|County||Area||Nonattainment in year||Redesignation to attainment||Classification||Part or whole county||Population (2000)|
|Cascade||Great Falls||95 96 97 98 99 00 01||NA||Not classified||Part||56,885|
|Missoula||Missoula||95 96 97 98 99 00 01||NA||Moderate <= 12.7ppm||Part||52,356|
|Yellowstone||Billings||95 96 97 98 99 00 01||NA||Not classified||Part||91,232|
KEY: NA = not applicable; ppm = parts per million.
NOTES: Nonattainment areas do not meet the national primary or secondary ambient air quality standard for the specified pollutant. Nonattainment areas are classified based on design values: Serious = an area with a design value of 16.5 ppm and above; Moderate = an area with a design value of 9.1 up to 16.4 ppm.
SOURCE: U.S. Environmental Protection Agency, Green Book, available at http://www.epa.gov/oar/oaqps/greenbk/anay.html as of Apr. 20, 2002.