The 2nd layer of the earth atmosphere, Stratosphere is explained in detail in this presentation....

1. The Earth’s Atmosphere
ِ‫ن‬ ‫ه‬‫م‬ْ‫ح‬ٰ‫ٱلر‬ ِ ‫ه‬ٰ
‫ٱَّلل‬ ِ‫م‬ْ‫س‬ِ‫ب‬
ِ‫يم‬ ِ‫ح‬ٰ‫ٱلر‬
Prepared By: Talha Liaqat
BS chemistry, KFUEIT

2. Different layers of the atmosphere
• The atmosphere is comprised of layers based
on temperature.
• These layers are the troposphere,
stratosphere, mesosphere and thermosphere.
• A further region at about 500 km above the
Earth's surface is called the exosphere.

3. Stratosphere
• The stratosphere is the 2nd layer of Earth's
atmosphere as you go upward.
• The troposphere the lowest layer, is right below the
stratosphere.
• The next higher layer above the stratosphere is
the mesosphere.
• The bottom of the stratosphere is around 10 km (6.2
miles or about 33,000 feet) above the ground at
middle latitudes.

4. Stratosphere
• The top of the stratosphere occurs at an altitude of
50 km (31 miles).
• Ozone, an unusual type of oxygen molecule that is
relatively abundant in the stratosphere
• Ozone heats this layer as it absorbs energy from
incoming ultraviolet radiation from the Sun.
• Temperatures rise as one moves upward through the
stratosphere.

5. • Temperatures rise as one moves upward through the
stratosphere.
• This is exactly the opposite of the behavior in the
troposphere in which we live, where temperatures
drop with increasing altitude.
• Commercial jet aircraft fly in the lower stratosphere to
avoid the turbulence which is common in the
troposphere below.
Stratosphere

6. Chemical composition of Stratosphere
Most of the compounds released at the Earth's surface do not reach the
stratosphere, instead they are:
• decomposed by the main tropospheric oxidants (hydroxyl radicals - OH,
nitrate radicals - NO3, ozone - O3)
• broken down by sunlight
• deposited back to the surface of the Earth in rain or as particles
• trapped in the cold tropopause.

7. Inorganic compounds in the stratosphere
• Stratospheric chemistry is dominated by the chemistry of ozone between 85
and 90% of all the ozone in the atmosphere is found in the stratosphere.
• Ozone is formed when sunlight breaks down molecular oxygen (O2) in the
stratosphere into oxygen atoms (O).
• The highly reactive oxygen atoms then react with more molecular oxygen to
form ozone (O3).
• Compounds such as ozone, nitrogen oxides, nitric acid, sulphuric acid,
chlorofluorocarbons halogens are the dominant chemicals in the
stratosphere.

8. Volacanic Eruptions
• Volcanic eruptions can inject large quantities of gases
and particles directly into the stratosphere.
• The particles such as and sulphur dioxide (SO2) which
is converted to sulphuric acid (H2SO4) emitted
include silicates and sulphates and these absorb
sunlight in the stratosphere.
• It lead to a temporary warming in the stratosphere
and a temporary cooling in the troposphere.
• These effects on temperature can last around 1 - 2
years.

9. The Ozone Layer
• The ozone layer or ozone shield is a region of Earth's stratosphere that
absorbs most of the Sun's ultraviolet radiation.
• It contains a high concentration of ozone (O3) in relation to other parts of
the atmosphere, although still small in relation to other gases in the
stratosphere.
• The ozone layer is mainly found in the lower portion of the stratosphere,
from approximately 15 to 35 km above Earth, although its thickness varies
seasonally and geographically.

10. The Ozone Layer

11. The Ozone Layer

12. Depletion of Ozone Layer
• The ozone layer can be depleted by free radical
catalysts.
• Free radicles including nitric oxide (NO), nitrous
oxide (N2O), hydroxyl (OH), atomic chlorine (Cl),
and atomic bromine (Br).
• The concentrations of chlorine and bromine
increased markedly.
• Man made organo-halogen compounds include
especially chlorofluorocarbons (CFCs)
and bromofluorocarbons.

13. Depletion of Ozone Layer
• These highly stable compounds are capable of
surviving the rise to the stratosphere.
• While Cl and Br radicals are liberated by the
action of ultraviolet light.
• Each radical is then free to initiate and catalyze a
chain reaction.
• Each chain reaction is capable of breaking down
over 100,000 ozone molecules.

14. Ozone Hole
• Nitrous oxide is the largest ozone-depleting
substance, and is expected to remain the largest
throughout the 21st century.
• The breakdown of ozone in the stratosphere
results in reduced absorption of ultraviolet
radiation.
• Unabsorbed and dangerous ultraviolet
radiation is able to reach the Earth's surface at a
higher intensity.
• Depletion of the protective ozone layer in the
upper atmosphere (stratosphere) is Called
Ozone Hole.