U.S. Code of Federal Regulations
Regulations most recently checked for updates: Aug 27, 2025
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 Interstate | I | IA | III | III | III |
Northern Washington Intrastate | II | III | III | III | III |
Olympic-Northwest Washington Intrastate | II | II | III | III | III |
Portland Interstate | I | IA | III | III | III |
Puget Sound Intrastate | I | IA | III | III | I |
South Central Washington Intrastate | I | III | III | III | III |