The vision of HiDALGO’s urban air pollution application is to create cleaner air in cities by using high performance computing (HPC) and mathematical technologies. To this end, the project will provide policy makers and society with an easy-to-use computational tool as a service that accurately and quickly forecasts air pollution in cities with very high resolution. Furthermore, a traffic control system will be developed as well to minimize air pollution while considering traffic flow constraints. The main part of the project is a HPC-framework for simulating the air flow in cities by taking into account real 3D geographical information of the city, applying highly accurate computational fluid dynamics (CFD) simulation on a highly resolved mesh (1-2 m resolution at street level) and using weather forecasts and reanalysis data as boundary conditions. Emission is computed from the weakly coupled traffic simulations and general emission data of other sources. For the demonstration area, the city of Győr, Hungary, a traffic monitoring sensor network with a plate recognition camera system will be developed. The monitoring system will be completed with affordable air quality sensors as well.