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"Dispersion modeling approaches for near road
Citation:
Heist, D., C. Hood, A. Venkatram, M. Snyder, V. Isakov, S. Perry, D. Carruthers, J. Stocker, AND S. Smith. "Dispersion modeling approaches for near road. 16th International Conference on Harmonisation within Atmospheric Dispersion Modeling for Regulatory Purposes, Varna, BULGARIA, September 08 - 11, 2014.
Impact/Purpose:
The National Exposure Research Laboratory (NERL) Atmospheric Modeling and Analysis Division (AMAD) conducts research in support of EPA mission to protect human health and the environment. AMAD research program is engaged in developing and evaluating predictive atmospheric models on all spatial and temporal scales for forecasting the air quality and for assessing changes in air quality and air pollutant exposures, as affected by changes in ecosystem management and regulatory decisions. AMAD is responsible for providing a sound scientific and technical basis for regulatory policies based on air quality models to improve ambient air quality. The models developed by AMAD are being used by EPA, NOAA, and the air pollution community in understanding and forecasting not only the magnitude of the air pollution problem, but also in developing emission control policies and regulations for air quality improvements.
Description:
Roadway design and roadside barriers can have significant effects on the dispersion of traffic-generated pollutants, especially in the near-road environment. Dispersion models that can accurately simulate these effects are needed to fully assess these impacts for a variety of applications. For example, such models can be useful for evaluating the mitigation potential of roadside barriers in reducing near-road exposures and their associated adverse health effects. Two databases, a tracer field study and a wind tunnel study, provide measurements used in the development and/or validation of algorithms to simulate dispersion in the presence of noise barriers. The tracer field study was performed in Idaho Falls, ID, USA with a 6-m noise barrier and a finite line source in a variety of atmospheric conditions. The second study was performed in the meteorological wind tunnel at the US EPA and simulated line sources at different distances from a model noise barrier to capture the effect on emissions from individual lanes of traffic. In both cases, velocity and concentration measurements characterized the effect of the barrier on dispersion.This paper presents comparisons with the two datasets of the barrier algorithms implemented in two different dispersion models: US EPA’s R-LINE (a research dispersion modelling tool under development by the US EPA’s Office of Research and Development) and CERC’s ADMS model (ADMS-Urban). In R-LINE the physical features revealed in the experiments have been used to enhance the effective surface roughness and friction velocity of the flow downwind of the barrier. The pollutant field is well-mixed below the height of the barrier and decreases exponentially above. The initial dispersion of the plume coming from the roadway is enhanced by the presence of the barrier. The ADMS algorithm considers the barrier as a one-sided street canyon; it allows for the channeling of the flow along the barrier and represents the road source as a combination of ground level and elevated sources with the weighting of the sources dependent on the wind direction and the barrier properties.