Evaluation of model for air pollution in the vicinity of roadside solid barriers

Roadside noise barriers and solid fences are common features along major highways in urban regions of Kazakhstan and are anticipated to have important effects on near-road air pollution through altering the dispersion of traffic emissions and resulting downstream concentrations. A 3-dimensional computational fluid dynamics (CFD) road model has been developed to simulate roadside barrier effects on near-road air quality and evaluate the influence of key variables, such as barrier height and wind direction. The CFD model is tested against experimental data and other existing models found in the literature, with several turbulence models tested to give optimal results, i.e., the standard k-ε model and the realizable k-ε model with different Schmidt numbers. The dispersion of a mixture of nitrogen oxides (denoted as NOx—a mix of NO and NO₂) was computed and the barriers were assumed to be straight and infinitely long. Dispersion of NOx was modeled for situations with no barriers along the highway, barriers on both sides, and for a single barrier on the downwind side of the highway. The modelling results are presented and discussed in relation to previous studies and the implications of the results are considered for pollution barriers along highways.