A geographic area in which levels of a criteria air pollutant meet
the health-based primary standard
(national ambient air quality
standard, or NAAQS) for the
pollutant. An area may have an
acceptable level for one criteria
air pollutant, but may have
unacceptable levels for others.
Thus, an area could be both
attainment and nonattainment at
the same time. Attainment areas
are defined using federal
pollutant limits set by the U.S.
Environmental Protection Agency.