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Air Quality Program

National Standards: Criteria Pollutants
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EPA sets national standards for air pollutants called “criteria pollutants.” These standards are known as National and State Ambient Air Quality Standards or “NAAQS.” States are required to meet national standards. A state can set more stringent air quality standards within their state. Washington adopts current federal NAAQS in state rule (Chapter 173-476 WAC, Ambient Air Quality Standards). The federal Clean Air Act requires EPA to review NAAQS every 5 years to make sure the standards protect human health and the environment. State regulations are updated when EPA revises or establishes a new standard.

The federal Clean Air Act requires EPA to set the standards based on scientific evidence. The standards must protect sensitive people including children, elderly, and those with existing heart and lung disease. EPA cannot consider the cost of the pollution controls when setting a standard. It is strictly health-based. However, EPA can take into account the cost of control strategies in implementing a standard.

EPA sets two types of NAAQS:

  1. Primary standards set limits to protect public health, including sensitive people such as children, the elderly, and those with existing heart and lung disease.
  2. Secondary standards set limits to protect public welfare, including decreased visibility, damage to animals, crops, vegetation, and buildings.

Each standard is measured in one of three ways:

  • Parts per million (ppm) by volume
  • Parts per billion (ppb) by volume
  • Micrograms per cubic meter of air (µg/m3)

When EPA establishes or revises a standard, Ecology and EPA evaluate areas of the state to determine their air quality status. See Air Quality Designations web page for more information.

Current NAAQS are listed on EPA's website.

Information about criteria pollutants and their NAAQS

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