How Does the Clean Air Act Work?

The Clean Air Act establishes health-based National Ambient Air Quality Standards (NAAQS) for six categories of pollutants, known as “criteria pollutants”: sulfur dioxide (SO2), nitrogen dioxide (NO2), carbon monoxide (CO), Ozone (O3), Lead (Pb), and Particulate Matter (PM10 and PM2.5). Each of the NAAQS sets an upper limit for a criteria pollutant in the ambient, or outdoor, air.  States use air monitoring to demonstrate whether the air meets those standards.  The current standards can be seen here.

The Clean Air Act requires the NAAQS to be reviewed every five years and revised if necessary.   During the review, EPA examines the latest peer-reviewed science to determine whether the standard needs to be strengthened to protect public health.

When a new standard is set, states have one year to recommend to EPA which areas are likely to meet the new standard (“attainment”) and which areas are not (“nonattainment”).  The Division for Air Quality (DAQ) considers a range of factors when making attainment designation recommendations for Kentucky, including:

  • Air quality and emissions data
  • Level of control of emission sources
  • Population density and degree of urbanization
  • Traffic and commuting patterns
  • Growth rate and patterns
  • Meteorology
  • Geography/topography
  • Jurisdictional boundaries

EPA has one year to review state designation recommendations, modify the recommendations if necessary, and make final attainment and nonattainment area designations.

What happens when an area gets designated nonattainment?  “The Clean Air Act requires pollutant levels in nonattainment areas to be reduced,” said DAQ director John Lyons, “and it takes a comprehensive strategy to make that happen.”  That’s where the State Implementation Plan (SIP) comes in.

The SIP is an air quality plan that shows how to attain or maintain the NAAQS.  Each state is responsible for developing a SIP to demonstrate how the NAAQS will be achieved, maintained, and enforced.  Specifically for nonattainment areas, the plan includes:

  • Enforceable emission limitations
  • Control measures
  • Emission inventories
  • Ambient air monitoring
  • Enforcement measures

A nonattainment area typically must achieve attainment status no later than five years after it was designated nonattainment.

“Tighter standards for several criteria pollutants have been adopted or proposed in the past few years, most recently for ozone and particulate matter”, said Lyons.  “As a result, some counties may find themselves in nonattainment for the first time in many years.”  The Division for Air Quality will continue to work closely with counties to attain and maintain air quality standards, to ensure clean air for all Kentuckians now and for years to come.

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