Presentation on theme: "Ian Longley Street canyon aerosol pollutant transport measurements in Manchester I.D. Longley, M.W. Gallagher, J.R. Dorsey, M. Flynn, K. Bower, I. Barlow."— Presentation transcript:
Ian Longley 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 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 SCAR – Street Canyon Aerosol Research Regulatory dispersion models are based upon a simple transport mechanism – PM 10 only. Numerical modelling – simple canyons. Field studies are rare. SCAR to apply eddy correlation techniques. Aim: Parameterised size- segregated aerosol emission rates.
Ian Longley Experimental site – Princess Street, Manchester
Ian Longley 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 Mean ultrafine aerosol spectra Left: SMPS spectrum from UMIST Land Rover Discovery TDi Left: average SMPS spectrum from SCAR, 2m height
Ian Longley 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 NO x activity.
Ian Longley Temporal variation in fine aerosol spectra (4.6nm<D p <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 Influence of wind speed and direction on fine aerosol number concentrations – 1. PARALLEL FLOW
Ian Longley Influence of wind speed and direction on fine aerosol number concentrations – 2. NE PERPENDICULAR Canyon vortex blows emissions away from instruments
Ian Longley 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 Parameterisation for w Traffic-induced turbulence
Ian Longley Parameterisation for w = 0.16 at a height of 3.5m wt = 0.0135 T 1/2 T = traffic flow rate (hr -1 )
Ian Longley Turbulent variances: w /U profiles
Ian Longley Turbulent variances: u /U profiles
Ian Longley Turbulent variances: v /U profiles
Ian Longley Spatial variation in w /U: 1. Sheltered zone Above: U/U roof Below: w /U Plan views of canyon
Ian Longley Spatial variation in w /U: 2. Convergence Above: U Below: w /U
Ian Longley Conclusions The flux of accumulation mode aerosol (100nm<D p <3m) 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 w based upon local wind speed and traffic flow rate.
Ian Longley 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