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Article: On the mechanism of air pollutant re-entrainment in two-dimensional idealized street canyons

TitleOn the mechanism of air pollutant re-entrainment in two-dimensional idealized street canyons
Authors
KeywordsAir exchange rate ACH
Local pollutant exchange rate ω
Pollutant exchange rate PCH
Street canyons
Urban canopy layer
Volume average pollutant concentration Θ
Issue Date2011
PublisherPergamon. The Journal's web site is located at http://www.elsevier.com/locate/atmosenv
Citation
Atmospheric Environment, 2011, v. 45 n. 27, p. 4763-4769 How to Cite?
AbstractThe two-dimensional (2D) idealized street canyon, which is the generic unit of a city, is the platform for our fundamental understanding of ventilation and pollutant removal at the neighborhood scale. The building-height-to-street-width aspect ratio h/. b is the key geometric parameters affecting the flow structures in a street canyon. In this study, a series of computational fluid dynamics (CFD) sensitivity tests were performed to examine how the air pollutant concentration in a street canyon is related to the aspect ratio. The Reynolds-averaged Navier-Stokes (RANS) equations and the Renormalization Group (RNG) k-ε turbulence model were used in the mathematical model. The spatial behaviors of air pollutant transport from the facades, streets, and roofs to the shear layer were depicted by the local pollutant exchange rate ω. Besides, the bulk quantities, air exchange rate ACH, pollutant exchange rate PCH, and volume average pollutant concentration Θ, were used to elucidate the ventilation and pollutant removal mechanisms of the street canyon. The aspect ratios tested were in the range 0.067 ≤ h/. b ≤ 2.5 that covered the isolated roughness, wake interference and skimming flow regimes in 2D street canyons. A local maximum Θ was determined in 0.2 ≤ h/. b ≤ 0.5 that is different from the monotonic ACH or PCH. The CFD results showed that the mildly elevated air pollutant concentration is not caused by poor pollutant removal but the pollutant re-entrainment from the shear layer aloft back into the street canyon. It is thus suggested that ACH, PCH, and Θ should be used as complementary indicators. © 2010 Elsevier Ltd.
Persistent Identifierhttp://hdl.handle.net/10722/124868
ISSN
2015 Impact Factor: 3.459
2015 SCImago Journal Rankings: 1.999
ISI Accession Number ID
Funding AgencyGrant Number
University of Hong Kong200811159170
Funding Information:

Two anonymous reviewers provided constructive suggestions. This study was partially funded by the University Research Committee Seed Funding Programme of Basic Research 200811159170 of the University of Hong Kong.

References

 

DC FieldValueLanguage
dc.contributor.authorLiu, CHen_HK
dc.contributor.authorCheng, WCen_HK
dc.contributor.authorLeung, TCYen_HK
dc.contributor.authorLeung, DYCen_HK
dc.date.accessioned2010-10-31T10:58:37Z-
dc.date.available2010-10-31T10:58:37Z-
dc.date.issued2011en_HK
dc.identifier.citationAtmospheric Environment, 2011, v. 45 n. 27, p. 4763-4769en_HK
dc.identifier.issn1352-2310en_HK
dc.identifier.urihttp://hdl.handle.net/10722/124868-
dc.description.abstractThe two-dimensional (2D) idealized street canyon, which is the generic unit of a city, is the platform for our fundamental understanding of ventilation and pollutant removal at the neighborhood scale. The building-height-to-street-width aspect ratio h/. b is the key geometric parameters affecting the flow structures in a street canyon. In this study, a series of computational fluid dynamics (CFD) sensitivity tests were performed to examine how the air pollutant concentration in a street canyon is related to the aspect ratio. The Reynolds-averaged Navier-Stokes (RANS) equations and the Renormalization Group (RNG) k-ε turbulence model were used in the mathematical model. The spatial behaviors of air pollutant transport from the facades, streets, and roofs to the shear layer were depicted by the local pollutant exchange rate ω. Besides, the bulk quantities, air exchange rate ACH, pollutant exchange rate PCH, and volume average pollutant concentration Θ, were used to elucidate the ventilation and pollutant removal mechanisms of the street canyon. The aspect ratios tested were in the range 0.067 ≤ h/. b ≤ 2.5 that covered the isolated roughness, wake interference and skimming flow regimes in 2D street canyons. A local maximum Θ was determined in 0.2 ≤ h/. b ≤ 0.5 that is different from the monotonic ACH or PCH. The CFD results showed that the mildly elevated air pollutant concentration is not caused by poor pollutant removal but the pollutant re-entrainment from the shear layer aloft back into the street canyon. It is thus suggested that ACH, PCH, and Θ should be used as complementary indicators. © 2010 Elsevier Ltd.en_HK
dc.languageengen_HK
dc.publisherPergamon. The Journal's web site is located at http://www.elsevier.com/locate/atmosenven_HK
dc.relation.ispartofAtmospheric Environmenten_HK
dc.subjectAir exchange rate ACHen_HK
dc.subjectLocal pollutant exchange rate ωen_HK
dc.subjectPollutant exchange rate PCHen_HK
dc.subjectStreet canyonsen_HK
dc.subjectUrban canopy layeren_HK
dc.subjectVolume average pollutant concentration Θen_HK
dc.titleOn the mechanism of air pollutant re-entrainment in two-dimensional idealized street canyonsen_HK
dc.typeArticleen_HK
dc.identifier.openurlhttp://library.hku.hk:4550/resserv?sid=HKU:IR&issn=1352-2310&volume=&spage=&epage=&date=2010&atitle=On+the+mechanism+of+air+pollutant+re-entrainment+in+two-dimensional+idealized+street+canyonsen_HK
dc.identifier.emailLeung, DYC:ycleung@hku.hken_HK
dc.identifier.authorityLeung, DYC=rp00149en_HK
dc.description.naturelink_to_subscribed_fulltext-
dc.identifier.doi10.1016/j.atmosenv.2010.03.015en_HK
dc.identifier.scopuseid_2-s2.0-79960584957en_HK
dc.identifier.hkuros179338en_HK
dc.relation.referenceshttp://www.scopus.com/mlt/select.url?eid=2-s2.0-79960584957&selection=ref&src=s&origin=recordpageen_HK
dc.identifier.volume45en_HK
dc.identifier.issue27en_HK
dc.identifier.spage4763en_HK
dc.identifier.epage4769en_HK
dc.identifier.eissn1873-2844-
dc.identifier.isiWOS:000293931100024-
dc.publisher.placeUnited Kingdomen_HK
dc.identifier.scopusauthoridLiu, CH=36872527400en_HK
dc.identifier.scopusauthoridCheng, WC=24283028300en_HK
dc.identifier.scopusauthoridLeung, TCY=46761203200en_HK
dc.identifier.scopusauthoridLeung, DYC=7203002484en_HK
dc.identifier.citeulike6966831-

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