Modeling and simulation of urban air pollution from the dispersion of vehicle exhaust: A continuum modeling approach

Air pollution has become a serious issue over the past few decades, and the transport sector is an important emission source. In this study, we model and simulate the dispersion of vehicle exhaust in a hypothetical city with a single central business district (CBD) in a complete day, deriving an average daily pollutant concentration, then use the distribution of wind direction over a year, to compute the distribution of average pollutant concentration in the city. All vehicles are assumed to be continuously distributed over the whole city, and the road network is relatively dense and can be approximated as a continuum. The model of Huang et al (2009 Huang, L., Wong, S. C., Zhang, M. P., Shu, C. W., & Lam, W. H. K. (2009). Revisiting Hughes’ dynamic continuum model for pedestrian flow and the development of an efficient solution algorithm. Transportation Research Part B, 43(1), 127–141.[Crossref] , [Google Scholar], Transportation Research Part B, 43(1): 127–141) is used to describe the traffic flow that satisfies the reactive dynamic user equilibrium principle, and the pollution dispersion model is governed by the advection-diffusion equation. The complete model is composed of a coupled system of a conservation law, an eikonal equation and an advection-diffusion equation. The problem is solved by the efficient fifth-order weighted essentially non-oscillatory scheme for the conservation equation and the advection-diffusion equation, and the fast sweeping method for the eikonal equation with third order total variation diminishing (TVD) Runge-Kutta time discretization. The numerical results show a reasonable temporal and spatial distribution of vehicle density and pollution concentration.