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Dispersion from Point Sources
• Pollutants emitted in plume form
Why does plume expand downwind?
What are the factors that influence the
history of plume?
www.epa.gov/.../muncpl/landfill/s
w_combst.htm
Impact on air quality depends on
dispersion, which depends on the
height of plume
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• Plume rise affects transport
– Effects maximum ground level concentrations (MGLCs)
– Effects distance of MGLCs
www.atmos.ucla.edu/.../ch
imneyplumes/Note03.html
Under what conditions can we have a higher Effective
Stack Height?
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Stack Plume: Looping
Strong turbulence
http://www.uwm.edu/~kahl/CoVis/Plume/stable.gif
Q: Is it at stable or unstable condition? High or low wind speed?
Does it happen during the day or night?
Is it good for dispersing pollutants?
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http://www.med.usf.edu/~npoor/3
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Stack Plume: Coning
Strong wind, no turbulence
What is the stability class? Good vertical mixing?
On sunny or cloudy days?
Good for dispersing pollutants?
What is the ground level concentration as a function of
distance from the stack?
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Stack Plume: Fanning
http://www.med.usf.edu/~npoor/4
Q: What is the stability class?
What is the top view of the plume?
What is the ground level concentration as a function of
distance from the stack?
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Stack Plume: Fumigation
Q: Why can’t the pollutants be dispersed upward?
Does it happen during the day or night?
What’s your opinion about requiring power plants to reduce
their power output from 3 am to 3 hours after sunrise?
What is the ground level concentration as a function of
distance from the stack?
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Stack Plume: Lofting
Q: Why can’t the pollutants be dispersed downward?
When does it happen?
Lofting is a transition stage. To which type of plume?
What is the ground level concentration as a function of
distance from the stack?
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Stack Plume: Trapping
Q: What is the stability class?
What is the ground level concentration as a function of
distance from the stack?
http://www.uwm.edu/~kahl/CoVis/Plume/
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Effect of Surface Discontinuity
(a)
(b)
Warm land
Cold water
(c)
Warm land
Cold land
Cold water
Warm water
Q: What is the ground level concentration as a function of
distance from the stack?
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Effects of Terrain on the Plume Pattern
Q: Does the shape of the building matter?
Is the wake bigger at stable or unstable condition?
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Impact of Building and Stack Location
Backwash
Q: Is stack height an important parameter?
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Downwash
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Impact of Stack Height: Stack Upwind of Building
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Impact of Stack Height: Building Supported Stack
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Impact of Stack Height: Stack Downwind of Building
Conclusions?
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Cases of Downwash
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Plume Affected by Natural Terrain Irregularity
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Plume Near Very Large Obstacle
Stable
Unstable
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Plume in a Valley
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Heat Island Effect
Q: When does the effect break?
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Plume Affected by Heat Island Effect
Toward a city
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Within a city
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Long-Range Transport
• Transport of pollutants hundreds/thousands of miles;
resulting in air quality problems far away from the source
Examples?
Planetary Transport
• Stable air above PBL retards vertical mixing
• Transport out of PBL to free troposphere takes few hours
to few days
• Transport to top of troposphere with uniform mixing takes
about a week (for long-lived pollutants, e.g. CO2, CH4,
CFC)
Why only long-lived?
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Summary
Take 2 minutes to summarize here what you have learned from this section
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