Issues in the 1999 Inventory/Changes in Assessment Results
After compiling the 1999 National Emissions Inventory (NEI) for hazardous air pollutants, and conducting several rounds of review through the State/local/Tribal agencies that provided EPA with much of the data, EPA finalized the 1999 NEI in August 2003. Subsequently, EPA conducted air quality modeling and risk analysis for the 1999 national-scale assessment. All of the corrections made during the reviews through August 2003 were incorporated into the 1999 national-scale assessment. Since August 2003, after the 1999 NEI was finalized, some States have submitted additional comments/corrections on the 1999 NEI. A full list of these additional suggested changes to the 1999 NEI for hazardous air pollutants is available as a 4 MB Microsoft Access file.
Ideally, EPA might redo the 1999 NEI and revise the national-scale assessment results to incorporate all of the suggested inventory changes, whether large or small; local or national; in all factors, including emissions rates, source locations, and source category classification. In practice, it is neither feasible nor useful to recreate the entire national-scale assessment to take into consideration these additional corrections in the emissions inventory. Consequently, EPA focused on the most practical and significant revisions as follows:
First, the Agency considered changes in emissions estimates but not any other inventory parameter (e.g., latitude/longitude of source). Changing parameters such as source locations would have required substantial new air quality and exposure modeling. Due to limited time and resources, the Agency did not rerun the models (ASPEN or HAPEM), but rather mathematically (using ratios) adjusted the exposure results to account for the identified error in the emissions inventory. The risk estimates were then recalculated for these adjusted exposure estimates. Any adjustments were applied evenly to the entire county (if the correction affected a single source or area no larger than an entire county) or State (if the correction applied to statewide emissions).
Second, the Agency prioritized the suggested changes based on potential impact on national-scale assessment results. Changes likely to have an insignificant impact on cancer risk or noncancer hazard (at the county or state level) were excluded. EPA used the following criteria to determine which inventory issues to address:
- Results in change to cancer risk of greater than 0.5 in a million or
- Results in change to noncancer hazard greater than 0.5
Excluding all of the suggested changes below these cutoffs is likely to have an insignificant impact on the results, even considering the possibility of cumulative impacts (e.g., where two small corrections might affect the same pollutant in the same county).
These changes in the national-scale assessment exposure and risk results affect 17 States and 22 pollutants as detailed in the following table (provided in both Excel spreadsheet and pdf format below).