Environments and Contaminants - Hazardous Air Pollutants
The Clean Air Act identifies 187 substances as hazardous air pollutants, or “HAPs.” HAPs are emitted into outdoor air from a range of industrial facilities and vehicles.
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Indicator
E4: Children living where hazardous air pollutants were greater than health benchmarks
Web update: 2022
Key Information
- In 2014, nearly all children lived in census tracts in which HAP concentrations combined exceeded the 1-in-100,000 cancer risk benchmark. In addition, nearly all schools were located in census tracts where HAPs concentrations combined to exceed the 1-in-100,000 cancer risk benchmark.
- In 2014, 0.3% of children lived in census tracts in which HAPs combined exceeded the 1-in-10,000 cancer risk benchmark. The pollutants that contributed most to this result were formaldehyde, benzene, carbon tetrachloride, and acetaldehyde. Formaldehyde and benzene are carcinogenic to humans, and carbon tetrachloride and acetaldehyde are considered likely to be carcinogenic to humans.
- In 2014, 0.1% of children lived in census tracts in which at least one HAP exceeded the benchmark for health effects other than cancer. In almost all cases, this result was attributable to the pollutant acrolein, which is a respiratory irritant. More than 90% of acrolein emissions are from wood-burning fires and mobile sources such as cars, trucks, buses, planes, and construction equipment.
Data Characterization
Data for this indicator are obtained from EPA's National Air Toxics Assessment computer model predictions of hazardous air pollutant (HAP) concentrations in outdoor air.
The model produces estimates of HAP concentrations from emissions data for all census tracts in the United States. Census tracts typically have about 4000 residents each.
About the Hazardous Air Pollutants Indicator
The Clean Air Act identifies 187 substances as HAPs such as benzene, trichloroethylene, formaldehyde, mercury, and chromium. HAPs are emitted into ambient air from a range of industrial facilities and vehicles. EPA sets federal regulations to reduce HAP emissions from these sources.
Child-specific health effects associated with HAPs include cancer, asthma and other respiratory diseases, birth defects, reproductive effects, and neurodevelopmental disorders.
The health effects of certain HAPs, such as benzene, chromium, nickel, and vinyl chloride, have been identified through studies of adult workers exposed to high levels on the job. For some HAPs, observational studies have been conducted in populations with lower exposure levels typical of the general population. For most HAPs, concerns about health effects come from laboratory animal studies.
For historic and contextual information about hazardous air pollutants and this indicator, see the Hazardous Air Pollutants section of America's Children and the Environment, Third Edition (pdf) .
Data Sources and Methods – Hazardous Air Pollutants
EPA's National Air Toxics Assessment (NATA) provided estimated levels of 181 Hazardous Air Pollutants (HAPs) in outdoor air for the year 2014. Under NATA, EPA developed modeled estimates of concentrations of HAPs in outdoor air using estimated emissions data from major, area, on-road mobile, and non-road mobile sources. EPA has replaced NATA with the Air Toxics Screening Assessment, or AirToxScreen, starting in 2017.
Indicator E4 uses the NATA data to display percentages of children ages 0 to 17 years living in census tracts that have modeled concentrations of HAPs in ambient air greater than the health benchmarks for 2014. The NATA data are compared with health benchmarks set by EPA and other environmental agencies. Two benchmarks reflect potential cancer risks, at levels representing a 1-in-100,000 chance that a person will develop cancer and a 1-in-10,000 chance. The third benchmark corresponds to the level below which exposures may be associated with non-cancer health effects such as effects on brain or lung development.
- Detailed Methods for Indicator E4 (pdf)
- Metadata for National Air Toxics Assessment (NATA)
- Metadata for Census: American Community Survey Data (pdf)