At x=0.64 H (about two-third of the way into the street, Fig. 6d), a similar picture applies, but the core of the vortex is further up and there is now a strong flow in the lower part of the canyon towards the lee of the building. This would cause any material in the street canyon (which, for example, might have come from advection along the street from upstream) to be driven into the recirculation region.
x
0.64 H
H