origin and composition of the atmosphere

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ORIGIN AND COMPOSITION OF THE ATMOSPHERE

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Planetesimals are objects of some Km of diameters that are thought to have formed during the solar system's formation.The origin of the Solar System has been tracked by Safronov's theory about 5 billion years ago, when an initial primordial nebula made of gas (mostly hydrogen and helium) and very diffuse dust grains (carbon and silicate) started to collapse gravitationally leading to the formation of a central protostar and of a surrounding, rotating disk structure, made from the material that was not incorporated in the protostar. During this disk phase (that can last up to 100 millions years), the grains of dust grow in size very rapidly (this phenomenon being called accretion) until, after a relatively short period, they form planetesimals. These planetseimals have a composition that depends on the region where they have formed (we find rocky planetesimals in the inner parts and ices in the outer parts) and are the "bricks" of the following formation of the planets. In fact in the last phase, the accretion of planets is possible, due to the impacts between planetesimals that can glue together, forming growing objects with a composition that is still respected by the actual structure of the solar system (where, in the inner parts, wet find rocky planets, while in the outer parts, planets are gaseous). Asteroids and comets are leftover planetesimals that have not been incorporated into a planet during this period.

http://www.ecology.com/archived-links/planetesimals/

THE BIRTH OF THE EARTH: ACCRETION OF PLANETESIMALS

5·109 years

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Inner core

Solid, radius 1200 km

External core

Líquid, radius 3470 km

Mantle

Radius 3470 km

Crust

Thickness 8 - 70 km

Adapted from:http://zebu.uoregon.edu/internet/images/earthstruc.gif

Structural diferentiation according to the density of different materials

THE INNER STRUCTURE OF THE EARTH

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Main component: Iron

Main component: Iron

Iron, magnesium, aluminium, silicon and oxigen

Sodium and aluminium silicate minerals

http://www.seismo.unr.edu/ftp/pub/louie/class/100/interior.html

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Originally formed by volatile compounds from volcanism at the earlier period of the Earth’s story. The gasses were kept back by gravity force. Since then, its composition undergone important variations because several physical, geological and biological processes.

THE ORIGIN OF OUR ATMOSPHERE

Actual volcanic eruptions have a mean composition of 85% H2O, 10% CO2 and SO2 and

nitrogen compounds (the rest).

Low percentage of H2O in the actual atmosphere

Low percentage of CO2 in the actual atmosphere

Predominance of nitrogen

Presence of other components of low concentration

Presence of an important fraction of O2

We have to explain…

http://www.xtec.es/~rmolins1/solar/es/planeta02.htm

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Dry air (majority components)

COMPOSITION OF THE ATMOSPHERE

Water steam: Until 4% (volum)

Adaptad from John M. Wallace y Peter V. Hobbs, Atmospheric Science: an introductory survey. Academic Press

Dry air (majority component)(% mass)

Composition below 100 km (percentages)

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(parts per million)

Ozone: 0-12 ppm

Minority components

COMPOSITION OF THE ATMOSPHERE (CONTINUED)

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WATER IN THE ATMOSPHERE

Low contents of water in the actual atmosphere

T

P

P3

T3

T3= 0.01 C = 273.16 K

TC

PC

1 atm

100 C

P3= 0.006112 bar

TC = 374.15 C = 647.30 K

PC = 221.20 bar

Both axis have not the same

scale

10 20 30º C10

20

30

40

mb

Room conditions

23 mb

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Low atmospheric contents in water

Limited ability to keep water steam in the air

Saturation and condensation

Precipitation and formation of the oceansHydrosphere

http://matap.dmae.upm.es/Astrobiologia/Curso_online_UPC/capitulo11/3.htmlInterdependence of the system

atmosphere / hydrosphere

WATER IN THE ATMOSPHERE (CONTINUED)

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Océano 97%

Hielo 2.4%

Otros 0.6%

Subsuelo 97%

Ríos y lagos 3,3%

Atmósfera 1,7%

Mass 1.36·1021 kg

The actual water content of the hydrosphere istwo magnitude orders LOWER than that have been injected into from the origin ot the Earth

* Filtration at subduction points* UV fotodisociation

How to explain this shortfall?

HYDROSPHERE

OceansIce

97 %2,4 %

Subsoil 0,6 %

Rivers & lakes 0,02 %Atmosphere 0,001 %

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The earth's surface is broken into seven large and many small moving plates. These plates, each about 50 miles thick, move relative to one another an average of a few inches a year.

At convergent boundaries, plates move toward each other and collide. Where an oceanic plate collides with a continental plate, the oceanic plate tips down and slides beneath the continental plate forming a deep ocean trench (long, narrow, deep basin.) An example of this type of movement, called subduction, occurs at the boundary between the oceanic Nazca Plate and the continental South American Plate. Where continental plates collide, they form major mountain systems such as the Himalayas.

http://geology.er.usgs.gov/eastern/plates.html

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Upper mantle

Oceanic crust

Continental crust

Ocean

Subduction (oceanic trench)

HYDROSPHERE. SUBDUCTION

Filtrations towards the mantle

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Fotodisociation

HYDROSPHERE. WATER FOTODISOCIATION

OOHH

HH104º

HH

HH

Molecule of water

OO

OOHH

HHOO

HH

HH

High atmosphere, low pressure conditions

High energy photons arise highly reactive free radicals, which recombinate as new chemical species. Specially hidrogen tends to run away because its low molecular mass.

UV high energy photons

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Low rate of carbon dioxide

Storing of carbon: * Rocks, salts, fossil oils* Atmosphere (free CO2) and ocean (solved CO2 * Biosphere

Oxigen presence in the crust:* Iron salts, carbonates y bicarbonates

Carbonates: arising by ionic exchange reactions (living beings)

H2CO3 + Ca++ CaCO3 + 2H +H2O + CO2 H2CO3

Estimation of carbon content in the Earth crust

(relative units)

Source: John M. Wallace y Peter V. Hobbs, Atmospheric Science: an introductory survey.

Academic Press. From P K Weyl, Oceanography.

John Wiley & Sons, NY, 1970

Marine biosphere 1

Continental biosphere 1

Atmosphere (CO2) 70

Ocean (solved CO2) 4000

Fossil oils 800

Salts 800000

Carbonates 2000000

CARBON DIOXIDE IN THE ATMOSPHERE

Geological and biological porcesses

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335

330

325

320

315

ConcentrationCO2 (ppm)

1958 1960 1962 1964 1966 1968 1970 1972 1974Año

Data from Mauna Loa observatory (Hawaii). Adapted from John M. Wallace y Peter V. Hobbs, Atmospheric Science: an introductory survey.

HUMAN ACTIVITY AND CO2 ATMOSFERIC CONTENT

Concentration increasing from 1750

Based on http://zebu.uoregon.edu/1998/es202/l13.html

1750

Actual

280 ppm

360 ppm

29%

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Atmospheric predominance of N2

The nitrogen content has been only slightly changed because its low reactivity

Around 20% fixed as nitrates (biological activity)

Other components of the atmosphere

SULPHUR: injected by volcanoes Acid rain

Sulphates in crust

NOBLE GASES: He, Ar From radiactive desintegrations

NITROGEN AND MINORITARY COMPONENTS

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OXIGEN

LIFE IN THE OCEANS

Water disociation (UV) 2H2O 2H2 + O2

Photosynthesis (visible light) H2O + CO2 {CH2O} + O2

Earlier living beings

(reducing environment) * 4109 años

Unicelular seaweedreleasing O2

2-3109 años

Formation O3 Decreasing UV

radiation in surface

LIFE ON THE SURFACE

Increased O2 releasing 4108 years

* See Miller’s experiment in http://matap.dmae.upm.es/Astrobiologia/Curso_online_UPC/capitulo9/4.html

SOURCES OF THE ATMOSPHERIC OXIGEN

O2 PRESENCE IN THE ATMOSPHERE AS A CONSEQUENCE OF

BIOLOGICAL PROCESSES

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ATMOSPHERIC PRESSURE

Below 100 km, for every height from the ground, pressure lies within an interval of 30% of a standard value.

Fluids equation: gdzdp

Vertical variation >> horizontal variationz

The air density decreases as height increses

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BP

BPgdzdP

z

Density and pressure are proportional

gdzdP Air is a compressible fluid

dzBgP

dP zP

P

dzBgP

dP

00

H

zzBgPPLn

0Bg

H 1 )/exp(0

HzPP

kmH 7It depends on the molecular mass of the gas

ATMOSPHERIC PRESSURE (CONTINUED)

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ATMOSPHERIC PRESSURE (EXAMPLE)

Mount Everest is the highest mountain in the Earth (8848 m). Explain which calculations may be performed to obtain the pressure on its top.Compare this pressure with the pressure in the seabed at 8848 m depth.Assume conditions of constant temperature. Data: Air density: 1.225 kg/m3; marine water density: 1030 kg/m3.

Ground level: 00 BP

Hence we estimate a value for B:0

0

PB

Pressure and density are proportional

Pa 1001325.1

kg/m 225.15

3

25 (s/m) 10209.1

Remember that...

BgH 1)/exp(

0HzPP m 8432

81.910209.1

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Ground level standard pressure

mb 8.354Pa 35481)8432/8848exp(51001325.1 P

From standard atmosphere calculator: P = 314.4 mbhttp://www.digitaldutch.com/atmoscalc/

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ATMOSPHERIC PRESSURE (EXAMPLE CONTINUED)


zT 5.615.288 z given in km, T given in K

256.515.288

25.1013

TP

T (K)288,2284,9281,7278,4275,2271,9268,7265,4262,2258,9255,7252,4249,2245,9242,7239,4236,2232,9230,6229,7226,4223,2219,9216,7

P (mb)St. Atm.1013,3954,6898,7845,6794,9746,8701,1657,6616,4577,3540,2505,1471,8440,3410,6382,5356,0331,0314,4307,4285,2264,4244,7226,3

P (mb)Ours

1013,3954,9899,9848,1799,3753,3709,9669,0630,5594,2560,0527,8497,4468,7441,8416,3392,3369,8354,8348,5328,4309,5291,7274,9

Calculus from standard atmosphere

Our calculus:

)/exp(0

HzPP

)8432/exp(25.1013 zP

z (m)0

5001000150020002500300035004000450050005500600065007000750080008500884890009500100001050011000

z (km)0,00,51,01,52,02,53,03,54,04,55,05,56,06,57,07,58,08,58,89,09,510,010,511,0

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0,0

200,0

400,0

600,0

800,0

1000,0

1200,0

0,0 2,0 4,0 6,0 8,0 10,0 12,0

z (km)

P (

mb

)

Standard atmosphere

Exponential dropping

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Comparison: pressure on the Everest top and pressure on the bottom of the sea

Oceanic trench

8848 m

-8848 m

Everest top

Pressure on the top

P = 314.4 mb(from standard atmosphere)

P = 354.8 mb(from our calculus)

The pressure exerted by a water column of height z is

gzP w 88488.91030

Pressure on the bottom

bar 893Pa 1093.8 7 P

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Troposphere

grad T -7 K·km-1

80% mass, 100% water steam Short times of permanence of particles

Estratosphere Very dry, O3 main concentration zoneHigh times of permanence of particles

Vertical mixture is scarce

99.9% mass

Mesosphere 99% rest

1% rest Termosphere

Charged particles (ionosphere)

Charged and non-charged particlesScarce collisions

TROPOPAUSE

ESTRATOPAUSE

MESOPAUSE

ATMOSPHERIC LAYERS

10 - 12 km

50 km

80 km

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Graphics obtained using yearly mean data from http://www-das.uwyo.edu/~geerts/cwx/notes/chap01/tropo.html

-80 -60 -40 -20 0 20 40 60 80

6

8

10

12

14

16

18

Altu

ra (

km)

Latitud (grados)

TROPOPAUSE HEIGHT

Troposphere

Estratosphere

Additional information:Map of tropopause pressures (mean values 1983-1998) http://www.gfdl.noaa.gov/~tjr/TROPO/TROPO.html

* Latitude

Over the equator the tropopause lies higher than upon the poles

* The season of the year

Factors affecting the height of the tropopause

* Temperature in troposphere

When temperature is low, the tropopause goes down because the convection decreases.

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STANDARD ATMOSPHERE

• Air temperatura at height 0 (sea level) is 15 ºC (288.15 K)

• Air pressure at height 0 is 1013.25 hPa

• Atmospheric air is considered as dry air and it behaves as an ideal gas

• Gravity acceleration is constant and its value is 980.665 cm/s2

• From sea level until 11 km the temperature decreases as height increases at a rate of 6.5 ºC/km: T = 288.15 K -( 6.5 K/km)· H (H: height in km)

• Throughout this layer pressure is calculated by P = 1013.25 hPa ·(288.15 K/T)^-5.256

• From 11 to 20 km the temperature remains constant: 216.65 K• Throughout this layer pressure is calculated by P = 226.32 hPa · exp(-0,1577·(H-

11km))

• From 20 to 32 km the temperature increases: T = 216.65 K + (H-20 km) (H: height in km)

• Throughout this layer pressure is calculated by • P = 54.75 hPa·(216.65K/T)^34.16319

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• From 32 to 47 km the temperature increases as height increases:

• T = 228.65 K + (2.8 K/km)·(H-32 km) (H: height in km)

• Throughout this layer pressure is calculated by

• P = 8.68 hPa · (228.65 K/T)^12.2011

• From 47 to 51 km the temperature remains constant at 270.65 K

• Throughout this layer pressure is calculated by

• P = 1.109 hPa · exp(-0,1262·(H-47km))

• The rest of upper levels can be obtained from the following references: A. Naya (Meteorología Superior en Espasa-Calpe); y, R.B.Stull (Meteorology for Scientists and Engineers)).

Standard atmosphere calculator:

Source: J. Almorox, http://www.eda.etsia.upm.es/climatologia/Presion/atmosferaestandar.htm

(until 86 km): http://www.digitaldutch.com/atmoscalc/

STANDARD ATMOSPHERE (CONTINUED)

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20

40

60

80

100

120

140

160

10-8 10-7 10-6 10-5 10-4 10-3 10-2 10-1 102 103101

Pressure (mb)

Density (g/m3)

Mean free path (m)

Height(km)

John M. Wallace y Peter V. Hobbs, Atmospheric Science: an introductory survey. Academic PressAdapted from CRC Handbook of Chemistry and Physics, 54th Edition. CRC Press (1973)

Graphic according with data from

STANDARD ATMOSPHERE. PRESSURE PROFILE

Mean path a molecule goes over before colliding another

Liquid water at room

conditions 106 g/m3

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Height

(km)

500/1500 Temperature (ºC)-50 0 50 100 150 200-100

10

20

30

40

50

60

70

80

90

100

110

120

130

140

150

160

490

500

510

520 Exosphere

Termosphere

Mesosphere

Stratosphere

Troposphere

STANDARD ATMOSPHERE. TEMPERATURE PROFILE

TROPOPAUSE

STRATOPAUSE

MESOPAUSE

Graphics from data in http://www.windows.ucar.edu/tour/link=/earth/images/profile_jpg_image.html

Temperature of termosphere is highly

dependent on sun activity. It may vary

from 500 ºC to 1500 ºC.

We live here!

TERMOPAUSE

TERMOPAUSE

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Diffusion tends to yield an atmosphere in which the mean molecular mass of the mixture components decreases as height increases. Each gas behaves in the same way as whether it were the only component in the mixture (ideal behaviour), and the density of each decreases exponentially as height increases. However the reference height H is different for each gas, and so the gasses having lower molecular mass are most abundant at the upper levels, because the density of the lighter gasses drops slower than that of the heavier gasses.

ATMOSPHERE COMPOSITION AS A FUNCTION OF HEIGHT

1. Diffusion by aleatory molecular movements

Height

Higher M, Higher B Lower M, lower B

The atmosphere composition varies as the height increases because the following reasons:

)/exp(0

HzPP Bg

H 1

Lower H Higher HP

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Could you demonstrate that really higher M implies higher B?

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2. Mixture for convection

Convection tends to homogenize the composition of the atmosphere. At low levels the mean free path is very small, so the time required for pulling apart different components is much larger than the time the turbulences take for arising a homogeneous mixture.

As a consequence, at low levels the atmosphere is a system well stirred whose components are very well mixed.

20

40

60

80

100

120

140

160

10-8 10-7 10-6 10-5 10-4 10-3 10-2 10-1 102 103101

m

km

Mean free path vs height

Above 100 km the mixture by convection is no longer as efficient as it was below, and it appears a difference in composition depending on the height.

The limit is about 100 km

ATMOSPHERE COMPOSITION AS A FUNCTION OF HEIGHT (CONTINUED)

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Most probable velocity:mM

kTv

2

Escape velocity: that velocity in what the kinetic energy of a particle is big enough to run away towards the infinitum. ( At a height of 500 km, the escape velocity from the Earth is about 11 kms-1)

Most probable velocity Hidrogen 3 kms-1

Oxigen 0.8 kms-1

Fraction of molecules with velocity equal to escape velocity

10 -6

10 -84

LOSE OF GASSES FROM THE ATMOSPHERE

Temperature at 500 km is 600 ºC Most probable velocity 3 kms-1

The lighter gasses did escape along the geological eras, so its actual abundance is low

http://www.iitap.iastate.edu/gccourse/chem/evol/evol_lecture.html

T: Absolute temperatureBoltzmann constant

k = 1.38·10-23 J K-1

m: Mass of the hidrogen atom

M: Molecular weight of a particular gas species

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Wind is the moving air from one place to another over the Earth surface. The air flux is related (among other causes) with pressure differences.

NO!

rur

PPgrad

Pressure gradient +

ru

The air tends to move

against the pressure gradient

WIND

1024

10201016

Pressure is a scalar

magnitude

-grad P

GRADIENT DIRECTION: THAT OF FASTER VARIATION OF THE SCALAR MAGNITUDE

…we need also consider the rotation of the Earth!

Blue arrows indicate the sense opposite to that of the gradient pressure

Do we conclude that wind moves as the blue arrows show?

GRADIENT SENSE: TOWARDS HIGHER VALUES OF THE MAGNITUDE

The change in pressure measured across a given distance is called a pressure gradient.

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rvaa RR 2

Centripetal force

Coriolis

Acceleration measured in a rotating reference frame

Acceleration measured in an inertial reference frame

rvaa RR 2

Rv

Rv2

Rv 2

North Pole

RvRv 2

Trajectory within an inertial reference frame

Trajectory within an accelerating reference frame

EARTH ROTATION EFFECTS

Within an rotating reference frame a Coriolis force proportional to appears, beeing responsible for the observed deviation

Rv 2

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Rv 2

Rv2

Deviation on the right-hand side respect the sense of the movement

Rv2

Rv 2

Deviation on the left-hand side respect the sense of the movement

N

S

Rv

Rv

CORIOLIS DEVIATIONSeen from a point over the surface

Sense of the movement

Coriolis deviation

NORTHERN HEMISPHERE

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SOUTHERN HEMISPHERE

Coriolis deviation

Sense of the movement

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GEOSTROPHIC WINDS

A

B

Geostrophic winds: winds balanced by the Coriolis and Pressure Gradient forces

Remember: if the Earth would not spin around its polar axis, the movement of the air masses will occur in the opposite sense to that the pressure gradient.

http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/fw/geos.rxml

Pressure gradientNorthern hemisphere

Gradient force

-grad P

Rv 2Coriolis force, proportional to

… and so on, up to the situation is…

A

B

…geostrophic winds blowing parallel to isobars

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Northern hemisphere: The Coriolis force arises deviation to the right

H

Within an anticyclone (H) the winds turn clockwise

L

Within a storm (L) the winds turn anticlockwise

ANTICYCLONES AND STORMS

Southern hemisphere: The Coriolis force arises deviation to the left

HWithin an anticyclone (H) the winds turn anticlockwise

L Within a storm (L) the winds turn clockwise

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11 Polar cell 22 Ferrell cell 33 Hadley cell

http://www.newmediastudio.org/DataDiscovery/Hurr_ED_Center/Easterly_Waves/Trade_Winds/Trade_Winds.html

ATMOSPHERIC GENERAL FLOW

Simple model

Air going down on the poles (cold areas) and air ascending on the equator (warm areas)

THIS SIMPLE MODEL HAVEN’T IN MIND THE EARTH’S ROTATION

Intertropical convergence zone

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ATMOSPHERIC GENERAL FLOW (CONTINUED)

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Polar Antarctic Circle

Polar Arctic Circle

WESTERN WINDS NEAR POLAR ZONES

ARCTIC ANTARCTIC

Relationship with the ozone hole over Antarctica

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Troposphere

The planetary boundary layer (PBL) is the atmospheric region, nearest the Earth surface (300-3000 m thickness), where it occurs the most of exchanges of energy

and matter. It is the zone where the interaction surface-atmosphere occurs.

PLANETARY BOUNDARY LAYER

Transport phenomena within PBL are related with turbulence

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1

10

100

1000

10000

Hei

ght (

mag

nitu

de o

rder

, m

)

RO

UG

HN

ES

S L

AY

ER

SU

RF

AC

E L

AY

ER

EX

TE

RN

L

AY

ER

TROPOPAUSE

LIM

IT L

AY

ER

(P

BL

)

TR

OP

OS

PH

ER

E

SURFACE ROUGHNESS

Turbulence: whirlpools arising from several causes

BASE OF THE CLOUDS

The planetary boundary layer is the part of the troposhpere directly influenced by the Earth surface. It is able to answer to the stimulation by surface forces wihin a temporal scale of 1 hour or less.

The forces associated with the Earth’s surface include drag friction, heat transfer, evaporation and transpiration, contaminant releasing and ground features able to modify the air flux.

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PLANETARY BOUNDARY LAYER (CONTINUED)

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SunriseSurface

warmingPBL stirring PBL increasing

thicknessPuesta de Sol

DAILY VARIATION OF THE PBL

Typical values at the end of the evening 1 km (0.2 km -

5 km)

SunsetNight begins

Surface cooling

Turbulence drops or

disappears

PBL thickness dropping

Typical values 100 m (20 m - 500 m)

1 km

(0.

2 km

-5 k

m)

100 m (20 m - 500 m)

Wind, temperature and other properties of the PBL undergo fewer daily variations over vast water surfaces as oceans and

great lakes than those over lands. This is because the greater specific heat of water.

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TEMPERATURE DAILY CYCLE

30 35 40 45 50T (ºC)

08:00

10:00

05:00

12:00

15:00

18:00

Height

15 cm

30 cm

60 cm

1.20 m

10.0 m

2.40 m

-2 cm

-5 cm

-15 cm

Typical summer profiles (land)(data: July and August mean, based on A. H. Strahler, Geografía Física)

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WATER CYCLE

Oceans

Atmosphere

1350·1015 m3

13·1012 m3

Eva

pora

tion

361·

1012

m3 /

yea

r

Prec

ipit

atio

n

324·

1012

m3 /

yea

r

Land

33.6·1015 m3

37·1

012 m

3 / y

ear

Und

ergr

aoun

d an

d su

rfac

e w

ater

Evaporation & transpiration

62·1012 m3/ year

99·1012 m3/ year

Precipitation

361·1012 m3/year

62·1012 m3/year

423·1012 m3/year

324·1012 m3/ year

99·1012 m3/ year

423·1012 m3/ year

ATMOSPHERIC BUDGET

Based onhttp://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/hyd/bdgt.rxml

Ambiental

Física

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Coriolis accelerationhttp://zebu.uoregon.edu/~js/glossary/coriolis_effect.htmlhttp://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/fw/crls.rxml

Anticyclonshttp://vppx134.vp.ehu.es/met/html/diccio/anticicl.htm

Stormshttp://vppx134.vp.ehu.es/met/html/diccio/borrasca.htm

S. Pal Arya, Introduction to Micrometeorology, 2th Edition. University Press.

http://www.rc-soar.com/tech/thermals.htm

http://f4bscale.worldonline.co.uk/Thermals.htm

Roland B. Stull, An Introduction to Boundary Layer Meteorology, Kluwer Academic Publishers

origin and composition of the atmosphere

Documents

actual structure

inner parts

mean composition

accretion of planets

outer parts

rocky planets

rocky planetesimals

academic press composition