On June 2, 2010, U.S. EPA finalized the 1-hour National Ambient Air Quality Standard (NAAQS) for sulfur dioxide (SO2) at 75 ppb.  The new 1-hour SO2 NAAQS was published in the Federal Register on June 22, 2010 (75 FR 35520), and the standard became effective on August 23, 2010.  The Clean Air Act (CAA) Section 107(d) requires U.S. EPA to promulgate initial area designations for the 1-hour SO2 NAAQS by June 3, 2012 (i.e. 2 years after the promulgation of the NAAQS).  Section 107(d) directs states to submit their recommendations for SO2 designations by June 3, 2011.

The Illinois EPA (IEPA) has identified four 1-hour SO2 non-attainment areas as follows based on ambient SO2 monitoring - Oglesby (LaSalle Township in La Salle County); Pekin (Pekin and Cincinnati Townships in Tazewell County); Lemont (Lemont Township in Cook County; and Lockport and DuPage Townships in Will County); and Wood River (Chouteau and Wood River Townships in Madison County).  IEPA will be holding public meetings in each of these areas before finalizing the recommendations.

Unlike previous NAAQS, the 1-hour SO2 NAAQS requires nonattainment designations consider both ambient monitoring and the results of dispersion modeling analyses of SO2 emissions sources.  Consequently, in late 2010, IEPA began collecting source specific information from hundreds of SO2 emitting sources across the state.  IEPA has begun the dispersion modeling efforts that will be used to make designations determinations for the remainder of the state.  Preliminary results are anticipated later this year.