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Street canyon aerosol pollutant transport measurements in Manchester

Street canyon aerosol pollutant transport measurements in Manchester. I.D. Longley , M.W. Gallagher, J.R. Dorsey, M. Flynn, K. Bower, I. Barlow J.R. Allan, M.R. Alfarra, H. Coe. Aerosol in Urban Street Canyons.

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Street canyon aerosol pollutant transport measurements in Manchester

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  1. Street canyon aerosol pollutant transport measurements in Manchester I.D. Longley, M.W. Gallagher, J.R. Dorsey, M. Flynn, K. Bower, I. Barlow J.R. Allan, M.R. Alfarra, H. Coe Ian Longley

  2. Aerosol in Urban Street Canyons • Fine aerosol, linked to adverse health effects (COMEAP, 2001, EPAQS,2000, Colville et al, 2001). • Fine aerosol from vehicle emissions. • Street canyons act as major emission sites. • Large numbers of people exposed. • Canyons re-circulate and trap pollutants. • Canyon emissions transported across and beyond city – affecting chemical and radiative atmospheric properties and the biosphere. • Need to understand transport within, and emission from, urban street canyons. Ian Longley

  3. SCAR – Street Canyon Aerosol Research • Regulatory dispersion models are based upon a simple transport mechanism – PM10 only. • Numerical modelling – simple canyons. • Field studies are rare. • SCAR to apply eddy correlation techniques. • Aim: Parameterised size- segregated aerosol emission rates. Ian Longley

  4. Experimental site – Princess Street, Manchester Ian Longley

  5. SCAR measurements • SMPS (TSI 3080 + nano DMA) • OPC (PMS ASASP-X) • FSSP • 20 Hz sonic anemometers • 18m mast • Platform lift for profiling • Mobile turbulence system • 4 campaigns in 2001: (3 x 1 week, 1 x 2 weeks) Ian Longley

  6. Mean ultrafine aerosol spectra • Left: SMPS spectrum from UMIST Land Rover Discovery TDi • Left: average SMPS spectrum from SCAR, 2m height Ian Longley

  7. Aerosol Chemistry(from Aerosol Mass Spectrometer, J.R. Allen, M.R. Alfarra, H.Coe) • Mode in the mass spectra at around 100-200nm consisting of aliphatic organic chemicals. • Organic activity within the Manchester sampling periods correlates well with NOx activity. Ian Longley

  8. Temporal variation in fine aerosol spectra (4.6nm<Dp<160nm) • Total number concentrations generally follow traffic flow • Road-side day-time concentrations are generally greater than night-time by a factor of around 4. • Day-time and night-time spectra are the same shape. Ian Longley

  9. Mean air flow: Channelling Ian Longley

  10. Mean air flow: Vertical flow Ian Longley

  11. Mean air flow: Vertical flow Ian Longley

  12. Mean air flow: Up-canyon Ian Longley

  13. Mean air flow: NE perpendicular Ian Longley

  14. Mean air flow: SW perpendicular Ian Longley

  15. Influence of wind speed and direction on fine aerosol number concentrations – 1. PARALLEL FLOW Ian Longley

  16. Influence of wind speed and direction on fine aerosol number concentrations – 2. NE PERPENDICULAR • Canyon vortex blows emissions away from instruments Ian Longley

  17. Influence of wind speed and direction on fine aerosol number concentrations – 3. SW PERPENDICULAR • Canyon vortex blows emissions towards instruments • Flow at pavement level disconnected from roof-top wind Ian Longley

  18. Vertical concentration gradients Ian Longley

  19. Vertical concentration gradients Ian Longley

  20. Accumulation mode (100nm<Dp<1mm) aerosol emission fluxes SCAR SASUA: Above Edinburgh* *Dorsey, J.R. et alAtmos. Environ. Vol.36, pp. 791-800. Ian Longley

  21. Horizontal fluxes Ian Longley

  22. Coarse particle fluxes SASUA All Experiments Aerosol Eddy Flux Measurements dp>1.9 mm Mode- CEH instrument Wind driven re-suspension Ian Longley

  23. Vertical turbulence Ian Longley

  24. Parameterisation for swTraffic-induced turbulence Ian Longley

  25. Parameterisation for sw • = 0.16 at a height of 3.5m swt = 0.0135 T1/2 T = traffic flow rate (hr-1) Ian Longley

  26. Turbulent variances: sw/U profiles Ian Longley

  27. Turbulent variances: su/U profiles Ian Longley

  28. Turbulent variances: sv/U profiles Ian Longley

  29. Spatial variation in sw/U:1. Sheltered zone Plan views of canyon Above: U/Uroof Below: sw/U Ian Longley

  30. Spatial variation in sw/U:2. Convergence Above: U Below: sw/U Ian Longley

  31. Conclusions • The flux of accumulation mode aerosol (100nm<Dp<3mm) have been measured in a city centre street canyon and found to be related to urban heat emission and traffic activity. • Street-level fine aerosol has been shown to be influenced by asymmetrical vortex flow within the canyon. • A vertical gradient was found in fine aerosol number concentrations below roof level. • A weak positive vertical gradient was seen in turbulent variances. However, greatly enhanced variances were seen at the bottom of the canyon. • A parameterisation has been derived for sw based upon local wind speed and traffic flow rate. Ian Longley

  32. Forthcoming analysis • More street-level accumulation mode flux data • Profiles of coarse aerosol concentrations • Improved parameterisation for wind-driven re-suspension • Spectral & quadrant analysis • SCAR-5: suburban street canyon • Improved parameterisation for turbulence, including traffic-layer turbulence Ian Longley

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