Development and Application of a Three-Dimensional Taylor–Galerkin Numerical Model for Air Quality Simulation near Roadway Tunnel Portals

Abstract

Since highway traffic has become one of the major emission sources of air pollution, air pollution prediction near roadway tunnel portals is a very important subject. Although many models have been suggested to predict pollutant concentrations near roadways, almost all models can be applied to only at-grade or cutoff straight highways. Therefore, a numerical model applicable to the site near roadway tunnels in complex terrain has been developed. The first stage of this study is to make a database of air quality and meteorological conditions near roadway tunnel portals. The second stage is a screening of several wind field models. The third stage is an evaluation of the numerical schemes for the advection equation, mainly carried out based on the results of the rotating cone problem. In this limited comparative study, the most accurate and high-speed computing scheme was the Taylor?Galerkin scheme. Next, a three-dimensional model based on this scheme was developed by operator splitting of locally one-dimensional calculations. The final stage is a validation study of the proposed model. The composite model consists of a wind field model, a model for the jet stream from a tunnel portal, and a model for the diffusion and advection of pollutants. The calculated concentrations near a tunnel portal have been compared to air tracer experimental data for two actual tunnels: the Ninomiya and the Hitachi Tunnels. Good evaluation scores were obtained for the Ninomiya Tunnel. Since predictive performance for the Hitachi Tunnel was not sufficient, some additional refinements of the model may be necessary.