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Effect of wind direction and speed on the dispersion of nucleation and accumulation mode particles in an urban street canyon

Kumar, P, Fennell, P and Britter, R (2008) Effect of wind direction and speed on the dispersion of nucleation and accumulation mode particles in an urban street canyon Science of The Total Environment, 402 (1). 82 - 94. ISSN 0048-9697

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Abstract

There have been many studies concerning dispersion of gaseous pollutants from vehicles within street canyons; fewer address the dispersion of particulate matter, particularly particle number concentrations separated into the nucleation (10-30�nm or N10-30) or accumulation (30-300�nm or N30-300) modes either separately or together (N10-300). This study aimed to determine the effect of wind direction and speed on particle dispersion in the above size ranges. Particle number distributions (PNDs) and concentrations (PNCs) were measured in the 5-2738�nm range continuously (and in real-time) for 17�days between 7th and 23rd March 2007 in a regular (aspect ratio�~�unity) street canyon in Cambridge (UK), using a newly developed fast-response differential mobility spectrometer (sampling frequency 0.5�Hz), at 1.60�m above the road level. The PNCs in each size range, during all wind directions, were better described by a proposed two regime model (traffic-dependent and wind-dependent mixing) than by simply assuming that the PNC was inversely proportional to the wind speed or by fitting the data with a best-fit single power law. The critical cut-off wind speed (Ur,crit) for each size range of particles, distinguishing the boundary between these mixing regimes was also investigated. In the traffic-dependent PNC region (UrUr�<<�Ur,critUr,crit), concentrations in each size range were approximately constant and independent of wind speed and direction. In the wind speed dependent PNC region (UrUr�>>�Ur,critUr,crit), concentrations were inversely proportional to Ur irrespective of any particle size range and wind directions. The wind speed demarcating the two regimes (Ur,critUr,crit) was 1.23���0.55�m s-�1 for N10-300, (1.47���0.72�m s-�1) for N10-30 but smaller (0.78���0.29�m s-�1) for N30-300.

Item Type: Article
Uncontrolled Keywords: Particle number distribution, Nucleation and accumulation mode particles, Traffic-produced turbulence, Street canyon, Particle dispersion, Wind-produced turbulence
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Divisions: Faculty of Engineering and Physical Sciences > Civil and Environmental Engineering
Depositing User: Symplectic Elements
Date Deposited: 20 Jul 2011 09:14
Last Modified: 08 Nov 2013 12:08
URI: http://epubs.surrey.ac.uk/id/eprint/6412

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