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Lecture 4Atmospheric compositions

Atmospheric structure

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Main pointsAtmospheric Compositions• The most abundant gases• The most abundant greenhouse gases• The most variable gasAtmospheric Structure• Profiles of temperature, density and pressure• Troposphere• Stratosphere• Inversion layer

Atmospheric Compositions

Composition of the Atmosphere

Air is composed of a mixture of gases:

Gas concentration (%)

N2 78 MajorO2 21 constituentsAr 0.9

99.9%

Composition of the Atmosphere

Air is composed of a mixture of gases:

Gas concentration (%)

N2 78O2 21Ar 0.9H2O variableCO2 0.037

MinorCH4

constituentsN2OO3

greenhousegases

Water VaporH2O

Water vapor H2O

Invisible The most abundant greenhouse gas Variable, why? Only substance is naturally in three phases:

solid, liquid, and a gas

solid liquid gas

Water? Or water vapor?

Composition of the Atmosphere

Air is composed of a mixture of gases:

Gas concentration (%)

N2 78O2 21Ar 0.9H2O variableCO2 0.037

MinorCH4

constituentsN2OO3

greenhousegases

Carbon DioxideCO2

Global Carbon Budget

The dashed land-use change line does not include management-climate interactions

The land sink was a source in 1987 and 1998 (1997 visible as an emission)Source: Le Quéré et al. 2012; Global Carbon Project 2012

Greatest variation in land carbon sink

Source: Le Quéré et al. 2012; Global Carbon Project 2012

Steadily increasingSteadily increasing

Huge fluctuation in land carbon sink!

Huge fluctuation in land carbon sink!

Hence atmospheric CO2Hence atmospheric CO2

What controls land carbon sink?

What controls land carbon sink?

Composition of the Atmosphere

Air is composed of a mixture of gases:

Gas concentration (%)

N2 78O2 21Ar 0.9H2O variableCO2 0.037

MinorCH4

constituentsN2OO3

greenhousegases

Freon (CFC) and Ozone (O3)

Freon (CFC) concentrations

Freon-11 Freon-12

Source: http://agage.eas.gatech.edu/

Refrigerators, air conditioners

Freons are greenhouse gases but, more

importantly, they also affect ozone…

• Concentrated in stratosphere (10-50km)

• Produced by absorbing UV radiation through the ozone-oxygen cycle:

O2 + UV O + O,O + O2 O3

• Ground-level ozone (troposphere) is created when intense sunlight reacts with nitrogen oxides (NOx) and volatile organic compounds (VOCs), which mainly come from vehicles, power plants, and industrial facilities.

Ozone (O3) production

VOC + NOx + + = ozone

The Ozone “Layer”

Good ozone up high

Bad ozone near by

Ozone (O3) destruction

CFCs: float up to stratosphere and constantly react with O3 to form ClO and O2:Cl + O3 ClO+ O2ClO + O Cl +O2Scientists estimate that one chlorine atom can destroy 100,000 "good" ozone molecules.

The Antarctic ozone hole, seen from space, Sept. 16, 2000. More Dobson units = more ozone. Image from NASA/TOMS

CFCChlorofluorocarbonsCIO chlorine monoxide

Figure 1-6 Simultaneous measurements of ozone (O3) and chlorine monoxide (CIO) made from a NASA aircraft as it flew into the Antarctic ozone hole in September 1987.

Ozone record: Halley Bay

Global average

O3 and ClO flying into the ozone hole

See The Earth System, ed. 2, Fig. 1-6 Figure 1-6 Simultaneous measurements of ozone (O3) and chlorine monoxide (CIO) made from a NASA aircraft as it flew into the Antarctic ozone hole in September 1987.

Paul Crutzen, Mario Molina and Sherwood Rowland have all made pioneering contributions to explaining how ozone is formed and decomposes through chemical processes in the atmosphere. Most importantly, they have in this way showed how sensitive the ozone layer is to the influence of anthropogenic emissions of certain compounds. The thin ozone layer has proved to be an Achilles heel that may be seriously injured by apparently moderate changes in the composition of the atmosphere. By explaining the chemical mechanisms that affect the thickness of the ozone layer, the three researchers have contributed to our salvation from a global environmental problem that could have catastrophic consequences.

The Nobel Prize in Chemistry 1995

Paul J. Crutzen Max-Planck-

Institute

Mario J.

Molina MIT

F. Sherwood

Rowland UC Irvine

Atmospheric Structure

Air density?Air pressure?Air temperature?

Vertical Profiles of Density

Density profile cannot be used to describe atmospheric structure!

The density of air decreases with height.

The density = Mass Volume

Atmospheric Pressure

Atmospheric Pressure at Sea Level:

1013.25 millibars (mb)

Pressure = force per unit area

Pressure profile cannot be used to describe atmospheric structure!

Vertical Profiles of Temperature

How do you think the temperature varies with height?

The Troposphere Temperature decreases with height.

lapse rate (6.5 oC/km)

top of troposphere the tropopause

higher is summer, lower in winter

tropopause is proportional to mean tropospheric temperature

where all the weather occurs

Unstable90% of all the gases on Earth is in this layer

Tropopause

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Why is a fire always going up?Hot and lighter!

Fire hot air

Why this balloon can carry so many people?

Because the air density is less than surroundings

Stable State

example: if you push the rock A along either side of the hill and then let go, it will return to its original position

Unstable State

example: if the rock rests on the top of the hill, a slight push will set it moving away from its original position

Stable?

Brick

Stable?