Assessment of Near-field Pollutant Dispersion: Effect of 1 Upstream Buildings 2 M. Chavez a* , B. Hajra a , T. Stathopoulos a , A. Bahloul b 3 4 a Department of Building, Civil and Environmental Engineering, Concordia University, 5 Montreal, Canada 6 b Institut de recherche Robert-Sauvé en santé et en sécurité du travail, Montreal, Canada 7 *Corresponding email: mau_chav@encs.concordia.ca 8 9 10 1. ABSTRACT 11 12 The prediction of pollutant dispersion in urban environment is an extremely complex phenomenon, 13 particularly in the vicinity of a cluster of buildings. Dispersion of effluents released from stacks 14 located on building roofs are severely affected by adjacent surroundings. This paper investigates 15 the impact of an upstream building on the near field of a pollutant source in terms of dilution 16 distribution on the roof of an emitting building. The study was carried out using Computational 17 Fluid Dynamics (CFD) approach with Realizable k-ε for turbulent flow modeling. A limited num- 18 ber of cases were also modelled in a wind tunnel for validation purposes. The study shows that 19 when the source is located within the recirculation zone, dilution is highly sensitive to the height 20 of the upstream building and much less sensitive to the width and length of the upstream building. 21 It is also shown that dilution value has an asymptotic behavior which defines the particular point 22 where dilution becomes independent of the upstream building configuration. Some discrepancies 23 between CFD and wind tunnel data were found, specifically for extreme configurations e.g. sig- 24 nificantly taller upstream building. These differences are mainly due to the inherent unsteady fluc- 25 tuations in the wake of buildings which are not detectable by RANS. 26 27 28 2. INTRODUCTION 29 30 Air quality in urban areas has gained increasing interest in recent years due to its significant influ- 31 ence in human health. In 2004, Health Canada estimated that air pollution caused nearly 6000 32 premature deaths each year in 8 cities in Canada (Judek et al., 2004). The Canadian Medical As- 33 sociation extended this study and estimated that approximately 21000 deaths could be attributed 34 to air pollution in 2008 in the entire country. The air pollution has a wide range of effects, with 35