How does this assessment of 1999 air toxics data compare to the 1996 national-scale assessment?
Due to the extent of improvements in our methodology (e.g., almost double the number of point sources in the emissions inventory, inclusion of over 100 additional air toxics, updated unit risk estimates), it is not meaningful to compare the two national-scale assessments. This is because any change in emissions, ambient concentrations, or risks may be due to either improvements in methodology or to real changes. We have made progress in reducing air toxics from stationary, mobile, and indoor sources. For example, by the end of 2004, EPA made significant progress finalizing National Emissions Standards for Hazardous Air Pollutants. These 96 rules, known as MACT standards, will reduce toxic emissions from over 160 categories of industrial sources. Many of these standards came into effect after 1999 and the air toxics reductions are not reflected in the results. When fully implemented, these rules collectively will reduce between one and two million tons of toxic air emissions compared to
