Air Toxics Ambient Monitoring

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Background

The goal of ambient air toxics monitoring is to support the reduction of public exposure to air toxics, also known as hazardous air pollutants (HAPs). Ambient toxics data play a critical role by characterizing HAPs concentrations to support three objectives.

  • Trends – Measurement of key HAPs in representative areas across the nation allows for a basic measure of differences across cities, regions, and specific areas of interest over time. Trends measurements provide an important means of accountability for the larger air toxics program.
  • Exposure Assessments – Understanding the relationship between ambient HAP concentrations, human activities, and the related personal exposures is critical for true exposure assessments. Ambient HAP measurements support exposure assessments by providing concentration data for comparison with personal measurements and sometimes can serve as a surrogate for actual human exposures. These ambient data are also used as inputs for detailed human exposure models that are used to estimate human exposure.
  • Air Quality Model Evaluation – Ambient HAP measurements provide basic ground truthing for air quality models that are used for exposure assessments, source-receptor characterization, the development of emission control strategies, and related assessments of air toxics program effectiveness.

National Air Toxic Trends Sites

The National Air Toxics Trends Station (NATTS) Network was developed to fulfill the need for long-term air toxics, also known as hazardous air pollutant (HAP), monitoring data of consistent quality. Among the principle objectives of the NATTS network are assessing trends and emission reduction program effectiveness, assessing and verifying air quality models (e.g., exposure assessments, emission control strategy development, etc.), and to provide data for direct input to source-receptor models. The network was initiated in 2003, and the current network configuration includes 25 sites (21 urban, 4 rural) across the United States. There are typically over 100 pollutants monitored at each NATTS, although only 19 of those are formally required. Target HAPs include volatile organic compounds (VOCs), carbonyls, PM10 metals, and polycyclic aromatic hydrocarbons (PAHs).

Map of NATTS Sites

Urban Air Toxics Monitoring Program

The Urban Air Toxics Monitoring Program (UATMP) is an air toxics monitoring program funded by the EPA that supports state, local, and tribal, monitoring agencies in conducting air toxic monitoring initiatives and studies.  The nature and scope of each UATMP study is varied and is determined by the monitoring agencies.   Data from the UATM is analyzed as part of the Air Toxics National Programs Annual Reports.

Community-Scale Air Toxics Ambient Monitoring

In 2003, the Office of Air Quality Planning and Standards, in conjunction with the Office of Transportation and Air Quality, the Office of Research and Development’s National Exposure Research Laboratory, and the 10 EPA Regional Offices, began conducting the Community-Scale Air Toxics Ambient Monitoring (CSATAM) grant competition. This competition is typically held every two or three years, depending on funding availability. The EPA awards these grants to support projects that assist state, local and tribal communities in identifying air toxics sources, characterizing the degree and extent of local air toxics problems, and tracking progress of air toxics reduction activities.

Projects conducted with these grants are intended to increase public awareness about air toxics, as well as promote the adoption of steps that will reduce emissions and exposure over time. Typical outputs or results of these projects may include but are not limited to: increasing the availability of air toxics data to the public; creating industrial source profiles in areas of elevated risk; conducting community-specific assessments of air toxics problems; evaluating new ambient air toxics sampling and analysis methods; and supporting risk or health assessments.;

More information on the CSATAM grant program including study reports and recent awards and can be found on the CASATAM web page.

Air Toxics Analysis Workshops

The EPA periodically holds Air Toxics Workshops to facilitate the communication of Air Toxics monitoring related issues and developments. The following links contain copies of the presentations from recent Air Toxics Workshops.

Sites and Data

The following links can be used to collect information on the number and locations of ambient air toxic monitoring sites and to download monitoring data.

Data Analysis And Reports

The EPA prepares a annual report summarizing and analyzing air toxic monitoring programs. Copies of the reports can be found on the following page.

Quality Assurance and Other Guidance Documents

This section contains links to EPA guidance documents intended to assist monitoring agencies as they implement the NATTS monitoring program.

Methods

Air toxics are measured using a variety of sampling and analysis methods.  The EPA maintains a collection of sampling and analysis methods for toxic organic compounds (EPA TO Methods) and inorganic toxic compounds (EPA IO Methods).  In addition to the EPA TO and IO Methods, the following documents provide information and guidance for the measurement of specific air toxics.

Acrolein

Ethylene Oxide

Hexavalent Chrome

HAP Metals  

HAP Organics

Ambient Monitoring Technology Information Center (AMTIC)

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Last updated on May 5, 2025