Airflow and diffusion modeling for neighborhood scale, urban air quality scenarios

In order to improve the present application of mesometeorological modeling to urban air quality and meteorology problems, a higher resolution, micrometeorological analysis could provide a more local and relevant set of meteorological conditions which directly affect the neighborhood scale of air quality. As a result of the increased resolution, i.e. 100m, the morphology of land features can now directly contribute to part of the underlying surface's interaction with the boundary layer of the atmosphere. For analyses with computational grids of 100m in x and y, morphological features such as buildings, vegetation, and simple surfaces can be more important than nominal changes in terrain elevation over the 100m grid. The Army Research Laboratory's high resolution wind model (HRW) with canopy and building effects is applied to several non-homogeneous, terrain-morphology scenarios to exhibit their effects upon neighborhood scale flow fields. The intent is not to replace mesoscale analyses, but rather to augment and enhance the coarser analysis with finer details that reflect locally-influenced changes in flow fields as well as the behavior of aerosol dispersion. HRW is a 2-dimensional, diagnostic, time independent model that simulates airflow over complex terrain including the effects of vegetation, buildings, and simple surfaces with a high computational resolution - such as 100 m (40-400m) and for a very local area - such as 5 km x 5 km (2 km to 20 km on a side). Example solutions are given for complex terrain and again for the added presence of morphological features upon these same flow fields. The wind fields are then prepared to drive a diffusion code to produce the downwind behavior of puffs and plumes. Most recently, HRW is used in tandem with a Gaussian Puff diffusion code where HRW's deformed, terrain-influenced and morphology-influenced wind fields drive the downwind diffusion of puffs and plumes modified by the interaction with the underlaying complex terrain and morphology features such as canopies and buildings. The resultant wind fields show that there can be notable differences between the terrain-morphology influenced simulations versus the terrain-only influenced wind fields. Other differences are noted as the result of changing atmospheric stability conditions from unstable to stable. These differences, of course, are seen also in the resultant diffusion analyses. A ‘coupled' set of HRW and the Gaussian puff code simulations are presented to exhibit these effects on the neighborhood scale.