Sensitivity of AERMOD (V21112) RLINEXT dispersion model outputs by source type to variability in single noise barrier height and separation distance

The U.S. Environmental Protection Agency (USEPA) introduced the RLINEXT modeling feature in the latest versions of AERMOD (since version v21112) to predict traffic-induced pollutant concentration when noise barriers are present. The research presented in this paper explores the impacts of noise barrier characteristics on AERMOD-predicted concentrations. The research finds that because AERMOD can currently only attach one barrier to each road side, and because that barrier only impacts the source to which it is attached, it is also important to split links so that they properly pair with barriers. Given the sensitivity of AERMOD-predicted concentrations to barrier characteristics (i.e., barrier heights and distances to roadway), the research also concludes that barriers must be appropriately matched with input links. This study investigated the sensitivity of CO concentration predicted by the latest AERMOD under various noise barrier conditions (barrier heights and distances between road and barrier) and meteorological conditions (wind directions and wind speeds). The results indicate that ground-level concentration of downwind receptors decreases with increased barrier heights, and that distant barriers have less of an impact on predicted concentrations. This study also explored the impact of noise barrier on both horizontal and vertical concentration profiles, indicating that concentrations rise behind the barrier as plumes are predicted to loft over the barrier. The sensitivity analysis associated with splitting roadway links to match with barriers indicated an impact on predicted concentration for certain receptors of up to 10%, but the overall the impact on maximum concentrations was marginal.