Air quality is a growing concern for the health of the global population living in large urban centres. The goal of this paper is to present methods and experiences concerning wind tunnel investigations carried out on a 1:500 scale model of a large neighbourhood of Geneva for a typical wind condition. Gas dispersion phenomena were reproduced in the wind tunnel by a mixture of air and SF6 released from 150 continuous point sources on the model building rooftops. Measurements of the 3D aerodynamic field and pollutant concentration were performed in order to validate a CFD open-source code. This experimental campaign is part of the long-term research project called Clean City and was undertaken at CMEFE laboratory of hepia (Haute Ecole du Paysage, d’Ingénierie et d’Architecture de Genève), University of Applied Sciences of Western Switzerland.