Classification of regions.

The Minnesota plan was evaluated on the basis of the following classifications: Air quality control region Pollutant Particulate matter Sulfur oxides Nitrogen dioxide Carbon monoxide Photochemical oxidants (hydrocarbons) Central Minnesota Intrastate II III III III III Southeast Minnesota-La Crosse (Wisconsin) Interstate II Ia III III III Duluth (Minnesota)-Superior (Wisconsin) Interstate I II III III III Metropolitan Fargo-Moorhead Interstate II III III III III Minneapolis-St. Paul Intrastate I I III I III Northwest Minnesota Intrastate II III III III III Southwest Minnesota Intrastate III III III III III [37 FR 10874, May 31, 1972, as amended at 39 FR 16346, May 8, 1974]