Sulfur dioxide (SO2) is a colorless, reactive gas produced when sulfur-containing fuels such as coal and oil are burned. Major sources include power plants and industrial boilers. Generally, air concentrations of SO2 are highest near large industrial complexes.

Health Effects of Sulfur Dioxide & Who is Most at Risk

Even short-term exposure to low levels of sulfur dioxide (SO2) in the air can:

  • Narrow the airways and cause breathing problems for children and adults who have asthma and are physically active outdoors.
  • Cause wheezing, chest tightness and shortness of breath even among healthy people who do not have asthma.

Symptoms worsen as SO2 levels in the air increase or when breathing becomes faster or deeper. Lung function typically returns to normal within an hour of exposure to SO2 ending.

Long-term exposure to sulfur dioxide can cause respiratory illness, alter the lungs' defense mechanisms, and aggravate existing cardiovascular or lung disease.

Children and adults who have asthma and are physically active outdoors are most likely to experience the health effects of sulfur dioxide.

Learn more on EPA’s website.

Environmental Effects of Sulfur Dioxide

Along with nitrogen oxides, sulfur dioxide in the air can significantly contribute to acid rain, which degrades soils, lakes and streams, accelerates corrosion of buildings and monuments, and reduces visibility. Sulfur dioxide also is a major precursor of fine particulate soot, which poses a significant health threat.

Sulfur Dioxide Standards

The health-based primary National Ambient Air Quality Standard (NAAQS) for sulfur dioxide is 75 parts per billion (ppb) as a 1-hour daily maximum.  The U.S. Environmental Protection Agency (EPA) established this standard in 2010.  The secondary welfare-based standard is 0.50 parts per million (ppm) averaged over 3-hours.  Monitored levels of SO2 in Massachusetts meet the SO2 standards and have been steadily decreasing.

For more information on sulfur dioxide monitoring, standards, and trends see MassDEP’s Annual Air Quality Reports.