Linking air toxic concentrations from CMAQ to the HAPEM5 exposure model at neighborhood scales for the Philadelphia area

The USEPA is developing a capability to link air toxics (AT) concentrations from an advanced photochemical grid model to a human exposure model. The basis for AT modeling is the Community Multi-scale Air Quality (CMAQ) modeling system. Because the AT model must adequately simulate the spatial distribution of “toxic hot spots” regions within an urban area, the CMAQ system must be applied at a fine-scale (~1 km) grid resolution. Furthermore, more advanced human exposure models have the ability to consider sub-grid scale concentration variability. Thus, the proposed neighborhood-scale modeling paradigm is to couple AT concentration estimates provided by CMAQ at relatively fine grid resolutions with within-grid variability obtained from ambient concentration distribution functions (CDFs) developed for each grid cell. For this effort, the CMAQ system is linked to a version of the Hazardous Air Pollution Exposure Model (HAPEM-5), which has the capability to incorporate CDFs. The AT version of CMAQ has been configured to run at 36, 12, and 4 km grid resolutions using the 1999 National Emission Inventory emission inventory and meteorological conditions from 2001 simulated with MM5. While the 36 km modeling domain encompasses the continental United States, the 12 and 4 km domains are centered over Philadelphia. The Industrial Source Complex (ISC) model is being applied to Philadelphia using a high resolution receptor network capable of providing within-grid concentration and subsequent CDF outputs. This presentation will highlight the outputs of CMAQ for several AT pollutants (formaldehyde, acetaldehyde, acrolein, benzene, and methylene dichloride) for the three grid resolutions, and the CDFs for each resolution. Linking the annual concentrations from CMAQ to the HAPEM-5 will be discussed. In addition, information on the monthly and seasonal AT concentrations will be presented and discussed.