How does this assessment of 2002 air toxics data compare to previous national-scale assessments?
Due to the extent of improvements in our methodology, (e.g., inventory improvements, modeling changes, background calculation revisions, changes in health benchmarks), it is not meaningful to directly compare the 2002 assessment with previous assessments. Before changes can be attributable to specific reduction efforts, these assessment changes must be considered. For example the average national cancer risk in 2002 fell from 42 to 36 in a million when compared to the 1999 assessment. Some of this change can be attributable to changes in the methodology used to estimate background concentrations. However, an examination of each source category also shows a reduction in risks between 2002 and 1999. These reductions may be attributable to progress in reducing air toxics from stationary and mobile sources. For example, in 2007, EPA finalized the National Emissions Standards for Hazardous Air Pollutants. These 96 rules, known as MACT standards, reduce toxic emissions from 174 categories of
