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National Air Toxics Assessment

2014 NATA: Assessment Results

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About the 2014 Assessment

This page provides the emissions data, ambient concentrations and health-effect results for the 2014 National Air Toxics Assessment. You can also find links to supporting files and web pages with more information about these results.

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. Often, more localized studies are needed to better characterize local-level risk. These studies often include air monitoring and more detailed modeling. 

The following files will help you navigate the NATA results:

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2014 NATA Emissions

The 2014 NATA used the 2014 National Emissions Inventory (NEI) as a starting point. The NEI is EPA’s comprehensive estimate of air pollution emissions from sources across the country. NEI supports air quality modeling and other activities within EPA’s Air Toxics Program. We updated these data from comments provided by 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. 

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

NOTE: Emission inventories submitted by state, local and tribal agencies vary in the level of detail and completeness. For this reason, you should not compare NATA risk estimates between states or regions without considering these inventory differences.

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2014 Modeled Ambient Concentrations, Exposures and Risks

The following tables present the EPA's 2014 NATA ambient concentration, exposure concentration and risk estimates across all 50 U.S. states, Puerto Rico, the Virgin Islands, and the District of Columbia.

You can view these data in several ways. Microsoft Excel- and Access-format files below contain data at national, state, county and census tract levels for each cancer riskHelpcancer riskThe probability of contracting cancer over the course of a lifetime, assuming continuous exposure (assumed in NATA to be 70 years). or hazard quotientHelphazard quotientThe ratio of the potential exposure to the substance and the level at which no adverse effects are expected. A hazard quotient less than or equal to one indicates that adverse noncancer effects are not likely to occur, and thus can be considered to have negligible hazard. endpoint. We show total risks and hazards, then break out the contribution for each NATA source type (for example, stationary point sources, on-road gasoline vehicles, etc.). 

The 2014 NATA National Respiratory Risk by Tract Source spreadsheet presents noncancer hazard indexesHelphazard indexThe sum of hazard quotients for toxics that affect the same target organ or organ system. A hazard index (HI) of 1 or lower means air toxics are unlikely to cause adverse noncancer health effects over a lifetime of exposure. for 14 target organ systems, or “endpoints.” Past NATA results suggest that the respiratory endpoint (the effect of air toxics on the lungs and the rest of the respiratory system) usually drives noncancer health effects. But we provide results for all 14 endpoints in the results spreadsheet. Information on these endpoints, such as the critical concentration used for each, can be found in the Supplemental Data files for NATA.

In the 2014 NATA results, results for stationary sources are broken into two groups: “point” and “nonpoint” sources. This reflects the way we modeled each source.

Each point source’s exact latitude and longitude coordinate is in the NATA source inventory. We used these locations in modeling. Large industrial complexes often have many individual point sources. We also modeled some smaller sources, such as dry cleaners, as point sources.

For other smaller sources, we may not have an exact location in the NATA inventory. We modeled these as nonpoint sources. Emissions from homes, such as wood-burning stoves and fireplaces or solvent emissions, are examples of nonpoint sources.

We usually inventory nonpoint sources by county. But a more precise location gives better modeling results. So we divided each county into smaller, square “grid cells,” then assign nonpoint emissions to each cell using population or another method that realistically distributes the emissions across the county (these are called “surrogates;” see the NATA Technical Support Document for more details).

We used a similar approach to assign most mobile source emissions. An exception is for airports, included as a nonroad source type under mobile sources. We modeled airports using their actual locations.

Nationwide Results

National cancer risk summaries:

National noncancer hazard index summaries:

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 5MB to 79MB.

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 1MB to 115MB.

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Area-Specific Air Toxics Studies

The following studies were conducted by local air quality agencies:

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