The United States Environmental Protection Agency (USEPA) has approved the Illinois State Implementation Plan (SIP) on October 6, 2014. The SIP modification request was submitted on March 28, 2014, revising the 1997 8-hr ozone maintenance plan for the Illinois portion of the Chicago-Gary-Lake County, Illinois-Indiana area (Greater Chicago area).

The SIP revision addressed the Motor Vehicle Emissions Budgets (MVEBs) for NOX and VOC through 2025 by adjusting the “safety margin”. The revision requested the allocation of 12 tons/day of VOC and 25 tons/day of NOX from the safety margins of the 2025 MVEBs. The USEPA approved these MVEBs and published the direct final rule on May 22, 2014. One adverse comment was received. USEPA responded to this adverse comment, saying that this revision to the maintenance plan will keep the emissions at or below the attainment levels, thereby complying with the National Ambient Air Quality Standards (NAAQS). The final rule becomes effective November 5, 2014.