Transcript PROPERTIES OF THE ATMOSPHERE

DEMOCRITUS UNIVERSITY OF THRACE
Department of Environmental Engineering
Prof. Dr. S. RAPSOMANIKIS
Director, Laboratory of Atmospheric Pollution and of
Pollution Control Engineering of Atmospheric
Pollutants
Vas Sofias 12, 67100 Xanthi, GREECE
Telfax +3025410-79379, email:[email protected]
webpage: http://www.airpollab.org
PROPERTIES OF THE ATMOSPHERE
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Troposphere: 0 - 11 km above ground
Stratosphere: above 11 km
99% of atmospheric mass within 30 km
Equivalent to a large pancake of 25,000 km
diameter
• Horizontal movements more pronounced than
vertical movements
Figure 1.1
Seinfeld & Pandis
• Temperature vs height
in different layers
of the atmosphere
HORIZONTAL ATMOSPHERIC MOTION GLOBAL
• Solar heating maximum at the equator
(2.4 X heating at the poles, annual average)
• Atmosphere carries heat from equator to poles
• Long horizontal distance vs short height,
break-up into tropical, temperate, and polar cells
(Figure 5.2 de Nevers)
• Rotation of Earth gives rise to different surface
wind patterns in these three zones:
• Tropical: southeasterly and northeasterly (trade
winds)
• Temperate: Westerlies
• Polar: Easterlies
Figure 5.2 de Nevers
• General circulation of
the atmosphere
HORIZONTAL ATMOSPHERIC MOTION LOCAL
• Land surface heats and cools faster than
ocean/lake surface.
• Daily and seasonal differences result in wind
patterns between land and water bodies.
(Figure 5.13 de Nevers)
• “Random” wind patterns between high
(anticyclone) and low pressure (cyclones) zones
superimposed on global and land-water winds
Figure 5.13 de Nevers
• Onshore, offshore
breezes
ANTICYCLONES - HIGH PRESSURE
• 1020 - 1030 mb
• Sinking air near the ground
• Evaporating moisture, clearing sky
• Weak winds, outward from center, clockwise in
the nothern hemisphere
CYCLONES - LOW PRESSURE
• 980 - 990 mb
• Rising air near the ground
• Condensing moisture, clouds and precipitation
• Strong winds, inward toward center, counterclockwise in the nothern hemisphere
WINDS
• GROUND LEVEL:
• Maximum, tornadoe: 200 mph (90 m/s)
• Typical: 10 mph (4.5 m/s)
• Velocity gradient in planetary boundary layer
• Frictionless velocity above ~ 500 m
(Figure 3.13 Wark & Warner)
• Wind rose used for reporting annual wind speed
and direction variation (Figure 5.14 de Nevers)
• Wind speed profile
Figure 3-13 Wark & Warner
WIND VELOCITY PROFILE
• Power law expression (empirical):
u z
  
u1  z1 
p
p  0.07  0.60
• p depends on environment (rural vs urban) and
atmospheric stability class (Table 3-3 Wark &
Warner)
• Reported wind speeds typically measured at 10 m
above ground
• Wind rose
Figure 5.14 de Nevers
TEMPERATURE LAPSE RATE
THE STANDARD ATMOSPHERE
• Compared with soil and water, the atmosphere is
relatively transparent to infrared radiation
• Soil and water surface absorb solar radiation,
heat up and heat the adjacent air by convection
• Atmospheric temperature decreases from
temperatures of 20 C at the surface, to around
- 50 C at the troposphere-stratosphere boundary
• “Standard” atmospheric lapse rate: 6.5 C/km
(average over day and night, summer and winter)
• A positive value is quoted for lapse rate although
temperature decreases with increasing height
(Figure 5.7, de Nevers)
ADIABATIC LAPSE RATE
Fluid statics:
dP
  g
dz
Thermodynamic behaviour:
ideal gas under reversible and
adiabatic (isentropic) conditions:
dP C p dT

P
R T
Small displacements of air packets in the atmosphere
can approximate isentropic conditions
(negligible friction and heat transfer)
Thus, Adiabatic Lapse Rate:
dT
gM

 10 C / km
dz
Cp
SUPERADIABATIC LAPSE RATE
• Lapse rate more than the adiabatic 10 C/km,
e.g. 12 C/km
• Small adiabatic displacements in the vertical
direction are enhanced by existing temperature
profile
• UNSTABLE conditions, leading to effective
mixing and dispersion
SUBADIABATIC LAPSE RATE
• Lapse rate less than the adiabatic 10 C/km,
e.g. 8 C/km
• Small adiabatic displacements in the vertical
direction are inhibited by existing temperature
profile
• STABLE conditions, leading to poor mixing and
dispersion
• Standard atmosphere
and adiabatic
temperature profiles
Figure 3-7 Wark, Warner & Davis
• Lapse rate as related to
atmospheric stability
Figure 3-8 Wark, Warner & Davis
Potential temperature, 
• The temperature that a volume of air would have
if brought by an adiabatic process from its
existing pressure P to a standard pressure P0,, of
1000 mbar
k 1
P0  k

  T 
P
• k = Cp/Cv,
• T: absolute
 1000 
 T

 P 
0.288
• Potential temperature
Figure 3-9 Wark, Warner & Davis
Figure 5.7 de Nevers
• Vertical temperature
distribution at various
times during day
INVERSIONS
• Temperature increases with height above ground
(I.e. positive dT/dz, negative lapse rate)
• Extremely stable conditions
• Radiation inversion: daily occurrence due to
cooling of ground surface at night
• Subsidence inversion: (elevated inversion,
inversion aloft): large regions of cold air sinking
from above due to weather patterns, heating at
adiabatic lapse rate
• Drainage inversion: due to horizontal motions,
cold air sliding in under warm air, or warm air
riding up on cold air
Subsidence inversion
• Adiabatic compression and warming of a layer of air
as it sinks to lower altitudes in the region of a high
pressure center.
• For an ideal gas:  dT 
1



 dP  adia C p 
• Cp ~ constant,  higher at the bottom
 dT 
 dT 

  

 dP  top
 dP  bottom
• Top warming faster, positive temperature gradient
could be established
Figure 3-10 Wark & Warner
• Subsidence, radiation
and combination
inversions
Figure
• Radiation inversion,
RidgeWarner
3-11Oak
Wark,
& Davis
FUMIGATION
• The daily radiation inversion starts breaking up
near the ground as the ground heats.
• This can lead to a sandwich phenomenon with an
inversion layer bounded by a stable layer above
and an unstable layer below.
• As the unstable layer from below reaches the
height of a pollutant plume in the inversion layer
the plume mixes downward, producing temporary
but high ground level concentrations.
(Figure 5.15 de Nevers)
Figure 5.15 de Nevers
• Fumigation
Atmospheric stability
• Two governing factors:
– Temperature gradient (lapse rate)
– Turbulence due to wind
• Dry adiabatic lapse rate : 10 C / km
• Saturated adiabatic lapse rate : 6 C /km
• “Standard” profile : 6.6 C / km
Atmospheric Stability Classes
(Pasquill 1961, Turner 1970)
Determinations based on inexpensive observations of
wind speed, solar radiation, cloudiness
A : Strongly unstable
B : moderately unstable
C : slightly unstable
D : neutral
E : slightly stable
F : moderately stable
G : strongly stable
Stability Classes
• Table 3-1 Wark,
Warner & Davis
• Table 6-1 de Nevers
Atmospheric Stability Classes
• Direct measurement of temperature gradient and
variation of wind direction.
• y , std deviation of horizontal wind direction
• z, std deviation of vertical wind direction
Table 3-2 Wark, Warner & Davis
• Comparison of
different stability
techniques
MIXING HEIGHT
• Common to find superadiabatic lapse rate near
ground level in the early afternoon under a strong
sun.
• This gives rise to an UNSTABLE well mixed layer,
above which there can be an adiabatic
(NEUTRAL) or subadiabatic (STABLE)
atmosphere. (Figure 5.9 de Nevers)
• Pollutants released at ground level will be
dispersed in this well mixed layer, the lower the
mixing height the higher the resultant pollutant
concentration
Figure 5.9 de Nevers
• Mixing height
MIXING HEIGHT
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Lower at night than during the day
Lower in the winter than in the summer
Can be strongly influenced by weather patterns
Typical values, 0 - 2000 m
(Figure 3.15 Wark, Warner & Davis
Winter mean mixing heights for U.S.)
MIXING HEIGHT MEASUREMENT
• Environmental temperature profile determined by
sending up a balloon that transmits temperature
vs height data for several km
• A dry adiabatic temperature line from the
maximum monthly surface temperature intersects
the previous line at the maximum mixing height
(Figure 3-14 Wark, Warner & Davis)
• Mixing height
estimation
Figure 3-14 Wark,Warner &
Davis
Plume
behaviour
• Figure 3-18 Wark,
Warner & Davis
Κλιματική Αλλαγή.
• Η άνοδος της
θερμοκρασίας στην
Ευρώπη, υπερέβη τον
παγκόσμιο μέσο όρο
αύξησης κατά τον 20ο αι.,
δηλαδή το 0.95 °C.
• Η μεγαλύτερη αύξηση
ήταν στην Ιβηρική
χερσόνησο, ΝΔ της
Ρωσίας και σε τμήματα
του Ευρωπαϊκού Αρκτικής
Περιοχής.
• Στην Ευρώπη τα 8
θερμότερα έτη
παρατηρήθηκαν μετά το
1990, με κορυφαίο το
2000.
Observed Emissions and Emissions Scenarios
Emissions are on track for 3.2–5.4ºC “likely” increase in temperature above pre-industrial
Large and sustained mitigation is required to keep below 2ºC
Linear interpolation is used between individual data points
Source: Peters et al. 2012a; CDIAC Data; Global Carbon Project 2013
European Fluxes Database Cluster
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