Journal of Wind Engineering and Industrial Aerodynamics 91 (2003) 1117–1131 Measurement of the turbulent mass flux with PTV in a street canyon G ! abor Dezs + o-Weidinger*, Adel Stitou, Jeroen van Beeck, Michel L. Riethmuller Department of Environmental and Applied Fluid Dynamics, von K ! arm ! an Institute for Fluid Dynamics, 1640 Rhode-Saint-Genese, Belgium Received 5 November 2001; received in revised form 22 May 2003; accepted 27 May 2003 Abstract Simultaneous measurement of velocity and concentration provides a tool for studying the turbulent diffusion. This quantity until now was mainly modeled and not measured and it plays an essential role in turbulent diffusion of pollutant. We present a new technique to measure the turbulent mass flux vector, u 0 c 0 ; based on the same PIV/PTV images, employed for both instantaneous velocity and concentration measurements. Then we applied the new technique to check the correctness of the model widely used for the turbulent mass flux in RANS simulations, in a street canyon type flow. We found places where the turbulent diffusion is opposite to the gradient in mean concentration. r 2003 Elsevier Ltd. All rights reserved. Keywords: Particle tracking velocimetry; Concentration measurement; Street canyon; Turbulent diffusion 1. Introduction Microclimate and air quality in urban areas such as street canyons has gained importance in the recent years. An important factor is pollution from vehicles in downtown streets. Street canyons are the typical architectural structures in urban environment and they represent the highly polluted zones. The emission occurs at ground level and so the pollution reaches the buildings, the pavement and the people ARTICLE IN PRESS *Corresponding author. Tel.: +32-235-99678; fax: +32-236-99600. E-mail address: dezso@vki.ac.be (G. Dezs + o-Weidinger). 0167-6105/03/$-see front matter r 2003 Elsevier Ltd. All rights reserved. doi:10.1016/S0167-6105(03)00054-0