2011 National Air Toxics Assessment
In 2015, EPA released the results of its 2011 national-scale assessment (NATA) of air toxic emissions. The purpose of NATA is to identify and prioritize air toxics, emission source types, and locations that are of greatest potential concern in terms of contributing to population risk. EPA uses the results of these assessments in many ways, including:
- To work with communities in designing their own local-scale assessments,
- To set priorities for improving data in emissions inventories, and
- To help direct priorities for expanding and improving the network of air toxics monitoring.
About the 2011 Assessment
The 2011 NATA assessment includes emissions, ambient concentrations, and exposure estimates for 180 of the 187 Clean Air Act air toxics plus diesel particulate matter. For 138 of these air toxics (those with health data based on chronic exposure), the assessment includes cancer or non-cancer health effects, or both, including non-cancer health effects for diesel PM. Eight air toxics were not included in this NATA assessment because either no emissions information was reported for them in 2011 or emission estimates useful for modeling could not be determined reliably from their reported emissions (e.g., radionuclides).
The assessment includes four steps that focus on the 2011 emissions year:
- Compiling a national emissions inventory of air toxics emissions from outdoor sources
- Estimating ambient concentrations of air toxics across the United States
- Estimating population exposures across the United States
- Characterizing potential public health risk due to inhalation of air toxics including both cancer and non-cancer effects
For information summarizing the 2011 assessment see:
NATA assessment methods continue to be improved. One important improvement in this 2011 assessment is the fuller integration of the Community Multiscale Air Quality (CMAQ) and AERMOD models, as a hybrid modeling system, to improve mass conservation, atmospheric transformation (formation and decay), and long-range transport. Forty HAP were modeled using CMAQ for the 2011 NATA, an increase from the four in the 2005 NATA. This improvement is coupled with other improvements, including: more detailed emissions inventories for oil and gas wells; more precise locations for airports; the use of MOVES and improved spatial allocation to estimate highway vehicle emissions; and enhanced mapping options using EPA’s GeoPlatform.
This assessment also includes a Technical Support Document (TSD). This document presents the approaches EPA used to conduct this NATA, including descriptions of how:
- emissions data are compiled and prepared for use as model inputs,
- ambient concentrations of air toxics are estimated,
- exposures to air toxics for populations are estimated,
- toxicity values are selected and assigned to chemicals,
- human health risks and hazards are characterized, and
- variability and uncertainty are addressed.