In June 2009, EPA released the results of its 2002 national-scale
assessment of   HYPERLINK
"http://www.epa.gov/ttn/atw/nata2002/gloss1.html" \l "airtoxics"  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 modeled   HYPERLINK
"http://www.epa.gov/ttn/atw/nata2002/02pdfs/2002polls.pdf"  180 of the
187 Clean Air Act air toxics (PDF)  (3pp, 15k) plus   HYPERLINK
"http://www.epa.gov/ttn/atw/nata2002/gloss1.html" \l "diesel"  diesel
particulate matter  (diesel PM). The assessment includes four steps that
focus on the year 2002:

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 2002 assessment, see the   HYPERLINK
"http://www.epa.gov/ttn/atw/nata2002/factsheet.html"  Fact Sheet  and  
HYPERLINK "http://www.epa.gov/ttn/atw/nata2002/risksum.html"  Summary of
Results  pages. The Summary of Results page also provides national maps
of cancer and noncancer effects.

The emissions used in the current assessment are from the 2002 emission
inventory which is the most complete and up-to-date available. Working
with the states, EPA updates air toxics emission inventories every 3
years. The next national-scale assessment will focus on 2005 emissions
and will be available in late 2009 or early 2010.

As part of EPA's National Air Toxics Assessment activities, EPA
conducted its first   HYPERLINK "http://www.epa.gov/ttn/atw/nata" 
national-scale assessment for the year 1996 . That assessment included
33 air pollutants (a subset of 32 air toxics on the Clean Air Act's list
of 187 air toxics plus diesel particulate matter (diesel PM). In
February of 2006, EPA released the second of its   HYPERLINK
"http://www.epa.gov/ttn/atw/nata1999/"  NATA assessments . This
assessment was based on emissions from the 1999 National Emission
Inventory and included the assessment of 177 hazardous air toxics plus
diesel particulate matter. 

