4. Composition of the Atmosphere
Air is composed of a mixture of gases:
Gas
N2
O2
Ar
concentration (%)
78
21
0.9
99.9%
Major
constituents
5. Composition of the Atmosphere
Air is composed of a mixture of gases:
Gas
greenhouse
gases
concentration (%)
N2
O2
Ar
H2O
CO2
CH4
N2O
O3
78
21
0.9
variable
0.037
Minor
constituents
7. Water? Or water vapor?
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
8. Composition of the Atmosphere
Air is composed of a mixture of gases:
Gas
greenhouse
gases
concentration (%)
N2
O2
Ar
H2O
CO2
CH4
N2O
O3
78
21
0.9
variable
0.037
Minor
constituents
10. 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
12. Composition of the Atmosphere
Air is composed of a mixture of gases:
Gas
greenhouse
gases
concentration (%)
N2
O2
Ar
H2O
CO2
CH4
N2O
O3
78
21
0.9
variable
0.037
Minor
constituents
16. Ozone (O3) production
• 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.
VOC + NOx +
+
= ozone
18. Ozone (O3) destruction
CFCs: float up to stratosphere and constantly react with O3 to form
ClO and O2:
Cl + O3 ClO+ O2
ClO + O Cl +O2
Scientists 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
CFCChlorofluorocarbons
CIO 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
20. See The Earth System, ed. 2, of 1-6
Figure 1-6 Simultaneous measurementsFig. ozone (O3) and
chlorine monoxide (CIO) made from a NASA aircraft as it
flew into the Antarctic ozone hole in September 1987.
21. The Nobel Prize in Chemistry 1995
Paul J. Crutzen
Max-Planck-Institute
Mario J. Molina
F. Sherwood Rowland
MIT
UC Irvine
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.
23. Vertical Profiles of Density
The density =
Mass
Volume
The density of air
decreases with height.
Density profile cannot be
used to describe
atmospheric structure!
24. Atmospheric Pressure
Pressure = force per unit area
Atmospheric Pressure at Sea Level:
1013.25 millibars (mb)
Pressure profile cannot
be used to describe
atmospheric structure!
25. Vertical Profiles of Temperature
How do you think
the temperature
varies with height?
26. 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
Unstable
90% of all the gases on Earth is in this layer
