Brian Barton
The Environmental Protection Agency (EPA) regulates criteria air pollutants through the Clean Air Act, which requires the EPA to set National Ambient Air Quality Standards (NAAQS) for six common air pollutants: particle pollution, ground-level ozone, carbon monoxide, sulfur dioxide, nitrogen dioxide, and lead. These pollutants are known as criteria air pollutants because the EPA develops human health-based and environmentally based criteria for setting permissible levels. The EPA tracks air concentrations through measurements at selected monitoring sites and emissions through engineering estimates of total tons released into the air annually. To improve air quality, the EPA works with state, tribal, and local air agencies to implement plans, such as state implementation plans (SIPs), to ensure that areas meet the NAAQS.
| Characteristics | Values |
|---|---|
| Number of criteria air pollutants | Six |
| Names of criteria air pollutants | Particle pollution, ground-level ozone, carbon monoxide, sulfur dioxide, nitrogen dioxide, and lead |
| Health and environmental impact | Harmful to human health, the environment, and can cause property damage |
| Most widespread health threats | Particle pollution and ground-level ozone |
| Primary standards | Protect public health, including sensitive populations such as asthmatics, children, and the elderly |
| Secondary standards | Protect public welfare, including against decreased visibility and damage to animals, crops, vegetation, and buildings |
| Regulatory efforts | Removal of lead from motor vehicle gasoline, resulting in a 98% decrease in lead levels in the air between 1980 and 2014 |
| Air pollution trends tracked | Air concentrations and emissions |
| Air concentrations | Actual measurements of pollutant concentrations in ambient (outside) air at selected monitoring sites |
| Emissions | Engineering estimates of total tons of pollutants released into the air annually |
| Clean Air Act requirements | Establish National Ambient Air Quality Standards (NAAQS), create a list of stationary source categories, set New Source Performance Standards (NSPS), and require pollution control equipment and emissions limitations for major stationary sources |
| State implementation plans (SIPs) | Developed by states designated as nonattainment to detail the path to attaining and maintaining NAAQS |
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What You'll Learn
The Clean Air Act
The Act also addresses emissions of hazardous air pollutants. Section 112 of the Clean Air Act was amended in 1990 to require the issuance of technology-based standards for "major sources" and certain "area sources". Major sources are defined as stationary sources that emit or have the potential to emit 10 tons or more of a hazardous air pollutant per year. The EPA establishes emission standards, known as "maximum achievable control technology" (MACT) standards, for these major sources to ensure the maximum degree of emissions reduction.
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National Ambient Air Quality Standards (NAAQS)
The Clean Air Act requires the Environmental Protection Agency (EPA) to set National Ambient Air Quality Standards (NAAQS) for six principal pollutants ("criteria pollutants") that are common in outdoor air and harmful to public health and the environment. These pollutants are particle pollution, ground-level ozone, carbon monoxide, sulfur dioxide, nitrogen dioxide, and lead. They are found all over the United States and can cause adverse health effects, including hospitalizations, emergency department visits, premature death due to worsening of chronic heart and lung diseases, increased symptoms of respiratory irritation, and increased asthma symptoms, among others.
The NAAQS are designed to protect public health and welfare. The two types of NAAQS standards are primary and secondary. Primary standards provide public health protection, including protecting the health of "sensitive" populations such as asthmatics, children, and the elderly. These limits are called primary standards and are based on human health. The secondary standards provide public welfare protection, including protection against decreased visibility and damage to animals, crops, vegetation, and buildings. These limits are called secondary standards and are intended to prevent environmental and property damage. The secondary standards also protect soils, water, wildlife, weather, climate, transportation hazards, economic values, and personal comfort and well-being.
The NAAQS are selected by the U.S. EPA Administrator at the conclusion of a public process that takes about five years. The process starts with a comprehensive review of the relevant scientific literature, which is summarized in the Integrated Science Assessment (ISA). Based on the ISA, the EPA performs 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 the retention or revision of existing NAAQS. Each of these three documents is released for public comment and peer review by the Clean Air Scientific Advisory Committee (CASAC), a subcommittee of U.S. EPA staff with expertise in one or more of the subject areas covered in the ISA.
The CASAC's role is to peer review the NAAQS documents, ensure they reflect the scientific community's thinking, 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 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, and publishes the final NAAQS in the Federal Register. Periodically, the standards are reviewed and sometimes revised, establishing new standards.
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Primary and secondary standards
The Clean Air Act requires the Environmental Protection Agency (EPA) to set National Ambient Air Quality Standards (NAAQS) for six commonly found air pollutants known as "criteria air pollutants". These pollutants are found all over the United States and can harm human health, the environment, and cause property damage. The six criteria air pollutants include particle pollution, ground-level ozone, carbon monoxide, sulfur dioxide, nitrogen dioxide, and lead.
The EPA sets both primary and secondary NAAQS for criteria pollutants. Primary standards are limits based on human health and provide public health protection, including protecting the health of "sensitive" populations such as asthmatics, children, and the elderly. These standards are set to ensure that the levels of pollutants in the air are safe for humans to breathe. The primary standards are based on scientific research and data about the effects of these pollutants on human health.
Secondary standards, on the other hand, are limits intended to prevent environmental and property damage. They provide public welfare protection, including protection against decreased visibility and damage to animals, crops, vegetation, and buildings. These standards are designed to protect the environment and natural resources from the harmful effects of air pollution. For example, elevated concentrations of sulfur dioxide (SO2) in the atmosphere can react with other compounds to form small particles that contribute to particulate matter pollution, reduce visibility, and cause regional haze.
To achieve these standards, the EPA works together with state, tribal, and local air agencies. They track air concentrations based on actual measurements of pollutant concentrations in the ambient (outside) air at selected monitoring sites throughout the country. Additionally, they consider emissions based on engineering estimates of the total tons of pollutants released into the air each year. The EPA periodically reviews and revises the standards as needed, and state, local, and tribal agencies use this information to develop emission reduction strategies, plans, and programs to attain and maintain the NAAQS.
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State Implementation Plans (SIPs)
A State Implementation Plan (SIP) is a collection of regulations and documents used by states to reduce air pollution in areas that do not meet the National Ambient Air Quality Standards (NAAQS). The Clean Air Act requires the EPA to set the NAAQS for six principal pollutants that are harmful to public health and the environment. These pollutants include particle pollution, ground-level ozone, carbon monoxide, sulfur dioxide, nitrogen dioxide, and lead.
The SIPs are designed to help states meet the NAAQS and protect public health and the environment. Each state's SIP is unique and tailored to its specific needs and challenges. For example, the New York State (NYS) SIP includes regulations and documents related to nitrogen dioxide levels, ozone levels, and regional haze. The Texas SIP, on the other hand, focuses on comprehensive air quality improvement strategies.
The development and implementation of SIPs involve collaboration between the EPA, state environmental agencies, and the public. State environmental agencies, such as the New York State Department of Environmental Conservation (NYSDEC), play a crucial role in developing and submitting SIPs to the EPA for approval. The NYSDEC, for instance, solicits comments from the public on all proposed SIPs before submitting them to the EPA.
Once a SIP is approved by the EPA, the state is responsible for implementing and enforcing the regulations outlined in the plan. The EPA provides support and guidance to states to help them attain and maintain the NAAQS. The EPA's website provides a dashboard that allows users to search for information on nonattainment and maintenance areas for current and revoked NAAQS, including the attainment status of designated areas.
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Stationary sources of air pollution
The Clean Air Act specifically addresses six common air pollutants, also known as "criteria air pollutants," which are pervasive throughout the United States. These pollutants include particle pollution, ground-level ozone, carbon monoxide, sulfur dioxide, nitrogen dioxide, and lead. Each of these pollutants poses a threat to human health, the environment, and property. Particle pollution and ground-level ozone are identified as the most widespread health hazards among the six.
To effectively regulate these criteria air pollutants, the EPA employs a two-pronged approach. Firstly, the agency monitors air concentrations through direct measurements of pollutant levels in the ambient (outside) air at various locations across the country. This provides real-world data on the presence and distribution of these harmful substances. Secondly, the EPA relies on emissions estimates, which are engineering calculations that predict the total amount of pollutants released into the atmosphere annually. By combining these two methods, the EPA can track air pollution trends and make informed decisions about setting standards and implementing controls.
The standards set by the EPA for criteria air pollutants fall into two categories: primary standards and secondary standards. Primary standards are based on the potential impact on human health, aiming to protect the public from the adverse effects of air pollution. On the other hand, secondary standards focus on preventing environmental degradation and property damage caused by these pollutants. By establishing and enforcing these standards, the EPA works collaboratively with state, tribal, and local air agencies to ensure that the air quality across the country meets the National Ambient Air Quality Standards (NAAQS).
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Frequently asked questions
Criteria pollutants are six common air pollutants found all over the United States. These include particle pollution, ground-level ozone, carbon monoxide, sulfur dioxide, nitrogen dioxide, and lead.
The EPA regulates criteria pollutants by developing human health-based and environmentally-based criteria for setting permissible levels. The Clean Air Act requires the EPA to set National Ambient Air Quality Standards (NAAQS) for these six common air pollutants.
Primary standards aim to protect public health, including sensitive populations such as asthmatics, children, and the elderly. Secondary standards focus on public welfare protection, including visibility, damage to animals, crops, vegetation, and buildings.
The EPA monitors two types of air pollution trends: air concentrations through measurements at selected sites and emissions based on engineering estimates of total tons of pollutants released annually.
