California Air Resources Board

Hundreds of scientific studies published over the past 50 years point to the harmful effects of air pollution. Adverse health effects related to air pollution exposure include hospitalizations, emergency department visits and premature death due to worsening of chronic heart and lung diseases, increased symptoms of respiratory irritation, increased asthma symptoms, and increased asthma medication usage, among others. Air pollution also can reduce agricultural crop yields, damage forests, ornamental and native plants, and create haze that reduces visibility. Ambient air quality standards are designed to prevent these effects.

What is an ambient air quality standard?

An air quality standard defines the maximum amount of a pollutant averaged over a specified period of time that can be present in outdoor air without harming public health, and thus, it defines clean air. The Clean Air Act Amendments of 1970 instruct the U.S. Environmental Protection Agency (U.S. EPA) to set primary National Ambient Air Quality Standards (NAAQS) to protect public health, and secondary NAAQS to protect plants, forests, crops and materials from damage due to exposure to six air pollutants. These pollutants include: particulate matter, ozone, nitrogen oxides, sulfur oxides, carbon monoxide, and lead. Download a PDF to learn more about current levels and averaging times for each NAAQS.

How are NAAQS selected?

NAAQS are selected by the U.S. EPA Administrator at the conclusion of a public process that takes about five years for completion. The process starts with a comprehensive review of the relevant scientific literature. The literature is summarized and conclusions are presented in a document called the Integrated Science Assessment (ISA). Based on the ISA, U.S. EPA staff perform a risk and exposure assessment, which is summarized in the Risk and Exposure Assessment (REA) document. The third document, the Policy Assessment (PA), integrates the findings and conclusions of the ISA and REA into a policy context, and provides lines of reasoning that could be used to support retention or revision of the existing NAAQS, as well as several alternative standards that could be supported by the review findings.

Each of these three documents is released for public comment and public peer review by the Clean Air Scientific Advisory Committee (CASAC), a sub-committee of U.S. EPA’s Science Advisory Board. Members of CASAC are appointed by the U.S. EPA Administrator for their expertise in one or more of the subject areas covered in the ISA. The committee’s role is to peer review the NAAQS documents, ensure that they reflect the thinking of the scientific community, and advise the Administrator on the technical and scientific aspects of standard setting. Each document goes through two to three drafts before CASAC deems it to be final. Once all three documents are final, they are given to the U.S. EPA Administrator to use in selecting a proposed NAAQS, which is released through the Federal Register for public comment. Following the close of the comment period, the Administrator considers the comments received, makes changes to the proposed NAAQS, if warranted, based on the comments received, and publishes the final NAAQS in the Federal Register.

When were the NAAQS last updated?

The Clean Air Act requires U.S. EPA to review, and revise if necessary, each of the NAAQS at five year intervals. This review schedule helps to ensure that NAAQS are based on the most recent scientific findings. The table below shows the year of completion for the most recent reviews for each NAAQS.

Visit U.S. EPA's Criteria Air Pollutant webpage for information regarding reviews that are currently under way.

What are the health and environmental effects of the NAAQS air pollutants?

Although there is some variability among the health effects of the six NAAQS pollutants, each has been linked to multiple adverse health effects including, among others, premature death, hospitalizations and emergency department visits for exacerbated chronic disease, and increased symptoms such as coughing and wheezing.

Below is the list of pollutants for which NAAQS were established. Follow the links for more information on the health and environmental effects specific to each pollutant.

• Particulate Matter (PM10 and PM2.5)
• Ozone (O₃)
• Nitrogen Oxides (NO_X)
• Sulfur Oxides (SO_X)
• Carbon Monoxide (CO)
• Lead

Attainment of Air Quality Standards

Federal law requires that all states attain the NAAQS. Nonattainment areas must develop plans to attain the NAAQS, and attainment areas must develop plans to maintain attainment. Failure of a state to reach attainment of the NAAQS by the target date can trigger penalties, including withholding of federal highway funds. For information, visit California’s State Implementation Plans and State Maintenance Plans.

California also has ambient air quality standards (CAAQS), which predate U. S. EPA’s formation in 1970 and the original NAAQS, which were adopted in 1971. In 1959 California enacted legislation requiring the state Department of Public Health to establish air quality standards and necessary controls for motor vehicle emissions. California law continues to mandate CAAQS, although attainment of the NAAQS has precedence over attainment of the CAAQS.

View state and federal designation maps showing which geographical areas of California do not meet the NAAQS and/or CAAQS.