Wind tunnel modelling of urban building exposure to outdoor pollution

The effects of the position of air pollution sources on the magnitude and spatial variation in concentrations on a building model were investigated in a boundary layer wind tunnel. The aim was to determine the region around the building from which pollution sources affect the building (region of influence of sources) and generate concentration patterns on its surface. The tests were carried out at a nominal building model scale of 1:100 and used continuous releases of a tracer gas at different locations within arrays of cubes representative of urban areas.The region of influence of sources around the test building was found to be variable in size depending on the area density of the array of buildings. The region of influence across the wind increased in size with increasing area density of the array. There was a limiting area density, however, beyond which this sensitivity of the region to the area density diminished. Sources closest to the test building generated the highest variation in concentrations on the building. This variation decreased with increasing source distance from the building and was sensitive to the area density of the array. Generally, the decay in the spatial variation in concentrations with increasing upwind source distance was smaller in higher density arrays.