In this study, the effect of air change rate on particle dispersion is investigated experimentally and numerically for different contaminant source positions. An experimental study is carried out on a reduced scale model for isothermal flow conditions and 0.5 mu m particles are used as contaminants. Particle motions, based on Lagrange approach, are modeled with a computational fluid dynamics (CFD) software ANSYS Fluent. It is found that pollutants outside the main flow region lead to 12 times higher concentration values. In addition, it is determined that the increase in air change rate decreases the concentration of pollutants in this region by 75%.