# 40 C.F.R. § 52.721 (2026): Classification of regions

> Federal · Regulations · In force

URL: https://www.frixlaw.com/law-library/statutes/CFR_T40_P52_S52_721

## Section

- **Citation:** 40 C.F.R. § 52.721 (2026)
- **Heading:** Classification of regions
- **Jurisdiction:** Federal
- **Kind:** Regulations
- **Status:** In force
- **Text as of:** August 14, 2026
- **Source:** Compiled text
- **Location:** Title 40 CFR: Protection of Environment / Chapter I / Part 52 / Subpart O / § 52.721: § 52.721   Classification of regions.

## Text

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 Interstate I I III III III East Central Illinois Intrastate III II III III III Metropolitan Chicago Interstate (Indiana-Illinois) I I I I I Metropolitan Dubuque Interstate I III III III III Metropolitan Quad Cities Interstate I III III III III Metropolitan St. Louis Interstate (Missouri-Illinois) I I III I I North Central Illinois Intrastate II IA III III III Paducah (Kentucky)-Cairo (Illinois) Interstate I II III III III Rockford (Illinois)-Janesville-Beloit (Wisconsin) Interstate II III III III III Southeast Illinois Intrastate III II III III III West Central Illinois Intrastate I IA III III III [37 FR 10862, May 31, 1972, as amended at 39 FR 16346, May 8, 1974; 45 FR 11493, Feb. 21, 1980]

## Nearby sections

- [40 C.F.R. § 52.720 (2026) § 52.720   Identification of plan.](https://www.frixlaw.com/law-library/statutes/CFR_T40_P52_S52_720.md)
- [40 C.F.R. § 52.721 (2026) § 52.721   Classification of regions.](https://www.frixlaw.com/law-library/statutes/CFR_T40_P52_S52_721.md)
- [40 C.F.R. § 52.722 (2026) § 52.722   Approval status.](https://www.frixlaw.com/law-library/statutes/CFR_T40_P52_S52_722.md)
- [40 C.F.R. § 52.724 (2026) § 52.724   Control strategy: Sulfur dioxide.](https://www.frixlaw.com/law-library/statutes/CFR_T40_P52_S52_724.md)
- [40 C.F.R. § 52.725 (2026) § 52.725   Control strategy: Particulates.](https://www.frixlaw.com/law-library/statutes/CFR_T40_P52_S52_725.md)
- [40 C.F.R. § 52.726 (2026) § 52.726   Control strategy: Ozone.](https://www.frixlaw.com/law-library/statutes/CFR_T40_P52_S52_726.md)
- [40 C.F.R. § 52.730 (2026) § 52.730   Compliance schedules.](https://www.frixlaw.com/law-library/statutes/CFR_T40_P52_S52_730.md)
- [40 C.F.R. § 52.731 (2026) § 52.731   Interstate pollutant transport provisions; What are the FIP requirements for decreases in emissions of nitrogen oxides?](https://www.frixlaw.com/law-library/statutes/CFR_T40_P52_S52_731.md)
- [40 C.F.R. § 52.732 (2026) § 52.732   Interstate pollutant transport provisions; What are the FIP requirements for decreases in emissions of sulfur dioxide?](https://www.frixlaw.com/law-library/statutes/CFR_T40_P52_S52_732.md)
- [40 C.F.R. § 52.736 (2026) § 52.736   Review of new sources and modifications.](https://www.frixlaw.com/law-library/statutes/CFR_T40_P52_S52_736.md)
- [40 C.F.R. § 52.737 (2026) § 52.737   Operating permits.](https://www.frixlaw.com/law-library/statutes/CFR_T40_P52_S52_737.md)
- [40 C.F.R. § 52.738 (2026) § 52.738   Significant deterioration of air quality.](https://www.frixlaw.com/law-library/statutes/CFR_T40_P52_S52_738.md)
- [40 C.F.R. § 52.739 (2026) § 52.739   Permit fees.](https://www.frixlaw.com/law-library/statutes/CFR_T40_P52_S52_739.md)
- [40 C.F.R. § 52.740 (2026) § 52.740   Interstate pollution.](https://www.frixlaw.com/law-library/statutes/CFR_T40_P52_S52_740.md)

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Source: Frix Law Library, https://www.frixlaw.com/law-library/statutes/CFR_T40_P52_S52_721. Check the current official text before relying on it. Not legal advice.