There are three federal primary standards for sulfur dioxide (SO2) - a 1-hour standard of 75 parts per billion (ppb), a 24-hour standard of 0.14 parts per million (ppm), and an annual average standard of 0.030 ppm. There is one federal secondary standard - a 3-hour standard of 0.5 ppm. All areas in California are designated attainment/unclassifiable for SO2.
Maps of current area designations can be found through the Resources tab on the left. Information about specific SO2 nonattainment areas and the efforts to bring them into attainment of the SO2 standards can be found on the California State Implementation Plan (SIP) webpage.
Sulfur Dioxide Primary Standards
- December 2017 - U.S. EPA completed the third round of sulfur dioxide (SO2) designations for California. All areas in California were designated as attainment/unclassifiable.
- February 2013 - U.S. EPA published notice in the Federal Register (FR) of proposed nonattainment designations for the 2010 primary federal sulfur dioxide (SO2) standards. No California areas were included in the proposal; all areas of the State remained undesignated.
- August 2012 - U.S. EPA published notice extending the deadline for designating areas with respect to the 2010 primary federal SO2 standard for up to 1 year. U.S. EPA had until June 3, 2013, to complete the initial designations (FR Notice August 3, 2012).
- June 2011 - CARB staff submitted area designation recommendations on June 20, 2011.
- June 2010 - U.S.EPA revised the primary SO2 standards (FR Notice June 22, 2010; effective August 23, 2010).
Additional information about activities related to SO2 can be found on U.S. EPA's SO2 home page.
Sulfur Dioxide Secondary Standard
- March 2012 - U.S. EPA took final action to retain the existing SO2 and NO2 secondary standards (FR Notice April 3, 2012; effective June 4, 2012).
Additional information about activities related to the secondary standards can be found on U.S. EPA's NO2/SO2 secondary standards webpage.