Thermal effects on the dispersion of rooftop stack emission in the wake of a tall building within suburban areas by wind-tunnel experiments

The influence of roof thermal effects on the dispersion of pollutants discharged from a rooftop stack in the wake of a high-rise building was investigated by means of wind-tunnel experiments. Six Ri cases and two stack emissions (S1 and S2) were considered. The distributions of temperature and pollutants, and visualization of pollutant diffusion were measured experimentally. Results show that as the Ri increases, the dimensionless temperature in the vertical center plane decreases, with its mean value reducing by 57%. According to the CRP value, the influence of Ri on pollutant distributions can be divided into two stages, namely the strongly influenced stage (0 ≤ Ri ​≤ ​0.78) and the weakly influenced stage (0.78 ≤ Ri ​≤ ​1.15). The mean pollutant concentration in the leeward wall and inner street canyon decreases rapidly with the Ri increasing (0 ≤ Ri ​≤ ​0.78), but changes little when Ri ​≥ ​0.78. Under the stack S2 emission, with Ri increasing, the obvious downwash effect gradually weakened, until Ri ​≥ ​0.97 the downwash effect disappeared eventually. Moreover, the visualization of pollutant diffusion further confirmed the above analysis results. This highlights the understanding of the influence of roof thermal effect on the local atmospheric environment. [Display omitted] •The effect of roof thermal buoyancy on pollutant diffusion was studied experimentally.•Six Ri cases from 0 to 1.15 and two discharge positions were considered.•The influence of Ri on pollutant distribution can be divided into two stages.•When Ri ​≥ ​0.78, the downwash effect gradually disappeared.•The visualization of pollutant diffusion further confirmed the above analysis results.