Probability law of concentration in plumes dispersing in an urban area |
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Authors: | Eugene Yee |
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Institution: | (1) Defence R&D Canada – Suffield, Stn Main, P.O. Box 4000, Medicine Hat, AB, Canada, T1A 8K6 |
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Abstract: | The relationships between various normalized higher-order concentration moments in plumes dispersing in a built-up (urban)
environment have been investigated using a large concentration data set obtained in a boundary-layer water channel. This data
set consists of measurements of plume dispersion in a number of idealized obstacle arrays (e.g., cubical and non-cubical obstacles
in aligned and staggered arrangements with uniform, random and alternating heights). A remarkably robust feature of all the
concentration data was the observed collapse of the third- and fourth-order normalized concentration moments on the second-order
normalized concentration moment. The data are shown to collapse to a series of universal curves (independent of the geometry
of the obstacle array) and these curves were found to be identical to those observed previously for open-terrain plumes. The
results imply that the probability law of concentration in a plume dispersing in either a built-up environment or open terrain
has a universal form that can be specified by at most two independent parameters. The universal functions representing the
relationships between the normalized concentration moments were found to be well modeled (approximated) using a two-parameter
clipped-gamma probability law for the concentration. Finally, the clipped-gamma distribution was found to be in very good
conformance with the measured probability distribution of concentration for plumes dispersing in a built-up environment. |
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Keywords: | Atmospheric diffusion Concentration fluctuations Pollutant dispersion Probability density function Urban canopy |
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