(a) Approval - On March 18, 1999, the Michigan Department of Environmental Quality submitted a request to redesignate the Detroit CO nonattainment area (consisting of portions of Wayne, Oakland and Macomb Counties) to attainment for CO. As part of the redesignation request, the State submitted a maintenance plan as required by 175A of the Clean Air Act, as amended in 1990. Elements of the section 175A maintenance plan include a base year (1996 attainment year) emission inventory for CO, a demonstration of maintenance of the ozone NAAQS with projected emission inventories to the year 2010, a plan to verify continued attainment, a contingency plan, and an obligation to submit a subsequent maintenance plan revision in 8 years as required by the Clean Air Act. If the area records a violation of the CO NAAQS (which must be confirmed by the State), Michigan will implement one or more appropriate contingency measure(s) which are contained in the contingency plan. The menu of contingency measures includes enforceable emission limitations for stationary sources, transportation control measures, or a vehicle inspection and maintenance program. The redesignation request and maintenance plan meet the redesignation requirements in sections 107(d)(3)(E) and 175A of the Act as amended in 1990.

(b) Approval - On December 19, 2003, Michigan submitted a request to revise its plan for the Southeast Michigan CO maintenance area (consisting of portions of Wayne, Oakland and Macomb Counties). The submittal contains updated emission inventories for 1996 and 2010, and an update to the 2010 motor vehicle emissions budget (MVEB). The 2010 MVEB is 3,842.9 tons of CO per day.

(c) Approval - On October 3, 2016, the State of Michigan submitted a revision to their Carbon Monoxide State Implementation Plan. The submittal established transportation conformity “Conformity” criteria and procedures related to interagency consultation, and enforceability of certain transportation related control and mitigation measures.