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:rapso@env.duth.gr

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.