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Reduction of air pollution concentrations due to a solid barrier downwind of a roadway: wind tunnel results and dispersion model development
Citation:
Francisco, D., D. Heist, A. Venkatram, L. Brouwer, AND S. Perry. Reduction of air pollution concentrations due to a solid barrier downwind of a roadway: wind tunnel results and dispersion model development. CMAS, Virtual, NC, November 01 - 05, 2021.
Impact/Purpose:
Reviewers abstract for the CMAS Conference
Description:
Noise barriers have been proposed as a mitigation measure to reduce human exposure to traffic-related air pollutants. This paper presents new results from wind tunnel studies examining the effect of solid roadside barriers of varying heights (from 3 m to 9 m) on concentrations downwind of a roadway. These wind tunnel results are used to further develop a mixed-wake algorithm that accounts for barrier effects within a steady-state air dispersion model. The mixed-wake algorithm combines two flow regimes, one for flow above the barrier and one for the recirculation region that develops downwind of the barrier. The regime representing the recirculation region exhibits a uniform vertical concentration profile while the concentrations in the upper regime rise to a peak above the barrier before decreasing with height. Observations of the barrier-induced flow field and concentration patterns, and the mixed-wake algorithm implemented into the air dispersion model will be described. The algorithm was implemented in the U.S. EPA regulatory air dispersion model, AERMOD, using the non-regulatory line-source option, RLINEXT. Both the wind tunnel and mixed-wake algorithm show that relative to a roadway without a barrier, a solid barrier substantially reduces concentrations immediately downwind of the barrier with the greatest reductions occurring with the tallest barriers. Model performance will be evaluated using geometric mean (MG), geometric standard deviation (SG), and the fraction of model results that are within a factor of two of the observations (FAC2).
