42 U.S. Code § 7511e - Transitional areas
If an area designated as an ozone nonattainment area as of November 15, 1990, has not violated the national primary ambient air quality standard for ozone for the 36-month period commencing on January 1, 1987, and ending on December 31, 1989, the Administrator shall suspend the application of the requirements of this subpart to such area until December 31, 1991. By June 30, 1992, the Administrator shall determine by order, based on the area’s design value as of the attainment date, whether the area attained such standard by December 31, 1991. If the Administrator determines that the area attained the standard, the Administrator shall require, as part of the order, the State to submit a maintenance plan for the area within 12 months of such determination. If the Administrator determines that the area failed to attain the standard, the Administrator shall, by June 30, 1992, designate the area as nonattainment under section 7407(d)(4) of this title.