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Use of Assessment Results

The results of EPA's national-scale assessments provide important information to help EPA and its partners at the State, local and Tribal level continue to develop and implement various aspects of the air toxics program. They have not been used directly to regulate sources of air toxics emissions. While regulatory priority setting is informed by EPA's national-scale assessments, risk-based regulations are based on more refined and source-specific data and assessment tools. More specifically, the 1999 assessment results will help:
  • identify air toxics and sources of greatest potential concern. This can be assessed at the national, State, local or community level. For example, since 2002 (year EPA released its 1996 national-scale assessment), community-level efforts to address air toxics have used the national-scale assessment as a starting point to identify potential air toxics and sources to investigate.

  • improve emissions inventories. The national-scale assessments have helped set priorities for the collection and refinement of air toxics data. For example, as a result of EPA's 1996 national-scale assessment, State and locals have provided more complete emissions inventory information on Chromium 6, which helps refine risk estimates for this pollutant.

  • direct efforts in expanding air toxics monitoring. For example, as a result of the 1996 national-scale assessment, EPA is in the process of developing a better monitoring method for acrolein, a top pollutant identified by both the 1996 and 1999 national-scale assessments for noncancer hazard (respiratory effects).

One of EPA's original goals for conducting national-scale assessments was to track trends and measure progress in the air toxics program. However, due to the extent of improvements in our methodology for the 1999 assessment (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 1999 assessment with the 1996 assessment. This is because any change in emissions, ambient concentrations, or risks may be due to either improvements in methodology or to real changes.

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