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National Air Toxics Assessment

NATA Overview

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What is NATA?

The National Air Toxics Assessment (NATA) is EPA's ongoing review of air toxicsHelpair toxicsPollutants known to cause or suspected of causing cancer or other serious health effects (also known as toxic air pollutants or hazardous air pollutants). in the United States. EPA developed NATA as a screening tool for state, local and tribal air agencies. NATA’s results help these agencies identify which pollutants, emission sources and places they may wish to study further to better understand any possible risks to public health from air toxics.

NATA gives a snapshot of outdoor air quality with respect to emissionsHelpemissionsPollutants released into the air. of air toxics. It suggests the long-term risks to human health if air toxics emissions are steady over time. NATA estimates the cancer risksHelpriskThe probability that adverse health effects will occur from exposure to a hazard. from breathing air toxics over many years. It also estimates noncancer health effects for some pollutants, including diesel particulate matterHelpparticulate matterParticles in the air, such as dust, dirt, soot, smoke, and liquid droplets; may have significant effects on human health. (PM). NATA calculates these air toxics concentrationsHelpconcentrationsA way to describe how much of a pollutant is in the air; usually shown as an amount, or mass, of pollutant per certain volume of air. In NATA, most concentrations are in micrograms (µg) of air pollutant per cubic meter (m3) of air (a “box” of air one meter on each side). and risks at the  census tractHelpcensus tractLand area defined by the U.S. Census Bureau. A tract usually contains from 1,200 to 8,000 people, with most having close to 4,000 people. Census tracts are usually smaller than 2 square miles in cities, but are much larger in rural areas. level. It only includes outdoor sources of pollutants.

Air quality specialists use NATA results to learn which air toxics and emission source types may raise health risks in certain places. They can then study these places in more detail, focusing where the risks to people may be highest.

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Why EPA developed NATA

EPA designed NATA to help reduce toxic air pollution and build on the large emissions cuts achieved in the United States since 1990. We also developed NATA to help air quality scientists collect air toxics emissions data and learn where health risks may be high.  These results help guide local air agencies as they study these emissions and places in more detail. 

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What NATA is not

To make NATA possible, we must make some assumptions about the air toxics emissions data that go into it. These assumptions mean that NATA can’t give precise exposures and risks for a specific person. Instead, NATA results are best applied to larger areas – counties, states and the nation. Results for smaller areas, such as a census tract, are best used to guide follow-up local studies.

NATA calculates concentration and risk estimates from a single year’s emissions data. The risk estimates assume a person breathes these emissions each year over a lifetime (or approximately 70 years). NATA only considers health effects from breathing these air toxics. It ignores indoor hazards, contacting or ingesting toxics, and any other ways people might be exposed.

Keep these limitations in mind when interpreting the results. Only use the results in ways for which the assessment methods are suited.

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How to access NATA

EPA has completed six assessments of nationwide long-term cancer risk estimates and noncancer hazards from breathing air toxics. The latest, the 2014 NATA, was released in 2018.

The previous NATA, released in 2015, is the 2011 National Air Toxics Assessment.

To view previous versions of NATA, you can search the EPA Archives for NATA in 2005, 2002, 1999 and 1996.

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How to use NATA results

NATA results are best used to focus on patterns and ranges of risks across the country.

You can use NATA to:

For example, communities use NATA to find out what data and research is needed to better assess their local risk from air toxics. Communities have found that using NATA helps inform and empower citizens to make local decisions about their community’s health. Local projects often improve air quality faster than federal regulations alone.

EPA uses the results of assessments to:

NATA assessments should not be used:

  • to pinpoint specific risk values in small areas such a census tract;
  • to characterize or compare risks at local levels (such as between neighborhoods);
  • to characterize or compare risks between states,
  • to examine trends from one NATA year to another,
  • as the sole basis for risk reduction plans or regulations;
  • to control specific sources or pollutants;
  • to quantify benefits of reduced air toxics emissions.

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Comparing NATAs

EPA has improved NATA assessments through:

  • better source and emission inventories;
  • modeling more air toxics; and
  • improved data on how air toxics affect your health.

Because of these changes, you should avoid comparing NATA assessments for different years. A change in emissions, pollutant concentrations, or risks may be due to NATA improvements, real changes in emissions or sources, or both.

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NATA's four steps

We use a four-step process to develop NATA assessments:

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

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Our NATA partners

NATA would not be possible without EPA’s partners at state, local, and tribal air agencies. These agencies helped us develop key parts of NATA, including the 2014 national emissions inventory upon which we based all NATA emissions data.

After we release NATA, communities actively partner with local governments. They use NATA data to develop local toxics inventories and to help develop community-supported plans 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 page 247 of that report.)

EPA’s Science Advisory Board (SAB) also gave us helpful comments. The SAB peer reviewed and endorsed NATA’s methods in 2001. The SAB review concluded that NATA provides "an important step toward characterizing the relationship between sources and risk of hazardous air pollutants."

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