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An experiment was carried out using a scale model of a tall building, with the goal of investigating the role of individual buildings in the dispersion of air pollution. Pollutant dispersion around an isolated building with a height-to-length aspect ratio of 1.4 is investigated using simultaneous particle image velocimetry and planar laser induced fluorescence. Dye is released from a ground-level point source five building heights upstream of the tall building. It was found that in this case the scalar plume was dispersed laterally strongly by the building, but only slightly vertically. It is hypothesized that this is due to 94% of the plume impinging below the stagnation point on the front of the building and being drawn into the horseshoe vortex. We expect this fraction would be lower in a case in which the building is in an array of smaller buildings, and that this would lead to more vertical dispersion. [ABSTRACT FROM AUTHOR]

The Kwinana Coastal Fumigation Study took place in early 1995 at Kwinana near Perth in Western Australia. The study involved surface and elevated meteorological and plume fumigation measurements in sea-breeze flows near the coast, and has yielded a comprehensive data set that is suitable for assessing meteorological and plume dispersion models. In this paper, we simulate the meteorology and turbulence on four case study days, and compare model results with the detailed surface and aircraft measurements taken during the study. These days had surface synoptic winds ranging from southerly to northeasterly, with either stable or near-neutral temperature profiles over the sea. The model used was based on that developed by Hurley ( Boundary-Layer Meteorol. 83, 43–73, 1997), but extended here to allow domain nesting, optional non-hydrostatic simulations, and a vegetative canopy at the surface. The model was forced by standard weather service synoptic data, and the simulations have captured the essential features of the strong sea-breeze circulation observed on these days. The boundary-layer structure over the sea was predicted to be near-neutral or stable in agreement with the observations on the particular day. The wind speed and direction in the sea-breeze flow were generally predicted well, although the predicted maximum inflow speed over the land was a little too high. The potential temperature was generally over-predicted, but temperature gradients agreed well. Predicted turbulence levels in the bottom-half of the thermal internal boundary layer compared well to the observations, but under-estimated the observations in the in the upper half of this layer. Near-surface measurements of meteorological variables were predicted well over the entire diurnal cycle, although the predicted sea-breeze onset was generally too early. A quantitative model evaluation for the near-surface sites showed the model performance to be better than that from other studies, with Index of Agreement (IOA) values of 0.8 (wind speed) and 0.96 (temperature), compared with values of 0.5–0.6 (wind speed) and 0.33 (temperature) obtained from other studies. The availability of new higher resolution synoptic analyses should obviate the lack of spatial and temporal resolution in synoptic inputs. The incorporation of these higher resolution synoptic inputs and new parameterisation schemes should improve future model performance. [ABSTRACT FROM AUTHOR]

Effects of stratocumulus clouds on the dispersion of contaminants are studied in the nocturnal atmospheric boundary layer. The study is based on a large-eddy simulation (LES) model with a bulk parametrization of clouds. Computations include Lagrangian calculations of atmospheric dispersion of a passive tracer released from point sources at various heights above the ground. The results obtained show that the vertical diffusion is non-Gaussian and depends on the location of a source in the boundary layer. [ABSTRACT FROM AUTHOR]