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Comparative study of measured and modelled number concentrations of nanoparticles in an urban street canyon

Kumar, P, Garmory, A, Ketzel, M, Berkowicz, R and Britter, R (2009) Comparative study of measured and modelled number concentrations of nanoparticles in an urban street canyon Atmospheric Environment, 43 (4). 949 - 958. ISSN 1352-2310

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Abstract

This study presents a comparison between measured and modelled particle number concentrations (PNCs) in the 10-300 nm size range at different heights in a canyon. The PNCs were modelled using a simple modelling approach (modified Box model, including vertical variation), an Operational Street Pollution Model (OSPM) and Computational Fluid Dynamics (CFD) code FLUENT. All models disregarded any particle dynamics. CFD simulations have been carried out in a simplified geometry of the selected street canyon. Four different sizes of emission sources have been used in the CFD simulations to assess the effect of source size on mean PNC distributions in the street canyon. The measured PNCs were between a factor of two and three of those from the three models, suggesting that if the model inputs are chosen carefully, even a simplified approach can predict the PNCs as well as more complex models. CFD simulations showed that selection of the source size was critical to determine PNC distributions. A source size scaling the vehicle dimensions was found to better represent the measured PNC profiles in the lowest part of the canyon. The OSPM and Box model produced similar shapes of PNC profile across the entire height of the canyon, showing a well-mixed region up to first [approximate]2�m and then decreasing PNCs with increased height. The CFD profiles do correctly reproduce the increase from road level to a height of [approximate]2�m; however, they do not predict the measured PNC decrease higher in the canyon. The PNC differences were largest between idealised (CFD and Box) and operational (OSPM) models at upper sampling heights; these were attributed to weaker exchange of air between street and roof-above in the upper part of the canyon in the CFD calculations. Possible reasons for these discrepancies are given.

Item Type: Article
Additional Information: NOTICE: this is the author’s version of a work that was accepted for publication in Atmospheric Environment. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Atmospheric Environment, 43(4), Feb 2009, DOI 10.1016/j.atmosenv.2008.10.025.
Uncontrolled Keywords: Dispersion, Modelling, Nanoparticles, Particle number concentration, Street canyon
Divisions: Faculty of Engineering and Physical Sciences > Civil and Environmental Engineering
Depositing User: Symplectic Elements
Date Deposited: 11 Jan 2012 14:21
Last Modified: 09 Jun 2014 13:41
URI: http://epubs.surrey.ac.uk/id/eprint/84301

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