COMPOSITION AND STRUCTURE OF
ATMOSPHERE
Prepared By: Ms.Nargis Shamim
WHY DOES EARTH HAVE AN ATMOSPHERE?
ATMOSPHERE?
• Earth is the only planet in the solar system with an
atmosphere that can sustain life. The blanket of gases
not only contains the air that we breathe but also
protects us from the blasts of heat and radiation
emanating from the sun. It warms the planet by day
and cools it at night.
• Earth's atmosphere is about 300 miles (480
kilometers) thick, but most of it is within 10 miles
(16 km) the surface. Air pressure decreases with
altitude.
WHAT WE ARE GOING TO STUDY
IN THIS CHAPTER?
• Introduction:
Atmosphere
Composition
Gases
Water Vapours
Dust Particles
Structure
I.
II.
III.
IV.
V.
Troposphere
Stratosphere
Mesosphere:
Ionosphere
Exosphere:
COMPOSITION OF THE ATMOSPHERE
1. The atmosphere is composed of
various gases, water vapours and
dust particles according to the
National Center for Atmospheric
Research.(NCAR)
2. The proportion of gases changes in
the higher of the atmosphere in such
a way that oxygen will be almost in
negligible quantity at the height
of 120km.
3. Similarly, CO2 and water vapours
are found only up to 90km from
the surface of the earth.
CHEMISTRY OF THE AIR
1. Gases
The most abundant naturally occurring gas
is Nitrogen (N2), which makes up about
78% of air.
Oxygen (O2) is the second most abundant
gas at about 21%.
The inert gas Argon (Ar) is the third most
abundant gas at 0.96%.
There are also trace amounts of carbon
dioxide (CO2), neon (Ne), helium (He),
methane (CH4), krypton (Kr), hydrogen
(H2), nitrous oxide (NO), xenon (Xe), ozone
(O3), iodine (I2), carbon monoxide (CO), and
ammonia (NH3) in the atmosphere.
CONTINUE..
2. Ozone gas: 10-50 km above earth surface and acts as
filter, absorbing ultraviolet rays from the sun. Ozone
prevents the rays from reaching the surface of earth.
3. Water vapours is variable gas, decreases with altitude.
 It also decreases from equator towards the poles.
 Acts like blanket allowing the earth to neither to
become too cold nor too hot. Also contributes to the
stability and instability in the air.
4. Dust particles: are in higher concentration in
subtropical and temperate regions due to dry winds in
comparison to equatorial and polar regions.
The composition of atmosphere varies with local
environmental factors also.
STRUCTURE OF ATMOSPHERE:
THERE ARE FIVE LAYERS IN THE STRUCTURE OF ATMOSPHERE DEPENDING UPON
.
TEMPERATURE
1. TROPOSPHERE
• Lowermost zone of the atmosphere with an average
height of 11 km.
• The upper boundary lies at about 9 km above poles and 18
km above equator.
• This is the most important layer of the atmosphere
because this layer of gases is responsible for all kinds of
weather forming or meteorological processes.
• The zone separating troposphere from the stratosphere is
known as tropopause.
• The air temperature at the tropopause is about – 80 degree
Celsius over the equator and about – 45 degree Celsius over
the poles.
• The troposphere play great role in sustaining life on
earth.
2. STRATOSPHERE
2nd layer starting from tropopause and
extending up to an average height of 50
km. The salient features;
• The temperature remain constant for a
height of 20 km (above tropopause) and
then increasing of temperature.
• It contains almost the entire concentration
of OZONE GAS that occurs above the
Earth in the form of a well defined
envelope distinguished as Ozone layer.
• The stratosphere itself has a layered
structure and so that there is no significant
mixing and turbulence of gases in this
layer.
3. MESOSPHERE
• The term literally means middle area.
• Third thermal zone of atmosphere which begins
at stratopause at about 50 km above the surface
and continues up to a height of about 80 km.
• In this layer, once again temperature starts
decreasing with the increase in altitude and
reaches up to minus 100 celsius at the height of
80km.
• Weather balloons and jet planes cannot fly high
enough to reach the mesosphere, the orbits of
the satellites are above the Stratosphere.
• Most meteors from space burn up in this layer.
• Coldest Layer ( Higher altitude = Colder temp)
4.THERMOSPHERE
• Thermosphere constitutes a layer of sphere called Ionosphere
• The fourth zone starts at about 80 km and extends up to 500 km
above the mesopause and beyond.
• In this zone temperature rising once again and reaches up to
1000 C and above due to presence of ions.
• A special zone known as ionosphere which posses electrically
charged particles lying next to mesosphere
• The thermosphere absorbs a lot of the UV radiation and X-ray
given off by the sun. When the sun is more active and
the thermosphere heats up more, this layer of earth's atmosphere
increases in size.
• Radio waves transmitted from the earth are reflected back to the
earth by this layer.
5. EXOSPHERE
• The exosphere is the uppermost layer of the
atmosphere and temperature starts increasing
with height.
• Gases are very sparse in this sphere due to the
lack of gravitational force.
• Therefore, the density of air is very less here.
• No clear upper boundary.
SO, THE FIVE LAYERS OF THE ATMOSPHERE
INCLUDE
1.
2.
3.
4.
5.
The troposphere, where we live;
The stratosphere, which contains the ozone layer;
The mesosphere, where meteors burn;
The thermosphere, where satellites orbit Earth.
The exosphere and ionosphere Communication on Earth depends on
satellites.
CONCLUSION
• The earth's atmosphere acts as an insulating layer that protects the earth's
surface from the intense light and heat of the sun. The atmosphere protects us
from UV rays and other short wavelength light that would otherwise do a lot
of damage to the DNA of living organisms. e.g.( abnormal growth)
• The main elements of atmosphere which are subject to change and which
influence human life on earth are temperature, pressure, winds, humidity,
clouds and precipitation.
THANK YOU!