The Clean Air Act (CAA) is the main federal law in the United States that helps control air pollution across the country. First passed in 1963 and changed many times over the years, it is one of the earliest and most important environmental laws in the United States.
Like many major U.S. environmental laws, the Clean Air Act is managed by the U.S. Environmental Protection Agency (EPA) with help from state, local, and tribal governments. The EPA creates detailed rules to follow the law’s requirements. These rules are carried out through programs that often involve complex processes. One key program sets limits for harmful air pollutants in outdoor air, and another sets limits for harmful emissions from specific sources. Other programs include rules about vehicle fuels, industrial facilities, and technologies that affect air quality. More recent programs address issues such as acid rain, protecting the ozone layer, and reducing climate change.
The Clean Air Act has been tested in court many times, with environmental groups wanting stricter rules and some states and companies wanting more flexibility. The exact benefits depend on how they are measured, but the Clean Air Act has greatly reduced air pollution and improved air quality in the United States. The EPA says these improvements have saved trillions of dollars and many thousands of lives each year.
Regulatory programs
The Clean Air Act in the United States is a law found in the United States Code (U.S.C.) at 42 U.S.C. chapter 85. This law was created by several acts passed by Congress. The 1963 act was the first to be called the Clean Air Act, and the 1970 act is most commonly referred to as the Clean Air Act today. In the U.S. Code, the law is divided into sections and subchapters, but the section numbers do not clearly match the subchapters. However, in the original bills that created the law, the major parts are called "Titles," and the sections are numbered by title (e.g., Title II starts with Section 201). In practice, the Environmental Protection Agency (EPA), courts, and lawyers often use the numbering based on titles.
Some parts of the law are very detailed, while others give only general guidelines. To follow these guidelines, the EPA created rules and regulations. These rules are published in the Federal Register, often with long explanations. The current Clean Air Act regulations are found in 40 C.F.R. Subchapter C, Parts 50–98. These parts usually match the major programs of the Clean Air Act.
Major programs under the Clean Air Act include:
National Ambient Air Quality Standards (NAAQS):
These standards set limits on how much of certain pollutants, such as ground-level ozone, carbon monoxide, particulate matter, lead, sulfur dioxide, and nitrogen dioxide, can be in outdoor air. Before 1965, there was no national program for setting air quality standards. Before 1970, the federal government did not have the main responsibility for creating these standards.
The 1970 Clean Air Act changes required the EPA to identify pollutants that harm public health and set NAAQS for them. Standards that protect health are called "primary" NAAQS, while standards that protect other aspects of public welfare, like agriculture, are called "secondary" NAAQS.
In 1971, the EPA set rules for sulfur oxides, particulate matter, carbon monoxide, and other pollutants. At first, lead was not included as a pollutant, but the EPA added it after a lawsuit in 1976.
The 1977 changes required the EPA to regularly review the NAAQS list and created a scientific group to help set these standards. The EPA added rules for PM2.5 in 1997 and updates the NAAQS based on new scientific information.
National Emissions Standards for Hazardous Air Pollutants (NESHAPs):
These standards control the amount of 187 harmful chemicals that can be released from industrial sources. These chemicals, called "air toxics," include substances that can cause cancer, birth defects, and other serious health problems. Examples include benzene, asbestos, formaldehyde, lead compounds, mercury, and dioxins.
The 1970 Clean Air Act required the EPA to list these pollutants and set standards for them. The 1990 changes added rules based on the best available technology to control emissions. Over time, the EPA created many NESHAPs for different industries and sources. These standards must be reviewed every eight years to ensure they protect public health.
New Source Performance Standards (NSPS):
These rules require new or modified industrial facilities to use the best pollution control technologies. The 1970 Clean Air Act required the EPA to set these standards based on the most effective ways to reduce emissions. The EPA created its first NSPS rules in 1971, covering power plants, incinerators, and other industrial sources. These rules apply only to new or modified facilities, which allows older facilities to continue operating.
The 1977 changes added a process called "new source review" to check if maintenance or other activities at a facility count as modifications that require following NSPS rules.
Acid Rain Program (ARP):
This program, created in 1990, is a system where power plants can buy and sell pollution permits. It aimed to reduce emissions of sulfur dioxide and nitrogen oxides, which cause acid rain. The program set a national limit on total emissions from power plants, which was reduced over time. Plants that reduced emissions below their limits could sell extra permits to other plants, encouraging cleaner technology. This program reduced sulfur dioxide emissions by 50% by 2000 and became a model for other pollution control systems.
Clean Air Act and states
In 1963, the law required states to create State Implementation Plans (SIPs) as part of a program where the federal government and states work together to control pollution. Instead of creating only a national program, the Clean Air Act (CAA) gave states the responsibility to make plans to meet the law’s requirements. The Environmental Protection Agency (EPA) then reviews, changes, and approves these plans. The EPA first created rules for SIPs in 1971 and 1972.
The 1970 Amendments added eight rules that an implementation plan must follow. The EPA must approve plans that meet the Senate’s three-year deadline for setting primary air quality standards, even if the agency believes the plan might not work. In the case Union Electric Co. v. Environmental Protection Agency, the Supreme Court decided that states can set emission rules stricter than national standards and can require the use of more advanced pollution control technologies.
The 1977 CAA Amendments added SIP requirements for areas that had not met the applicable National Ambient Air Quality Standards (NAAQS), called "nonattainment areas." In these areas, states had to create plans to improve air quality until all available pollution control measures were used. Because progress was slower than expected, major changes to SIP rules for nonattainment areas were added in the 1990 CAA Amendments.
The 1977 CAA Amendments also added "Prevention of Significant Deterioration" (PSD) rules to SIPs. These rules protect areas that already meet the NAAQS, such as wilderness areas and national parks, by ensuring good air quality is maintained. The new law also required "New Source Review" to check if new projects that could pollute would meet PSD rules.
The Clean Air Act gave the EPA the power to enforce the law and required states to create SIPs to meet new air quality standards by 1977. This system, where the federal government and states work together, continues today. The law says states should lead pollution control efforts because local conditions like geography, industry, and transportation affect air quality. However, states cannot have weaker pollution controls than the national minimum set by the EPA. If a SIP is not approved, the EPA can take over enforcement in that state. For example, California could not meet the 1970 standards, leading to a lawsuit and a federal SIP for the state. The federal government also helps states with research, studies, designs, and money for clean air programs.
The law prevents states from setting standards stricter than federal rules, except for California, which has special permission due to past smog problems. When California sets new vehicle emission standards, they must be approved by the EPA. The most recent approval was in 2009. Twelve other states followed California’s standards, which became the standard car companies used to avoid making different systems for each state. In September 2019, President Donald Trump tried to cancel California’s special permission, saying stricter rules made cars too expensive and unsafe. EPA leader Andrew Wheeler said the agency respects states but cannot let one state set rules for the whole country. California’s governor, Gavin Newsom, called the move a political attack and planned to sue the federal government. Twenty-three states, the District of Columbia, and cities like New York City and Los Angeles joined California in the lawsuit. In March 2022, the Biden administration canceled Trump’s rule, allowing California to keep its stricter auto emission standards.
History
Between the Second Industrial Revolution and the 1960s, the United States faced growing air pollution problems. After the 1948 Donora smog event, the public began to see air pollution as a serious issue. States started passing laws to reduce pollution, and Congress discussed whether to take more action. At the time, the main federal agencies focused on air pollution were the United States Bureau of Mines, which worked to reduce smoke from burning coal, and the United States Public Health Service, which studied how pollution affected lung health.
In 1955, Congress passed the first federal law to address air pollution. The Air Pollution Control Act of 1955 gave money to the U.S. Public Health Service for research and training but did not directly control pollution sources. This program was later extended in 1959, 1960, and 1962 while Congress considered more regulations.
Starting in 1963, Congress began creating stronger federal laws to reduce air pollution nationwide. These programs were first managed by the U.S. Secretary of Health, Education, and Welfare and the Air Pollution Office of the U.S. Public Health Service. Later, they were moved to the newly created Environmental Protection Agency (EPA) before major changes in 1970. The EPA has managed the Clean Air Act since then, and Congress added more rules in 1977 and 1990. Most recently, the U.S. Supreme Court’s decision in Massachusetts v. EPA allowed the EPA to regulate greenhouse gases under the Clean Air Act.
The Clean Air Act of 1963 (Pub. L. 88–206) was the first federal law that allowed the U.S. government to take direct action to control air pollution. It expanded the 1955 research program, encouraged cooperation between federal, state, and local governments to reduce pollution, and gave $95 million over three years to support state pollution control efforts. It also allowed the Secretary of Health, Education, and Welfare to organize conferences and take direct action against air pollution that crossed state lines when states did not act.
The Motor Vehicle Air Pollution Control Act (Pub. L. 89–272) updated the 1963 Clean Air Act and set the first federal standards for vehicle emissions, starting with the 1968 car models. These standards reduced emissions compared to 1963 levels: 72% less hydrocarbons, 56% less carbon monoxide, and 100% less hydrocarbons from car engines. The law also added rules to address air pollution that crossed international borders.
The Air Quality Act of 1967 (Pub. L. 90–148) gave money to state agencies to plan pollution control efforts, allowed the creation of groups to manage air pollution across states, and required the Secretary of Health, Education, and Welfare to define air quality regions and develop technical standards for states to follow. It also required states to create plans to improve air quality and allowed the government to take direct action during air pollution emergencies. This law also supported more studies on pollution sources, monitoring methods, and control techniques. For the first time, the federal government could investigate how pollution traveled between states and conduct large-scale air quality monitoring and inspections. By 1970, all 50 states had air pollution control programs, up from only six states in 1960, due to federal funding and laws from the 1960s.
In 1970, Congress made major changes to the Clean Air Act, requiring strong federal and state rules to control pollution from both factories and vehicles. The law created the National Ambient Air Quality Standards (NAAQS), New Source Performance Standards (NSPS), and National Emissions Standards for Hazardous Air Pollutants (NESHAPs). It also strengthened federal enforcement to meet pollution reduction goals.
To enforce these rules, EPA Administrator William Ruckelshaus focused much of his time on the automobile industry, which was required to reduce emissions by 90% under the new law. This was a change from earlier, weaker laws that had failed to cut emissions.
Major changes to the Clean Air Act happened in 1977 (1977 CAAA). These changes focused on protecting air quality in areas that met federal standards and managing pollution in areas that did not meet those standards. A non-attainment area is a place where air quality does not meet federal standards. These changes required permits to ensure air quality standards were met. They also included a policy called offset trading, which allowed new pollution sources to reduce their emissions by buying extra pollution cuts from existing sources.
In 1990 (1990 CAAA), the Clean Air Act was updated again. These changes gave the federal government more power to control pollution, including programs to reduce acid rain and manage permits for factories. The NESHAPs program was expanded to control more toxic air pollutants. Rules for meeting and maintaining air quality standards were changed and improved. Other updates included protections for the ozone layer, stronger enforcement, and more research.
The 1990 amendments added rules to control acid rain and factory permits. To reduce sulfur dioxide emissions, a cap-and-trade program was introduced, giving power companies more flexibility to meet goals. The law also expanded the NESHAP program to control 189 harmful air pollutants across many industries. New rules were added
Effects
A 2022 review study in the Journal of Economic Literature found strong evidence showing that the Clean Air Act (CAA) significantly improved air quality.
A 2011 study by the Environmental Protection Agency (EPA) compared the 1970 and 1977 regulatory programs to the updates made by the 1990 Clean Air Act Amendments. By 2020, these updates were estimated to cost the United States about $60 billion each year. However, they also provided benefits worth about $2 trillion annually, including health improvements and lives saved. A 2020 study for the Natural Resources Defense Council estimated that these benefits included avoiding 370,000 premature deaths, preventing 189,000 hospital admissions, and providing economic benefits of up to $3.8 trillion—32 times the cost of the regulations. Other studies have reached similar conclusions.
Mobile sources, such as cars, trains, and boat engines, have reduced emissions of pollutants like hydrocarbons, carbon monoxide, nitrogen oxides, and particles by 99% since the 1970s. Emissions of volatile organic chemicals, carbon monoxide, nitrogen oxides, and lead from individual cars have also dropped by more than 90%. This reduction has led to lower national emissions of these pollutants, even though total miles driven yearly has increased by more than 400%. Since the 1980s, ground-level ozone levels have decreased by 25%, mercury emissions have dropped by 80%, and atmospheric lead pollution has been reduced by 90% due to the switch from leaded gasoline to unleaded gasoline. A 2018 study found that the Clean Air Act helped reduce pollution emissions by 60% in the manufacturing industry between 1990 and 2008.
Legal challenges
Since the Environmental Protection Agency (EPA) was first created, the power given to it by Congress under the Clean Air Act has been challenged in many court cases. Some of the most important legal cases involving the Clean Air Act include the following:
Current challenges
Poor air quality remains a problem in the United States. Studies show that ethnic minority individuals are 1.5 times more likely to live in areas with high air pollution compared to ethnic majority individuals. At the same time, the United States is still dealing with the effects of the COVID-19 pandemic. Research has found that people who live in areas with air pollution are 8% more likely to have long-term health problems from the virus, which can sometimes lead to serious illness or death. This creates differences between minority and majority communities, even though the pollution these communities face often results from redlining. Redlining is a practice that forced minority communities to live in areas with more polluting industries and busy roadways.
The Sierra Club and the Environmental Protection Agency (EPA) have suggested ways to improve air quality. These include funding transportation that uses clean energy, setting lower limits on pollution, and making sure the Clean Air Act is followed more strictly. The Clean Air Act has worked well since it was created in 1970. However, the fossil fuel industry has tried to weaken its rules, leading to worse air pollution in many areas.
An example of an area where air quality remains poor is the San Joaquin Valley. This region has bad air quality because of harmful farming practices, heavy traffic on major roads, and the oil industry. The main pollutant in the area is fine particulate matter, known as PM 2.5. Exposure to PM 2.5 can cause health problems for pregnant women, including worse asthma, lower lung function, weaker immunity, and a higher chance of giving birth early. Other health issues linked to PM 2.5 include chronic bronchitis, reduced lung function in children, and more hospital visits for heart and lung problems. These issues can lead to early death, especially for people with existing health conditions. In 2004, pollution from PM 2.5 decreased because of fewer farming and burning activities. However, PM 2.5 is still common today, and pollution levels have risen again. Organizations like the California Air Resources Board (CARB) have called for stronger rules to reduce harmful emissions. Now, the EPA, CARB, and the San Joaquin Valley Air Pollution Control District are working together to enforce the Clean Air Act and support efforts to live more sustainably.
Future challenges
As of 2017, some U.S. cities still do not meet all national air quality standards. Many thousands of early deaths may still be caused by fine-particle pollution and ground-level ozone pollution.
Climate change makes it harder to manage common air pollutants in the U.S. because warmer and drier summers can cause air that doesn't move easily. Long-lasting droughts that can lead to wildfires may cause high levels of air particles in certain areas.
Air pollution that moves across borders (both into and out of the U.S.) is not directly controlled by the Clean Air Act. This requires agreements with other countries, especially Canada and Mexico.
Environmental justice remains a continuing challenge for the Clean Air Act. By reducing pollution, the Clean Air Act helps lower higher exposure to air pollution among minority and low-income communities. However, African American populations are often found in areas with the worst air quality. Large numbers of people in low-income and minority communities live in the most polluted areas across the United States. This situation makes health problems worse for these groups. High exposure to air pollution is linked to health issues such as asthma, cancer, early death, and infant deaths. These conditions affect minority and low-income communities more than others. Pollution reduction from the Clean Air Act is connected to fewer cases of these health problems and can support fairness for communities most affected by air pollution and poor health.