Greta Jimenez
Hazardous air pollutants (HAPs), also known as toxic air pollutants or air toxics, are air pollutants that are known or suspected to cause cancer or other serious health and environmental issues. HAPs can be released into the environment from natural sources, such as volcanic eruptions and forest fires, but most are a result of human-made sources. The Clean Air Act requires the EPA to regulate emissions of HAPs, with federal, state, and local governments working to reduce the release of 188 toxic air pollutants into the environment.
| Characteristics | Values |
|---|---|
| Number of HAPs | 188 |
| Known to cause | Cancer and other serious health effects, such as reproductive issues or birth defects |
| Also known as | Toxic air pollutants, air toxics |
| Examples | Asbestos, benzene, dioxin, methylene chloride, perchloroethylene, toluene, cadmium, chromium, lead compounds, mercury, 1-bromopropane, 2-methylnaphthalene |
| Regulated by | EPA, federal, state, and local governments |
| Emitted by | Natural sources, such as volcanic eruptions and forest fires, and human-made sources |
| HAPs solutions | Abatement systems, Catalytic Oxidizer |
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What You'll Learn
Natural and human-made sources
Hazardous air pollutants (HAPs) are those pollutants that are known or suspected to cause cancer and other serious health issues in humans. They can be categorised into natural and human-made sources.
Natural Sources
Natural sources of HAPs include volcanic eruptions and forest fires. These natural disasters release toxic air pollutants into the atmosphere, which can have detrimental effects on human health and the environment. For example, volcanic eruptions can release toxic gases such as sulfur dioxide (SO2) and hydrogen sulfide (H2S), which can lead to respiratory problems and other health issues in nearby populations. Forest fires, on the other hand, can release large amounts of particulate matter, carbon monoxide (CO), and other toxic chemicals, which can have both short-term and long-term impacts on human health and the environment.
Human-Made Sources
HAPs have several human-made sources, which can be divided into mobile, stationary, and indoor sources. Mobile sources include cars, trucks, and buses, which emit pollutants through fuel combustion. Stationary sources include factories, refineries, power plants, and manufacturing plants, which can release pollutants through emissions from stacks and vents, process emissions, and equipment leaks. Indoor sources of HAPs include certain building materials and cleaning solvents, which can release toxic chemicals into the air inside homes, offices, and other buildings.
In addition to these direct sources, HAPs can also originate from indirect human activities, such as the use of alternative fuels and the disposal of toxic waste. For example, the combustion of gasoline can release hazardous pollutants such as benzene, toluene, and xylenes, while the dry cleaning industry may use perchloroethylene, which is another hazardous air pollutant.
Protecting Human Health and the Environment
Due to the serious health and environmental impacts of HAPs, various organisations, such as the Environmental Protection Agency (EPA) in the United States, have developed programs and regulations to control and reduce HAP emissions. These include setting emission standards, implementing the Clean Air Act and its amendments, and developing tools to monitor and assess the risks associated with HAPs, such as the National-Scale Air Toxics Assessment (NSA) and the Air Toxics Screening Assessment (AirToxScreen). By addressing both natural and human-made sources of HAPs, these efforts contribute to protecting human health and preserving ecological systems.
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HAPs and air permits
Hazardous air pollutants (HAPs), also known as toxic air pollutants or air toxics, are known or suspected to cause cancer and other serious health issues, including reproductive problems and birth defects. HAPs can be released into the environment from natural sources, such as volcanic eruptions and forest fires, but most are a result of human-made sources. The Clean Air Act requires the US Environmental Protection Agency (EPA) to regulate HAPs from industrial facilities in two phases.
The EPA works with state, local, and tribal governments to reduce air emissions of toxic air pollutants. Any facility emitting air pollutants above certain levels is required to obtain an air permit, which specifies the pollutant limits they must meet. The EPA uses HAP emissions and ambient monitoring data to develop regulatory programs that limit emissions from stationary sources.
There are two types of federal air regulations: the National Emission Standards for Hazardous Air Pollutants (NESHAPs) and New Source Performance Standards (NSPSs). NESHAPs cover both major and area sources. A major source is defined as any emission point that emits at least 10 tons of any particular HAP per year or more than 25 tons of any combination of HAPs per year. Area sources have the potential to emit less than 10 tons per year of a single HAP or 25 tons per year of any combination of HAPs. Many small businesses are area sources.
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HAPs and health effects
Hazardous air pollutants (HAPs), also referred to as toxic air pollutants or air toxics, are known or suspected to cause cancer or other serious health issues. HAPs are associated with elevated cancer levels and adverse health effects, including reproductive issues and birth defects. Examples of HAPs include asbestos, benzene, dioxin, methylene chloride, perchloroethylene, toluene, and metals like cadmium, chromium, lead compounds, and mercury. These pollutants can be released into the environment from natural sources such as volcanic eruptions and forest fires, but most are a result of human-made factors.
The Clean Air Act, amended in 1990, has made reducing emissions of urban air toxics a priority for the EPA. The EPA works with state, local, and tribal governments to reduce air emissions of these toxic pollutants. Any facility emitting air pollutants above certain levels must obtain an air permit specifying the pollutant limits they must adhere to.
The Missouri Air Pollution Control Program establishes Screening Model Action Levels (SMALs) as emission threshold levels. If a project's potential emissions surpass these levels, a site-specific ambient impact analysis is required. On January 5, 2022, the EPA added 1-bromopropane to the list of hazardous air pollutants under the Clean Air Act, responding to previous public petitions. The Missouri Department of Natural Resources then proposed new 24-hour and annual RALs to monitor air quality concerning 1-bromopropane in future air construction permits.
Risk Assessment Levels (RALs) refer to ambient concentrations of air toxics that are not expected to cause adverse cancerous and non-cancerous health effects during a defined exposure period. These levels are determined based on animal toxicity studies, human clinical studies, and human epidemiology studies. The department's Air Pollution Control Program can review a RAL for consistency with EPA guidelines, and revisions may take up to eight weeks to be approved.
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HAPs and environmental effects
Hazardous air pollutants (HAPs), also referred to as toxic air pollutants or air toxics, are known or suspected to cause cancer and other serious health issues. HAPs are associated with elevated cancer levels and adverse health effects, including reproductive issues and birth defects. Examples of HAPs include asbestos, benzene, dioxin, methylene chloride, perchloroethylene, toluene, and metals like cadmium, chromium, lead compounds, and mercury. These pollutants can be released into the environment through natural sources, such as volcanic eruptions and forest fires, but most often they originate from human-made sources.
The Clean Air Act, amended in 1990, has made reducing emissions of urban air toxics a priority for the US Environmental Protection Agency (EPA). The EPA works with state, local, and tribal governments to limit and reduce the emission of HAPs. Any facility emitting air pollutants above certain thresholds is required to obtain an air permit, which stipulates the pollutant limits they must meet. The EPA also uses ambient monitoring data and emissions data to develop regulatory programs that aim to restrict emissions from stationary sources.
One tool used to manage HAPs is Risk Assessment Levels (RALs). RALs are ambient concentrations of air toxics that are considered safe and are not expected to cause adverse health effects during a defined exposure period. These levels are established based on animal and human clinical and epidemiological studies, taking into account vulnerable populations such as the elderly, pregnant women, children, and individuals with respiratory conditions. If a project's potential emissions exceed the RAL, further measures must be implemented to reduce the ambient impact, such as permit restrictions or installing controls, until the toxic concentrations fall below the RALs.
Additionally, the EPA has amended the list of hazardous air pollutants under the Clean Air Act to include 1-bromopropane, addressing concerns raised by the public. This amendment prompted the Missouri Department of Natural Resources to propose new 24-hour and annual RALs for air quality analyses specific to 1-bromopropane in future air construction permits. The department also develops Screening Model Action Levels (SMALs), which are emission threshold levels used to determine if a site-specific ambient impact analysis is necessary.
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HAPs and emission control
Hazardous air pollutants (HAPs), also known as toxic air pollutants or air toxics, are known or suspected to cause cancer and other adverse health effects. HAPs can be released into the environment from both natural sources, such as volcanic eruptions and forest fires, and human-made sources. The Clean Air Act (CAA) requires the US Environmental Protection Agency (EPA) to regulate HAPs from categories of industrial facilities in two phases. The EPA works with state, local, and tribal governments to reduce air emissions of 188 toxic air pollutants.
To comply with the CAA, facilities must meet the control standards for HAPs in their processes. The specific system a facility needs depends on the particular pollutant that requires treatment. For example, a catalytic oxidizer was used to cut ethylene oxide (EtO) emissions from a medical sterilization facility, while an enclosed flare successfully abated waste acid gas exhaust from a midstream processor during plant shutdowns.
The EPA develops national enforcement initiatives that focus on significant environmental risks and noncompliance patterns. For Fiscal Years 2014 to 2016, the Cutting Hazardous Air Pollutants National Initiatives Strategy focused on categories of sources that emit HAPs. The EPA conducts inspections of regulated facilities to determine compliance, including inspections of processes with emissions points and against design and work practice standards. Sources subject to National Emission Standards for Hazardous Air Pollutants (NESHAPs) must perform an initial performance test to demonstrate compliance and may be required to install and operate continuous emission monitors.
The Missouri Department of Natural Resources sets Screening Model Action Levels (SMALs) as emission threshold levels to determine if a site-specific ambient impact analysis is required. The department's Air Pollution Control Program can review a Risk Assessment Level (RAL) for an individual HAP to ensure consistency with EPA guidelines. On January 5, 2022, the EPA amended the list of hazardous air pollutants under the CAA to add 1-bromopropane in response to public petitions. The Indiana Department of Environmental Management (IDEM) maintains a HAPs emissions inventory that includes a list of the sources of these pollutants in Indiana and the estimated amount of emissions from each source.
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Frequently asked questions
HAPs are air pollutants known or suspected to cause cancer and other serious health and environmental issues, such as reproductive effects or birth defects.
Examples of HAPs include asbestos, benzene, dioxin, methylene chloride, perchloroethylene, toluene, and metals such as cadmium, chromium, lead compounds, and mercury.
HAPs can be released from natural sources, such as volcanic eruptions and forest fires, but most are a result of human-made sources.
The Clean Air Act requires the EPA to regulate HAPs. All levels of government work to regulate 188 toxic air pollutants to reduce their emissions.
Emission threshold levels, known as Screening Model Action Levels (SMALs), are established by the Missouri Air Pollution Control Program. If potential emissions exceed these levels, a site-specific ambient impact analysis is required.
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