RESULTS FROM THREE FIELD TRACER EXPERIMENTS ON THE NEIGHBOURHOOD SCALE IN THE CITY OF BIRMINGHAM UK

摘要

The physical processes governing flow and pollutant dispersion at the neighbourhood scale, a spatial scale intermediate between the street scale and the city scale, is not well understood. Furthermore, it is not clear whether a traditional approach using averaged characteristics such as the aerodynamic roughness length is sufficient to predict the concentration field at this scale. To investigate pollutant dispersion in a real urban area, three field experiments were designed within the UK-URGENT programme sponsored by NERC. The experiments were performed in the City of Birmingham using a finite duration release of inert, non-toxic and non-depositing tracers, vis. per-fluoromethylcyclohexane (PMCH) and perfluoromethylcyclopentane (PMCP). Measurements were taken using air bag samplers placed in an arc at 3.5 km (first experiment) and 1 km (second and third experiments) from the source; some trap samplers were placed outside the main arc in the outskirts of the city. Measurements were analysed in the laboratory using a novel gas-chromatography technique. Data so obtained were compared with predictions from a simple steady-state model and a time-dependent model. The concentration-time series were very asymmetrical with a sharp rise, a plateau followed by a relatively slow decrease and finally a long-lived plateau above (or possibly very slow decrease to) the background level.