1. Transport and dispersion of air pollution
Topic 4 Ms Sherina Kamal
Transport and dispersion of air pollution
25/4/2017

2. Outline pollutant transport in the atmosphere Vertical Horizontal
Adiabatic & environmental lapse rate
Atmospheric stability
Temperature inversion
Horizontal
Wind speed
Wind direction
Plume rise
Dispersion model
Gaussian plume equation derivatives
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3. Vertical pollutant transport in the atmosphere
Adiabatic lapse rate
the rate at which atmospheric temperature decreases with increasing altitude in conditions of ……………………………..
is when two objects that are at different temperatures balance each other out
the condition under which two substances in physical contact with each other exchange no heat energy
Environmental lapse rate
The actual decrease in temperature with an increase in altitude through the troposphere
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4. Vertical pollutant transport in the atmosphere
Atmospheric stability
Resistance of the atmosphere to vertical motion
Temperature inversion
Warm air on top of cooler air
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5. Temperature inversion
Play a significant role in air pollution meteorology
4 ways to produce inversion:
Cool a layer of air from below
Heat a layer of air from above
Flow a layer of warm air
Flow a layer of cold air under a layer of warm air
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7. 25/4/2017

8. Vertical pollutant transport in the atmosphere
Wind speed
Increases with elevation, most of the time, in most of the troposphere
Reasoning: ground friction slows the wind
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9. Vertical pollutant transport in the atmosphere
Wind direction
the direction from which the wind is blowing
it is expressed in degrees measured clockwise from geographical north
Wind vanes do not respond to changes in wind direction when the wind speed is less than one metre per second or two knots
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10. Wind direction In estimating wind direction at any time and
any location; can use the following rule of
thumb:
Major, rapidly moving storms and fronts overwhelm all local influences; local ground-level winds blow the way the major storms dictate
In deep valleys the daily alternation-wind up the valley in the daytime, down at night
Onshore and offshore breezes dominate when there is no major storm
Absent of all preceding/any other effects of local topography

11. Plume rise
Gases that are emitted from stacks are often pushed out by fans
As the turbulent exhaust gases exit the stack they mix with ambient air
This mixing of ambient air into the plume - entrainment
As the plume entrains air into it, the plume diameter grows as it travels downwind
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12. Plume rise These gases have momentum as they enter the atmosphere
Often these gases are heated and are warmer than the outdoor air
In these cases the emitted gases are less dense than the outside air and are therefore buoyant
Buoyant: able/tend to keep afloat or rise to the top of a gas or liquid
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13. Plume rise
A combination of the gases' momentum and buoyancy causes the gases to rise.
This is referred to as plume rise and allows air pollutants emitted in this gas stream to be lofted higher in the atmosphere
Since the plume is higher in the atmosphere and at a further distance from the ground, the plume will disperse more before it reaches ground level
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14. Plume rise
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15. Effect of temperature profile on plume rise
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16. Dispersion model
Gaussian plume
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17. Gaussian plume
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