Composition of the Atmosphere
Variable Components of the atmosphere
0-4% by volumn
Aerosol - fine solid or liquid particles
suspended in the air (0.001 to 10 m )
10-50 km (stratosphere)
Formation of Ozone
CFCs such as CFCl 3
CFCl 3 UV Cl CFCl 2
Cl O ClO
ClO O 3 Cl 2O 2
Depletion of Ozone
The Ozone Hole
Ozone concentration drops
sharply over Antarctica
The Ozone Hole
1. Polar winter leading to the formation of circumpolar winds to develop the
polar vortex which isolates the air within it.
2. Cold temperatures; cold enough for the formation of Polar Stratospheric
Clouds. As the vortex air is isolated, the cold temperatures persist.
3. The chlorine reservoir species HCl and ClONO2 become very active on the
surface of the polar stratospheric clouds. The most important reactions are:
HCl ClONO 2 NHO 3 Cl 2
ClONO 2 H 2 O NHO 3 HOCl; HOCl HCl H 2 O Cl 2
Cl 2 h Cl Cl
Protecting the atmosphere’s ozone layer
An international agreement known as the Montreal Protocol on
substances that deplete the Ozone Layer was concluded under
the auspices of United Nations in late 1987.
Global Ozone Recovery Predictions
Extent of the Atmosphere
Atmospheric pressure P:
Force F acting on unit area due
to the weight of the atmosphere.
unit : kg m -1s - 2 , Pascal
M 5.14x1018 kg,
g 9.8 ms -1,
R 6.37x106 m
P 105 Pa,
103 hPa 103 mb
1 hPa 100 Pa 1mb
International System (SI) of units
or Metric system
Pressure Decreases with Altitude
Thermal Structure of the Atmosphere
Temperature unit : K, o C, F
t F t 32;
t (t F 32);
T t 273.16
atoms as they
•Averaged Surface temperature is
288.16K, or 15C.
•Decreases 6.5C per km up to 11 km
•Nearly all weather happens in this layer
Height of the tropopause
varies with latitude
Inversion: negative lapse rate.
Temperature increase with height.
The temperature at first remains nearly constant to
a height of about 20km, and then, increases sharply
until the stratopause.
The coldest layer of the atmosphere
Contains only a minute fraction of the air mass. The temperature rises owing to the
absorption of very shortwave solar radiation by atoms of O and N.
Vertical Variations in Composition
(from lowest to highest)
N2, O, He, H.
(80/90 km above)
The makeup of the air is
uniform in terms of the
proportions of its
component of gases.
(0 – 80/90 km)
Ionosphere: (80/90-400km) Molecules and atoms are
ionized by shortwave solar radiation into ions and electrons.
Australis (southern lights) from Space
Borealis (northern lights) from Alaska
Aurora results from the interaction between solar flare activity and Earth’s
magnetic field. Solar flare are massive magnetic storms emitting fast-moving
atomic particles (protons and electrons). As they approach the Earth, they are
captured by Earth’s magnetic field, which guides them toward the magnetic poles.
They impinge on the ionosphere and energize the atoms of oxygen and nitrogen
molecules to cause them to emit light.
Structure of the Atmosphere
Troposphere: Lowest 10 (mid-lat) to 16 km (tropics) . Where the weather
happens. Tropopause is top boundary, ~75% of the atmosphere
Lapse rate: Temperature decrease with height in the Troposphere,
standard = 6.5C per kilometer in the troposphere.
Inversion: Negative lapse rate, temperature increases.
Stratosphere: Temperature constant at about –55C then increases with
height to 45-50 km where it is about –5 to 0 C. Warmed by O3 absorption
(30-60 km) of solar UV. Stratopause is top boundary, ~ 99% of the
Mesosphere: Temperature decreases with height reaching < -85C.
Mesopause is top boundary, above 99.9% of the atmosphere at 80-85 km.
Thermosphere: Above the mesosphere. Temperature increases greatly
because air absorbs sunlight, but radiates inefficiently.
Boundary of Space: 100 km
Ionosphere: Overlaps Meosphere and thermosphere. Reflects AM radio at
night but during the day extends lower (100 km 60 km) and absorbs
most AM radio energy.
Ozone layer: 10-50 km, produced by sunlight breaking up oxygen Protects
us from solar UV.