The 2008 Ozone National Ambient Air Quality Standards (NAAQS) - both primary and secondary standards were promulgated on March 12, 2008 and became effective on May 27, 2008. The 8-hr ozone NAAQS was set in 2008 at a level of 0.075 ppm. Once a NAAQS is promulgated for a criteria pollutant, area designations need to be assigned and this occurred July 20, 2012 for this ozone standard. The following two areas in Illinois were designated as marginal non-attainment of the 2008 8-hr ozone NAAQS:

  • Chicago - Naperville, IL-IN-WI (Chicago area)
    • Cook, DuPage, Grundy (partial), Kane, Kendall (partial), Lake, McHenry and Will Counties
  • St. Louis - St. Charles - Farmington, MO-IL (Metro East area)
    • Madison, Monroe and St. Clair Counties

On March 6, 2015, the United States Environmental Protection Agency (USEPA) has published a final rule regarding the "Implementation of the 2008 National Ambient Air Quality Standards for Ozone: State Implementation Plan Requirements". The rule lays out the elements required for a State Implementation Plan (SIP) such as attainment demonstrations, modeling guidance, reasonable further progress (ROP), reasonably available control measures (RACM), major new source review (NSR), emission inventories and SIP submittal timings. The rule also discusses the revoking of the 1997 ozone NAAQS and the applicable anti-back sliding requirements that apply when the rule is revoked.

The marginal non-attainment areas in the Illinois have three (3) years from the date of last designation (i.e., July 20, 2015) to show attainment with the 2008 8-hr ozone NAAQS. The attainment status is determined based on the ozone monitoring data from 2012 to 2014. The monitoring data in Illinois from 2012 was the worst monitoring data (over the reviewed time period), which is threatening the area designations. However, per the provisions of the Clean Air Act (CAA), a state can request for a 1 to 2 year extension for showing attainment if the existing monitoring data meets certain criteria. The criteria includes that the 4th highest daily maximum 8-hr average in the attainment year is 0.075 ppm or less. With this added leeway in the CAA, the Metro East area is expected to qualify for a 1-year extension. However, the Chicago area's monitoring data is not favorable for this extension, which means this area will likely be classified as in moderate non-attainment for 8-hr ozone NAAQS per the requirements of the CAA. If this happens, the consequences with respect to air permitting projects would be minimal, due to major source or major modification thresholds being the same for marginal and moderate non-attainment ozone areas. Additionally, the Metro East area may be able to demonstrate attainment, if the 2013-2015 monitoring data meets the criteria for an attainment per the provisions of the CAA.

The 1997 ozone 8-hr standard will be revoked effective April 6, 2015 which means there will be consequent anti-backsliding requirements. Anti-backsliding requirements are for retaining and preserving the air quality improvements that were achieved under the previous NAAQS. Since, Illinois is in attainment of the revoked 1979 1-hr ozone and the 1997 8-hr ozone standards, the anti-backsliding requirement is the Illinois' maintenance plan for the 1997 8-hr ozone standard.