DEMOCRITUS UNIVERSITY OF THRACE Department of Environmental Engineering Prof. Dr. S. RAPSOMANIKIS...

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.