Regulations last checked for updates: May 03, 2025

Title 40 - Protection of Environment last revised: Nov 03, 2025
All TitlesTitle 40Chapter IPart 52Subpart O - Subpart O—Illinois
View all text of Subpart O [§ 52.719 - § 52.750]
§ 52.721 - Classification of regions.

The Illinois plan was evaluated on the basis of the following classifications:

Air quality control region Pollutant
Particulate matter Sulfur oxides Nitrogen dioxide Carbon monoxide Ozone
Burlington-Keokuk InterstateIIIIIIIIIII
East Central Illinois IntrastateIIIIIIIIIIIIII
Metropolitan Chicago Interstate (Indiana-Illinois)IIIII
Metropolitan Dubuque InterstateIIIIIIIIIIIII
Metropolitan Quad Cities InterstateIIIIIIIIIIIII
Metropolitan St. Louis Interstate (Missouri-Illinois)IIIIIII
North Central Illinois IntrastateIIIAIIIIIIIII
Paducah (Kentucky)-Cairo (Illinois) InterstateIIIIIIIIIIII
Rockford (Illinois)-Janesville-Beloit (Wisconsin) InterstateIIIIIIIIIIIIII
Southeast Illinois IntrastateIIIIIIIIIIIIII
West Central Illinois IntrastateIIAIIIIIIIII
[37 FR 10862, May 31, 1972, as amended at 39 FR 16346, May 8, 1974; 45 FR 11493, Feb. 21, 1980]
authority: 42 U.S.C. 7401
cite as: 40 CFR 52.721
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