Chapter 5. Air Pollution Meteorology Selami DEMİR Asst. Prof.
Air Meteorology -6
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Air Pollution
Meteorology and Control
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Air pollution Meteorology
What is clean air ?
78% Nitrogen + 21% Oxygen + 1% Trace
340 ppm CO2(0.034%)
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Mixing/DispersionMeteorology
VerticalTemperature
Lapse Rate
Horizontal Wind
Speed
Direction
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1. Vertical DispersionVertical mixing of air and dispersion of pollutants depends
on the kind of atmospheric stability prevailing at any giventime
Atmospheric stability depends on the rate of change of airtemperature with altitude, that may prevail at a particulartime and location
But the rate at which the air temperature drops called theenvironmental lapse rate or ambient lapse rate
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Lapse RatesTemperature Change With Height
Lapse rate is the rate of change of temperature withheight
Lapse rate is defined as = -Tz
Atmospheric pressure decrease withincreasing height above the ground
Atmosphere cools with height What rate ? Dry (Adiabatic) 10C/km
Wet (Adiabatic) 6C/km
(Release of heat with condensation)
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Mesopause
Mesospher
e
Thermosphere
Troposphere
Tropopause
Stratospher
e
Stratopause
TEMPERATURE PROFILE OFATMOSPHERE
Ionosphere
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No exchange of heat of the parcel of airunder consideration with the outside airThe lapse rate is in dependent of theprevailing atmospheric temperature gradientat any given timeA moving parcel of air will always cool down1o C per 100 m it rises in the atmosphere
and will warm up 1o C for every 100 m sinkThe adiabatic lapse rate usually differs fromthe environmental lapse rate becoz of factorssuch as geographic features, wind ,andsunlight
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Contd
Environmental lapse rates are classified as beingeither strong or week (super adiabatic or subadiabatic )
Strong lapse rates are associated with unstableatmosphere, while week lapse rates are associatedwith a stable atmosphere
Increase in actual air temperature with increrasingaltitude is called a temperature inversion stableatmosphere
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Inver
sion
Inver
sion
Subadiabatic
Subadiabatic
Superadiabatic
Superadiabatic
TTT - 1T - 1
100100
mm
ElevationElevation
(m)(m)
Temperature (Temperature (ooC)C)
Adiabatic Lapse RateAdiabatic Lapse Rate
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Lapse RatesSuperadiabatic, Strong, UnstableTemperature Reduction > 1 oC/100m
Subadiabatic, Weak, StableTemperature Reduction < 1 oC/100m
NeutralTemperature Reduction = 1 oC/100m
Inversion (Extreme Subadiabatic)Temperature Increase with Height
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Monroe Power Plant
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Vertical Expansion of Continuous Plumes
Fanning The plume has alarge spread horizontally
and very little vertically.
Typically occurs at night in a very stableboundary layer with strong surfaceinversion and weak variable winds
Fumigation Is when the plume material gets rapidly
brought down to the ground level due to
downward mixing This situation occurs shortly after sunrise
due to surface heating and is slowlyreplaced by an unstable layer that growsup to the top of the plume
This condition is usually short-lived butresults in the highest ground levelconcentrations
Looping occurs in very unstable and convective
conditions during midday and afternoon
Large convection eddies take the plumematerial in successively upward anddownward motions
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Vertical Expansion of Continuous Plumes
Coning This is when the plume looks like a cone in
both the horizontal and vertical scale
This usually occurs under cloudy andwindy conditions
Lofting The plume stays above the surface
inversion
This occurs shortly after transition fromunstable to stable conditions near sunset.
The plume can be thin or become quitethick
Depending on the height of the stack andthe rate of deepening of the inversionlayer, the lofting condition may be verytransitory or it may persist for severalhours
Trapping Plumes released in unstable atmosphere
disperse their material uniformlythroughout the air (the Planetary BoundaryLayer PBL)
Trapping can lead to very high ground levelconcentrations when the inversion layer islow and there are weak winds
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2. Horizontal Dispersion ofpollutants
Horizontal dispersion or spreading of air pollutantsdepends on wind speed and direction
The concentration of air pollutants decreases withincreasing wind speed because, as the pollutants aredischarged from the source, they are more rapidlyseparated and dispersed by the swiftly moving air
Wind velocity data, plotted in a graph called windrose
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Wind RoseWind roses are divided into 16 wind directions
Each wind direction is divided into wind
speeds As the percent of time the wind blows from a
particular directions gets larger, the portion ofthe bar representing the wind speed gets
larger both in length and width
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Wind Rose
20http://www.epa.gov/ttn/naaqs/ozone/areas/wind.htm#dlfi
1 knot = 1.82 km/hr
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Contd
Winds develop because of the combined effects oftemperature gradients and the rotation of Earthpoles while friction and the forces resulting fromEarths rotation deflect the air movement
Important factors that affect circulation patterns includetopography, daily and seasonal variation in surface
Since soil and rock warm up and cool faster thanwater winds shoreline directed toward the water atnight and inland during the day
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Vertical Expansion of Continuous Plumes
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Lapse Rates and AtmosphericStability
Strong Lapse Condition (Looping)Superadiabatic lapse rate
-strong instabilities
Associated with clear
daytime conditions ,strong solar heating &light winds
High probability of highconcentrations
sporadically at groundlevel close to stack.
WindWind
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Lapse Rates and AtmosphericStability
Weak Lapse Condition (Coning)Stable with small-scale
turbulence
Associated with cloudy
moderate to strongwinds
Pollutants travel fairlylong distances beforereaching ground level
in significant amountsOccurs in neutral
atmospheric conditions
WindWind
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Lapse Rates and AtmosphericStability
Inversion Condition (Fanning)Occurs under large
negative lapse rate
Extremely stableatmosphere
If plume density issimilar to air, travels
downwind atapproximately sameelevation
WindWind
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StabilityInversion Below, Lapse Aloft
(Lofting)Favorable in the sense
that less impacts atground level.
Pollutants go up intoenvironment.
They are created whenatmospheric conditions
are unstable above theplume and stable below
WindWind
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StabilityWeak Lapse Below, Inversion Aloft
(Trapping)Most dangerous plume:
contaminants are all comingdown to ground level.
They are created when
atmospheric conditions arestable above the plume andunstable below.
This happens most often afterthe daylight sun has warmedthe atmosphere, which turns a
night time fanning plume intofumigation for about a half anhour.
WindWind
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ACTUAL
ADIABATIC (1C/100 m)
1000 m (say)
20 C19 C18 C
20 C AirParcel
19 C Air
Parcel at
1100 m
1100 m
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ADIABATIC (1C/100 m)
1000 m (say)
20 C 21C 22 C
20 C Air
Parcel
21 C Air
Parcel at
1100 m
1100 m
900 m
ACTUAL
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ADIABATIC (1C/100 m)
1000 m (say)
20 C19.5 C19C
20 C Air
Parcel
19 C Air
Parcel at
1100 m
1100 m
ACTUAL
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WIND
Adiabatic
Actual
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Scenarios
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Adiabatic
Actual
He
igh
t
Temperature
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Scenarios
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Adiabatic
Actual
He
igh
t
Temperature
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Scenarios
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Adiabatic
Actual
He
igh
t
Temperature
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Stability
36http://www.tpub.com/content/aerographer/14312/css/14312_47.htm
Wet Lapse
Rate
Dry Lapse Rate
Average
Unstable
Stable
Height
Temperature
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ReviewDispersion and Mixing Influenced by :Wind
SpeedDirectionWind Rose
Temperature Lapse RatesDry adiabaticWet AdiabaticStability