EPA Designates Areas as Attainment and Nonattainment for the 24-Hour PM2.5 National Air Quality Standards
"# On December 22, 2008, the Environmental Protection Agency (EPA) designated areas throughout the US as "nonattainment" and "unclassifiable/attainment" for the 24-hour national air quality standards for fine particulate matter (PM2.5).

# After EPA sets a new National Ambient Air Quality Standard (NAAQS) or revises an existing NAAQS, EPA formally identifies or "designates" areas as unclassifiable/attainment (meeting the standard or expected to be meeting the standard despite a lack of monitoring data), nonattainment (not meeting the standard), or unclassifiable (insufficient data to classify).

# In making the decision to designate 211 counties or parts of counties as nonattainment, EPA carefully assessed the recommendations provided by states and tribes, as well as additional supporting information provided by states, tribes, and the public. These nonattainment areas include counties with monitors violating the standards and nearby areas that contribute to that violation. Affected states and tribes will be required to take steps to reduce the pollution that forms these particles. The majority of U.S. counties – over 3,000 – including tribal lands will not have to take additional steps to meet these standards, but will need to continue working to maintain clean air..."