Keywords
atmospheric dispersion, maximum concentration, turbulence, molecular diffusion, generalised pareto distribution
Start Date
1-7-2010 12:00 AM
Abstract
When considering the possible hazard or nuisance associated with a release of toxic ormalodorous gas into the atmosphere, large concentrations are especially important, but relativelylittle work has been done on measuring or modelling the distribution of large concentrations of acontaminant dispersing in a turbulent flow. We have previously applied statistical extreme valuetheory to field experiment measurements, analysing large concentrations at a handful of positions.We have also been involved in using a related moment-based method to give more comprehensivespatial coverage for a steady source in a wind tunnel. In the latter case, however, we did notcalculate confidence intervals for the estimates. In the present paper we analyse measurementsfrom steady source wind tunnel measurements, with particular emphasis on the spatial variationof the estimated maximum possible concentration. We use bootstrapping to obtain confidenceintervals for the moment-based method, and use an improved version of this method. We showthat this method agrees well with the results from maximum likelihood fitting to exceedances of ahigh threshold. We find that the centreline maximum concentration, normalised by the centrelinemean concentration, increases downwind from a value just greater than 1 near the source, to a peakvalue of about 5, before decreasing again. Across the plume the maximum concentration onlyvaries slowly. These observations are explained in terms of the physical processes of turbulentadvection and molecular diffusion.
The Spatial Variation of the Maximum Possible Pollutant Concentration from Steady Sources
When considering the possible hazard or nuisance associated with a release of toxic ormalodorous gas into the atmosphere, large concentrations are especially important, but relativelylittle work has been done on measuring or modelling the distribution of large concentrations of acontaminant dispersing in a turbulent flow. We have previously applied statistical extreme valuetheory to field experiment measurements, analysing large concentrations at a handful of positions.We have also been involved in using a related moment-based method to give more comprehensivespatial coverage for a steady source in a wind tunnel. In the latter case, however, we did notcalculate confidence intervals for the estimates. In the present paper we analyse measurementsfrom steady source wind tunnel measurements, with particular emphasis on the spatial variationof the estimated maximum possible concentration. We use bootstrapping to obtain confidenceintervals for the moment-based method, and use an improved version of this method. We showthat this method agrees well with the results from maximum likelihood fitting to exceedances of ahigh threshold. We find that the centreline maximum concentration, normalised by the centrelinemean concentration, increases downwind from a value just greater than 1 near the source, to a peakvalue of about 5, before decreasing again. Across the plume the maximum concentration onlyvaries slowly. These observations are explained in terms of the physical processes of turbulentadvection and molecular diffusion.
