Modeling of the urban heat island in the form of mesoscale wind and of its effect on air pollution dispersal

A steady state two-dimensional mathematical model is presented to study the dispersion of air pollutants under the effect of urban heat island (UHI), when the pollutants are assumed to be emitted from the ground based area source. Urban heat islands generate their own mesoscale (or local) winds; therefore, for the simulation of UHI, the mesoscale wind is included in the model. The model takes into account the removal of pollutants through wet and dry deposition processes. The obtained mathematical model is solved using implicit Crank-Nicolson finite difference scheme under stability dependent meteorological parameters involved in wind velocities and eddy diffusivity profiles. The results show that the mesoscale wind produced by urban heat island help the pollutants to circulate and move in upward direction, thus making the problem of air pollution more severe in urban areas. The analysis of the proposed mathematical model leads to conclude that the concentration level of pollutants aggravates under urban heat island effect in all atmospheric conditions viz, unstable, neutral and stable; however, the concentration distribution of pollutants differs in each atmospheric condition. (C) 2009 Elsevier Inc. All rights reserved.