U.S. Code of Federal Regulations

Regulations most recently checked for updates: Aug 27, 2025

§ 52.2471 - Classification of regions.

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

Air quality control region Pollutant
Particulate matter Sulfur oxides Nitrogen
dioxide
Carbon
monoxide
Ozone
Eastern Washington-Northern Idaho InterstateIIAIIIIIIIII
Northern Washington IntrastateIIIIIIIIIIIIII
Olympic-Northwest Washington IntrastateIIIIIIIIIIIII
Portland InterstateIIAIIIIIIIII
Puget Sound IntrastateIIAIIIIIII
South Central Washington IntrastateIIIIIIIIIIIII
[81 FR 1131, Jan. 11, 2016]