Pollutant dispersion in tree-lined canyons: aligning wind-tunnel experiments with large-eddy simulation

Pollutant dispersion in tree-lined canyons: aligning wind-tunnel experiments with large-eddy simulation | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Pollutant dispersion in tree-lined canyons: aligning wind-tunnel experiments with large-eddy simulation Sofia Fellini, Dipanjan Majumdar, Pietro Salizzoni, Maarten van Reeuwijk This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7076545/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Vegetation is increasingly integrated into urban environments to improve microclimate and air quality. However, the role of trees in pollutant dispersion within street canyons remains complex and debated. This study presents a detailed comparison between high-resolution wind tunnel experiments and large-eddy simulations (LES) using uDALES. Such a comparison is essential to validate the physical realism of numerical models and assess their ability to capture the complex, vegetation-induced interactions that govern urban ventilation and pollutant transport. The analysis includes velocity and concentration measurements in an idealised street canyon with varying tree densities. Special attention is given to the definition of reference scales for the flow and scalar fields, ensuring consistency across methods through the use of friction velocity and canyon geometry as scaling quantities. The tree drag length also proves crucial for aligning the aerodynamic resistance of physical and simulated vegetation. The simulations reproduce key features of the mean flow, both with and without trees—notably the structure and extent of large-scale recirculation cells—but tend to underestimate turbulent kinetic energy and scalar fluxes. This suggests that tree models acting solely as momentum sinks do not fully capture vegetation-induced turbulence. Despite these limitations, the LES captures the dominant ventilation mechanisms at the canyon roof. The estimated bulk exchange velocity shows no systematic dependence on tree number or drag intensity, in contrast with previous studies, highlighting the need for context-specific assessments of urban vegetation effects. Full Text Additional Declarations No competing interests reported. Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-7076545","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":483529425,"identity":"88e744de-0b98-4cdf-8990-d9db1ba7f112","order_by":0,"name":"Sofia Fellini","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA8klEQVRIie2PMQrCMBiFXwm0i9i1gqRX+KUXSvEAOnYQLBTaxQM4iMdwTik4eQAHh7o4OejWoYNJC+LSqptgviU/Sb68F8Bg+EmsUgIcQ8eKISJgyPQu9SmMlBLAZlo5QA3aoT6H6UOt6MRUKXgT42eJJSsQV4+n5Xl74rbj5iXmdadChwL5ChSoYhmFu4samAruKUbeTMoB6jBlVuqFu0INzPb6FH89RV6Dlq2y+UDBcYpiABJ2o8QfKPovxZho0qSIffOXgAQF3cWyhN2vEfmuk11G1eLEXTc/l7eadxdrs56TbBfxRnhFfnHXYDAY/oUHO11FvAQIL7IAAAAASUVORK5CYII=","orcid":"","institution":"Polytechnic University of Turin","correspondingAuthor":true,"prefix":"","firstName":"Sofia","middleName":"","lastName":"Fellini","suffix":""},{"id":483529426,"identity":"eb13fe28-673e-4ffc-b8bd-a29a9798a936","order_by":1,"name":"Dipanjan Majumdar","email":"","orcid":"","institution":"Imperial College London","correspondingAuthor":false,"prefix":"","firstName":"Dipanjan","middleName":"","lastName":"Majumdar","suffix":""},{"id":483529427,"identity":"4773c054-4cdf-4dcd-a640-8dc6b07f8894","order_by":2,"name":"Pietro Salizzoni","email":"","orcid":"","institution":"École Centrale de Lyon","correspondingAuthor":false,"prefix":"","firstName":"Pietro","middleName":"","lastName":"Salizzoni","suffix":""},{"id":483529428,"identity":"ce87b6bc-0e6e-4861-a2bd-d31beeca8f77","order_by":3,"name":"Maarten van Reeuwijk","email":"","orcid":"","institution":"Imperial College London","correspondingAuthor":false,"prefix":"","firstName":"Maarten","middleName":"van","lastName":"Reeuwijk","suffix":""}],"badges":[],"createdAt":"2025-07-08 15:53:21","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-7076545/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-7076545/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":88983531,"identity":"9af5b9dd-02eb-43e5-9c13-a81da43cd269","added_by":"auto","created_at":"2025-08-13 12:02:19","extension":"pdf","order_by":1,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":7959202,"visible":true,"origin":"","legend":"","description":"","filename":"submission.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7076545/v1_covered_f766bd20-a12d-4021-8fea-66cd7ecb9a4c.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Pollutant dispersion in tree-lined canyons: aligning wind-tunnel experiments with large-eddy simulation","fulltext":[],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":false,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":true,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":true,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"","lastPublishedDoi":"10.21203/rs.3.rs-7076545/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7076545/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"Vegetation is increasingly integrated into urban environments to improve microclimate and air quality. 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