Modeling traffic pollutants in a street canyon by CFD: Idealized line sources versus multiple realistic car sources

Idealized sources arecommonly used toreproduce thetraffic emission instreet canyons inexperimental and numerical investigations. However, itremains unclear whether idealized sources canaccurately reproduce the pollutant dispersion compared tomore realistic sources. The goal ofthispaper istoinvestigate theimpact of idealized and realistic sources ontraffic-induced pollutant concentration inastreet canyon bynumerical simulation with Computational Fluid Dynamics (CFD). First, thescale-adaptive simulation (SAS) results ofmean velocity and concentration arecompared with wind-tunnel (WT) data foridealized line sources (ILS) and a satisfactory agreement isfound between theSAS and WTresults. Next, SAS areperformed toinvestigate the impact onmean velocity andmean pollutant concentration ofILSversus multiple realistic carsources (MRCS) cases, designed tomimic aconfiguration oftraffic jam-like conditions (i.e.rows ofidling cars) inastreet canyon. Different levels ofgeometrical simplifications ofsources andtotal emission rates areconsidered. Although this research study focuses onthese aforementioned specific setofconditions andconclusions relate solely tothese circumstances, theSAS results show that theoverall-averaged concentration associated with MRCS and the simplified source-geometry cases isabout 1.18–6.22 times larger than that byILS.Thus, ILSmay beinadequate toreproduce thepollutant concentration inrealscenarios. This study cancontribute toenhancing thepollution prediction accuracy andreduce thepotential riskofhuman exposure.