# Effects of Roof-Edge Roughness on Air Temperature and Pollutant Concentration in Urban Canyons

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## Abstract

The influence of roof-edge roughness elements on airflow, heat transfer, and street-level pollutant transport inside and above a two-dimensional urban canyon is analyzed using an urban energy balance model coupled to a large-eddy simulation model. Simulations are performed for cold (early morning) and hot (mid afternoon) periods during the hottest month of the year (August) for the climate of Abu Dhabi, United Arab Emirates. The analysis suggests that early in the morning, and when the tallest roughness elements are implemented, the temperature above the street level increases on average by 0.5 K, while the pollutant concentration decreases by 2% of the street-level concentration. For the same conditions in mid afternoon, the temperature decreases conservatively by 1 K, while the pollutant concentration increases by 7% of the street-level concentration. As a passive or active architectural solution, the roof roughness element shows promise for improving thermal comfort and air quality in the canyon for specific times, but this should be further verified experimentally. The results also warrant a closer look at the effects of mid-range roughness elements in the urban morphology on atmospheric dynamics so as to improve parametrizations in mesoscale modelling.

## Keywords

Energy balance model Large-eddy simulation Mid-range roughness element Urban canyon Urban micro-climatology## Notes

### Acknowledgements

Useful discussions with Leon Glicksman and Christoph Reinhart are acknowledged. We thank Kathleen Ross for assisting Amir A. Aliabadi and Leslie K. Norford with arrangements for travelling to United Arab Emirates for a relevant workshop in Masdar Institute of Science and Technology. Assistance of Ricky Leiserson and Philip Thompson with the setting up of the simulation platform is appreciated at Massachusetts Institute of Technology (MIT). We thank Matthew Kent and Joel Best with the setting up of the simulation platform at the University of Guelph. The help of Muhammad Tauha Ali in field installations and measurements is acknowledged. We thank the reviewers of the manuscript for their careful comments. E. Scott Krayenhoff was supported by NSF Sustainability Research Network (SRN) Cooperative Agreement 1444758 and NSF SES-1520803. This work was partially funded by a Cooperative Agreement between the Masdar Institute of Science and Technology, Abu Dhabi, United Arab Emirates and the Massachusetts Institute of Technology, Cambridge, MA, USA and by the National Research Foundation Singapore through the Singapore MIT Alliance for Research and Technology’s Centre for Environmental Sensing and Modelling interdisciplinary research program.

## References

- Aliabadi AA, Staebler RM, de Grandpré J, Zadra A, Vaillancourt PA (2016a) Comparison of estimated atmospheric boundary layer mixing height in the Arctic and southern Great Plains under statically stable conditions: experimental and numerical aspects. Atmos-Ocean 54(1):60–74CrossRefGoogle Scholar
- Aliabadi AA, Staebler RM, Liu M, Herber A (2016b) Characterization and parametrization of Reynolds stress and turbulent heat flux in the stably-stratified lower Arctic troposphere using aircraft measurements. Boundary-Layer Meteorol 161(1):99–126CrossRefGoogle Scholar
- Armstrong PR, Jiang W, Winiarski D, Katipamula S, Norford LK (2009) Efficient low-lift cooling with radiant distribution, thermal storage, and variable-speed chiller controls-part II: annual use and energy savings. HVAC&R Res 15(2):402–432CrossRefGoogle Scholar
- Arnfield AJ (2003) Two decades of urban climate research: a review of turbulence, exchanges of energy and water, and the urban heat island. Int J Climatol 23(1):1–26CrossRefGoogle Scholar
- Balogun AA, Tomlin AS, Wood CR, Barlow JF, Belcher SE, Smalley RJ, Lingard JJN, Arnold SJ, Dobre A, Robins AG, Martin D, Shallcross DW (2010) In-street wind direction variability in the vicinity of a busy intersection in central London. Boundary-Layer Meteorol 136(3):489–513CrossRefGoogle Scholar
- Blackman K, Perret L, Savory E, Piquet T (2015) Field and wind tunnel modeling of an idealized street canyon flow. Atmos Environ 106:139–153CrossRefGoogle Scholar
- Bredberg J (2000) On the wall boundary condition for turbulence models. Internal report 00/4, Department of Thermo and Fluid Dynamics, Chalmers University of Technology, Göteborg, Sweden, 21 ppGoogle Scholar
- Bueno B, Norford L, Hidalgo J, Pigeon G (2012) The urban weather generator. J Build Perf Simulat 6(4):269–281CrossRefGoogle Scholar
- Castro IP, Robins AG (1977) The flow around a surface-mounted cube in uniform and turbulent streams. J Fluid Mech 79(2):307–335CrossRefGoogle Scholar
- Cheng H, Castro IP (2002) Near wall flow over urban-like roughness. Boundary-Layer Meteorol 104(2):229–259CrossRefGoogle Scholar
- Christen A, Rotach MW, Vogt R (2009) The budget of turbulent kinetic energy in the urban roughness sublayer. Boundary-Layer Meteorol 131(2):193–222CrossRefGoogle Scholar
- Coceal O, Thomas TG, Castro IP, Belcher SE (2006) Mean flow and turbulence statistics over groups of urban-like cubical obstacles. Boundary-Layer Meteorol 121(3):491–519CrossRefGoogle Scholar
- Efros V (2006) Large eddy simulation of channel flow using wall functions. Thesis, Department of Thermo and Fluid Dynamics, Chalmers University of Technology, Göteborg, Sweden, 37 ppGoogle Scholar
- Eliasson I, Offerle B, Grimmond CSB, Lindqvist S (2006) Wind fields and turbulence statistics in an urban street canyon. Atmos Environ 40(1):1–16CrossRefGoogle Scholar
- Flores F, Gerreaud R, Munoz RC (2013) CFD simulations of turbulent buoyant atmospheric flows over complex geometry: solver development in OpenFOAM. Comput Fluids 82:1–13CrossRefGoogle Scholar
- Giometto MG, Christen A, Meneveau C, Fang J, Krafczyk M, Parlange MB (2016) Spatial characteristics of roughness sublayer mean flow and turbulence over a realistic urban surface. Boundary-Layer Meteorol 160(3):425–452CrossRefGoogle Scholar
- Goodfriend E, Katopodes Chow F, Vanella M, Balaras E (2016) Large-eddy simulation of flow through an array of cubes with local grid refinement. Boundary-Layer Meteorol 159(2):285–303CrossRefGoogle Scholar
- Greenshields CJ (2015) OpenFOAM: The Open Source CFD Toolbox, User Guide, Version 3.0.1. Tech. rep., OpenFOAM Foundation Ltd., PO Box 56676, London, W13 3DB, UK, 230 ppGoogle Scholar
- Hamdi R, Masson V (2008) Inclusion of a drag approach in the town energy balance (TEB) scheme: offline 1D evaluation in a street canyon. J Appl Meteorol Clim 47:2627–2644CrossRefGoogle Scholar
- Hanna S, Chang J (2012) Acceptance criteria for urban dispersion model evaluation. Meteorol Atmos Phys 116(3):133–146CrossRefGoogle Scholar
- Harman IN, Barlow JF, Belcher SE (2004) Scalar fluxes from urban street canyons part II: model. Boundary-Layer Meteorol 113(3):387–409CrossRefGoogle Scholar
- Huang Y, Hu X, Zeng N (2009) Impact of wedge-shaped roofs on airflow and pollutant dispersion inside urban street canyons. Build Environ 44(12):2335–2347CrossRefGoogle Scholar
- Huang YD, He WR, Kim CN (2015) Impacts of shape and height of upstream roof on airflow and pollutant dispersion inside an urban street canyon. Environ Sci Pollut R 22(3):2117–2137CrossRefGoogle Scholar
- Inagaki A, Kanda M (2008) Turbulent flow similarity over an array of cubes in near-neutrally stratified atmospheric flow. J Fluid Mech 615:101–120CrossRefGoogle Scholar
- Jayatillaka CLV (1969) The influence of Prandtl number and surface roughness on the resistance of the laminar sublayer to momentum and heat transfer. Prog Heat Mass Transfer 1:193Google Scholar
- Kanda M, Moriwaki R, Kasamatsu F (2004) Large-eddy simulation of turbulent organized structures within and above explicitly resolved cube arrays. Boundary-Layer Meteorol 112(2):343–368CrossRefGoogle Scholar
- Kastner-Klein P, Berkowicz R, Britter R (2004) The influence of street architecture on flow and dispersion in street canyons. Meteorol Atmos Phys 87(1):121–131Google Scholar
- Kim JJ, Baik JJ (2003) Effects of inflow turbulence intensity on flow and pollutant dispersion in an urban street canyon. J Wind Eng Ind Aerodyn 91(3):309–329CrossRefGoogle Scholar
- Klein P, Clark JV (2007) Flow variability in a North American downtown street canyon. J Appl Meteorol Clim 46:851–877CrossRefGoogle Scholar
- Klein PM, Galvez JM (2015) Flow and turbulence characteristics in a suburban street canyon. Environ Fluid Mech 15(2):419–438CrossRefGoogle Scholar
- Krayenhoff ES, Voogt JA (2007) A microscale three-dimensional urban energy balance model for studying surface temperatures. Boundary-Layer Meteorol 123(3):433–461CrossRefGoogle Scholar
- Krayenhoff ES, Voogt JA (2010) Impacts of urban albedo increase on local air temperature at daily-annual time scales: model results and synthesis of previous work. J Appl Meteorol Clim 49:1634–1648CrossRefGoogle Scholar
- Krayenhoff ES, Santiago JL, Martilli A, Christen A, Oke TR (2015) Parametrization of drag and turbulence for urban neighbourhoods with trees. Boundary-Layer Meteorol 156(2):157–189CrossRefGoogle Scholar
- Krpo A, Salamanca F, Martilli A, Clappier A (2010) On the impact of anthropogenic heat fluxes on the urban boundary layer: a two-dimensional numerical study. Boundary-Layer Meteorol 136(1):105–127CrossRefGoogle Scholar
- Kusaka H, Kondo H, Kikegawa Y, Kimura F (2001) A simple single-layer urban canopy model for atmospheric models: comparison with multi-layer and slab models. Boundary-Layer Meteorol 101(3):329–358CrossRefGoogle Scholar
- Launder BE, Spalding DB (1974) The numerical computation of turbulent flows. Comput Meth Appl Mech Eng 3(2):269–289CrossRefGoogle Scholar
- Lemonsu A, Grimmond CSB, Masson V (2004) Modeling the surface energy balance of the core of an old mediterranean city: Marseille. J Appl Meteorol 43:312–327CrossRefGoogle Scholar
- Li XX, Leung DYC, Liu CH, Lam KM (2008) Physical modeling of flow field inside urban street canyons. J Appl Meteorol Clim 47:2058–2067CrossRefGoogle Scholar
- Li XX, Britter RE, Koh TY, Norford LK, Liu CH, Entekhabi D, Leung DYC (2010) Large-eddy simulation of flow and pollutant transport in urban street canyons with ground heating. Boundary-Layer Meteorol 137(2):187–204CrossRefGoogle Scholar
- Li XX, Britter RE, Norford LK, Koh TY, Entekhabi D (2012) Flow and pollutant transport in urban street canyons of different aspect ratios with ground heating: large-eddy simulation. Boundary-Layer Meteorol 142(2):289–304CrossRefGoogle Scholar
- Louka P, Belcher SE, Harrison RG (2000) Coupling between air flow in streets and the well-developed boundary layer aloft. Atmos Environ 34(16):2613–2621CrossRefGoogle Scholar
- Martilli A, Santiago JL (2007) CFD simulation of airflow over a regular array of cubes. part II: analysis of spatial average properties. Boundary-Layer Meteorol 122(3):635–654CrossRefGoogle Scholar
- Martilli A, Clappier A, Rotach MW (2002) An urban surface exchange parameterisation for mesoscale models. Boundary-Layer Meteorol 104(2):261–304CrossRefGoogle Scholar
- Masson V (2000) A physically-based scheme for the urban energy budget in atmospheric models. Boundary-Layer Meteorol 94(3):357–397CrossRefGoogle Scholar
- Masson V, Grimmond CSB, Oke TR (2002) Evaluation of the town energy balance (TEB) scheme with direct measurements from dry districts in two cities. J Appl Meteorol 41:1011–1026CrossRefGoogle Scholar
- Masson V, Gomes L, Pigeon G, Liousse C, Pont V, Lagouarde JP, Voogt J, Salmond J, Oke TR, Hidalgo J, Legain D, Garrouste O, Lac C, Connan O, Briottet X, Lachérade S, Tulet P (2008) The Canopy and Aerosol Particles Interactions in TOlouse Urban Layer (CAPITOUL) experiment. Meterol Atmos Phys 102:135–157CrossRefGoogle Scholar
- Nakamura Y, Oke TR (1988) Wind, temperature and stability conditions in an east-west oriented urban canyon. Atmos Environ 22(12):2691–2700CrossRefGoogle Scholar
- Nazarian N, Kleissl J (2016) Realistic solar heating in urban areas: air exchange and street-canyon ventilation. Build Environ 95:75–93CrossRefGoogle Scholar
- Rafailidis S (1997) Influence of building areal density and roof shape on the wind characteristics above a town. Boundary-Layer Meteorol 85(2):255–271CrossRefGoogle Scholar
- Raupach MR, Thom AS, Edwards I (1980) A wind-tunnel study of turbulent flow close to regularly arrayed rough surfaces. Boundary-Layer Meteorol 18(4):373–397CrossRefGoogle Scholar
- Reynolds AJ (1975) The prediction of turbulent Prandtl and Schmidt numbers. Int J Heat Mass Transfer 18(9):1055–1069CrossRefGoogle Scholar
- Roache PJ (1997) Quantification of uncertainty in computational fluid dynamics. Annu Rev Fluid Mech 29:123–160CrossRefGoogle Scholar
- Rotach MW, Vogt R, Bernhofer C, Batchvarova E, Christen A, Clappier A, Feddersen B, Gryning SE, Martucci G, Mayer H, Mitev V, Oke TR, Parlow E, Richner H, Roth M, Roulet YA, Ruffieux D, Salmond JA, Schatzmann M, Voogt JA (2005) BUBBLE-an urban boundary layer meteorology project. Theor Appl Climatol 81(3):231–261CrossRefGoogle Scholar
- Rotta JC (1964) Temperaturverteilungen in der turbulenten grenzschicht an der ebenen Platte. Int J Heat Mass Transfer 7(2):215–228CrossRefGoogle Scholar
- Roulet YA, Martilli A, Rotach MW, Clappier A (2005) Validation of an urban surface exchange parameterization for mesoscale models-1D case in a street canyon. J Appl Meteorol 44:1484–1498CrossRefGoogle Scholar
- Saathoff P, Gupta A, Stathopoulos T, Lazure L (2009) Contamination of fresh air intakes due to downwash from a rooftop structure. J Air Waste Manag Assoc 59(3):343–353CrossRefGoogle Scholar
- Santiago JL, Martilli A (2010) A dynamic urban canopy parameterization for mesoscale models based on computational fluid dynamics Reynolds-averaged Navier-Stokes microscale simulations. Boundary-Layer Meteorol 137(3):417–439CrossRefGoogle Scholar
- Santiago JL, Martilli A, Martin F (2007) CFD simulation of airflow over a regular array of cubes. Part I: three-dimensional simulation of the flow and validation with wind-tunnel measurements. Boundary-Layer Meteorol 122(3):609–634CrossRefGoogle Scholar
- Santiago JL, Coceal O, Martilli A (2013) How to parametrize urban-canopy drag to reproduce wind-direction effects within the canopy. Boundary-Layer Meteorol 149(1):43–63CrossRefGoogle Scholar
- Santiago JL, Krayenhoff ES, Martilli A (2014) Flow simulations for simplified urban configurations with microscale distributions of surface thermal forcing. Urban Clim 9:115–133CrossRefGoogle Scholar
- Tabor GR, Baba-Ahmadi MH (2010) Inlet conditions for large eddy simulation: a review. Comput Fluids 39(4):553–567CrossRefGoogle Scholar
- Takano Y, Moonen P (2013) On the influence of roof shape on flow and dispersion in an urban street canyon. J Wind Eng Ind Aerodyn 123((Part A)):107–120Google Scholar
- Tominaga Y, Stathopoulos T (2013) CFD simulation of near-field pollutant dispersion in the urban environment: a review of current modeling techniques. Atmos Environ 79:716–730CrossRefGoogle Scholar
- Uehara K, Murakami S, Oikawa S, Wakamatsu S (2000) Wind tunnel experiments on how thermal stratification affects flow in and above urban street canyons. Atmos Environ 34(10):1553–1562CrossRefGoogle Scholar
- van Driest ER (1956) On turbulent flow near a wall. J Aeronaut Sci 23(11):1007–1011CrossRefGoogle Scholar
- Vardoulakis S, Fisher BEA, Pericleous K, Gonzalez-Flesca N (2003) Modelling air quality in street canyons: a review. Atmos Environ 37(2):155–182CrossRefGoogle Scholar
- White FM (2003) Fluid mechanics, 5th edn. McGraw-Hill Higher Education, New York, 866 ppGoogle Scholar
- Yaghoobian N, Kleissl J, Paw-U KT (2014) An improved three-dimensional simulation of the diurnally varying street-canyon flow. Boundary-Layer Meteorol 153(2):251–276CrossRefGoogle Scholar
- Yassin MF (2011) Impact of height and shape of building roof on air quality in urban street canyons. Atmos Environ 45(29):5220–5229CrossRefGoogle Scholar
- Yuan C, Ng E, Norford LK (2014) Improving air quality in high-density cities by understanding the relationship between air pollutant dispersion and urban morphologies. Build Environ 71:245–258CrossRefGoogle Scholar