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Effects of Wind Shear on Pollution Dispersion

机译：风切变对污染扩散的影响

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Using an accurate numerical method for simulating advection and diffusion of pollution puffs, itrnis demonstrated that relatively small changes in wind speeds or direction with height inducesrnappreciable horizontal dispersion that cannot be accurately simulated using classical puffrndiffusion models. Using idealized winds, it is shown that individual puffs of pollutionrnpreferentially disperse in the horizontal direction aligned with the mean wind shear vector in thernatmospheric planetary boundary layer (PBL). Even if wind directions are constant in the PBL, thernspeed shear in the lowest constant flux surface layer induces appreciable horizontal dispersionrnalong the mean wind direction. Using a more realistic and typical observed late afternoon PBLrnwind profile, it is shown that a Lagrangian puff model cannot reasonably simulate the observedrntransport and dispersion of a puff of pollution for a 3-4 hour period. These results suggest thatrnshear-related dispersion effects are probably the dominant mechanism of horizontal dispersion inrnthe atmosphere. For assessing long-range dispersion of atmospheric pollutants, the commonrnassumption that pollutants disperse as spherical “puffs” is inherently inaccurate since the effectsrnof horizontal dispersion along the direction of ambient wind shear experienced by a dispersingrnpollution puff are not accurately accounted for. If a puff model is used to assess long rangerntransport and dispersion, it is demonstrated that if peak concentrations are correctly simulated,rnthen the overall area impacted by pollution will be severely skewed, and there will be many areasrnwhere concentrations are severely over- or under-estimated. If larger horizontal puff dispersionsrnare assumed so as to encompass the actual impact area, then peak concentrations calculated byrnLagrangian puff model are severely underestimated. These results suggest that horizontalrndispersion of pollutants should be proportional to the wind shear across the vertical depth of thernatmosphere containing pollutants.
机译：Itrnis使用一种精确的数值方法来模拟污染吹的对流和扩散，证明风速或风向随高度的变化相对较小，会引起可观的水平弥散，而传统的吹扩散模型无法准确地模拟这种弥散。使用理想化的风，表明在大气层行星边界层（PBL）中，与自然风切变矢量一致的水平方向上的单个污染物优先分散。即使在PBL中风向是恒定的，在最低恒定通量表层的热切变也会在平均风向范围内引起明显的水平散布。使用更现实和典型的下午晚些时候的PBLn风廓线，表明拉格朗日粉扑模型不能合理地模拟3-4小时内观察到的粉扑污染的传播和扩散。这些结果表明，与剪切有关的弥散效应可能是大气中水平弥散的主要机制。在评估大气污染物的远距离扩散时，污染物作为球形“粉扑”扩散的常见假设本质上是不准确的，因为不能准确地解释沿污染物扩散粉尘沿环境风切变方向的水平扩散效应。如果使用吹气模型评估长距离的运输和扩散，则表明如果正确模拟了峰值浓度，那么受污染影响的整个区域将严重偏斜，并且将有许多区域的浓度严重过高或过低。估计。如果假定较大的水平粉扑弥散度包含实际影响区域，则严重低估了由拉格朗日粉扑模型计算出的峰值浓度。这些结果表明，污染物的水平分布应与含污染物的大气垂直深度上的风切变成正比。

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