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National Air Toxics Assessment

NATA Limitations

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.

We suggest you use NATA results cautiously. The uncertainty – and thus the accuracy – of the results varies by place and by pollutant. Often, more localized studies are needed to better characterize local-level risk. These studies often include air monitoring and more detailed modeling. 

NATA has some limitations you should consider when looking at the results:

  • Data gaps
  • Pollutant concentrations used in risk calculations based on computer model simulations, not direct measurements
  • Default assumptions (used routinely in any risk assessment)
  • Assessment design limitations (intended to address some questions but not others)
  • Regional differences in emissions data completeness

Also keep in mind that NATA’s results:

  • apply best to larger areas, not specific places;
  • apply to groups, not to specific people;
  • include direct impacts from U.S. sources only;
  • apply only to the analysis year (when the source data were collected);
  • assume a person breathes the air toxics emitted in the analysis every day for 70 years;
  • only reflect exposures and risks from certain air toxics;
  • only include toxics released into the outdoor air;
  • estimate health impacts only from breathing air toxics;
  • reflect just some of the variation in background pollutant concentrations;
  • may give concentrations that are too high or too low for some air toxics and in some places;
  • make some assumptions when data are missing or in error;
  • may not accurately capture sources that emit only at certain times (e.g., prescribed burning or facilities with short-term deviations such as startups, shutdowns, malfunctions and upsets);
  • include risk estimates that are uncertain.