Simulation of rail yard emissions transport to the near-source environment

Özet

Rail yards are important nodes in the freight transportation network. However, they are also a focus ofpublic health concern when located in highly populated areas. Field characterization of near-rail yard airquality is challenging due to spatially- and temporally-variable emissions. Numerical models can providevaluable insight into factors affecting emission dispersion and resulting near-field air pollution. Thisstudy utilizes computational fluid dynamics (CFD) modeling to investigate near-field air pollution surroundinga generic, moderate-sized intermodal rail yard with emissions of a neutrally buoyant gaseouspollutant. Rail yard and surrounding neighborhood structures were added in succession to a base case tostudy the influence of surface roughness on the generic pollutant's spatial concentration profile. Aspatially weighted emissions scenario revealed highly variable pollutant levels in downwind neighborhoods,strongly affected by wind direction. Rail yard topography resulted in a modest increase in nearfieldpollution levels. Densely located two-story homes surrounding the rail yard reduced downwindconcentrations by 16% and 15% at 25 m and 100 m downwind of the rail yard boundary, respectively. A6 m boundary wall surrounding the rail yard, with four open sections enabling traffic flow, reduceddownwind pollution levels by 25% and 12% at 25 m and 100 m downwind, respectively. While averagepollution levels were lower with the addition of neighborhoods and a surrounding boundary wall, highspatial variability in pollution levels resulted in some near-field areas experiencing increased pollutionthat are offset by reductions in other areas.