National Air Toxics Assessment

NATA Overview

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What is NATA?

The National-Scale Air Toxics Assessment (NATA) is EPA's ongoing comprehensive evaluation of air toxics in the U.S. EPA developed the NATA as a state-of-the-science screening tool for State/Local/Tribal Agencies to prioritize pollutants, emission sources and locations of interest for further study in order to gain a better understanding of risks.  NATA assessments do not incorporate refined information about emission sources, but rather, use general information about sources to develop estimates of risks which are more likely to overestimate impacts than underestimate them. NATA provides estimates of the risk of cancer and other serious health effects from breathing (inhaling) air toxics in order to inform both national and more localized efforts to identify and prioritize air toxics, emission source types and locations which are of greatest potential concern in terms of contributing to population risk.  This in turn helps air pollution experts focus limited analytical resources on areas and or populations where the potential for health risks are highest.  Assessments include estimates of cancer and non-cancer health effects based on chronic exposure from outdoor sources, including assessments of non-cancer health effects for Diesel Particulate Matter (PM). Assessments provide a snapshot of the outdoor air quality and the risks to human health that would result if air toxic emissions levels remained unchanged. 

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Why NATA was developed

The NATA assessments were designed to help guide efforts to cut toxic air pollution and build upon the already significant emissions reductions achieved in the US since 1990.

NATA was developed as a tool to inform both national and more localized efforts to collect air toxics information, characterize emissions, and help prioritize pollutants/geographic areas of interest for more refined data collection and analyses. 

The goal is to identify those air toxics which are of greatest potential concern in terms of contribution to population risk. Ambient and exposure concentrations, and estimates of risk and hazard for air toxics in each State are typically generated at the census tract level.

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What NATA is not

NATA results provide answers to questions about emissions, ambient air concentrations, exposures and risks across broad geographic areas (such as counties, states and the Nation) at a moment in time. As such, they help the EPA identify specific air toxics compounds, and specific source sectors such as stationary sources or mobile sources, which generally produce the highest exposures and risks in the country. These assessments are based on assumptions and methods that limit the range of questions that can be answered reliably. The results cannot be used to identify exposures and risks for specific individuals, or even to identify exposures and risks in small geographic regions such as a specific census block, i.e., hotspots.

These assessments use emissions data for a single year as inputs to models which will yield concentration and risk estimates. These estimates reflect chronic exposures resulting from the inhalation of the air toxics emitted and do not consider exposures which may occur indoors or as a results of exposures other than inhalation, i.e., dermal or ingestion.

These limitations, or caveats, must always be kept in mind when interpreting the results, and the results should be used only to address questions for which the assessment methods are suited.

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How to access NATA

EPA has completed five assessments that characterize the nationwide chronic cancer risk estimates and noncancer hazards from inhaling air toxics. The latest, the 2011 NATA, was made available to the public in late 2015.

The previous NATA, released in 2011, is the 2005 National-Scale Air Toxics Assessment.

Previous versions of NATA are available in the EPA Archives.

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How to use NATA results

The results of assessments are best used to focus on geographic patterns and ranges of risks across the country. You can use NATA to do all of the following:

  • Prioritize pollutants and emission sources
  • Identify locations of interest for further investigation
  • Provide a starting point for local-scale assessments
  • Focus community efforts
  • Inform monitoring programs
  • To prioritize schools for monitoring outdoor air toxics

For example, assessments made at the community level, have relied on assessments to prioritize data and research needs to better assess the local risk from air toxics. Communities have found that accessing NATA data helps inform and empower citizens to make local decisions concerning the health of their communities. In some cases, local projects can achieve environmental improvements sooner than federal regulations alone.

EPA uses the results of assessments to do all of the following:

  • Set priorities for improving data in emission inventories
  • Direct priorities in expanding EPA's air toxics monitoring network
  • More effectively target risk reduction activities
  • Identify pollutants and industrial source categories of greatest concern
  • Help set priorities for the collection of additional information
  • Improve understanding of the risk from air toxics
  • Work with communities in designing their own assessment
  • Link Air Toxics to Criteria Pollutant Program

NATA assessments should not be used for any of the following:

  • As a sole means for identifying localized hotspots*
  • As a definitive means to pinpoint specific risk values within a census tract
  • To characterize or compare risks at local levels such as between neighborhoods
  • As the sole basis for developing risk reduction plans or regulations
  • To control specific sources or pollutants
  • To quantify benefits of reduced air toxic emissions

*For analysis of air toxics in these smaller areas, other tools such as monitoring and local-scale assessments should be used to evaluate potential hot spots using more refined and localized data.

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Comparing data across assessments

For each assessment, EPA has improved its methodology by doing all of the following:

  • Use a better and more complete inventory of emission sources
  • Increase the number of air toxics evaluated
  • Improve upon health data information used in assessments

Due to the extent of improvements in methodology, it is not meaningful to compare the assessments. This is because any change in emissions, ambient concentrations, or risks maybe due to either improvement in methodology or to real changes in emissions or source characterization.

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How NATA assessments are developed

NATA assessments generally include a four step process including:

  1. Compile a national emissions inventory from outdoor sources.
  2. Estimate ambient concentrations of air toxics across the United States.
  3. Estimate population exposures across the United States.
  4. Characterize potential public health risks due to inhalation of air toxics.

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NATA is a collaborative process

EPA collaborated with State, local and Tribal agencies to develop the information that is contained in the assessment. Communities have been actively involved in partnerships with local governments to use NATA data to develop local toxics inventories and to provide the basis for developing a community-supported plan for reducing toxic emissions. The National Research Council (NRC) in their review of the 1996 NATA, emphasized in their 2004 report on "Air Quality Management in the United States" Exitthat, "NATA has provided a tool for exploring control priorities and has served as a preliminary attempt to establish a baseline for tracking progress in reducing HAP emissions." (See p.247 of that report).

Aside from interactions with other environmental agencies, EPA has sought to collaborate with EPA’s Science Advisory Board which provided helpful comments through their peer review process. The methods used for these assessments were peer-reviewed and endorsed by EPA's Science Advisory Board in 2001. The SAB review concluded that NATA represents, "an important step toward characterizing the relationship between sources and risk of hazardous air pollutants."

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