The scientific interest in improving the air quality tools that provide a detailed description – source oriented – of atmospheric processes and the impact of specific large industrial emission points is growing. This paper describes the results of using a state-of-the-art third-generation air quality modelling system (MM5-CMAQ) over a pilot test industrial site in the Madrid mesoscale domain. The MM5 model is a web-based non-hydrostatic mesoscale meteorological model developed by PSU/NCAR, and the CMAQ (Community Multiscale Air Quality Modelling System) is a third-generation air quality dispersion model developed by the US EPA. Both are modular codes and include an interface called MCIP, which assures full consistency with the numerical methods in the advection and diffusion schemes in the meteorological module and the chemistry and dispersion module. The application has been done with the CBM-IV chemical scheme (simple version). The results of running the so-called ON/OFF approach – in other words, the differences between the simulation with full industrial emissions and no industrial emissions – show that the MM5-CMAQ modelling system can be used as an excellent tool for evaluating the impact of different emission sources in an operational mode. Results also show that increases up to 50% on average and larger values for hourly impacts for ozone concentrations are found in the surrounding areas of the industrial plant. In addition, we see that the distance where the industrial emissions are impacting on the air quality can be larger than 40 km.