Field Monitoring And Numerical Simulation Of Vehicle Exhaust Gas Pollution At Urban Street-Canyon Road Intersection

With the rapid increase of vehicle ownership in cities, lots of exhaust gas from vehicles has deteriorated the air quality in the urban area. Blocked by the high-density and high-rise buildings on road, the vehicle exhaust is rather difficult to diffuse from the street canyon to the outside atmosphere. Hence it is easy to congregate the concentration of the vehicle exhaust and damage human health. Recently, many researches on control of vehicle exhaust pollution have such methods as wind tunnel test, field test and numerical simulation. Considering the test period and the test cost, field monitoring and numerical simulation are applicable to this study.The street intersections, the most common form of urban road traffic, have serious road traffic pollution. Moreover, it has features of heavy traffic flow, high density population and a forest of buildings. The dispersion of vehicle exhaust has a close relationship with the complex structure surface, meteorological parameter and traffic emission intensity. Based on the actual urban street intersections in Xi'an, this study investigated the building layout at street intersections and simulated the flow field inside those intersections. Then, we were monitoring the change of PM₁₀ concentration inside the selectd typical intersection and trying to discover the main influencing factors. Next, this study used the method of AP-42 and fuel estimation to estimate the traffic emission intensity about PM₁₀. According to this, this study got an important and basic data of traffic emission intersity on road.It has been shown that the mean high of adjacent buildings has two typical distribution characteristics in Xi'an city. It is suggested that Realizable k ? ? turbulence model apply to the study of flow around building. Under the dominated wind direction, it is easy for airflow to form the residency vortex at typical street canyon road intersections.The parameter has two effects on traffic emission intensity of PM₁₀ concentration. Humidity is to affect the intensity values, and air temperature and wind speed are to affect the dispersion of PM₁₀ concentration. Local wind speed, caused by complex building structure surface, has an obvious non-linear correlation with sample concentration. The ratio of fine particles (<1.0μm) emitted from the vehicles, have a close correlation with sample concentration under the high humidity condition, but have insignificant correlation with the traffic flow. The fine particles and the high humidity condition are the main reasons for the PM₁₀ concentration pollution at street intersection. And air temperature and airflow affected by complex building surfaces mainly affect the PM₁₀ dispersion and distribution. Although natural gas used for automobile is helpful to reduce the car exhaust gas pollution, PM₁₀ concentration of raise dust obviously higher than that of car exhaust due to particle deposition on traffic road.