National Air Toxics Assessments

What is NATA?

The National-Scale Air Toxics Assessment (NATA) is EPA's ongoing comprehensive evaluation of air toxics in the U.S.. EPA developed the NATA in 2002 as a state-of-the-science screening tool. NATA assessments estimate the risk of cancer and other serious health effects from breathing (inhaling) air toxics. Assessments include estimates of cancer and non-cancer health effects based on chronic exposure from outdoor sources, including assessments of non-cancer health effects for Diesel Particulate Matter (PM) . Assessments provide a snapshot of the outdoor air quality and the risks to human health that would result if air toxic emissions levels remained unchanged.

How do I access NATA assessments?

To date, EPA has completed two assessments that characterize the nationwide health risk estimates from inhaling air toxics. You can access NATA assessments from individual assessment pages:

Why was NATA developed?

The NATA assessments were designed to help guide efforts to cut toxic air pollution and build upon the already significant emissions reductions achieved in the US since 1990.

NATA was developed as a tool to inform both national and more localized efforts to collect air toxics information, characterize emissions and help prioritize pollutants/geographic areas of interest for more refined data collection.

The goal is to identify those air toxics which are of greatest potential concern in terms of contribution to population risk. Risk assessment results are estimated at the census tract level.

How should I use NATA results?

The results of assessments are best used to focus on geographic patterns and ranges of risks across the country. You can use NATA to do all of the following:

prioritize pollutants and emission sources
identify locations of interest for further investigation
provide a starting point for local-scale assessments
focus community efforts
inform monitoring programs

For example, assessments made at the community level, have relied on assessments to prioritize data and research needs to better assess the local risk from air toxics. Communities have found that accessing NATA data helps inform and empower citizens to make local decisions concerning the health of their communities. In some cases, local projects can achieve environmental improvements sooner than federal regulations alone.

EPA uses the results of assessments to do all of the following:

set priorities for improving emission inventories
direct priorities in expanding EPA's air toxics monitoring network
more effectively target risk reduction activities
identify pollutants and industrial source categories of greatest concern
help set priorities for the collection of additional information
improve understanding of the risk from air toxics
Link Air Toxics to Criteria Pollutant Program

What NATA is not.

Given its broad scope, NATA assessments are subject to a number of limitations and uncertainties. Generally, the limitations and uncertainties relate to assumptions that simplify our national air models. Assumptions are needed to cover gaps in the large database used as model input.

NATA assessments should not be used for any of the following:

as a sole means for identifying localized hotspots*
a definitive means to pinpoint specific risk values within a census tract
to characterize or compare risks at local levels such as between neighborhoods
as the sole basis for developing risk reduction plans or regulations
to control specific sources or pollutants
quantify benefits of reduced air toxic emissions

*For analysis of air toxics in these smaller areas, other tools such as monitoring and local-scale assessments should be used to evaluate potential hot spots using more refined and localized data.

Can I compare data across assessments?

For each assessment, EPA has improved its methodology by doing all of the following:

use more complete inventories
increase the number of air toxics evaluated
improve upon health data information used in assessments

Due to the extent of improvements in methodology, it is not meaningful to compare the assessments. This is because any change in emissions, ambient concentrations, or risks maybe due to either improvement in methodology or to real changes in emissions.

How are NATA assessments developed?

NATA assessments generally include a four step process including:

Compile national air toxics emissions inventory of outdoor stationary and mobile sources. The compiled information is called the National Emissions Inventory (NEI)
Estimate ambient concentrations of air toxics based on an air dispersion model.
Estimate population exposures based on a screening-level inhalation exposure model.
Characterize potential cancer and noncancer public health risks due to inhalation of air toxics.

Is NATA a collaborative process?

EPA collaborated with state, local and tribal agencies to develop the information that is contained in the assessment. Communities have been actively involved in partnerships with local governments to use NATA data to develop local toxics inventories and which provide the basis for developing a community-supported plan for reducing toxic emissions.

NATA 1996 has also been peer reviewed by National Academy of Sciences (NAS). The National Research Council (NRC) of the NAS in their 2004 report on "Air Quality Management in the United States" indicated that NATA 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. (p. 247)