Sulfur Dioxide (SO2)
Nature and Sources of the Pollutant: Sulfur dioxide belongs to the family of sulfur oxide gases (SOx). These gases are formed when fuel containing sulfur (mainly coal and oil) is burned, and during metal smelting and other industrial processes.
Health and Other Effects: The major health concerns associated with exposure to high concentrations of SO2 include effects on breathing, respiratory illness, alterations in pulmonary defenses, and aggravation of existing cardiovascular disease. Major subgroups of the population that are most sensitive to SO2 include asthmatics and individuals with cardiovascular disease or chronic lung disease (such as bronchitis or emphysema) as well as children and the elderly. EPA's health-based national air quality standard for SO2 is 0.03 ppm (measured on an annual average) and 0.14 ppm (measured over 24 hours). Emissions of SO2 also can damage the foliage of trees and agricultural crops. EPA has a secondary SO2 national ambient air quality standard of 0.50 ppm (measured over 3 hours) designed to prevent this type of environmental deterioration. Together, SO2 and NOX are the major precursors to acid rain, which is associated with the acidification of lakes and streams, accelerated corrosion of buildings and monuments, and reduced visibility.