What Are the National Ambient Air Quality Standards (NAAQS)?

Part 4 of the Clean Air Act series from Compliance Assurance Associates, Inc. (CAA). Read Part 1 on Title V Permits, Part 2 on State Implementation Plans, and Part 3 on New Source Performance Standards.

Most air quality regulations trace back to a single question: how clean does the air need to be?

The National Ambient Air Quality Standards, commonly called NAAQS, are the U.S. Environmental Protection Agency’s benchmarks for certain common outdoor air pollutants. These standards help define acceptable air quality levels for pollutants that can affect public health and the environment.

For facility operators, one important distinction matters: NAAQS are not facility-specific permit limits. A permit may include emission limits, monitoring requirements, operating restrictions, or control technology requirements, but the NAAQS themselves apply to outdoor air quality at the area or regional level.

Even so, NAAQS help explain why many permit requirements exist. They influence State Implementation Plans (SIPs), attainment designations, permitting requirements, and the compliance obligations that may apply to facilities in different parts of the country.

Understanding NAAQS is a helpful step in understanding why an air permit says what it says.

What the NAAQS Are — and Are Not

The NAAQS are national outdoor air quality standards for pollutants that are common in ambient air and considered harmful to public health or welfare.

There are 2 types of NAAQS:

  • Primary standards are designed to protect public health, including sensitive populations such as children, older adults, and people with respiratory or cardiovascular conditions
  • Secondary standards are designed to protect public welfare, including effects on visibility, crops, vegetation, ecosystems, buildings, and materials

These standards are not written as individual emission limits for a single stack, process, or facility. Instead, they are ambient air quality standards. EPA sets the standards, and states develop plans to attain and maintain them.

The Six Criteria Pollutants Covered by NAAQS

The NAAQS apply to six criteria pollutants. These pollutants are called “criteria pollutants” because EPA regulates them based on health and environmental criteria.

The six criteria pollutants are:

  • Particulate matter, including PM2.5 and PM10
  • Ground-level ozone
  • Carbon monoxide
  • Sulfur dioxide
  • Nitrogen dioxide
  • Lead

Each pollutant has its own standard and method of evaluation. For example, ozone is evaluated differently than fine particulate matter, and sulfur dioxide is evaluated differently than carbon monoxide.

Particulate matter is also divided into different size categories. PM2.5 refers to fine particles that are 2.5 micrometers or smaller in diameter, while PM10 refers to particles that are 10 micrometers or smaller in diameter.

Criteria pollutants are separate from Hazardous Air Pollutants (HAPs), which are regulated under a different Clean Air Act framework.

How Are the NAAQS Reviewed?

EPA periodically reviews the NAAQS to determine whether existing standards should be retained or revised based on current scientific evidence.

For facility operators, the important point is not the review process itself. The key takeaway is that when a NAAQS changes, it can affect how areas are classified and how states plan for compliance. Those changes may eventually affect permitting, control requirements, or compliance planning for certain facilities.

This is one reason air quality requirements can change over time, even for facilities that have operated under the same permit framework for years.

Attainment, Nonattainment, and Maintenance Areas

NAAQS are closely tied to area designations.

An attainment area is an area that meets a particular NAAQS.

A nonattainment area is an area that does not meet a particular NAAQS based on air quality data and EPA designation. Nonattainment status can lead to more stringent permitting requirements, additional planning obligations, and new or revised requirements for affected sources.

A maintenance area is an area that was previously designated nonattainment but has since demonstrated compliance with the standard. These areas remain subject to continued planning to help ensure the area does not fall back into nonattainment.

This connects directly to State Implementation Plans. SIPs explain how a state will attain, maintain, and enforce the NAAQS. When a standard changes or an area designation changes, the SIP process may also change.

EPA’s Green Book is a commonly used resource for checking area designations and nonattainment status. Facilities located near county or area boundaries may need to pay close attention to designation changes because requirements can vary depending on location.

Why Do NAAQS Matter to Facility Operators?

Facilities do not usually “comply with NAAQS” directly in the same way they comply with a permit limit, testing requirement, or monitoring condition. However, NAAQS help drive many of the requirements that do apply to facilities.

For example, nonattainment status may affect:

  • New Source Review applicability
  • Permitting thresholds
  • Offset requirements
  • Control technology requirements
  • SIP-based emission limits
  • Monitoring, reporting, or operational expectations
  • Future permit revisions

Changes to NAAQS can also create a ripple effect. A revised standard may lead to new area designations. New designations may lead to SIP revisions. SIP revisions may lead to new or revised requirements for certain source categories. Over time, those changes can show up in permits, control strategies, monitoring obligations, and compliance deadlines.

This is especially important for companies operating in multiple states. NAAQS establish national air quality benchmarks, but states may adopt requirements that are more specific to local air quality needs.

Key Points

  • The NAAQS set ambient air quality benchmarks that support many federal and state air regulations
  • The six criteria pollutants covered by NAAQS are particulate matter, ozone, carbon monoxide, sulfur dioxide, nitrogen dioxide, and lead
  • NAAQS include primary standards for public health and secondary standards for public welfare
  • EPA periodically reviews the NAAQS and may revise them based on current scientific evidence
  • Changes to NAAQS can affect whether an area is classified as attainment, nonattainment, or maintenance
  • Facilities do not usually comply with NAAQS directly, but NAAQS changes can affect compliance obligations through permits, SIPs, and related requirements

Questions About Air Quality Requirements?

NAAQS help shape the regulatory framework behind air permitting, State Implementation Plans, and visible emissions compliance. For facilities managing air permits or Method 9 certification needs, understanding the larger Clean Air Act framework can make compliance planning more effective.

Compliance Assurance Associates, Inc. (CAA) provides smoke school training, Method 9 certification support, visible emissions resources, and compliance-focused services for Clients across regulated industries.

Visit CAA’s services page to learn more, or contact CAA by email or phone with questions about upcoming smoke school options, Method 9 certification, or visible emissions training needs.

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Compliance Assurance Associates, Inc. (CAA) supports regulated facilities and visible emissions observers working to meet Clean Air Act requirements. Through in-person smoke school, virtual reality (VR) smoke school options, and Method 9 certification support, CAA helps students and Clients build and maintain the visible emissions skills their compliance programs depend on.