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 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 [81 FR 1131, Jan. 11, 2016]