To amend the Clean Air Act to provide needed flexibility to States regarding the designation of certain counties as nonattainment areas for ozone under the 8-hour ozone standard, and for other purposes.

Amends the Clean Air Act to require the Administrator of the Environmental Protection Agency to redesignate as transitional any area designated as a nonattainment area for the eight-hour ozone national primary or secondary ambient air quality standard (the standard) if: (1) the area is a single county; (2) the county does not qualify as a rural transport area because of an adjacent standard metropolitan statistical area or consolidated metropolitan statistical area; (3) the county is not in an established ozone transport region; (4) the Governor of the State demonstrates that ozone control measures in effect for the county will provide for attainment of the standard by the deadline for submission of applicable State Implementation Plan (SIP) provisions; and (5) the Governor makes a binding commitment that the State air pollution control agency will apply lowest achievable emission rate determinations to stationary sources as if the redesignation had not occurred and obtain emission offsets for ozone and ozone precursors for each such source if the standard is not met by the SIP deadline.

Requires each county redesignated as transitional to be treated as an attainment or unclassifiable area for purposes of provisions addressing the prevention of significant deterioration of air quality.

Directs the Administrator to review transitional counties within three years of redesignation and to redesignate as nonattainment those counties that have failed to attain the standard. Requires States to submit SIP revisions for such counties that provide for the emission offsets mandated by this Act.