On this page:
- What is AirToxScreen?
- Why EPA developed AirToxScreen
- What AirToxScreen is not
- How to use AirToxScreen results
- Comparing Assessments
- AirToxScreen's four steps
- Our AirToxScreen partners
What is AirToxScreen?
The Air Toxics Screening Assessment (AirToxScreen) is EPA's ongoing review of air toxicsPollutants known to cause or suspected of causing cancer or other serious health effects (also known as toxic air pollutants or hazardous air pollutants). in the United States. 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.
AirToxScreen gives a snapshot of outdoor air quality with respect to emissionsPollutants released into the air. of air toxics. It suggests the long-term risks to human health if air toxics emissions are steady over time. AirToxScreen estimates the cancer risksThe probability that adverse health effects will occur from exposure to a hazard. from breathing air toxics over many years. It also estimates noncancer health effects for some pollutants, including diesel particulate matterParticles in the air, such as dust, dirt, soot, smoke, and liquid droplets; may have significant effects on human health. (PM). AirToxScreen calculates these air toxics concentrationsA way to describe how much of a pollutant is in the air; usually shown as an amount, or mass, of pollutant per certain volume of air. In AirToxScreen, most concentrations are in micrograms (µg) of air pollutant per cubic meter (m3) of air (a “box” of air one meter on each side). and risks at the census tractLand area defined by the U.S. Census Bureau. A tract usually contains from 1,200 to 8,000 people, with most having close to 4,000 people. Census tracts are usually smaller than 2 square miles in cities, but are much larger in rural areas. level. It only includes outdoor sources of pollutants.
Air quality specialists use AirToxScreen results to learn which air toxics and emission source types may raise health risks in certain places. They can then study these places in more detail, focusing where the risks to people may be highest.
Why EPA developed AirToxScreen
EPA designed AirToxScreen to help reduce toxic air pollution and build on the large emissions cuts achieved in the United States since 1990. We also developed AirToxScreen to help air quality scientists collect air toxics emissions data and learn where health risks may be high. These results help guide local air agencies as they study these emissions and places in more detail. AirToxScreen is the successor to the previous National Air Toxics Assessment, or NATA.
What AirToxScreen is not
To make AirToxScreen possible, we must make some assumptions about the air toxics emissions data that go into it. These assumptions mean that AirToxScreen can’t give precise exposures and risks for a specific person. Instead, AirToxScreen results are best applied to larger areas – counties, states and the nation. Results for smaller areas, such as a census tract, are best used to guide follow-up local studies.
AirToxScreen calculates concentration and risk estimates from a single year’s emissions data using meteorological data for that same year. The risk estimates assume a person breathes these emissions each year over a lifetime (or approximately 70 years). AirToxScreen only considers health effects from breathing these air toxics. It ignores indoor hazards, contacting or ingesting toxics, and any other ways people might be exposed.
Keep these limitations in mind when interpreting the results. Only use the results in ways for which the assessment methods are suited.
How to use AirToxScreen results
AirToxScreen results are best used to focus on patterns and ranges of risks across the country.
You can use AirToxScreen to:
- prioritize pollutants and emission source types;
- identify places of interest for further study;
- get a starting point for local assessments;
- focus community efforts;
- inform monitoringThe process of collecting outdoor air samples to determine how much of an air pollutant is present at a location. programs.
For example, communities use AirToxScreen to find out what data and research is needed to better assess their local risk from air toxics. Communities have found that using AirToxScreen helps inform and empower citizens to make local decisions about their community’s health. Local projects often improve air quality faster than federal regulations alone.
EPA uses the results of assessments to:
- improve data in emission inventoriesA listing, by source, of the location and amount of air pollutants released into the air during some period (in AirToxScreen, a single year).;
- learn where to expand our air toxics monitoring network;
- help target risk reduction activities;
- identify pollutants and source types of greatest concern;
- help decide what other data to collect;
- better understand risks from air toxics;
- work with communities to design their own assessment.
AirToxScreen assessments should not be used:
- to pinpoint specific risk values in small areas such a census tract;
- to characterize or compare risks at local levels (such as between neighborhoods);
- to characterize or compare risks between states,
- to examine trends from one assessment year to another,
- as the sole basis for risk reduction plans or regulations;
- to control specific sources or pollutants;
- to quantify benefits of reduced air toxics emissions.
Over the years, EPA has improved its air toxics screening assessments in several ways, including
- better source and emission inventories;
- updates to models used;
- modeling more air toxics;
- the latest science on how air toxics affect your health.
Because of these changes and other reasons, you should avoid comparing assessments for different years. A change in emissions, pollutant concentrations, or risks may be due to method improvements, real changes in emissions or sources, or both.
AirToxScreen's four steps
We use a four-step process to develop AirToxScreen assessments:
- Compile a national emissions inventory of outdoor air toxics sources.
- Estimate ambient concentrations of air toxics across the United States.
- Estimate population exposures across the United States.
- Determine potential public health risks from breathing air toxics.
Our AirToxScreen partners
AirToxScreen would not be possible without EPA’s partners at state, local, and tribal air agencies. These agencies helped us develop key parts of AirToxScreen, including the national emissions inventories upon which we base all assessments' emissions data.
After we release AirToxScreen, communities actively partner with local governments. They use AirToxScreen data to develop local toxics inventories and to help develop community-supported plans for reducing toxic emissions. The National Research Council (NRC) in their review of the 1996 NATA, emphasized in their 2004 report on "Air Quality Management in the United States" that the assessment "has provided a tool for exploring control priorities and has served as a preliminary attempt to establish a baseline for tracking progress in reducing HAP emissions." (See page 247 of that report.)
EPA’s Science Advisory Board (SAB) also gave us helpful comments. The SAB peer reviewed and endorsed EPA’s assessment methods in 2001. The SAB review concluded that the assessments provide "an important step toward characterizing the relationship between sources and risk of hazardous air pollutants."