related documents


Sulfur Dioxide Monitoring Network