Mich. Comp. Laws § 290.650d
Beginning June 1 through September 15 of 2007 and for that period of time each subsequent year, the vapor pressure standard shall be 7.0 psi for dispensing facilities in Wayne, Oakland, Macomb, Washtenaw, Livingston, Monroe, St. Clair, and Lenawee counties. The director retains the authority to implement the vapor pressure 7.0 psi requirement or 7.8 psi requirement in areas where it is determined necessary to attain or maintain national ambient air quality standards. If an area of the state that is required to use a low vapor pressure fuel of 7.8 psi or 7.0 psi has been redesignated by the United States environmental protection agency as in attainment of national ambient air quality standards, and the Michigan department of environmental quality has demonstrated that maintenance of the national ambient air quality standards can be achieved without the use of low vapor pressure fuel, the director may, with the approval of the United States environmental protection agency, terminate the low vapor pressure fuel requirement for that area.
MCL 290.650d