Even short-term exposure to low levels of SO 2 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 SO 2 levels in the air increase or when breathing becomes faster or deeper. Lung function typically returns to normal within an hour of exposure to SO 2 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 SO 2 generally also lead to the formation of other sulfur oxides (SO x ). Control measures that reduce SO 2 can generally be expected to reduce peoples' exposures to all gaseous SO x . This may have the important co-benefit of reducing the formation of fine sulfate particles, which pose significant public health threats.
SO x 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 NAAQS for particulate matter (PM) are designed to provide protection against these health 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.