40 C.F.R. § 52.1171
Classification of regions.
Cite as 40 C.F.R. § 52.1171 (2026)
The Michigan plan was evaluated on the basis of the following classifications: Air quality control region Pollutant Particulate matter Sulfur oxides Nitrogen dioxide Carbon monoxide Ozone Metropolitan Detroit-Port Huron Intrastate I I III III III Metropolitan Toledo Interstate I I III III I South Central Michigan Intrastate II II III III III South Bend-Elkhart (Indiana)-Benton Harbor (Michigan) Interstate I IA III III III Central Michigan Intrastate II III III III III Upper Michigan Intrastate III III III III III [37 FR 10873, May 31, 1972, as amended at 39 FR 16346, May 8, 1974; 45 FR 29801, May 6, 1980]