The Assessment System for Population Exposure Nationwide (ASPEN). A. S. Rosenbaum and Y. H. Wei, Systems Applications International, Inc., 101 Lucas Valley Road, San Rafael, CA 94903; and D. A. Axelrad and T. J. Woodruff, U.S. Environmental Protection Agency, Office of Policy, Planning and Evaluation, 401 M St. SW (2123), Washington, DC 20460
As part of EPA’s Cumulative Exposure Project, long-term cumulative concentrations of approximately 150 hazardous air pollutants (HAPs) are being modeled at the census tract level for the 48 contiguous states. This presentation describes the ASPEN modeling system being used to make these concentration estimates. ASPEN is a modified version of EPA’s Human Exposure Model (HEM), which includes both an air dispersion module and a mapping module for extrapolating concentration estimates to population centroids. The HEM uses a Gaussian modeling approach with optional first-order decay and a simple deposition algorithm. In ASPEN the deposition algorithm has been improved, simple treatment of secondary formation of HAPs has been incorporated, and simulation of area and mobile source emissions has been modified. The broad scope of the Cumulative Exposure Project made it necessary to neglect detailed treatment of some chemical and physical processes involved in formation and dispersion of air toxics. The potential impacts of these simplifications were investigated with sensitivity analyses, using 54 census tracts in Greenpoint/Williamsburg area of Brooklyn, NY (G/W) as a test site. The findings show that most of the simplifications are not likely to have a large impact on the accuracy of long-term average concentrations estimates that are the focus of the Cumulative Exposure Project.
The views expressed in this presentation are those of the authors, and do not necessarily represent those of the U.S. Environmental Protection Agency.