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 fuel-burning industrial facilities.
According to the EPA, the largest sources of SO2 emissions are from fossil fuel combustion at power plants (73%) and other industrial facilities (20%).
Smaller sources of SO2 emissions include industrial processes such as extracting metal from ore, and the burning of high sulfur-containing fuels by locomotives, large ships, and non-road equipment. Recent federal measures to limit sulfur in fuels have reduced SO2 emissions from on-road and off-road mobile sources such as cars, trucks, and construction equipment.
Sulfur Dioxide is part of a larger category of related chemicals, often referred to as 'sulfur oxides' or SOX.
The current primary National Ambient Air Quality Standard (NAAQS) for SO2 is 75 parts per billion (ppb) averaged over 1-hour. The secondary standard is 0.5 parts per million (ppm) averaged over 3 hours.
More information about Sulfur Dioxide can be found at http://www.epa.gov/so2-pollution.
Contact: Mary Peyton Wall, Manager, (803) 898-4064
Health Effects
Even short-term exposure to low levels of 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.
Emissions that lead to high concentrations of SO2 generally also lead to the formation of other sulfur oxides (SOx). Control measures that reduce SO2 can generally be expected to reduce peoples' exposures to all gaseous SOx. This may have the important co-benefit of reducing the formation of fine sulfate particles, which pose significant public health threats.
SOx can react with other compounds in the atmosphere to form small particles. These particles penetrate deeply into sensitive parts of the lungs and can cause or worsen respiratory disease, such as emphysema and bronchitis, and can aggravate existing heart disease, leading to increased hospital admissions and premature death. EPA's national ambient air quality standards (NAAQS) for particulate matter (PM) are designed to provide protection against these health effects.
Environmental Effects
Sulfur dioxide and nitrogen oxides are the major precursors of acid rain, which acidifies 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.