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DEMOCRITUS UNIVERSITY OF THRACE Department of Environmental Engineering
Prof. Dr. S. RAPSOMANIKISDirector, Laboratory of Atmospheric Pollution and of
Pollution Control Engineering of Atmospheric Pollutants
Vas Sofias 12, 67100 Xanthi, GREECETelfax +3025410-79379, email:[email protected]
webpage: http://www.airpollab.org
PROPERTIES OF THE ATMOSPHERE
• 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, counter-clockwise 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)
Figure 3-13 Wark & Warner
• Wind speed profile
WIND VELOCITY PROFILE
• Power law expression (empirical):
• 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
60.007.011
pz
z
u
up
Figure 5.14 de Nevers
• Wind rose
TEMPERATURE LAPSE RATETHE 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
dzg
Thermodynamic behaviour:
ideal gas under reversible and
adiabatic (isentropic) conditions:
dP
P
C
R
dT
Tp
Small displacements of air packets in the atmosphere
can approximate isentropic conditions
(negligible friction and heat transfer)
Thus, Adiabatic Lapse Rate:
10 C / kmdT
dz
gM
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
Figure 3-7 Wark, Warner & Davis
• Standard atmosphere and adiabatic temperature profiles
Figure 3-8 Wark, Warner & Davis
• Lapse rate as related to atmospheric stability
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 = Cp/Cv,
• T: absolute
288.01
0 1000
PT
P
PT
k
k
Figure 3-9 Wark, Warner & Davis
• Potential temperature
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:
• Cp ~ constant, higher at the bottom
• Top warming faster, positive temperature gradient could be established
padia CdP
dT 1
bottomtop dP
dT
dP
dT
Figure 3-10 Wark & Warner
• Subsidence, radiation and combination inversions
Figure 3-11 Wark, Warner & Davis• Radiation inversion,
Oak Ridge
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
• 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)
Figure 3-14 Wark,Warner & Davis
• Mixing height estimation
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-industrialLarge and sustained mitigation is required to keep below 2ºC
Linear interpolation is used between individual data pointsSource: Peters et al. 2012a; CDIAC Data; Global Carbon Project 2013
VOCALS STATION OF GREECE
http://www.europe-fluxdata.eu/home/sites-list
VOCALS FOOTPRINT
What sort of lifestyle can the Earth sustain?
• Answers to some of these challenges can be found in the increased use of renewable energy.
• Many of the environmental problems we currently face are rooted in the way European land is used, and in the European economic structure and lifestyle.