The Use of LES CFD Urban Models and Mesoscale Air Quality Models for Urban Air Quality Simulations

Abstract

Most of CFD urban models are based on the so called RANS approach (Reynolds averaged Navier Stokes equations). Recently, the advance of computer capabilities has pushed the inclusion of Large Eddy Simulation technique (LES) which has a different approach by using a spatial filter resolving the large eddies in the atmosphere and modelling the small eddies. One of the recent open models with LESS approach is the PALM4U model developed by the Leibnitz Hannover University in Germany. We have used an area in the downtown of Madrid city to set up the PALM4U model with 2 m spatial resolution. The vertical extent of the model is set up on 300 m with the same equally spaced resolution. The system receives the boundary and initial conditions from the WRF/Chem mesoscale air quality model developed by NOAA/ESRL/GSD (US) team. WRF/Chem is a well know state-of-the-art meteorological and chemical models for mesoscale applications. Results of the simulations show a high sensitivity to the changes in type of trees in urban parks with strong impacts (hot spots) in several areas located several hundreds of meters away of the part. The system composed by both models is a reliable tool to be use for studying the impact of natural based solutions (NBS) in urban environments and for other pollution applications with very high spatial resolution. Hot spots, energy efficiency and health impact assessments at urban level are also areas where this complex tool can be applied.