Boundary-Layer Meteorology

, Volume 147, Issue 2, pp 281–300 | Cite as

Pollutant Plume Dispersion in the Atmospheric Boundary Layer over Idealized Urban Roughness

  • Colman C. C. Wong
  • Chun-Ho Liu


The Gaussian model of plume dispersion is commonly used for pollutant concentration estimates. However, its major parameters, dispersion coefficients, barely account for terrain configuration and surface roughness. Large-scale roughness elements (e.g. buildings in urban areas) can substantially modify the ground features together with the pollutant transport in the atmospheric boundary layer over urban roughness (also known as the urban boundary layer, UBL). This study is thus conceived to investigate how urban roughness affects the flow structure and vertical dispersion coefficient in the UBL. Large-eddy simulation (LES) is carried out to examine the plume dispersion from a ground-level pollutant (area) source over idealized street canyons for cross flows in neutral stratification. A range of building-height-to-street-width (aspect) ratios, covering the regimes of skimming flow, wake interference, and isolated roughness, is employed to control the surface roughness. Apart from the widely used aerodynamic resistance or roughness function, the friction factor is another suitable parameter that measures the drag imposed by urban roughness quantitatively. Previous results from laboratory experiments and mathematical modelling also support the aforementioned approach for both two- and three-dimensional roughness elements. Comparing the UBL plume behaviour, the LES results show that the pollutant dispersion strongly depends on the friction factor. Empirical studies reveal that the vertical dispersion coefficient increases with increasing friction factor in the skimming flow regime (lower resistance) but is more uniform in the regimes of wake interference and isolated roughness (higher resistance). Hence, it is proposed that the friction factor and flow regimes could be adopted concurrently for pollutant concentration estimate in the UBL over urban street canyons of different roughness.


Atmospheric boundary layer Computational fluid dynamics  Large-eddy simulation Pollutant plume dispersion  Two-dimensional street canyons  Urban roughness elements 



This study was jointly supported by the Strategic Research Areas and Themes, Computational Sciences, and the University Research Committee Seed Funding Programme of Basic Research 200910159028 of the University of Hong Kong. The computation is supported in part by a Hong Kong UGC Special Equipment Grant (SEG HKU09). The technical support from Lillian Y.L. Chan, Frankie F.T. Cheung, Tony W.K. Cheung, and W.K. Kwan with HKUCC is appreciated.


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Copyright information

© Springer Science+Business Media Dordrecht 2012

Authors and Affiliations

  1. 1.Department of Mechanical EngineeringThe University of Hong KongHong KongChina

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