Classification of regions.

The Illinois plan was evaluated on the basis of the following classifications: Air quality control region Pollutant Particulate matter Sulfur oxides Nitrogen dioxide Carbon monoxide Ozone Burlington-Keokuk Interstate I I III III III East Central Illinois Intrastate III II III III III Metropolitan Chicago Interstate (Indiana-Illinois) I I I I I Metropolitan Dubuque Interstate I III III III III Metropolitan Quad Cities Interstate I III III III III Metropolitan St. Louis Interstate (Missouri-Illinois) I I III I I North Central Illinois Intrastate II IA III III III Paducah (Kentucky)-Cairo (Illinois) Interstate I II III III III Rockford (Illinois)-Janesville-Beloit (Wisconsin) Interstate II III III III III Southeast Illinois Intrastate III II III III III West Central Illinois Intrastate I IA III III III [37 FR 10862, May 31, 1972, as amended at 39 FR 16346, May 8, 1974; 45 FR 11493, Feb. 21, 1980]