Classification of regions.

The Oklahoma plan was evaluated on the basis of the following classifications: Air quality control region Pollutant 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]