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 If it is assumed that  w is made up of a contribution from the mean wind and a contribution from the traffic, then it can be suggested that Introduction.

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Presentation on theme: " If it is assumed that  w is made up of a contribution from the mean wind and a contribution from the traffic, then it can be suggested that Introduction."— Presentation transcript:

1  If it is assumed that  w is made up of a contribution from the mean wind and a contribution from the traffic, then it can be suggested that Introduction Vehicle emissions of particles and pollutant gases are causing increasing concern due to their adverse effects upon the health of the public. The greatest numbers of people are exposed to the highest concentrations of such pollutants where the sources are most concentrated - in urban street canyons. In such canyons dispersion is constrained by the buildings and complicated by recirculation and the enhanced and highly localised turbulence associated with such a complex space. Regulation of urban air quality increasingly relies upon simple dispersion models such as ADMS-Urban (McHugh et al, 1997). Such models are based upon a simplified empirical transport scheme treating aerosol purely as a PM 10 metric and do not describe the differing behaviour of different size ranges or number concentrations. Recent concerns over the appropriateness of the PM 10 metric for regulation purposes (e.g. EPAQS, 2000, Harrison & Yin, 2000) has, in part, led to a need to understand the size-segregated behaviour of aerosols better in campaigns such as this one. Objectives The experimental campaign was named Street Canyon Aerosol Research, or SCAR. The principal aim of SCAR was to obtain the emission velocity and ventilation fluxes of aerosol from the canyon space. It was intended that these fluxes could then be parameterised with regard to controlling factors. The factors expected to have most influence over these fluxes were wind speed and direction and traffic flow both directly and indirectly through thermally and mechanically produced turbulence. Measurements of Aerosol Pollutant Transport in a Manchester Street Canyon I.D. Longley, M. Flynn, J.D. Dorsey, P.I. Williams, M.W. Gallagher, J.R. Allan, M.R. Alfarra, H. Coe. University Of Manchester Institute of Science and Technology, Manchester, UK Activities A measurement campaign has been conducted in an asymmetric street canyon with busy one-way traffic (Princess Street) in central Manchester. The principal experimental period (SCAR-4) covered two weeks (Monday to Friday, 24-hour operation) in October 2001, preceded by three week-long preparatory experiments in February, April and May The eddy correlation method was used to determine fluxes of size segregated accumulation mode aerosol. Measurements of accumulation mode aerosol and trace gases at a static location were made concurrently with measurements on a platform lift giving vertical profiles. Size segregated measurements of ultra-fine and coarse particle concentrations were also made simultaneously at various heights. Also, a small mobile system has made measurements of turbulence at various pavement locations within the canyon. Table 1. Instruments deployed during SCAR-4 discussed in this poster: Mean aerosol number concentrations (SMPS data, 4.7nm 1.5 ms -1, allowing a vertical profile to be constructed, showing enhanced shear near the roof level. Turbulent variances  Due to the positive stresses and dependence of stress upon wind direction it was found that the variances were best presented as standard deviations normalised by local sonic wind speed, i.e  u,v,w /U.   w /U was well-relate to sonic wind speed U, with increased values when U < 1.5 ms -1, indicating the relative importance of other sources, such as thermal and traffic-induced turbulence, when wind speeds are low.  A vertical profile of  w /U (when U > 1.5 ms -1 ) shows a weak positive gradient, but with a layer of greatly enhanced turbulence in the lower 2m or so.   v /U followed a similar pattern to  w /U, but  u /U was different in having larger values.  ‘Hot-spots’ of  w /U occurred wherever U/U roof fell below about 0.3. This was more likely to happen in the ‘sheltered zone’ at the downwind end of the canyon. This zone extended over a greater length of the canyon in more perpendicular winds, and when the wind blew over the higher canyon wall.  ‘Hot spots’ also occurred where winds blowing from opposite ends of the canyon met. Conclusions  The flux and emission velocity of fine mode aerosol (100nm


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