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Volume 8, Issue 8 (Suppl)
J Earth Sci Clim Change
ISSN: 2157-7617 JESCC, an open access journal
Earth Science Congress 2017
September 18-19, 2017
September 18-19, 2017 Hong Kong
6
th
International Conference on
Earth Science and Climate Change
Characterizing pollutant plume dispersion in urban atmospheric surface layer
Ziwei Mo and Chun-Ho Liu
University of Hong Kong, Hong Kong
I
n highly urbanized cities, narrow streets are flanked by closely packed, high-rise buildings, forming arrays of street canyons.
The dynamics below the urban canopy layer are different from those in the atmospheric surface layer (ASL) aloft. Moreover,
the building-induced drag modifies the wind and pollutant dispersion. Advanced understanding of the pollutant dispersion
over urban areas is utmost important for public health and the formulation of pollution control strategy. Gaussian plume
model is the conventional method for pollutant dispersion prediction. Its accuracy mainly depends on the functionality of
the empirical dispersion coefficients (σy in lateral and σz in vertical directions). ASL turbulence is complicated by land feature
such as natural terrain or building morphology. It in turn influences the dispersion coefficient (especially σz), which, however,
is often overlooked in the practice of pollutant dispersion modeling. Friction factor f, as a measure of surface roughness in
engineering flows, has been adopted to parameterize street-level ventilation using both large-eddy simulation (LES) and wind
tunnel experiments. As an extended effort of our on-going research studies, we report in this paper our attempt to parameterize
the vertical dispersion coefficient σz in the conventional Gaussian plume model in terms of fiction factor and other flow
variables. Analytical solution shows that the vertical dispersion coefficient σz in the Gaussian plume model is proportional to
the friction length scale Lf (=x1/2×δ1/2×f1/4, where x is the distance after the pollutant source and δ the ASL thickness). Wind
tunnel measurements are used to verify the newly proposed equation in which σz and Lf show a close correlation coefficient
R
2
=0.933. The analytical solution and wind tunnel measurements collectively demonstrate the importance of dynamics and
surface roughness on the plume dispersion over urban areas.
ziwei.mo@gmail.comJ Earth Sci Clim Change 2017, 8:8 (Suppl)
DOI: 10.4172/2157-7617-C1-031