40 CFR 52.1921 - Classification of regions.

Regulations last checked for updates: Feb 11, 2026

Title 40 - Protection of Environment last revised: Dec 22, 2026

§ 52.1921 - Classification of regions.

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

Air quality control region	Pollutant
Air quality control region	Particulate matter	Sulfur oxides	Nitrogen dioxide	Carbon monoxide	Ozone
Central Oklahoma Intrastate	I	III	III	III	I
Northeastern Oklahoma Intrastate	I	III	III	III	I
Southeastern Oklahoma Intrastate	III	III	III	III	III
North Central Oklahoma Intrastate	III	III	III	III	III
Southwestern Oklahoma Intrastate	III	III	III	III	III
Northwestern Oklahoma Intrastate	III	III	III	III	III
Metropolitan Fort Smith Interstate	II	III	III	III	III
Shreveport-Texarkana-Tyler Interstate	II	III	III	III	III

[37 FR 10887, May 31, 1972, as amended at 45 FR 9741, Feb. 13, 1980]

authority: 42 U.S.C. 7401

cite as: 40 CFR 52.1921