A wind tunnel study of the effect of downstream buildings on near-field pollutant dispersion

The effect of near-field pollutant dispersion characteristics for the case of downstream buildings in the urban environment has been presented in this paper. Wind tunnel data were obtained for nine different building configurations, three exhaust momentum ratios (M) and three stack heights (hs), for wind azimuth of 0°. Tracer gas concentrations were measured on the roof, windward and leeward walls of each building. When a tall downstream building was located within the recirculation length of the emitting building, higher rooftop concentration was measured on the emitting building than for the isolated building case. Results also show that the height and across wind dimension of the downstream building, as well as the spacing between buildings are critical parameters in assessing plume dilution. ASHRAE 2007 and ASHRAE 2011, which apply Gaussian-based models for the evaluation of dilution, are unable to model the effect of adjacent buildings; the former yielded lower dilution for all cases examined whilst the latter was found to be suitable only for specific limited cases. Design guidelines for the placement of stack and intakes to avoid or minimize plume re-ingestion are proposed.