CHAPTER 14 Plume Dispersion

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CHAPTER 14Plume Dispersion
Objectives
Assess environmental impact of an emission source
in terms of legislated standards for

• Toxicity, and
• Odour

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In Ontario this constitutes regulation 419/05
httpwww.rwdi.com/regulation419/
Pg. 176 course notes
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Our task is to estimate the impact of an emission
source from an industrial plant
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Plume dispersion occurs in the y- and z-directions
Plume is convected by the wind in the x-direction
Z-axis starts from ground level
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Turbulent dispersion
y-direction
z-direction
Where sy and sz are dispersion parameters that
must be estimated
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Recall from our treatment of particle diffusion
where
D is the particle diffusivity
Pg. 49-50 course notes
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Diffusion mechanisms

• Solute (gas or liquid) diffusion occurs by random
  molecular motion.
• Particle diffusion occurs by random Brownian
  motion.
• Plume dispersion occurs by random turbulent
  motion.

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sy and sz must be estimated
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Ground-level concentrations will depend on
Wind
Wind rose shows average direction and magnitude
of the wind vector
Pg. 178 course notes
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Atmospheric stability
Dry adiabatic lapse rate (stable, neutral
atmosphere)
Natural balance between hydrostatic head, ? g dA
dZ, and pressure forces
Pg. 179 course notes
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Super-adiabatic lapse rate
A buoyant atmosphere
Pg. 180 course notes
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Sub-adiabatic lapse rate
Pg. 180 course notes
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The Gaussian plume model
The concentration of material downwind in the
x-direction varies as the inverse of the local
transport velocity, i.e.,
A Gaussian type distribution is used in the
y-direction
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If we choose
The distribution will provide an integrated
concentration of unity across the transverse
cross-section
starting to look like a normal distribution!
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Z- direction requires special treatment
When the edge of the plume reaches the ground
we assume perfect reflection!
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(z - H) term accounts for the above ground
contribution
(z H) term accounts for the imaginary source
below ground
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Final form of the Gaussian plume model

• Product of the y- and z-direction distributions
• Q is the emission rate in mass per unit time

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Variation of C with x is contained in the
behaviour of ?y and ?z with downstream position,
x, from the emission source.
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Fig 6-14 and 7-14, pg. 184 and 185
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Stability classes A - F
Table 1-14 pg. 186
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Mathematical models for sy
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Mathematical models for sz

• for class C, and

• piecewise (in x) for other different classes

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Pg. 187 course notes
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But
Pg. 188 course notes