Fast response measurements of the dispersion of nanoparticles in a vehicle wake and a street canyon |
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| Authors: | Prashant Kumar Alan Robins Rex Britter |
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| Affiliation: | 1. Faculty of Engineering and Physical Sciences, University of Surrey, Guildford GU2 7XH, UK;2. Senseable City Laboratory, Massachusetts Institute of Technology, Boston, MA 02139, USA;1. VITO, Flemish Institute for Technological Research, Boeretang 200, B-2400 Mol, Belgium;2. Department of Mathematical Modelling, Statistics and Bioinformatics, Ghent University, Coupure Links 653, 9000 Gent, Belgium;3. Department of Civil and Environmental Engineering, Faculty of Engineering and Physical Science (FEPS), University of Surrey, GU2 7XH, United Kingdom;4. Environmental Flow (EnFlo) Research Centre, FEPS, University of Surrey, GU2 7XH, United Kingdom;1. Aerosol Physics, Faculty of Natural Sciences, Tampere University of Technology, FI-33101 Tampere, Finland;2. Division of Environmental Health and Risk Management, School of Geography, Earth and Environmental Sciences, University of Birmingham Edgbaston, Birmingham B15 2TT, United Kingdom;3. Department of Environmental Sciences / Center of Excellence in Environmental Studies, King Abdulaziz University, PO Box 80203, Jeddah 21589, Saudi Arabia;4. Helsinki Region Environmental Services Authority, FI-00240 Helsinki, Finland;5. Atmospheric Composition Research, Finnish Meteorological Institute, FI-00101 Helsinki, Finland;1. School of Food and Chemical Engineering, Beijing Technology and Business University, Beijing 100048, China;2. State Key Joint Laboratory of Environment Simulation and Pollution Control, School of Environment, Tsinghua University, Beijing 100084, China;3. State Environmental Protection Key Laboratory of Sources and Control of Air Pollution Complex, Tsinghua University, Beijing 100084, China;1. Department of Shipping and Marine Technology, Chalmers University of Technology, 412 96 Gothenburg, Sweden;2. IVL Swedish Environmental Research Institute, PO Box 5302, 400 14 Gothenburg, Sweden |
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| Abstract: | The distributions of nanoparticles (below 300 nm in diameter) change rapidly after emission from the tail pipe of a moving vehicle due to the influence of transformation processes. Information on this time scale is important for modelling of nanoparticle dispersion but is unknown because the sampling frequencies of available instruments are unable to capture these rapid processes. In this study, a fast response differential mobility spectrometer (Cambustion Instruments DMS500), originally designed to measure particle number distributions (PNDs) and concentrations in engine exhaust emissions, was deployed to measure particles in the 5–1000 nm size range at a sampling frequency of 10 Hz. This article presents results of two separate studies; one, measurements along the roadside in a Cambridge (UK) street canyon and, two, measurements at a fixed position (20 cm above road level), centrally, in the wake of a single moving diesel-engined car. The aims of the first measurements were to test the suitability and recommend optimum operating conditions of the DMS500 for ambient measurements. The aim of the second study was to investigate the time scale over which competing influences of dilution and transformation processes (nucleation, condensation and coagulation) affect the PNDs in the wake of a moving car. Results suggested that the effect of transformation processes was nearly complete within about 1 s after emission due to rapid dilution in the vehicle wake. Furthermore, roadside measurements in a street canyon showed that the time for traffic emissions to reach the roadside in calm wind conditions was about 45 ± 6 s. These observations suggest the hypothesis that the effects of transformation processes are generally complete by the time particles are observed at roadside and the total particle numbers can then be assumed as conserved. A corollary of this hypothesis is that complex transformation processes can be ignored when modelling the behaviour of nanoparticles in street canyons once the very near-exhaust processes are complete. |
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