Prediction of pollution dispersion under urban heat island circulation for different atmospheric stratification

摘要

The background atmospheric stratification with inversion layers in association with urban heat island phenomena affects the city ventilation and pollution transport. In this study, the effects of different stratification including ground inversion, isotherm, sub-adiabatic and super-adiabatic profiles with an inversion layer on pattern, intensity and extend of urban heat island induced circulation (UHIC) are investigated. The effect of the UHIC pattern on pollutant transport for two different scenarios are studied. The study is conducted using a modified CFD model that is adopted to include temperature background layers, compressibility and anelasticity of the atmosphere. The modified CFD model and results of simulation are validated against the available data in literature for UHIC pattern and pollution transport scenarios. The results indicate that background temperature profile controls the convergence and divergence of flow, and it affects the mixing height of flow inside of urban area, significantly. The flow speed at the urban border for inversion, isotherm, and sub-adiabatic stratification is 55%, 52%, and 40% less than super-adiabatic stratification, respectively. It is observed that the existence of inversion layer is essential for convergence of flow in case of super-adiabatic stratification. In case of ground inversion, pollutants that are released inside urban area are transferred to higher levels in rural area. The induced flow due to ground inversion transfers thepollutant in rural area into the urban dome. The pollutant concentration for inversion, isothermal and super-adiabatic profiles is 350%, 200%, and 150% more than subadiabatic stratification, respectively.