The present CFD-based numerical study aims to enhance our understanding of pollutant mixing in ventilated rooms, exploring both gaseous and particulate pollutants under various air change rates and inlet/outlet configurations. Results of the 3D simulations showed that, in an isothermal room configuration, perfect pollutant mixing does not exist, although a homogeneous partitioning of the total volume seems to emerge after one hour. This homogeneity is mainly observed in zones with medium to high airflow, where the occupants breathe, excluding the corners of the room. The questioning of the perfect mixing hypothesis led to conclude that conventional one-zone models used in IAQ are inadequate for characterizing people exposure. A suitably adapted methodology will be developed to identify possible macroscopic corrections to nodal modelling which improve pollutant concentration evaluation in the breathing zone.