The atmospheric boundary layer (ABL) generated represents wind flow over rough terrain, in accordance with VDI guidelines. It is simulated using vortex generators and arrays of roughness elements within the facility. The vortex generators comprise three spires modeled based on the design suggested by Irwin, featuring a base width of 0.5 m, a top width of 0.04 m, and an added base extension. The roughness elements comprises a combination of 0.06 × 0.06 m² and 0.04 × 0.04 m² sized ‘L-shaped’ metal components on a fetch of 12 m.

To investigate the dependence of obtained pollutant concentrations on Reynolds number, measurements were conducted at four locations (P30, P34, P48, and P74) under varying reference wind velocities. Pure ethylene was used as a tracer gas and released from source location S1, with a constant emission flow rate maintained throughout the experiment at each location. Tests were performed for six different wind speeds for all four locations corresponding to Reynolds numbers ranging from 7.4 × 10⁴ to 2.1 × 10⁵, based on the reference height of the tallest building (0.33 m). Additional two velocities were also tested for locations P30 and P34 resulting in Reynolds numbers of 2.3 × 10⁵ and 2.5 × 10⁵. The reference wind speeds at reference height ranged from 3.5 to 11.7 m/s. Pollutant concentrations were recorded for 300 s at each location. Ambient atmospheric conditions of temperature, pressure, and relative humidity were also monitored throughout the measurement period.

Source strength dependency tests were conducted at three locations: P22, P48, and P74. For each location, the wind speed was kept constant while five different ethylene emission rates (C1–C5), ranging from 0.184 to 0.588 L/min under ambient atmospheric conditions, were emitted from S1. Pollutant concentration data were recorded for a duration of 300 s at each location. As in Experiment 2, ambient atmospheric parameters of temperature, pressure, and relative humidity were also monitored during the measurements.

Tracer gas (ethylene) was released from one of the two source locations (S1 or S2) at a time. Pollutant concentration measurements were conducted at 76 locations within the urban area at a height of 5 mm above ground level (reduced scale) to investigate dispersion patterns across the target area. Additional repeated measurements were performed to quantify uncertainty. At each measurement location, pollutant concentration data were recorded for durations ranging from 60 to 300 s, depending on the stationarity of the observed time series.