Large-eddy simulation of the optimal street-tree layout for pedestrian-level aerosol particle concentrations – A case study from a city-boulevard

Visa fullständig post



Permalänk

http://hdl.handle.net/10138/315086

Citation

Karttunen , S , Kurppa , M , Auvinen , M , Hellsten , A & Järvi , L 2020 , ' Large-eddy simulation of the optimal street-tree layout for pedestrian-level aerosol particle concentrations – A case study from a city-boulevard ' , Atmospheric Environment. X , vol. 6 , 100073 . https://doi.org/10.1016/j.aeaoa.2020.100073

Titel: Large-eddy simulation of the optimal street-tree layout for pedestrian-level aerosol particle concentrations – A case study from a city-boulevard
Författare: Karttunen, Sasu; Kurppa, Mona; Auvinen, Mikko; Hellsten, Antti; Järvi, Leena
Upphovmannens organisation: INAR Physics
Urban meteorology
Institute for Atmospheric and Earth System Research (INAR)
Helsinki Institute of Sustainability Science (HELSUS)
Helsinki Institute of Urban and Regional Studies (Urbaria)
Datum: 2020-04-07
Språk: eng
Sidantal: 15
Tillhör serie: Atmospheric Environment. X
ISSN: 2590-1621
DOI: https://doi.org/10.1016/j.aeaoa.2020.100073
Permanenta länken (URI): http://hdl.handle.net/10138/315086
Abstrakt: Street vegetation has been found to have both positive and negative impacts on pedestrian-level air quality, but the net effect has remained unclear. In this study, the effect of street trees on aerosol mass (PM10 and PM2.5) and number in a boulevard-type street canyon with high traffic volumes in Helsinki is examined using the large-eddy simulation model PALM. Including a detailed aerosol module and a canopy module to comprise permeable trees, PALM allows to examine the effect of street trees in depth. The main aim is to understand the relative importance of dry deposition and the aerodynamic impact of street trees on the different aerosol measures at pedestrian-level and to find a suitable street-tree layout that would minimise the pedestrian-level aerosol particle concentrations over the boulevard pavements. The layout scenarios were decided together with urban planners who needed science-based knowledge to support the building of new neighbourhoods with boulevard-type streets in Helsinki. Two wind conditions with wind being parallel and perpendicular to the boulevard under neutral atmospheric stratification are examined. Adding street trees to the boulevard increases aerosol particle concentrations on the pavements up to 123%, 72% and 53% for PM10, PM2.5 and total number, respectively. This shows decreased ventilation to be more important for local aerosol particle concentrations than dry deposition on vegetation. This particularly for PM10 and PM2.5 whereas for aerosol number, dominated by small particles, the importance of dry deposition increases. Therefore the studied aerosol measure is important when the effect of vegetation on pedestrian-level air quality is quantified. Crown volume fraction in the street space is one of the main determining factors for elevated mass concentrations on the pavements. The lowest pedestrian-level mass concentrations are seen with three rows of trees of variable height, whereas the lowest number concentrations with four rows of uniform trees. The tree-height variation allows stronger vertical turbulent transport with parallel wind and largest volumetric flow rates with perpendicular wind. Introducing low (height <1 m) hedges under trees between the traffic lanes and pavements is found to be a less effective mitigation method for particle mass than introducing tree-height variability, and for particle number less effective than maximising the tree volume in the street canyon. The results show how street trees in a boulevard-type street canyon lead to decreased pedestrian-level air quality with the effect being particularly strong for larger aerosol particles. However, with careful planning of the street vegetation, significant reductions in pedestrian-level aerosol particle concentrations can be obtained.
Subject: 1172 Environmental sciences
1171 Geosciences
CFD
LES
Pollutant dispersion
Street canyon
Urban vegetation
Urban ventilation
WIND
QUALITY
URBAN CANOPY
CANYONS
AIR-POLLUTANT DISPERSION
DRY DEPOSITION SCHEME
VENTILATION
CFD SIMULATION
TURBULENT-FLOW
VEGETATION
Referentgranskad: Ja
Licens: cc_by_nc_nd
Användningsbegränsning: openAccess
Parallelpublicerad version: acceptedVersion


Filer under denna titel

Totalt antal nerladdningar: Laddar...

Filer Storlek Format Granska
1_s2.0_S2590162120300125_main.pdf 1.833Mb PDF Granska/Öppna
1_s2.0_S2590162120300125_main.pdf 1.969Mb PDF Granska/Öppna

Detta dokument registreras i samling:

Visa fullständig post