U.S. EPA Disclaimer

EPA strongly cautions that these study results should not be used to draw conclusions about local exposure concentrations or risk. The results are most meaningful when viewed at the regional or county level; for smaller areas, the study becomes less certain. In addition, these results represent conditions in 1999 rather than current conditions and only include exposures from outdoor sources of particulate matter.

The results provide answers to questions about emissions, ambient air concentrations, exposures and risks across broad geographic areas for the year 1999. As such, they help the EPA identify specific air toxics compounds, and specific source sectors such as stationary sources or mobile sources, which generally produce the highest exposures and risks in the country. But they also are based on assumptions and methods that limit the range of questions that can be answered reliably. They cannot be used to identify exposures and risks for specific individuals, or even to identify exposures and risks in small geographic regions such as a specific neighborhood. These limitations, or caveats, must always be kept in mind when interpreting the results. The results should be used only to address questions for which the assessment methods are suited.

All risk estimates are based on exposure estimates for the median individual within each census tract, which EPA considers to be a "typical" exposure. Some individuals may have substantially higher or lower exposures based on where they spend their time. The study is not designed to quantify these individual extremes.