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APPLICATION OF THE URBANIZED VERSION OF MM5 FOR HOUSTON
Citation:
Dupont, S., S. Burian, AND J.K S. Ching. APPLICATION OF THE URBANIZED VERSION OF MM5 FOR HOUSTON. Presented at 3 CMAS Workshop, Research Triangle Park, NC, October 27-29, 2003.
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:
Since most of the primary atmospheric pollutants are emitted inside the roughness sub-layer (RSL) and consequently the first chemical reactions and dispersion occur in this layer, it is necessary to generate detailed meteorological fields inside the RSL to perform air quality modeling at high spatial resolutions. At neighborhood scale (on order of 1-km horizontal grid spacing), the meteorological fields are strongly influenced by the presence of the vegetation and building morphology of varying complexity, which requires developing more detailed treatment of the influence of canopy structures in the models and using additional morphological databases as input. The assumptions of the roughness approach, used by most of the mesoscale models, are unsatisfactory at this scale. Hence, a detailed urban and rural canopy parameterization (Dupont et al., 2003c), called DA-SM2-U, has been developed inside the Penn State/NCAR Mesoscale Model (MM5) to simulate the meteorological fields within and above the urban and rural canopies. DA-SM2-U uses the drag-force approach to represent the dynamic and turbulent effects of the buildings and vegetation, and a modified version of the soil model SM2-U (Dupont et al., 2003a and b), called SM2-U(3D), to represent the thermodynamic effects of the canopy elements. A first evaluation of DA-SM2-U on the city of Philadelphia (USA) (Dupont et al., 2003c) with a simple urban morphology representation has shown that the model is capable of simulating the important features observed in the urban and rural areas.
The improvement of the urban canopy representation in mesoscale models requires the knowledge of more parameters. These parameters can be divided into three categories: i) the empirical parameters which are deduced from calibration of the models; ii) the "material parameters" which correspond to the physical properties of the surface materials of the canopy elements, they can be easily found in the literature from tables; and iii) the morphological parameters which depend on the structure and on the 3D arrangement of the canopy elements (buildings, vegetation, etc). The morphological parameters are variable from one city to another, and need to be averaged on few 100-m2 with a vertical resolution of a couple of meters to be used at neighborhood scales. Thus, these parameters may be the most difficult parameters to estimate.
Here, the DA-SM2-U version of MM5 is applied to Houston, Texas (USA), in order to study the influence of the morphological parameter resolution on the meteorological fields to know if a detailed resolution of these parameters is required or not for simulating at neighborhood scales. To provide the most accurate representation of these morphological parameters for the entire MM5 computational domain, a Houston GIS Urban Database has been created. This paper describes the DA-SM2-U model and the procedures used to create the morphological parameters on Houston, while the simulation results will be presented during the oral presentation.
This paper has been reviewed in accordance with United States Environmental Protection Agency's peer and administrative review policies and approved for presentation and publication