Lecture4 sep16-bb
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Transcript of Lecture4 sep16-bb
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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?