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Air Quality Designations

An air quality designation indicates whether air quality in a particular area meets or does not meet the National Ambient Air Quality Standards (NAAQS) for one or more of the six common, “criteria” air pollutants. The United States Environmental Protection Agency (U.S. EPA) sets the NAAQS to limit outdoor air concentrations for each of the criteria pollutants, which include: carbon monoxide (CO), lead (Pb), nitrogen dioxide (NO2), ozone (O3), particulate matter (PM), and sulfur dioxide (SO2).

When U.S. EPA issues a new or revised NAAQS, both U.S. EPA and states must work to implement the new requirements. The first step in the process is for U.S. EPA to issue air quality designations, or determine which areas of the country are, or are not, meeting the NAAQS based on air quality factors including air monitoring data and recommendations from states. Possible designations include:

  • Nonattainment: Areas that fail to meet a new or revised standard and/or are determined to contribute significantly to nearby areas that fail to meet the NAAQS are designated as “nonattainment” areas. U.S. EPA must also classify nonattainment areas according to the severity of the pollution. Classifications include marginal, moderate, serious, severe, and extreme. Timeframes for areas to come into attainment correspond with their classification. Attainment demonstrations are state implementation plans (SIPS) describing how the area will attain the NAAQS. IDEM’s Nonattainment Status of Counties page includes a map of nonattainment areas and historical information on designations.
  • Attainment: Areas are designated as attainment if data shows pollutant concentrations at or below the NAAQS and they are not determined to be contributing significantly to nearby areas that fail to meet the standards.
  • Unclassifiable: Unclassifiable areas are those for which a determination cannot be made based on available information.

IDEM Recommendations and U.S. EPA Designations for Indiana

Within one year of a new or revised NAAQS, states provide U.S. EPA with recommendations concerning appropriate designations for counties and metropolitan areas based on ambient air quality data and other factors that may influence air quality such as population, contributions from stationary emissions sources and vehicles. Within two years of a new or revised NAAQS, U.S. EPA must issue air quality designations for all areas of the country utilizing air quality data and initial recommendations from the states. IDEM has submitted recommendations for the following criteria pollutants:

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