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LINKING AIR TOXIC CONCENTRATIONS FROM CMAQ TO THE HAPEM5 EXPOSURE MODEL AT NEIGHORHOOD SCALES FOR THE PHILADELPHIA AREA
Citation:
Ching, J.K S., T E. Pierce Jr., T. Palma, W T. Hutzell, R. Tang, A. Cimorelli, AND J Herwehe. LINKING AIR TOXIC CONCENTRATIONS FROM CMAQ TO THE HAPEM5 EXPOSURE MODEL AT NEIGHORHOOD SCALES FOR THE PHILADELPHIA AREA. Presented at 5th Symposium on the Urban Environment, Vancouver, BC, Canada, August 23-27, 2004.
Impact/Purpose:
The objective of this task is to develop and evaluate numerical and physical modeling tools for simulating ground-level concentrations of airborne substances in urban settings at spatial scales ranging from ~1-10 km. These tools will support client needs in the areas of air toxics and homeland security. The air toxics tools will benefit the National Air Toxics Assessment (NATA) program and human exposure modeling needs within EPA. The homeland security-related portion of this task will help in developing tools to assess the threat posed by the release of airborne agents. Both sets of tools will consider the effects induced by urban morphology on fine-scale concentration distributions.
Description:
This paper provides a preliminary demonstration of the EPA neighborhood scale modeling paradigm for air toxics by linking concentration from the Community Multi-scale Air Quality (CMAQ) modeling system to the fifth version of the Hazardous Pollutant Exposure Model (HAPEM5). For this demonstration, annual simulations of CMAQ are performed at multiple scales at 36, 12, and 4 km grid sizes. The domain for 36 km size included the continental U. S., while the smaller grid sizes included nexted domains that encompassed Philadelphia and the state of Delaware. In this application, specific air toxics species were defined and added to the Carbon Bond-IV mechanism. HAPEM5 allowed for the introduction of temporal and spatial (sub-grid)varibilities. Temporal variability was estimated using hourly outputs for a year at each grid cell. The sub-grid variability was estimated using customized software designed to provide gridded Probability Density Functions (PDFs) to describe the concentration distributions from running the Gaussian dispersion model ISC in fine receptor mode. This application demonstrates that a more robust set of information can be gathered for HAPEN5 than by applying the ISC approach. For example, this methodology provides considerably larger dynamic range of temporal and spatial variability not available using ISC alone. Moreover, using CMAQ allows for more accurate estimation of secondary species such as formaldehyde and acetaldehyde, which are not treated explicitly in models such as ISC.
Although this work was reviewed by EPA and approved for publication it may not necessarily reflect official agency policy