The dispersion of various pollutants emitted from truck and passenger vehicles: a wind-tunnel study

In recent years, investigation of the dispersion of exhaust gas from vehicles has received increasing attention in various studies using various approaches, including on-field measurements, experimental laboratory models, and software simulations. This study aimed to investigate the effects of changes in vehicle traffic conditions, fuel type used in an engine, and vehicle size on the emission and dispersion of gaseous pollutants from the exhaust pipe in a wind tunnel. The results showed that pollutant concentration decreases along the tailpipe centerline as the exhaust gas moves backward and the flow pattern changes significantly from 11.5 to 15 m/s. However, for the passenger car, the small recirculation region in the near-wake region at an inflow air velocity of 11.5 m/s carries away more particles compared to an incoming velocity of 15 m/s, resulting in lower gaseous concentrations in both longitudinal and transverse directions. The gaseous dispersion behind the truck and the car is wider for an inflow air velocity of 11 m/s, especially for NO, NO2, and SO2. The results also showed that the pollutant concentrations of the truck exhaust plume were higher than those of the passenger car in lower inflow air velocity in both longitudinal and transverse directions. The lower concentration of dispersed gaseous pollutants behind the passenger car model compared to the truck model may be attributed to the shape and height of the truck model, which can trap more particles behind the vehicle. Finally, the dispersion pattern of SO2 is almost identical to that of NO2, and the dispersion of the exhaust gas plume related to CO and NO pollutants is more prolonged than that of CO2 and NO2 particles along the tailpipe centerline. The findings of this study may help in estimating the concentration of pollutants along urban highways.