52.721—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 |