40 C.F.R. § 51.906
Redesignation to nonattainment following initial designations for the 8-hour NAAQS.
Cite as 40 C.F.R. § 51.906 (2026)
For any area that is initially designated attainment or unclassifiable for the 8-hour NAAQS and that is subsequently redesignated to nonattainment for the 8-hour ozone NAAQS, any absolute, fixed date applicable in connection with the requirements of this part is extended by a period of time equal to the length of time between the effective date of the initial designation for the 8-hour NAAQS and the effective date of redesignation, except as otherwise provided in this subpart. [70 FR 71700, Nov. 29, 2005]