{"data":{"id":"us/40-cfr-52.721","jurisdiction":"us","citation":"40 CFR 52.721","heading":"Classification of regions.","body":"The Illinois plan was evaluated on the basis of the following classifications:\nAir quality control region Pollutant\nParticulate matter Sulfur oxides Nitrogen dioxide Carbon monoxide Ozone\nBurlington-Keokuk Interstate I I III III III\nEast Central Illinois Intrastate III II III III III\nMetropolitan Chicago Interstate (Indiana-Illinois) I I I I I\nMetropolitan Dubuque Interstate I III III III III\nMetropolitan Quad Cities Interstate I III III III III\nMetropolitan St. Louis Interstate (Missouri-Illinois) I I III I I\nNorth Central Illinois Intrastate II IA III III III\nPaducah (Kentucky)-Cairo (Illinois) Interstate I II III III III\nRockford (Illinois)-Janesville-Beloit (Wisconsin) Interstate II III III III III\nSoutheast Illinois Intrastate III II III III III\nWest Central Illinois Intrastate I IA III III III","path":["Title 40—Protection of Environment","CHAPTER I—ENVIRONMENTAL PROTECTION AGENCY","SUBCHAPTER C—AIR PROGRAMS","PART 52—APPROVAL AND PROMULGATION OF IMPLEMENTATION PLANS","Subpart O—Illinois"],"source_url":"https://www.ecfr.gov/api/versioner/v1/full/2026-08-25/title-40.xml","current_through":"2026-08-25","vintage":"","retrieved_at":"2026-08-27T02:26:04Z","sha256":"1cd5d197894e0ba7c57ca11c9b6c43ba227730aceb14553c0c9f7fb9555770a4","source_id":"us-cfr","stale":true,"prev":"us/40-cfr-52.720","next":"us/40-cfr-52.722"},"notice":"GroundRules: Original legal text. Not legal advice."}