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 sulfure 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.

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 Standards (NAAQSs) for sulfur dioxide in the air, established by the U.S. Environmental Protection Agency (EPA), are .03 parts per million (ppm) averaged over the course of an entire year and .14 ppm averaged over a 24-hour period.

The secondary standard for protection of crops, vegetation and buildings is .50 ppm averaged over a three-hour period.

Long-Term Sulfur Dioxide Trends

Massachusetts has seen a steady drop in sulfur dioxide emissions to the air thanks to a number of effective pollution control initiatives. Today air concentrations of SO2 in Massachusetts are well below the level of the health-based National Ambient Air Quality Standard (NAAQS) established by the U.S. Environmental Protection Agency (EPA).


SO2 Trends 1985-2007 Annual Arithmetic Means Standard =0.03 ppm