Urban surface modifications and their potential effects on air quality in the Houston-Galveston region

Earlier meteorological and air quality modeling study of the impacts of increased surface albedo and reforestation in the Houston-Galveston Texas region were inconclusive due to the relatively high level of noise introduced by the meteorological model. As a result, the signal of interest, i.e., changes in ozone concentration, was unclear. That study used earlier versions of MM5 and CAMx, but recent improvements in those models and in available input data sets can now improve model performance. For example, the EPA version of MM5 has been modified (as uMM5) to: (a) better simulate canopy-layer meteorological fields by use of a drag-force approach in lieu of typical roughness length theory, (b) more accurately simulate at finer resolutions, e.g., 1 km, and (c) accept available fine-resolution input parameters based on urban morphological and LULC data developed as part of an US EPA effort.

This paper thus describes simulations that used uMM5, more recent aerometric data from the Texas2000 field study, new urban morphological data, and USFS developed reforestation scenarios to simulate the changes in near-surface urban heat island (UHI) intensities. Results showed a decreased (by 0.9 K) midday/maximum UHI value. Resulting uMM5 met fields will used in future Houston-Galveston CMAQ SIP simulations.