Air Quality Index – sulfur dioxide

What is sulfur dioxide?

Sulfur dioxide, a colorless, reactive gas, is produced when sulfur-containing fuels such as coal and oil are burned. Generally, the highest levels of sulfur dioxide are found near large industrial complexes. Major sources include power plants, refineries, and industrial boilers.

What are the health effects and who is most at risk?

Sulfur dioxide is an irritant gas that is removed by the nasal passages. Moderate activity levels that trigger mouth breathing, such as a brisk walk, are needed for sulfur dioxide to cause health effects in most people.

• People with asthma who are physically active outdoors are most likely to experience the health effects of sulfur dioxide. The main effect, even with very brief exposure (minutes), is a narrowing of the airways (called bronchoconstriction). This may be accompanied by wheezing, chest tightness, and shortness of breath, which may require use of medication that opens the airways. Symptoms increase as sulfur dioxide levels or breathing rate increases. When exposure to sulfur dioxide ceases,lung function typically returns to normal within an hour,even without medication.
• At very high levels, sulfur dioxide may cause wheezing, chest tightness, and shortness of breath even in healthy people who do not have asthma.
• Long-term exposure to sulfur dioxide may cause respiratory symptoms and illness, and aggravate asthma. People with asthma are the most susceptible to sulfur dioxide. However, people with other chronic lung diseases or cardiovascular disease, as well as children and older adults, may also be susceptible to these effects.