40 CFR 52.1971 - Classification of regions.

Regulations last checked for updates: Feb 06, 2026

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

§ 52.1971 - Classification of regions.

The Oregon 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
Portland Interstate	I	IA	III	I	I
Southwest Oregon Intrastate	II	III	III	III	III
Northwest Oregon Intrastate	III	III	III	III	III
Central Oregon Intrastate	II	III	III	III	III
Eastern Oregon Intrastate	II	III	III	III	III

[37 FR 10888, May 31, 1972, as amended at 45 FR 42278, June 24, 1980]

authority: 42 U.S.C. 7401

cite as: 40 CFR 52.1971