A series of experiments was conducted in the closed-circuit Atmospheric Boundary Layer Wind Tunnel at Eindhoven University of Technology, involving a building model at a reduced geometric scale of 1:40. The building model includes a working single-flow mechanical ventilation system and a pollutant source above the roof. The aim of this test was to provide an experimental benchmark to quantify pollutant re-introduction due to both building ventilation and atmospheric wind effects. The steady-state normalized pollutant concentration at the exhaust ventilation fan was measured for 13 reference wind directions (0°, 15°, 30°, 45°, 50°, 60°, 75°, 90°, 135°, 180°, 225°, 270° and 315°) and 3 reference wind speeds (6.4 m/s, 9.0 m/s and 11.1 m/s), leading to 39 wind conditions. For the two most critical scenarios, an internal mapping of the normalized pollutant concentration was conducted on a 3x3x3 grid inside the building. For one wind condition, the normalized pollutant concentration