Air Pollution And Control

1. 18-02-2018 1APC PRESENTATION

2. •Temperature lapse rates.
•Environmental lapse rates.
•Atmospheric stability.
•Plume behaviour.
•Stack height and dispersion.
2/19/2018 APC PRESENTATION 2
contents

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4. • Air pollutants emitted from anthropogenic sources
must first be transported and diluted in the
atmosphere before these undergo various physical and
photochemical transformations and ultimately reach
their receptors.
• The pollutant concentration reach dangerous levels
near the source of emission.
• Hence it is important to understand the natural
processes that are responsible for their dispersion.
• Effective dispersion of pollutants depends on the
degree of stability of the atmosphere and its turbulent
structure.
2/19/2018 APC PRESENTATION 4
Temperature Lapse Rate

5. The Environmental Lapse Rate (ELR) is the rate
at which the measured temperature of the air
in the environment outside the air parcel
decreases with height.
We send up balloons with instrument packages
called radiosondes to measure the
temperature at different levels above the
Earth’s surface.
2/19/2018 5APC PRESENTATION
Environmental Lapse Rate

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7. Atmospheric stability refers to the tendency for
air parcels to move vertically.
7APC PRESENTATION
Atmospheric Stability

8. Basic concept – when the temperature of the air
parcel is greater than the temperature of the
surrounding environment, then it will rise, and
when the temperature of the air parcel is less
than the surrounding environment, then it will
sink.
2/19/2018 8APC PRESENTATION
Atmospheric Stability

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11. •Environmental lapse rate is less than the dry
adiabatic lapse rate , a rising air parcel becomes
cooler and more dense than its surroundings and
tends to fall back to its original position. Such an
atmospheric condition is called stable and the lapse
rate is said to be sub-adiabatic.
•Under stable conditions there is very little vertical
mixing and pollutants can only disperse very slowly.
As a result , their levels can build up very rapidly in
the environment.
•Instability and stability may be defined with
reference to a neutrally stable atmosphere where
the environmental lapse rate is equal to the dry
adiabatic lapse rate for dry or unsaturated air, and
wet adiabatic lapse rate.
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13. • Effects of plumes are considered local within
500 metres of the stack, and regional beyond
this.
• Mixing or dispersion of the waste gases and
products into the atmosphere = plume
behaviour.
2/19/2018 13APC PRESENTATION
Plume Behaviour

14. • Fanning plumes
• Looping plumes
• Coning plumes
• Fumigating
• Lofting
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14APC PRESENTATION
Types of
Plumes

15. • Fanning Plumes
– Require stable air and slow vertical movement of the
emission
– common after calm clear nights
– temperature inversion limits the rise of the plume into the
upper atmosphere
– creates a higher conc. of polluted air at lower
levels
– exists for several hours
– Commonly seen from Eraring Power station
2/19/2018 15APC PRESENTATION
The Fanning
Plume

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17. • Looping plumes
– Require windy conditions which cause the plume can
swirl up and down
– common in the afternoon.
– Moderate and strong winds are formed on sunny
days creating unstable conditions
– Exists for several hours.
2/19/2018 17APC PRESENTATION
Looping plumes

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19. • Coning plumes
– Require moderate winds and overcast days
– wider than it is deep, and is elliptical in shape
– exists for several hours.
2/19/2018 19APC PRESENTATION
Coning plumes

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21. • Fumigating plume
– Is short-lived (fraction of an hour), but reaches the
earth's surface.
– occur when the conditions move from stable to
unstable
– A fanning plume develops overnight under stable
conditions but as the day heats up, unstable air is
produced
2/19/2018 21APC PRESENTATION
Fumigating plume

22. • Fumigating plume (cont)
– unstable air causes the plume to move up and down
- can cause localised pollution.
– become looping or coning plumes as the air
conditions stabilise.
2/19/2018 22APC PRESENTATION
Fumigating Plume

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24. • Lofting plume
– When plume is above the inversion layer (or there is no
inversion), it becomes a lofting plume.
– Normal wind direction and speed will disperse the plume
into the atmosphere without effect from ground warming
or cooling.
2/19/2018 24APC PRESENTATION
lofting Plume

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28. • H=VsDs/u{1.5+2.68*10-3Pa(Ts-Ta/Ts)Ds}
•Pa=atmospheric pressure,mb
•Ts =stack gas temperature,K
•Ta =ambient air temperature at stack
height,K
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