In February 2006, EPA released the results of its national-scale assessment of 1999 air toxics emissions. The purpose of the national-scale assessment is to identify and prioritize air toxics, emission source types and locations which 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.
The national-scale assessment includes 177 air pollutants (a subset of the air toxics on the Clean Air Act's list of 187 air toxics plus diesel particulate matter (diesel PM)). The assessment includes four steps that focus on the year 1999:
- 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 noncancer effects.
For information summarizing the 1999 assessment, see the fact sheet
The data are from 1999 since emissions inventories from that year are the most complete and up-to-date available. Working with the states, EPA updates air toxics emissions inventories every 3 years. The next national-scale assessment will focus on the 2002 emissions inventory which was completed in December 2005.