Dispersion in a street canyon for a wind direction parallel to the street axis

We investigate pollutant dispersion in a street canyon for an external wind direction parallel to the street axis a case which has been poorly documented in the literature The study is performed numerically and analytically by means of a model based on a series of simplifying assumptions The range of validity of these assumptions is discussed by comparing analytical and numerical results for two different street aspect ratios Our results show that for a critical length of the street ground level concentration can be higher than those observed in a street canyon whose axis is perpendicular to the external wind direction We show that this critical length depends on the street aspect ratio (C) 2010 Elsevier Ltd All rights reserved