Sulfur Dioxide Air Pollutant and Sources

A white cloud with the chemical formula for sulfur dioxide, which is SO2

Sulfur dioxide, or SO₂, is a gas composed of one sulfur atom and two oxygen atoms in each molecule. Sulfur dioxide can react with other chemicals in the air to form other pollutants, known as secondary pollutants. These secondary pollutants include sulfate aerosols, particulate matter and acid rain. High concentrations of SO₂ in the air generally also lead to the formation of other sulfur oxides, SO_x.

The largest source of SO₂ in the air is the burning of fossil fuels that contain sulfur — coal or oil — in power plants and other industrial facilities. Other sources of SO₂ emissions include locomotives, ships, and other vehicles and equipment that burn fuel that contains sulfur, industrial processes such as extracting metal from ore, and natural sources such as volcanoes. More information is available on EPA's Sulfur Dioxide (SO2) Pollution webpage.

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 Air Monitoring Sites tab to learn more about these sites. Click on the Monitoring Data tab to learn more about the data collected from this sites.

For information about other ambient air pollutants that the department monitors, visit Air Pollutants and Sources.

Health Effects

Short-term exposures to sulfur dioxide, SO₂, can harm the human respiratory system and make breathing difficult. People with asthma, particularly children, are sensitive to these effects of SO₂.

High concentrations of SO₂ in the air generally also lead to the formation of other sulfur oxides, SO_x. Sulfur oxides react with other compounds in the air to form small particles, which contribute to particulate matter air pollution. Small particles may penetrate deeply into the lungs and in sufficient quantity can contribute to health problems.

Monitoring Data

Sulfur Dioxide

In 2010, EPA not only established a new one-hour standard, but also introduced a new form for determining compliance. The primary National Ambient Air Quality Standard (NAAQS), based on health effects, for SO₂ is 75 parts per billion (ppb) averaged over one hour. 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.

Air Quality Analysis for Sulfur Dioxide - Weekly Monitor Data