CFD modeling of fine scale flow and transport in the Houston metropolitan area, Texas

Fine scale modeling of flows and air quality in Houston, Texas is being performed; the use of computational fluid dynamics (CFD) modeling is being applied to investigate the influence of morphologic structures on the within-grid transport and dispersion of sources in grid models with grid sizes of order 1 km. This study provides a basis for examining, understanding and eventually leading to improving parameterizations of sub-grid variability in the concentration fields for air pollutants and/or toxic agents. Several cells of 1 km size are chosen in different parts of Houston, Texas that contain different characteristic mix of urban morphologic structures (e.g., buildings, street canyons, tree canopies, paved areas) for this study. One key aspect of this investigation will be to examine the consequences of utilizing various input background meteorological forcing to the CFD simulations. Typically, one assumes arbitrary background flow, which may not be representative of the actual flow at the specific grid cell. This study will examine input meteorology from model outputs from an urbanized form of MM5 at 1 km grid resolution, but implemented an advanced urban module called DA-SM2U (Dupont et al., 2004). This module requires an advanced set of urban canopy parameters, UCPs, gridded at 1 km resolution, which have been developed using the same set of detailed, high (order 1 m) resolution data for the CFD study for provide full measure of consistency. For examining sensitivity, these CFD results will be contrasted against the use of other inputs meteorology such as (a) using standard version of MM5, and (b) airport observations.