Bronte Wells
Air pollution is a pressing issue, with almost half of Americans breathing in unsafe levels of air pollutants, according to a report by the American Lung Association. The air pollutants of concern include carbon monoxide, ground-level ozone, lead, nitrogen oxides, particulate matter, and sulfur dioxide. To combat this, the Clean Air Act (CAA) was enacted in 1970 and is the United States' primary federal air quality law. The CAA is administered by the Environmental Protection Agency (EPA) and has been amended several times to reduce air pollution and protect public health and welfare. The EPA sets emission standards, reviews and approves state implementation plans, and provides technical input on the National Ambient Air Quality Standards (NAAQS). Despite the efforts of the EPA, air pollution remains a significant problem, and rolling back environmental regulations could worsen the situation.
| Characteristics | Values |
|---|---|
| Environmental agency | EPA (US Environmental Protection Agency) |
| Role of the agency | To maintain public health by reducing pollutant emissions and improving air quality |
| Air pollution sources | Household combustion devices, motor vehicles, industrial facilities, forest fires, residential energy for cooking and heating, power generation, agriculture/waste incineration |
| Pollutants | Particulate matter, carbon monoxide, ozone, nitrogen dioxide, sulfur dioxide, mercury, benzene, volatile organic compounds, etc. |
| Health risks | Respiratory and other diseases, reduced oxygen reaching the body's organs and tissues, neurological effects in children, behavioural problems, learning deficits, lowered IQ, high blood pressure, heart disease, cancer |
| Environmental risks | Damage to the natural characteristics of the atmosphere, higher levels of ultraviolet radiation, depletion of the ozone layer |
| Strategies | National Clean Diesel Campaign, Clean School Bus USA, SmartWay Transport Partnership, wood smoke reduction initiatives, collision repair campaign, Community Action for a Renewed Environment (CARE) |
| Regulations | Clean Air Act, National Ambient Air Quality Standards, National Emissions Standards for Hazardous Air Pollutants |
| Progress | Since the Clean Air Act was signed into law in 1970, emissions of the six most common air pollutants have fallen by 78%; however, recent analyses show air pollution has been on the rise since 2021 |
What You'll Learn
The Clean Air Act (CAA)
One of the key goals of the CAA was to set and achieve NAAQS in every state by 1975, addressing the risks posed by widespread air pollutants to public health and welfare. To achieve these standards, the Act directed states to develop state implementation plans (SIPs), which consist of emission reduction strategies, applicable to appropriate industrial sources within each state. The CAA requires all areas of the country to meet or strive to comply with the NAAQS, and the New Source Review (NSR) program is a key mechanism to achieve this, involving a preconstruction review process for new and modified stationary sources.
The CAA has been amended several times, notably in 1977 and 1990, to set new goals and deadlines for achieving NAAQS, as many areas had failed to meet the initial targets. The 1990 amendments also aimed to address issues such as acid rain, ground-level ozone, urban air pollution, toxic air emissions, and stratospheric ozone depletion. These amendments established a national operating permits program and strengthened enforcement to improve compliance with the Act.
Section 112 of the CAA specifically addresses emissions of hazardous air pollutants, requiring the EPA to establish "maximum achievable control technology" (MACT) standards for major sources, with regular reviews to determine and address any residual risks. The CAA also calls for collaboration between state, local, tribal, and federal governments to address air pollution problems, utilising the latest scientific and technological advancements.
The CAA has achieved significant reductions in air pollution, contributing to the protection of public health and the environment. It demonstrates that clean air and a healthy economy can coexist.
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National Ambient Air Quality Standards (NAAQS)
The National Ambient Air Quality Standards (NAAQS) are limits on the concentration of six principal "criteria" air pollutants (CAP) that cause smog, acid rain, and other health hazards. These six criteria air pollutants are:
- Ozone (O3)
- Atmospheric particulate matter (PM2.5/PM10)
- Lead (Pb)
- Carbon monoxide (CO)
- Sulfur oxides (SOx)
- Nitrogen oxides (NOx)
The Clean Air Act requires the United States Environmental Protection Agency (EPA) to set these standards for pollutants that are common in outdoor air, harmful to public health and the environment, and that come from numerous and diverse sources. The CAA was last amended in 1990.
The NAAQS are health-based and consist of two types of standards: primary and secondary. The primary standards are designed to protect the health of "'sensitive' populations such as asthmatics, children, and the elderly. The secondary standards are concerned with protecting the environment. They are designed to address visibility, damage to crops, vegetation, buildings, and animals. The EPA established the NAAQS according to Sections 108 and 109 of the U.S. Clean Air Act.
The units of measure for the standards are parts per million (ppm) by volume, parts per billion (ppb) by volume, and micrograms per cubic meter of air (µg/m3). For example, the level of the annual NO2 standard is 0.053 ppm. The previous SO2 standards were 0.14 ppm for 24 hours and 0.03 ppm annually. The primary standard for carbon monoxide was set at 9 ppm averaged over an 8-hour period and 35 ppm over a 1-hour period.
The Clean Air Act also requires major stationary sources to install pollution control equipment and meet specific emissions limitations. One of the key programs designed to achieve compliance with the NAAQS is the New Source Review (NSR) program, a preconstruction review process for new and modified stationary sources. The EPA also establishes emission standards that require the maximum degree of reduction in emissions of hazardous air pollutants, commonly referred to as "maximum achievable control technology" or "MACT" standards.
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Criteria Air Pollutants
The Clean Air Act (CAA) is the federal law that regulates air emissions from stationary and mobile sources in the US. The 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 criteria air pollutants are:
- Carbon Monoxide
- Ground-level Ozone
- Lead
- Nitrogen Oxides (NOx)
- Particulate Matter
- Sulfur Dioxide (SO2)
These pollutants are harmful to human health and the environment, and can also cause property damage. The EPA designates areas as "attainment" or "nonattainment" for each of the pollutants. If an area is designated as "nonattainment", states must develop a State Implementation Plan (SIP) that details the path to achieving and maintaining the NAAQS.
The EPA's Clean Air Markets Division (CAMD) runs programs to reduce air pollution from power plants and address environmental problems such as acid rain, ozone, and particle pollution. The EPA also sets emission standards, commonly referred to as "maximum achievable control technology" or "MACT" standards, that require the maximum degree of reduction in emissions of hazardous air pollutants.
Despite these regulations, almost half of Americans are breathing in dangerous levels of air pollutants, according to a report by the American Lung Association (ALA). The report found that over 156 million people live in areas with unhealthy levels of soot or smog, with people of color and Latino Americans being the most impacted.
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State Implementation Plans (SIPs)
A SIP is a collection of regulations, narrative, rules, technical documentation, and agreements that a state uses to implement, maintain, and enforce the National Ambient Air Quality Standards (NAAQS). These standards, established by the EPA, set the criteria for acceptable levels of six common and harmful air pollutants: carbon monoxide, ground-level ozone, lead, nitrogen oxides, particulate matter, and sulfur dioxide. The NAAQS are designed to protect public health and welfare from the detrimental effects of air pollution.
The development of SIPs involves a collaborative process between the states and the EPA. Each state is responsible for creating a plan that is tailored to its unique industrial sources and air pollution challenges. The EPA, in turn, reviews and approves SIPs to ensure they meet the requirements of the CAA. This review process includes opportunities for public comment, allowing stakeholders and community members to provide input and ensure transparency.
SIPs are dynamic and adaptable, recognising that air pollution levels and sources can change over time. For instance, if a state fails to submit a SIP or if a submitted SIP is disapproved by the EPA, the CAA requires the EPA to step in and promulgate a Federal Implementation Plan (FIP) to address the specific requirements. Additionally, SIPs in states with areas that do not meet the NAAQS, known as "'nonattainment' areas", must include additional measures to reduce air pollution in those regions.
The EPA has established various pollution control standards to support the implementation of SIPs, including Reasonably Available Control Technology (RACT), Best Available Control Technology (BACT), and Lowest Achievable Emissions Rate (LAER). These standards provide guidance on the technology and methods available to control and reduce specific air pollutants. By utilising these standards, states can effectively implement their SIPs and make meaningful progress towards achieving the NAAQS.
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Environmental rollbacks
The Trump administration has been criticized for its environmental rollbacks, with a focus on dismantling climate and environmental regulations, policies, and programs. The administration has taken steps to weaken the Environmental Protection Agency (EPA) by ordering layoffs and funding cuts, threatening the nation's ability to monitor and protect air quality.
The EPA, created in 1970, has worked to ensure Americans have clean air to breathe, providing air quality forecasts and enforcing the law on polluters. The Clean Air Act (CAA), a comprehensive federal law, regulates air emissions from stationary and mobile sources and authorizes the EPA to establish National Ambient Air Quality Standards (NAAQS) to protect public health and welfare and regulate hazardous air pollutant emissions. The CAA also requires major stationary sources to install pollution control equipment and meet specific emissions limitations.
Despite these measures, a report by the American Lung Association (ALA) revealed that nearly half of Americans (approximately 156 million people) lived in areas with unsafe levels of air pollutants between 2021 and 2023, a 16% increase from the previous year. This issue disproportionately affects people of color, with Latino Americans being three times more likely to breathe in toxic air pollutants. Soot and smog can cause severe health issues, including premature death, asthma attacks, heart attacks, strokes, preterm births, and impaired cognitive functioning.
The Environmental Integrity Project and experts in the field have expressed concern over the rollbacks, warning that they could exacerbate the pollution crisis and negatively impact vulnerable communities. Harold Wimmer, president and CEO of the ALA, stated that efforts to reduce staff, funding, and programs at the EPA leave families more vulnerable to harmful air pollution. Dr. Neil W. Schluger, a professor of Medicine, echoed these sentiments, emphasizing the well-established dangers of high-level pollution exposure.
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Frequently asked questions
The Clean Air Act is the United States' primary federal air quality law, which was initially enacted in 1963 and has been amended many times since. The CAA is the comprehensive federal law that regulates air emissions from stationary and mobile sources. The CAA is administered by the U.S. Environmental Protection Agency (EPA), in coordination with state, local, and tribal governments.
The CAA regulates key pollutants such as carbon monoxide, nitrogen oxides, particulate matter, volatile organic compounds, hydrocarbons, and carbon dioxide. The CAA also requires major stationary sources to install pollution control equipment and meet specific emissions limitations.
Since the Clean Air Act was enacted in 1970, air quality in the United States has generally improved, with levels of key pollutants dropping by nearly 80%. However, millions of Americans still breathe polluted air, and according to a 2025 report, almost half of Americans are breathing in unsafe levels of air pollutants.
The National Ambient Air Quality Standards are standards and implementation information for each of the six common air pollutants. The NAAQS set standards for concentrations of certain pollutants in outdoor air, and the CAA requires all areas of the country to meet or strive to comply with these standards.
