This project aims at understanding the effects of radiative transfer on air pollution dispersion in urban areas at both the street scale and the neighbourhood scale. Numerical models will be developed, for that purpose, that will help design and manage our cities, buildings and traffic systems in order to produce sustainable, safer, healthier, and more comfortable urban environments.Radiation modelling will be coupled with 3D fluid dynamics, urban geometry, particle and pollutant transport, traffic and environmental conditions to produce the first model able to take into account radiation transport effects at both street and neighbourhood scales. Benchmark numerical simulations at the street scale will provide detailed information on radiative transfer effects subject to various environmental conditions: presence of clouds, humidity, turbulence level, etc. These results will help to derive simple physically relevant models for the simulations at the, much more computationally expensive, neighbourhood scale. The intensive use of fully adaptive methods for both radiation and fluid dynamics will also contribute to make feasible the simulations at this scale.