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Sulfur Dioxide
Health and Environmental Effects
National Ambient Air Quality Standards
What is Sulfur Dioxide?
Sulfur dioxide (SO2) belongs to the family of gases called sulfur oxides (SOx). Ambient sulfur dioxide results largely from stationary sources such as coal and oil combustion, steel mills, refineries, pulp and paper mills and from nonferrous smelters.
Health and Environmental Effects
The major health concerns associated with exposure to high concentrations of sulfur dioxide include effects on breathing, respiratory illness, alterations in pulmonary defenses, and aggravation of existing cardiovascular disease. Children, the elderly, and people with asthma, cardiovascular disease or chronic lung disease (such as bronchitis or emphysema), are most susceptible to adverse health effects associated with exposure to SO2. SO2 is also a primary contributor to acid deposition, or acid rain, which causes acidification of lakes and streams and can damage trees, crops, historic buildings and statues. In addition, sulfur compounds in the air contribute to visibility impairment in large parts of the country. This is especially noticeable in national parks.
National Ambient Air Quality Standards
There are three National Ambient Air Quality Standards (NAAQS) for SO2:
- an annual arithmetic mean of 0.03 ppm (80 µg/m3);
- a 24-hour level of 0.14 PPM (365 µg/m3);
- and a 3-hour level of 0.50 PPM (1300 µg/m3).
The first two standards are primary (health-related) standards, while the 3-hour NAAQS is a secondary (welfare-related) standard. The annual mean standard is not to be exceeded, while the short-term standards are not to be exceeded more than once per year.