The 1996 National-Scale
Air Toxics Assessment (NATA)
In the late 1990s,
the U.S. EPA undertook the National-scale Air Toxics Assessment
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.
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
2. Prediction of Ambient
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
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.
to Air Toxics Program Page
Last Updated: 1/22/03