Classification of regions.

The Iowa plan was evaluated on the basis of the following classification: Air quality control region Pollutant Particulate matter Sulfur oxides Nitrogen dioxide Carbon monoxide Photochemical oxidants (hydrocarbons) Metropolitan Omaha-Council Bluffs Interstate I II III III III Metropolitan Sioux Falls Interstate II III III III III Metropolitan Sioux City Interstate III III III III III Metropolitan Dubuque Interstate I III III III III Metropolitan Quad Cities Interstate I III III III III Burlington-Keokuk Interstate I I III III III Northwest Iowa Intrastate III III III III III North Central Iowa Intrastate IA III III III III Northeast Iowa Intrastate I III III III III Southwest Iowa Intrastate III III III III III South Central Iowa Intrastate I III III III I Southeast Iowa Intrastate III III III III III [37 FR 10865, May 31, 1972, as amended at 39 FR 16346, May 8, 1974]