Airflow and pollutant transport in street canyons

In this work the dispersion of gaseous and particulate exhaust emissions in different street canyons were studied. For two-dimensional sections of canyon models airflow, pollutant dispersion and deposition patterns in the streets and on the surrounding buildings were analyzed. Effects of building size, street width, and wind velocity on the pollutant transport were examined. While the stress transport turbulence models were used in most of the analysis, the predictions of other turbulence models were also examined. Depending on wind speed, building height, and street width, it was found that large recirculation regions in canyons might form. Under certain conditions, also pollutants emitted from vehicle exhaust may trap inside the street canyon. Variations of transport and deposition of emitted particulate pollutants with particle size and relaxation time were also studied. It was shown that the amount of deposited particles in street canyons reduces when the wind speed increases. The simulation results were compared with the available wind tunnel experiments and favorable agreement was found.