On June 22, 2010, the U.S. EPA replaced the existing annual and 24-hour primary sulfur dioxide (SO2) air quality standards with a new 1-hour SO2 standard set at a level of 75 parts per billion (ppb) to better protect public health by reducing public exposure to high short-term concentrations of SO2. For more information, including a fact sheet on the revision, please visit U.S. EPA: Sulfur Dioxide: Regulatory Actions.
The Governor made boundary recommendations to the U.S. EPA on May 25, 2011, for areas that meet, areas that do not meet, or areas that cannot be classified for the new standard. The recommendations are based on such factors as sources of SO2 emissions and monitors currently measuring sulfur dioxide at levels above the standard.
U.S. EPA's decision on final area designations is expected by June 03, 2013.
The current secondary standard (for protection of the environment/public welfare) is 0.5 ppm averaged over a 3-hour period. U.S. EPA review of the secondary standard was completed in 2012.