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Modeled Human Exposure

Information provided for informational purposes onlyNote: EPA no longer updates this information, but it may be useful as a reference or resource.
Health Effects Criteria
This link provides cancer and non-cancer information which is associated with each toxic air pollutant as well as a reference to the source of that information.

Exposure Concentrations Maps
These maps allow you to view 1996 exposure concentration estimates (in micrograms per cubic meter) based on the median concentration in each county. You can select the entire U.S. or any State in the United States (except Alaska and Hawaii) plus Puerto Rico and the Virgin Islands. The maps are color-coded (by percentile breakdown relative to the rest of the country) to show how each county's median exposure concentration compares to the rest of the U.S.

Exposure Concentrations Bar Charts
This link allows you to view three types of bar charts for each air pollutant:
  1. A comparison of statewide exposure concentration estimates.
  2. A representation of the contribution of each of the four major source types as well as background estimates to each statewide average exposure concentration estimate.
  3. A chart for each State containing median exposure concentration estimates for each pollutant.
Note that you need Adobe Acrobat 4.0 (or higher) to be able to correctly view and print these bar charts. You can obtain this version free of charge at: http://www.adobe.com/products/acrobat/readstep2.html.

Exposure Concentrations Data Tables
There are two types of tables you will be able to view from this link: one type is organized so you can see exposure concentrations specific to an individual pollutant, and the other is organized so you can see the median exposure concentrations for each of the 32 air toxics and diesel PM for each county in a State. All of these tables are available as either a downloadable file in Excel Spreadsheet format or as an Adobe Acrobat pdf file. Both types of tables contain information about exposure concentration distributions (i.e., as percentiles) as well as a breakdown of exposure concentrations into major, area, onroad mobile and nonroad mobile and background contributions. The county information includes a designation as urban or rural.

Results of the Exposure Assessment at the Census-Tract/County/State Level
This link provides Excel spreadsheets (zipped files) of the individual pollutant results at the census-tract, as well as county/state level. These data are provided for those who wish to do their own technical analyses and comparisons using the most refined output available from this national-scale assessment. In performing such analyses, it is extremely important that users be mindful of the purposes for which the national-scale assessment was developed. In our judgment, it would be inappropriate to use these results alone to draw conclusions about local concentrations and risk. The results are most meaningful when viewed at the State or national level. There are important limitations that affect how the data should be used and interpreted. These limitations are related to gaps in emissions data, limitations in the computer models used, and limitations in the overall design of the assessment (intended to address some questions but not others). Please see the limitations section of this website for more details.
About the Exposure Model (HAPEM4)
The HAPEM4 model has been designed to predict the "apparent" inhalation exposure for specified population groups and air toxics. Through a series of calculation routines, the model makes use of census data, human activity patterns, ambient air quality levels, climate data, and indoor/outdoor concentration relationships to estimate an expected range of "apparent" inhalation exposure concentrations for groups of individuals. Further technical details about the HAPEM4 model are available. Other exposure and risk models can be found at the FERA (Fate, Exposure, and Risk Analysis) Website.

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