Study On Line-Source Dispersion Model For Vehicle Exhaust Pollutant From Highway

It is important to calculate the pollutants concentration distribution of vehicles emission, which can be used in air quality environmental impact assessment of highway subjects, air pollution simulation on road environment and pollution control in vehicles emission.It is crucial to set up a dispersion model applicable to roadway in order to predict the effects of vehicle emission pollutants on air quality. Based on the atmospheric diffusion equation, considering the characteristics of height-dependent wind speed and air turbulence motion, a roadway line-source dispersion model is established. Parameters in the model are modified and the accuracy and validity of the model is examined The sensitivity of the parameters in the model is also studied. The main factors which affect the concentration distribution of the vehicles emission are determined, and the detailed effects of the main factors are analyzed. Then, through two engineering cases, the impacts of road construction on pollutants distribution are discussed, which can also provide guidance for the engineering application. According to the researches above, pollution control measures are put forward. The main conclusions are summarized as below:(1) Atmospheric diffusion equation of multipoint sources that is applicable for pollutants diffusion characteristics of vehicles emission is established. Under the vertical and horizontal boundary conditions, finite-length and infinite-length line-sources concentration distributions are analytically solved.(2) The determination of parameters in the model of vehicles pollutants diffusion is studied and discussed. Pollutants concentration is simulated under the meteorological conditions of near surface layer and low wind speed. Compared with other models, this model has higher precision.(3) Sensitivity analysis in the model shows that metrological conditions and engineering parameters of road and road activities are the main factors which affect the pollutants concentration distribution. According to analysis of the sensitive parameters, it is indicated that atmospheric stability and height of roadbed have marked effects on the pollutants concentration distribution near the road. The effect that the length of line sources is mainly on one side of the road and far away from the road, but the ending effect should be considered. Other parameters, such as wind speed vehicle speed, traffic volume and emission factors, also have signification influences on concentration distribution. But these influences will be little after a dispersion scope.(4) The efficiency of this model is verified through the simulation of two engineering cases. The result shows that the model is useful to simulate and predict the pollutant concentration, and has practical value for air quality study of road.(5) The influence of different road construction on air pollutants diffusion is analyzed. It turns out that road tunnel causes pollutants diffusing along with the wind, and the high concentration distribution on a large range. High roadbed promotes the diffusion of the pollution concentration, the maxim concentration appears at one side of road and then the concentration will be same at each side.(6) According to analysis of influence factors of pollutants distribution and simulation of concentration distribution, the control measures of vehicles emission pollution is introduced, which also supplies the theory and guidance to emission pollution prevention of vehicles on road.