EPA Sets New Air Quality Standard for Sulfur Dioxide

EPA is issuing a final new health standard for sulfur dioxide (SO2). This one-hour health standard will protect millions of Americans from short-term exposure to SO2, which is primarily emitted from power plants and other industrial facilities. Exposure to SO2 can aggravate asthma and cause other respiratory difficulties. People with asthma, children, and the elderly are especially vulnerable to the effects of SO2.

EPA is setting the one-hour SO2 health standard at 75 parts per billion (ppb), a level designed to protect against short-term exposures ranging from five minutes to 24 hours. EPA is revoking the current 24-hour and annual SO2 health standards because the science indicates that short-term exposures are of greatest concern and the existing standards would not provide additional health benefits. EPA is also changing the monitoring requirements for SO2. The new requirements assure that monitors will be placed where SO2 emissions impact populated areas. Any new monitors required by this rule must begin operating no later than Jan. 1, 2013. EPA is expecting to use modeling as well as monitoring to determine compliance with the new standard.

(1) Exhaust from automobiles, power plants, and factory smokestacks fills the air with sulfur dioxide and nitrogen oxide gases. (2) Some of the gases become attached to particles in the air and fall to earth as dry deposition. (3) Great quantities of sulfur dioxide and nitrogen oxides mix with the moisture in clouds to form sulfuric acid. (4) These acids fall, with the rest of the water in the clouds, as acid rain, or wet deposition. (5) The acids poison trees, crops, and other plants. (6) Sulfuric and nitric acids build up in rivers and lakes, killing fish and polluting the water. (ARRF)

The final rule also changes the Air Quality Index to reflect the revised SO2 standard. This change will improve states’ ability to alert the public when short-term SO2 levels may affect their health. EPA estimates that the health benefits associated with this rule range between $13 billion and $33 billion annually. These benefits include preventing 2,300 to 5,900 premature deaths and 54,000 asthma attacks a year. The estimated cost in 2020 to fully implement this standard is approximately $1.5 billion.

The first National Ambient Air Quality Standards for SO2 were set in 1971, establishing both a primary standard to protect health and a secondary standard to protect the public welfare. Annual average SO2 concentrations have decreased by 71 percent since 1980. The final rule addresses only the SO2 primary standards, which are designed to protect public health. EPA will address the secondary standard – designed to protect the public welfare, including the environment – as part of a separate review to be completed in 2012. EPA expects to identify or designate areas not meeting the new standard by June 2012.

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