Neighbourhood-Scale Flow Regimes and Pollution Transport in Cities

Edward J. Bannister, Xiaoming Cai, Jian Zhong, A. Rob Mackenzie

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Cities intimately intermingle people and air pollution. It is very difficult to monitor or model neighbourhood-scale pollutant transport explicitly. One computationally efficient way is to treat neighbourhoods as patches of porous media to which the flow adjusts. Here we use conceptual arguments and large-eddy simulation to formulate two flow regimes based on the size of patches of different frontal-area density within neighbourhoods. One of these flow regimes distributes pollutants in counter-intuitive ways, such as producing pollution ‘hot spots’ in patches of lower frontal-area density. The regimes provide the first quantitative definition of the ‘urban background’, which can be used for more precisely targeted pollution monitoring. They also provide a conceptual basis for further research into neighbourhood-scale air-pollution problems, such as parametrizations in mesoscale models, and the transport of fluid constituents in other porous media.
Original languageEnglish
Pages (from-to)259-289
Number of pages31
JournalBoundary-Layer Meteorology
Issue number2
Early online date24 Dec 2020
Publication statusPublished - 1 May 2021

Bibliographical note

Funding Information:
The authors thank two anonymous reviewers for constructive comments that helped improve the presentation of the ideas in this manuscript. The authors are grateful to Chantal Jackson for her expertise in redrawing several figures in this paper and to Dr Steve Jones for his helpful comments on later drafts of the work. The authors thank the Natural Environment Research Council for funding this research under grant references NE/L002493/1 and NE/S003487/1. Author contributions: XMC and EJB conceived of the study; JZ adapted and debugged the model; EJB performed model runs, analyzed and presented the data, and wrote the original draft; all authors (a) reviewed and edited drafts; and (b) contributed to refining the methodology. The authors declare no competing interests. Please contact the corresponding author for data, code, and other materials used in this study. The computations described in this paper were performed using the University of Birmingham’s BlueBEAR high-performance-computing service.

Publisher Copyright:
© 2020, The Author(s).


  • Neighbourhood scale
  • Scalar transport
  • Urban background
  • Urban canopy
  • Urban pollution


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