Epa-Regulated Air Pollutants: What Are They?

The US Environmental Protection Agency (EPA) is responsible for regulating air pollutants, as outlined in the Clean Air Act (CAA). The CAA requires the EPA to set National Ambient Air Quality Standards (NAAQS) for six common air pollutants, also known as criteria air pollutants. These criteria air pollutants include particle pollution and ground-level ozone, which are the most widespread health threats. The EPA also regulates toxic air pollutants, or hazardous air pollutants (HAPs), which are known or suspected to cause cancer and other serious health issues. The CAA requires major stationary sources of air pollution, such as power plants, to install pollution control equipment and meet specific emissions limitations. The EPA's Clean Air Markets Division (CAMD) runs programs to address environmental problems caused by air pollution, such as acid rain and ozone depletion.

The Clean Air Act

The 1977 amendments set more rigorous requirements for reducing emissions in areas that did not meet the NAAQS, and established the Prevention of Significant Deterioration (PSD) regulations for areas that did meet the standards. The PSD regulations are designed to prevent any significant deterioration in air quality above an established baseline level.

National Ambient Air Quality Standards

The United States Environmental Protection Agency (EPA) established the National Ambient Air Quality Standards (NAAQS) under the Clean Air Act (CAA). The NAAQS are limits on the atmospheric concentration of six principal pollutants, also known as "criteria pollutants", that are common in outdoor air and are considered harmful to public health and the environment. These six criteria air pollutants (CAP) are:

• Ozone (O3)
• Atmospheric particulate matter (PM2.5/PM10)
• Lead (Pb)
• Carbon monoxide (CO)
• Sulfur oxides (SOx)
• Nitrogen oxides (NOx)

The Clean Air Act identifies two types of NAAQS: primary and secondary standards. The primary standards are designed to protect the health of "sensitive" populations such as asthmatics, children, and the elderly, with an adequate margin of safety. The secondary standards are designed to protect the public welfare from adverse effects, including damage to crops, vegetation, buildings, and animals. The EPA established the NAAQS according to Sections 108 and 109 of the US Clean Air Act, which was last amended in 1990.

The NAAQS are reviewed and revised periodically to ensure they remain effective and relevant. The most recent review took place in 1996, during which the EPA considered implementing a new NAAQS for 5-minute peaks of SO2 affecting sensitive populations. However, the Agency decided to maintain the existing standards. In 2010, the EPA replaced the dual primary standards with a new 1-hour standard set at 75 ppb. The EPA "took final action" in 2012 to uphold the existing NAAQS.

The EPA's Clean Air Markets Division (CAMD) administers programs that aim to reduce air pollution from power plants and address issues such as acid rain, ozone depletion, and particle pollution. The Clean Air Act also requires the EPA to regulate emissions of toxic air pollutants from a list of industrial sources known as "source categories". These toxic air pollutants include mercury, polychlorinated biphenyls (PCBs), benzene, and volatile organic compounds (VOCs).

Stationary sources of air pollution

The Clean Air Act (CAA) requires the EPA to regulate emissions of toxic air pollutants from a list of industrial sources known as "source categories". These sources include factories, refineries, boilers, and power plants, which are classified as stationary sources of air pollution. These stationary sources emit a variety of air pollutants, and the EPA is tasked with developing and implementing standards and guidelines to control these emissions.

The CAA also mandates that major stationary sources must install pollution control equipment and adhere to specific emissions limitations. Additionally, under the 1990 CAA amendments, major stationary sources are required to obtain operating permits. The EPA's Clean Air Markets Division (CAMD) manages programs aimed at reducing air pollution from power plants to address issues such as acid rain, ozone depletion, particle pollution, and interstate transport of air pollution.

The EPA's website provides access to databases with detailed information on air pollution control measures. One such database is the RACT/BACT/LAER Clearinghouse (RBLC), which contains case-specific details on the "Best Available" air pollution technologies mandated to reduce emissions from stationary sources. Another database, the New Source Review Policy and Guidance Database, offers policy and guidance documents interpreting construction permit regulations under the CAA's Title VI, which focuses on protecting the stratospheric ozone layer.

The Clean Air Act requires the EPA to establish National Emissions Standards for Hazardous Air Pollutants (NESHAPs), which include toxic air pollutants such as mercury, polychlorinated biphenyls (PCBs), benzene, and volatile organic compounds (VOCs). These standards aim to reduce excess emissions and create cleaner air for communities. The EPA also regulates mobile sources of air pollution by setting vehicle fuel standards and mandating emission-control components for motor vehicles and nonroad engines.

Toxic air pollutants

The Clean Air Act (CAA) requires the US Environmental Protection Agency (EPA) to regulate emissions of toxic air pollutants from a published list of industrial sources known as "source categories". These toxic air pollutants, also called hazardous air pollutants (HAPs), are known or suspected to cause cancer, serious health issues (including reproductive effects or birth defects), or adverse environmental effects. The EPA is working with state, local, and tribal governments to reduce air emissions of HAPs.

The Clean Air Act identifies two types of National Ambient Air Quality Standards (NAAQS): primary standards and secondary standards. Primary standards aim to protect public health, including that of sensitive populations like asthmatics, children, and the elderly. Secondary standards aim to protect public welfare, including protection against decreased visibility and damage to animals, crops, vegetation, and buildings. The EPA is required to periodically review and revise these standards as necessary.

The EPA's list of HAPs includes benzene, found in gasoline; perchloroethylene, emitted by some dry cleaning facilities; and methylene chloride, used as a solvent and paint stripper in several industries. Other HAPs include dioxins, asbestos, toluene, and metals such as cadmium, mercury, chromium, and lead compounds.

The Clean Air Act also requires major stationary sources of air pollution, like power plants, to install pollution control equipment and meet specific emissions limitations. This act further mandates controls on mobile sources of air pollution, regulating both the composition of fuels and emission-control components in motor vehicles and non-road engines.

Hazardous air pollutants

The Clean Air Act (CAA) requires the United States Environmental Protection Agency (EPA) to regulate hazardous air pollutants from specific categories of industrial facilities. The EPA's efforts to reduce these pollutants have been a priority since the passage of the Clean Air Act Amendments in 1990. The CAA also mandates controls on air pollution from mobile sources, such as motor vehicles and non-road engines, by regulating both fuel composition and emission-control components.

The EPA has classified 188 pollutants as hazardous. Some examples of hazardous air pollutants include gases such as hydrogen chloride, benzene, and toluene, as well as compounds and metals like asbestos, cadmium, mercury, and chromium. These pollutants can contaminate not only the air we breathe but also settle into waterways, rivers, and lakes, leading to potential ingestion through drinking water or consumption of fish from these waters.

Major sources of outdoor toxic air pollutants include emissions from coal-fired power plants, industries, refineries, and vehicles. Certain industries produce specific toxins, such as ethylene oxide leaks from medical equipment sterilization facilities. Additionally, chemical releases from accidents at industrial facilities or during the transport of hazardous materials can result in the release of air toxics.

Indoor air quality is also affected by hazardous air pollutants from sources like tobacco smoke, building materials (including asbestos), and consumer products such as cleaning supplies and air fresheners. The EPA uses hazardous air pollutant emissions and ambient monitoring data to develop regulatory programs aimed at limiting emissions from stationary sources. These programs are vital to protecting public health and the environment from the harmful effects of hazardous air pollutants.

Frequently asked questions