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The 1996 National-Scale Air Toxics Assessment (NATA)

In the late 1990s, the U.S. EPA undertook the National-scale Air Toxics Assessment (NATA). This assessment, based on the 1996 national emissions inventory (NEI), yielded results useful in understanding the amounts and possible health effects of 33 toxic air pollutants. (For more information regarding this list of federal hazardous air pollutants (HAPs), please click here.) The analysis consisted of four primary steps.

These include:

1. Emission Inventory Preparation

The emissions inventory is a compilation of the types and amounts of the 32 toxic pollutants plus diesel particulate matter emitted to the ambient air by a wide variety of sources. U.S. EPA categorizes the different air pollution sources for the hazardous air pollutants of concern into four primary source categories. USEPA divides the sources into four categories: Point (manufacturing facilities, utilities, etc.), Area and Other (small industrial facilities, dry cleaners, residential fuel combustion, consumer product use, backyard burning, etc.), On-road Mobile (cars, trucks, motorcycles, and buses), and Nonroad Mobile (construction equipment, agricultural vehicles, etc.).

2. Prediction of Ambient Air Concentrations

The U.S. EPA 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 a county average basis on the NATA website. The scale used on the county maps shows how concentrations in each county compare to the concentrations predicted for the rest of the country.

3. Population Exposure Estimates

The U.S. EPA 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.

4. Risk Characterization

    In this step, U.S. EPA considers the risk of both cancer and non-cancer health effects from inhalation of the 33 HAPs nationwide. Not only was EPA able to identify the air toxic compounds posing the most cancer risk nationwide in this analysis, but they also learned that one non-carcinogen, acrolein, posed the greatest relative hazard for health effects other than cancer in 1996.

    To learn more about the national and state level health risks associated with the presence of air toxics in the ambient atmosphere, click here.

Although the results are not refined enough to suggest specific risk-based regulatory action, the U.S. EPA 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.

  • Establish a baseline for tracking trends over time in modeled ambient concentrations of toxics.

  • Establish a baseline for measuring progress toward meeting goals for inhalation risk reduction from ambient air toxics.

The Air Toxics Program performed a review and summary of the Vermont-specific NATA information. To see what the 1996 NATA results mean for Vermont, please click here.

Return to Air Toxics Program Page


Last Updated: 1/22/03


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