Meso-urban meteorological and photochemical modeling of heat island mitigation

A fine-resolution, meso-urban meteorological model Was updated and applied, using new data and techniques in this study, in driving fine-resolution photochemical simulations to evaluate the air-quality impacts of urban heat island mitigation. The drag-force-based formulation of the model improves the simulation of fine-resolution meteorological and air-pollutant concentration fields in the urban canopy layer. Compared to the meso scale, the meso-urban modeling of heat island mitigation produces larger localized impacts oil meteorology and ozone air quality and captures phenomena of interest that are typically not detectable at the coarser scale. These include, for example, cool islands, heat islands, flow convergence associated with heat island circulation, flow divergence at the leading edge Of urban areas, and vertical variation in turbulent kinetic energy budget components within the canopy layer in response to vertical changes in densities of buildings and vegetation. They also include fine-resolution features in the simulated ozone concentration field and its response to Surface modifications. Model results show that heat island mitigation is effective in reducing local ozone concentrations. This paper presents results from Sacramento, California, as an example using increased urban albedo as the control mechanism. For the region, episodic conditions, and surface modification scenarios examined in this paper, air temperature is decreased by up to 3 degrees C. Changes in ozone consist overwhelmingly of decreases but call also involve increases with the latter being confined to small areas and short time intervals. While larger reductions in ozone are detected, decreases Of Lip to 5-10 ppb are more representative and the daily maximum 8-h average can be decreased by Lip to 13%. (c) 2008 Elsevier Ltd. All rights reserved.