Upwind Noise Barriers Reduce Near-Road Air Pollution Concentrations

We propose a dispersion model to estimate the impact of an upwind solid noise barrier next to a highway on air pollution concentrations downwind of the road.  The model is based on data from wind tunnel experiments conducted by Heist et al. (2009).  The model assumes that the upwind barrier has two main effects: 1) it creates a recirculation zone behind the barrier that sweeps the emissions from the highway back towards the wall, and 2) it enhances vertical dispersion and initial mixing.  By combining the upwind barrier model with the mixed wake model for a downwind barrier described in Schulte et al. (2014), we are able to model dispersion of emissions from a highway with noise barriers on both sides.  The model provides a good description of measurements made in the wind tunnel. The presence of an upwind barrier causes reductions in concentrations relative to those measured downwind of a road with no barriers. The reduction can be as large as that caused by a downwind barrier if the recirculation zone covers the width of the highway. Barriers on both sides of the highway result in larger reductions downwind of the barriers than those caused by a single barrier either upwind or downwind. As expected, barrier effects become small beyond 10 barrier heights downwind of the highway.