Learn About Particle Pollution Designations

On this page:

• Particle pollution designations process
• Basis for air quality designations 

Particle pollution designations process

Particle pollution, also known as particulate matter (PM), contains microscopic solids or liquid droplets that are so small that they can be inhaled and cause serious health problems. The size of particles is directly linked to their potential for causing health problems. Small particles less than 10 micrometers (PM₁₀) in diameter pose the greatest problems, because they can get deep into your lungs, and some may even get into your bloodstream. Fine particles less than 2.5 micrometers (PM_2.5) also affect the environment. In fact they are the main cause of reduced visibility (haze) in parts of the United States, including many of our treasured national parks and wilderness areas.

Within 2 years of setting new or revised National Ambient Air Quality Standards (NAAQS), the Clean Air Act requires the EPA to designate areas as meeting (attainment) or not meeting (nonattainment) the standard.

After we have issued a new or revised NAAQS, the Clean Air Act requires states to submit, and gives Tribes the opportunity to submit, initial area designation recommendations within 12 months. Tribes are not required to provide recommendations but are invited to do so and to participate in the process.  If the EPA plans to issue a designation that modifies a state recommendation, the EPA must notify the state no later than 120 days before the final designation.

Basis for air quality designations

The EPA’s final designations are based on:

• The most recent 3 years of air quality monitoring data,
• Recommendations submitted by the states and Tribes, and
• Other technical information.

The EPA provided guidance for the particle pollution designations process in the preamble to the PM NAAQS rule. As in recent designations, when making boundary recommendations, the EPA encouraged air agencies to evaluate five factors:

1. Air Quality Data,
2. Emissions and Emissions-related Data,
3. Meteorology,
4. Geography/Topography, and
5. Jurisdictional Boundaries.