Failure to meet the NAAQS for a criteria pollutant in a particular AQCR. In 1977, Congress divided all areas of the country into two categories: those that failed to meet NAAQS (i.e., nonattainment areas) and PSD areas. Nonattainment areas are further categorized as "extreme," "severe," "moderate," or "marginal." The more polluted the area, the more stringent the restrictions.