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Overview of 1999 NATA

The USEPA has compiled a National-scale Air Toxics Assessment (NATA) for 1999 that examines exposure to over 100 hazardous air pollutants throughout the country. The assessment followed the four step process listed below. For more detailed information, go to the National Air Toxics Assessment (NATA)


The emission inventory describes the type and amount of emissions of HAPs from a wide variety of sources. USEPA divides the sources into four categories:  

  • Major (large manufacturing facilities, utilities, etc.)

  • Area/nonpoint (small industrial facilities, dry cleaners, residential fuel combustion, consumer product use, etc.)

  • On-road mobile (cars, trucks and buses) and

  • Nonroad mobile (construction equipment, agricultural vehicles, etc.).

To see summaries of the NJ emissions information used by NATA click here.


The USEPA used a sophisticated dispersion model, known as ASPEN, to predict how the pollutants from the sources in the emission inventory would move through the air and be distributed throughout the country. The results are shown on the NATA website.


USEPA also took the extra step of trying to adjust the predicted air concentrations to account for activity patterns that move people around during the day, thus making their exposure a composite of multiple concentrations experienced in various places.


In this step, USEPA considers the risk of both cancer and non-cancer effects from inhalation of these hazardous air pollutants nationwide. In this analysis they were able to identify the pollutants posing the most cancer risk nationwide. They also identified one non-carcinogen (acrolein) as posing the greatest relative hazard for health effects other than cancer.

Although the results are not refined enough to suggest specific risk-based regulatory action, the USEPA expects that the assessment results can help to:

  • Identify air toxics of greatest potential concern.
  • Characterize the relative contributions to air toxics concentrations and population exposures of different types of air toxics emissions sources (e.g. major, mobile).
  • Set priorities for the collection of additional air toxics data and research to improve estimates of air toxics concentrations and their potential public health impacts. Important additional data collection activities will include upgraded emission inventory information, ambient toxics monitoring, and information on adverse effects to health and the environment.
  • Track trends over time in modeled ambient concentrations of toxics.
  • Measure progress toward meeting goals for risk reduction from inhalation of ambient air toxics.

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