CFD modelling of traffic-related air pollutants around an urban street-canyon in Suzhou

The wind flow field around urban street-building configurations has an important influence on the microscale pollutant dispersion from road traffic, affecting overall dilution and creating localized spatial variations of pollutant concentration. It is important to understand these small-scale effects not only for assessing personal exposure to pollutants in the vicinity of roads, but also because air quality in a city as a whole is assessed on the basis of data from a few urban monitoring sites. This paper reports some outcomes of a study aimed at exploring the transfer and diffusion characteristics of vehicular exhaust emissions and the constraints associated with significant monitoring locations such as street canyons, courtyards and enclosed spaces, and the conditions propitious to pollutant diffusion and air dispersion in urban areas. The wind field around a street-canyon in the city of Suzhou (China) has been modelled by using the Computational Fluid Dynamic technique. The results have been analysed to better understand the values of gaseous pollutants, meteorological parameters and traffic flows measured by means of automatic analyzers along the same street-canyon at two different heights. It has been found that the model correctly describes the vortex recirculation pattern around the building geometry studied and it is very useful in assessing the micro-scale pollution trends.