The document describes the composition and structure of Earth's atmosphere. It is divided into multiple layers based on chemical composition, thermal properties, and electromagnetic properties. The major layers from lowest to highest are: the troposphere, stratosphere, mesosphere, thermosphere, and exosphere. Each layer has unique characteristics such as varying temperature profiles and concentrations of different gases. The thermosphere and lower layers contain the ionosphere, where solar radiation ionizes gases to form a region that can reflect radio waves.

1. C0MPOSITION AND
STRUCTURE OF
ATMOSPHERE
ALI HASSAN VIRK

3. ATMOSPHERE
DEFINITION
Atmosphere refers to the gases
surrounding a star or planetary
body held in place by gravity. A
body is more likely to retain
an atmosphere over time if
gravity is high and the
temperature of
the atmosphere is low

4. FORMATION OF
ATMOSPHERE
As Earth cooled, an
atmosphere formed mainly
from gases spewed from
volcanoes. It included
hydrogen sulfide, methane,
and ten to 200 times as much
carbon dioxide as today's
atmosphere. After about half a
billion years, Earth's surface
cooled and solidified enough
for water to collect on it.

5. COMPOSITION OF THE ATMOSPHERE
MAJOR GASES
The most common atmospheric gas, nitrogen (chemical symbol N2) is
largely inert, meaning that it does not readily react with other substances
to form new chemical compounds. The next most common gas, oxygen
(O2), is required for the respiration (breathing) of all animal life on Earth,
from humans to bacteria. In contrast to nitrogen, oxygen is extremely
reactive. It participates in oxidation, examples of which include apples
turning from white to brown after being sliced, the rusting of iron, and
the very rapid oxidation reaction known as fire. Just under 1% of the
atmosphere is made up of argon (Ar), which is an inert noble gas,
meaning that it does not take part in any chemical reactions under normal
circumstances. Together, these three gases account for 99.96% of the
atmosphere.

6. TRACE GASES
A trace gas is a gas that makes up an
extremely small portion of a mixture of gases.
These include:
carbon dioxide
methane
oxides of nitrogen
ozone
 water vapor
 AMMONIA
 argon (the most abundant trace gas
representing about 0.934% of the Earth's
atmosphere)

9. STRUCTURE OF ATMOSPHERE
STRUCTURE OF ATMOSPHERE CAN BE DIVIDED
INTO THREE WAYS;
CHEMICAL COMPOSITION
Homosphere
Hetrosphere
THERMAL PROPERTIES
ELECTROMAGNETIC PROPERTIES

10. HOMOSPHERE
The homosphere is the layer of
an atmosphere where the bulk
gases are homogeneously
mixed due to turbulent mixing
or eddy diffusion. The bulk
composition of the air is mostly
uniform so the concentrations
of molecules are the same
throughout the homosphere.
It is about 80-100kms.
It consists of 99%mass of
Earth,s of atmosphere

11. HETROSPHERE
The heterosphere is the layer of an
atmosphere where the gases are
separated out by molecular
diffusion with increasing altitude
such that lighter species become
more abundant relative to heavier
species.
OCCURS ABOVE 100KMS
Heterosphere is the upper portion
of a two-part division of the
atmosphere according to the
general homogeneity of
atmospheric composition; the layer
above the homosphere.

12. ELECTROMAGNETIC PROPERTIES:
The division of atmosphere on the
basis of electromagnetic properties;
A. Non-ionosphere
B. Ionosphere
NON-IONOSPHERE:
 It lies from surface to height of
60km.
IONOSPHERE:
 The layer of the earth's atmosphere
which contains a high concentration
of ions and free electrons and is able
to reflect radio waves. It lies above
the mesosphere and extends from
about 80 to 1,000 km above the
earth's surface.

13. HOW IS THE IONOSPHERE FORMED?
• If we travel about 30 miles from Earth's surface up to the edge of space at
about 600 miles from the surface, we'll encounter a layer of the atmosphere
called the ionosphere.
• In the ionosphere, radiation from the sun is so powerful that it ionizes, or
breaks electrons free from different atoms present in the atmosphere. Due
to fluxes in solar radiation, temperatures in the ionosphere vary from 200
Kelvin (or -99 degrees Fahrenheit) to 500K (or 440 degrees Fahrenheit).
• Atoms in oxygen and nitrogen are the main targets of ionization. Very high
light energy from the sun excites atoms in these atoms during a process
called photoionization. The atoms, in turn, release negatively charged
particles called electrons. The atoms gain a positive charge as they release
the electron and more chemical reactions happen. When these chemical
reactions occur, some energy from the excited electrons is released as light,
creating a phenomenon called air glow, which is the diffused light that
allows us to see objects in the dark, even on extremely dark nights.

14. LAYERS OF IONOSPHERE
• D region:
• The D region is the lowest region of the ionosphere,
extending between 40 and 55 miles above the surface.
The D region doesn't stay electrically charged at night,
like other layers do. Without the sun's ionizing radiation,
the oxygen and nitrogen molecules combine to become
neutral, and this layer no longer deflects radio waves
back to Earth.
• E region:
• Unlike the D region, the E region remains charged at
night. Although, some of the ionization does decrease,
it's still enough to continue to bounce radio waves for
long distance communication.
• F region:
• The F region sits about 100 miles from the surface and
has the greatest concentration of ions compared to the
other layers. This layer maintains a mostly steady state of
ions, even at night. The F region can be divided into two
subregions, F1, which is closer to the earth, and a larger
layer, F2, which is farther away and has the greatest
concentration of ions.
•

15. THERMAL PROPERTIES
THE ATMOSPHERE IS DIVIDED INTO
FOUR ISOTHERMAL LAYERS;
TROPOSPHERE
STRATOSPHERE
MESOSPHERE
THERMOSPHERE
ALL LAYERS ARE CHARACTERIZED BY
UNIFORM CHANGE OF
TEMPERATURE.
THE TOP BOUNDARY OF EACH LAYER
IS DONATED BY PAUZE WHERE THE
TEMPERATURE PROFILE ABRUPTLY
CHANGE.

16. TROPOSPHERE  The following Characteristics below are:
 Most of the weather phenomena take place in this layer,that’s
Why this is called’ ZONE OF WEATHER’ The troposphere
contains almost all the water vapor and most of the dust.
 IT COMPROMISES 80% OF THE ATMOSPHERE.
 This layer subject to intense mixing due to both horizontal and
vertical mixing and because of this troposphere literally
means’ TUNROVER’
 Temperature decreases with height at an average rate of 10C
per 167m of height above sea level. This calls the normal lapse
rate.
 The troposphere extends up to a height of about 18km at the
equator and declines gradually to a height of 8km at the poles.
 The upper limit of the troposphere calls the tropopause. The
temperature stops decreasing in it. It may be as low as -580C.

17. STRATOSPHERE
• It is the second layer of the atmosphere as you go
upward. The troposphere, the lowest layer, is right
below the stratosphere.
• The stratosphere contains approximately 19% of
the earth's total atmospheric gases. 90% of the
ozone layer is found in the stratosphere's upper
crust. This ozone layer is important for man's
survival, and for the survival of life on earth, as it
absorbs the UV radiation from the sun that would
otherwise be deadly.
• A HIGHT OF ABOUT 50KM ABOVE EARTH SURFACE
• The stratopause (formerly Mesopeak) is the level
of the atmosphere which is the boundary between
two layers: the stratosphere and the mesosphere.
In the stratosphere the temperature increases
with altitude, and the stratopause is the region
where a maximum in the temperature occurs.

18. MESOSPHERE
The mesosphere is a layer of Earth's atmosphere.
The mesosphere is directly above
the stratosphere and below the thermosphere. It
extends from about 50 to 85 km (31 to 53 miles)
above our planet.
Temperature decreases with height throughout the
mesosphere. The coldest temperatures in Earth's
atmosphere, about -90° C (-130° F), are found near
the top of this layer.
The boundary between the mesosphere and the
thermosphere above it is called the mesopause. At
the bottom of the mesosphere is the stratopause,
the boundary between the mesosphere and the
stratosphere below.
Most meteors vaporize in the mesosphere. Some
material from meteors lingers in the mesosphere,
causing this layer to have a relatively high
concentration of iron and other metal atoms.
Very strange, high altitude clouds called "noctilucent
clouds" or "polar mesospheric clouds" sometime
form in the mesosphere near the poles.

19. THERMOSPHERE
 The thermosphere is a layer of Earth's
atmosphere. The thermosphere is directly
above the mesosphere and below
the exosphere. It extends from about 90
km (56 miles) to between 500 and 1,000
km (311 to 621 miles) above our planet.
 Solar activity strongly influences
temperature in the thermosphere. The
thermosphere is typically about 200° C
(360° F) hotter in the daytime than at
night, and roughly 500° C (900° F) hotter
when the Sun is very active than at other
times. Temperatures in the upper
thermosphere can range from about 500°
C (932° F) to 2,000° C (3,632° F) or higher.

20. THERMOSPHERE
The boundary between the thermosphere and
the exosphere above it is called the
thermopause.
Much of the X-ray and UV radiation from the
Sun is absorbed in the thermosphere. When the
Sun is very active and emitting more high
energy radiation, the thermosphere gets hotter
and expands or "puffs up“
many satellites orbit within the thermosphere,
changes in the density of (the very, very thin) air
at orbital altitudes brought on by heating and
expansion of the thermosphere generates a
drag force on satellites.

21. EXOSPHERE
• The exosphere is the outermost layer of
our atmosphere.
• The exosphere is the very edge of our
atmosphere. This layer separates the rest
of the atmosphere from outer space
• It’s about 6,200 miles (10,000 kilometers)
thick. That’s almost as wide as Earth itself.
The exosphere is really, really big. That
means that to get to outer space, you have
to be really far from Earth.
• The exosphere has gases like hydrogen and
helium, but they are very spread out.
There is a lot of empty space in between.
There is no air to breathe, and it’s very
cold.
•