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National Air Toxics Assessment

2011 NATA: Assessment Results

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About the 2011 Assessment

This page provides the inventory inputs, ambient and exposure concentrations, and results for the 2011 National-scale Air Toxics Assessments.  There are also links to supporting files and web pages. EPA suggests that the results of this assessment be used cautiously, as the overall quality and uncertainties of the assessment will vary from location to location as well as from pollutant to pollutant.  In many cases more localized assessments, including monitoring and modeling, may be needed to better characterize local-level risk.

The following files will assist in navigating the results of this assessment:

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2011 NATA Emissions

The National Emissions Inventory (NEI) is EPA’s comprehensive emissions inventory. It is used to support air quality modeling and other activities within the Air Toxics Program. The starting point for the 2011 NATA inventory was the 2011 NEI. These data were modified based on comments provided by regional, state, local, and tribal agencies during the NATA review.  The resulting emission files, accessed below, reflect the emissions used in NATA.

The county level emissions summary reflects all revisions made as a result of review comments. The stationary point source tables – Facility and Process Level Summaries – provide the detailed emissions data. Most of the changes made as a result of the review were made to the stationary point source information. 

NOTE: Emission inventories submitted by State, Local, and Tribal agencies may vary in the level of detail and completeness. For this reason, NATA risk estimates should not be compared across these agencies in different geographic regions without considering differences in their respective inventories.

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2011 Modeled Ambient Concentrations, Exposures and Risks

The following tables present the EPA's 2011 NATA ambient concentration, exposure concentration, and risk estimates across the United States plus Puerto Rico, the Virgin Islands, and the District of Columbia. The 2011 NEI, after review by State, Local, and Tribal agencies, was used as input to the AERMOD and CMAQ models to generate ambient concentrations.  The ambient concentrations were used as input to the inhalation exposure model (HAPEM7) to generate exposure concentrations. Exposure modeling is an important step in this assessment because it takes into account that people move from one location to another (e.g., from outside environments to inside environments).  Exposure concentrations were then used with health-benchmark information to estimate risks or hazards.  More information on the 2011 NATA methods can be found on the Assessment Methods page or in the Technical Support Document.

These data are presented in different ways. The Access and Excel files contain risks at nationwide, state, county, and census tract levels for each risk or hazard quotient endpoint. Additionally, the data are presented by 41 source sectors. 

While the file, 2011 NATA National Respiratory Risk by Tract Source spreadsheet, presents the non-cancer results specifically for the respiratory endpoint, the individual state and pollutant files provide the non-cancer information for other endpoints (e.g., neurological, reproductive system), when a dose-response value was available for that air toxic. Information on these additional endpoints, (e.g., the endpoint and critical concentration used for each), can be found in Appendix H of the 2011 NATA Technical Support Document

In the 2011 NATA results, results for stationary sources are broken into two groups:  “point” and “nonpoint” sources.  These designations reflect the way each emission source was modeled.  Point sources are those that have the location of their emissions identified with latitude and longitude coordinates. These can include larger sources such as large industrial complexes as well as some smaller sources, such as dry cleaners. Nonpoint sources are those where the specific location for the emission source is not known.  These are generally smaller sources or sources related to residential activity such as residential wood combustion or consumer and commercial solvent usage.  Emissions from these nonpoint sources, which are generally inventoried on a county-wide basis, are allocated to a census tract for modeling using appropriate surrogates.

This nonpoint source approach was used for mobile source emissions as well.

For the airports modeled in NATA, the locations of these emissions were actually known and thus, were modeled at their actual locations.  However, the risk results for airports are summarized under the mobile source category, in the nonroad source group.

Nationwide Results

Pollutant Specific Results

After you select a pollutant, press download to open or save the associated MS Access ZIP file. Please note that file sizes range from 28K to 42MB.

State Summary Files

After you select a state, press download to open or save the associated MS Access ZIP file. Please note that file sizes range from 622K to 160MB.

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Area-Specific Air Toxics Studies

The following studies were conducted by local air quality agencies:

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