Key Takeaways
- National Ambient Air Quality Standards (NAAQS) in the Clear Air Act establish nationwide limits on the concentrations of six common airborne pollutants, also known as criteria air pollutants.
- The NAAQS have contributed to improvements in air quality and public health, and have a periodic review process that integrates scientific research with policy decision-making.
- Policymakers must still determine a “safe” level for harmful pollutants; achieving compliance is also challenging, as it requires coordinated action across sectors.
Background
Air pollution remains one of the most significant environmental risks to public health. Exposure to polluted air has been linked to a variety of health conditions, including respiratory and cardiovascular disease, worsened mental health, impaired neural function, weakened immune system, and increased cancer risks. Children, older adults, and people with asthma or other respiratory conditions are particularly vulnerable. Although the majority of air pollution comes from the energy and transportation sectors, the effects are seen in the ambient air quality: the pollution in the air people breathe every day.
In response, federal air pollution policy in the United States has evolved:
Marked the first federal legislation to regulate air pollution and established research programs to develop air quality monitoring and pollution control technologies. | |
Authorized the Environmental Protection Agency (EPA) to establish and implement National Ambient Air Quality Standards (NAAQS) to protect public health and regulate hazardous emissions in the air. | |
Established provisions relating to prevention of air quality deterioration in areas that are meeting federal standards (areas of attainment), as well as created requirements for areas that did not meet federal standards (areas of nonattainment). | |
Increased the authority and responsibility of the federal government in enforcing the NAAQS and expanded the scope of the NAAQS to decrease acid rain and protect the ozone layer. |
How the NAAQS Work
To protect public health and welfare, NAAQS establish nationwide limits on the concentration of six common pollutants, known as criteria air pollutants, in outdoor air. The criteria air pollutants are carbon monoxide, lead, nitrogen dioxide, ozone, particulate matter, and sulfur dioxide. These pollutants are widely present in the atmosphere and have significant impacts on human health and ecosystems.
The Clean Air Act identifies two types of NAAQS:
- Primary standards, which provide public health protection, including protecting the health of “sensitive” populations such as asthmatics, children, and the elderly.
- Secondary standards, which provide public welfare protection, including protection against decreased visibility and damage to animals, crops, vegetation, and buildings.
Three Main Stages of NAAQS
The process of creating new standard has three main stages:
- Review—planning, assessing, and deciding the standards;
- Designations—determining whether areas meet the standards; and
- Implementation—attaining and maintaining the standards.
Review: Planning, Assessing, and Deciding the Standards
The Clean Air Act requires the review and revision of the standards based on the science behind them. However, some requirements may remain in place in some areas of the U.S. until they have implemented the established standards. This is typically related to ozone pollution. Over time, the NAAQS have become more stringent, especially for pollutants such as ozone and fine particulate matter.
Designations: Determining Whether Areas Meet the Standards
After the EPA sets new NAAQS or revises an existing standard, the EPA determines which areas of the country meet the new standards. Based on information from air quality monitors and models, geographic areas are classified into three categories:
- Attainment area, where the air quality meets or is cleaner than the national standard;
- Nonattainment area, where the air quality doesn’t meet the national standard; and
- Unclassifiable area, where the EPA cannot determine an area’s status based on available information.
Implementation: Attaining and Maintaining the Standards
Once an area receives a designation, governments are responsible for developing State Implementation Plans (SIPs) that describe how they will achieve and maintain compliance with the NAAQS. These plans are prepared by state and local air quality agencies and submitted to the EPA for approval.
SIPs must demonstrate that the state has the necessary air quality management programs in place and identify the specific measures used to meet the standards. In areas designated as nonattainment, states are required to adopt additional pollution reduction strategies to bring pollutant concentrations within the limit.
Strengths of the NAAQS
NAAQS act as a tool in driving long-term air quality improvements and protecting Americans from pollution-related health problems. By establishing limits on harmful airborne pollutants, the standards provide a clear goal for air quality control nationwide. The EPA estimates that between 1980 and 2021, total emissions of the six criteria air pollutants dropped by 71% while the economy grew by 182%. According to an analysis of the 1990 Clean Air Act amendments, reductions in fine particle pollution and ozone pollution were estimated to have the following positive effects by 2020:
- Avoided approximately 120,000 emergency room visits, 200,000 cases of heart disease (acute myocardial infarction), and 2.475 million cases of respiratory problems such as asthma exacerbation and chronic bronchitis.
- Prevented 17 million lost workdays due to health problems.
- Kept kids healthy and in school, preventing 5.4 million lost school days.
Another strength of the NAAQS lies in its review process, which integrates scientific research with policymaking. A historical review of the NAAQS program notes that its review cycle involves interaction of science and policy, which enables the EPA and others to develop scientific and analytical questions to be addressed in future reviews. This iterative process encourages the incorporation of environmental health research into air quality regulation. In this way, the standards can evolve alongside advances in scientific knowledge and reflect improved understanding of pollution risks and public health impacts.
Limitations and Challenges of the NAAQS
One limitation of the NAAQS is the accuracy of identifying a safe pollution level for certain pollutants. For pollutants such as fine particulate matter, evidence suggests that health risks may persist even at very low exposure levels. In other words, there may be no clear threshold where pollution no longer causes harm. There is ongoing debate on whether current standards can be sufficiently protective when translating complex evidence in cases where no safe threshold has been identified into a concentration limit.
Another key challenge of NAAQS is translating the standards into effective regulatory actions. The NAAQS regulate the six criteria air pollutants in the ambient environment rather than emissions from individual sources, so achieving compliance requires coordinated policy measures across multiple sectors. Implementation of the NAAQS, therefore, depends heavily on SIPs and less on direct federal action.
Conclusion
By establishing nationwide limits on the criteria air pollutants and requiring states to develop plans to meet the standards, NAAQS have been conducive to improving air quality. At the same time, the process of determining appropriate standards and implementing them across diverse sources of pollution remains a challenge. Air quality policy will continue to be shaped by uncertainty regarding pollution thresholds and the challenges of effective regulatory action, especially given the variation in SIPs across states. As scientific understanding of air pollution continues to evolve, policymakers and public health stakeholders will need to further address these challenges, keeping the NAAQS framework responsive to emerging evidence while still guiding air quality management efforts.
FAQ:
What is the Clean Air Act?
The Clean Air Act is the comprehensive federal law that regulates air pollution. It allows the Environmental Protection Agency (EPA) to establish standards of air pollution to protect public health and welfare.
What are the National Ambient Air Quality Standards (NAAQS)?
The NAAQS establish nationwide limits on the concentration of six principal pollutants in outdoor air. They are set by the EPA under the authority provided by the Clean Air Act.
Who is responsible for implementing the standards?
The EPA sets the national standards, but individual states are responsible for developing State Implementation Plans (SIPs) for achieving and maintaining compliance with the standards
What happens if an area fails to meet the standards?
Areas that exceed national standards are designated as “nonattainment areas.” They must then adopt additional pollution control strategies and regulatory measures to reduce emissions and bring air quality within national limits.