Nonattainment Area:

A Nonattainment Area is a region in which the level of a Criteria Air Pollutant is higher than allowed by the federal NAAQS. For ground-level ozone, the one-hour standard is 120 parts per billion. EPA puts a City or metropolitan area on its "nonattainment" list when ozone exceeds, or violates, the standard more than once a year averaged over a three-year period.