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National Air Toxics Assessment

2014 National Air Toxics Assessment

In August 2018, EPA released the results of its 2014 National Air Toxics Assessment (NATA). NATA helps assess which air toxics and emission source types may pose health risks. NATA also helps EPA and other agencies determine which places may need further study to better understand risks.

EPA uses NATA results in many ways, including to:

  • help communities design their own local assessments;
  • improve emissions inventories; and
  • learn where we can expand and improve the air toxics monitoring network.

About the 2014 Assessment

The 2014 NATA assessment includes emissions, ambient concentrations, and exposure estimates for about 180 of the 187 Clean Air Act air toxics plus diesel particulate matter (diesel PM). For about 140 of these air toxics (those with health data based on long-term exposure), the assessment estimates cancer risks, from the potential for noncancer health effects, or both. This includes noncancer health effects for diesel PM. We did not include eight air toxics in this NATA assessment because either no emissions data were reported for them in 2014 or we couldn’t reliably make emissions or health-related estimates (radionuclides, for example).

NATA includes four steps:

  1. Compile a national inventory of air toxics emissions from outdoor sources from emissions year 2014.
  2. Estimate ambient concentrations of air toxics across the United States.
  3. Estimate population exposures.
  4. Characterize potential public health risks due to breathing air toxics (including both cancer and noncancer effects).

For information summarizing the 2014 assessment, see the 2014 NATA fact sheet.

EPA continues to improve NATA assessment methods, including the integration of the Community Multiscale Air Quality (CMAQ) and AERMOD models. This hybrid modeling system includes mass conservation, atmospheric chemistry, and long-range transport for 52 air toxics in the 2014 NATA. This is an increase from 41 in 2011 and just 4 in the 2005 NATA.

Other NATA improvements include:

  • a more realistic way to allocate mobile and nonpoint source emissions;
  • more detailed emissions inventories for oil and gas wells;
  • more complete weather data used in modeling;
  • health benchmarks updated with the latest science; and
  • an updated NATA map app, designed to be more intuitive and easier to use.

This assessment also includes a Technical Support Document (TSD). This document presents the approaches EPA used to conduct this NATA, including descriptions of how we:

  • compile emissions data and prepare them for use as model inputs;
  • estimate ambient concentrations of air toxics;
  • estimate exposures to air toxics for different source and pollutant groups;
  • characterize human health risks and hazards; and
  • address the assessment’s variability and uncertainty.