Air Toxics Screening Assessment
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2019 AirToxScreen: Assessment Results

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About the 2019 Assessment

This page provides the emissions data, ambient concentrations and health-effect results for the 2019 Air Toxics Screening Assessment, or AirToxScreen. You can also find links to supporting files and web pages with more information about these results.

EPA developed AirToxScreen as a screening tool for state, local and tribal air agencies. AirToxScreen’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 AirToxScreen results:

2019 AirToxScreen Emissions

The 2019 AirToxScreen used the 2017 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 for 2019 from comments provided by state, local and tribal agencies during the AirToxScreen review. The resulting emission files, accessed below, reflect the emissions used in AirToxScreen.

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 AirToxScreen risk estimates between states or regions without considering these inventory differences.

2019 Modeled Ambient Concentrations, Exposures and Risks

The following tables present the EPA's 2019 AirToxScreen 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 riskThe probability of contracting cancer over the course of a lifetime, assuming continuous exposure (assumed in NATA to be 70 years). or hazard 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 AirToxScreen source type (for example, stationary point sources, on-road gasoline vehicles, etc.). 

The 2019 AirToxScreen National Respiratory Risk by Tract Source spreadsheet presents noncancer hazard indexesThe 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 assessment 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 AirToxScreen.

In the 2019 AirToxScreen 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 AirToxScreen 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 AirToxScreen 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 AirToxScreen 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:

National concentration 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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Last updated on January 9, 2023