The document summarizes the key layers of Earth's atmosphere: 1. The troposphere is the lowest layer where weather occurs. It contains around 75% of the atmosphere's mass. 2. The stratosphere lies above the troposphere, containing the ozone layer which absorbs ultraviolet rays. 3. Above the stratosphere is the mesosphere where temperatures drop with increasing altitude.

1. Introduction to environment
Dr. Shagufta Parveen

2. Air around us
• We live at the bottom of an invisible ocean called the
atmosphere, a layer of gases surrounding our planet.
• The combination of gases present in our air, like
oxygen, carbon dioxide, and water vapor, surround
the Earth in a large belt called the atmosphere.
• It is the Envelop of air surrounding us

3. Components of air
• By volume, dry air contains
1. 78.09% nitrogen,
2. 20.95% oxygen,
3. 0.93% argon,
4. 0.04% carbon dioxide,
5. small amounts of other gases.
Air also contains a variable amount of
water vapor, on average around 1% at sea
level, and 0.4% over the entire atmosphere

4. Atmosphere and climate
• The ability of Earth’s atmosphere to keep our planet warm is what
makes it so important to climate change.
• Gases present in atmosphere determine the climate of planet
• A layer of carbon dioxide, in our atmosphere is specifically
responsible for determining climatic especially heat changes
Global warming is caused by
the greenhouse effect, a natural process
by which the atmosphere retains some of
the Sun’s heat, allowing the Earth to
maintain the necessary conditions to host
life. Without the greenhouse effect, the
average temperature of the planet would
be -18 º C.

6. Atmospheric temperature
• Atmospheric temperature is a measure of the
temperature at different levels of the earth's
atmosphere.
• The average temperature of the atmosphere is
15 ° C. This temperature is defined as the
statistical measure obtained at the highest
and lowest temperatures.

7. Atmospheric pressure
• Atmospheric pressure, also known as barometric
pressure is pressure within the earth's
atmosphere.
• The typical atmosphere is a pressure unit defined
as 101,325 Pa which is equal to 760 mm Hg,
29.9212 inches Hg, or 14.696 psi.
• The atm unit is about the same as the
atmospheric pressure at sea level on Earth, that
is, the atmospheric pressure at sea is almost 1
atm.

9. Layers of atmosphere
• Thermosphere.
• Mesosphere.
• Stratosphere.
• Troposphere.

10. Troposphere
• The troposphere is the lowest layer of Earth's
atmosphere and site of all weather on Earth.
• The total average height of the troposphere is 13 km
• It contains 75% of the atmosphere's mass and 99% of
the total mass of water vapour and aerosols.
• The bottom of the troposphere is at Earth's surface.
• Air is warmest at the bottom of the troposphere near
ground level. Air gets colder as one rises through the
troposphere.

11. Increasing height decrease atmospheric
pressure as there is less overlying mass left
above so atmospheric pressure decrease with
increasing height
Pressure on Earth varies with the altitude
of the surface; so air pressure on
mountains is usually lower than air
pressure at sea level.
Scientists calculate the atmospheric
pressure at sea level by measuring the
height of a column of mercury and
calculating the pressure the atmosphere
has to exert to raise the column to that
height.

12. Troposphere

13. The troposphere is the lowest layer of the
atmosphere, characterized by a temperature
that decreases with altitude. The top of the
troposphere is called the tropopause, which
occurs at an altitude of 18 km at the equator
but only 8 km at the poles (the cruising
altitude of commercial airliners is typically 10
km). Gravity, combined with the
compressibility of air, causes the density of an
atmosphere to fall off exponentially with
height, such that Earth's troposphere contains
80% of the mass and most of the water vapor
in the atmosphere, and consequently most of
the clouds and stormy weather.

14. Stratosphere
• Second major layer of earth atmosphere
• The stratosphere is subdivided (coated)
at temperatures
• high and cool warm layers are close to
Earth
• Increase in temperature and altitude is
the result of the absorption of ultraviolet
rays into the ozone layer.
The lower edge of the stratosphere is as high
as 20 km (66,000 ft; 12 mi), at midlatitudes
around 10 km (33,000 ft; 6.2 mi), and at poles
of about 7 km (23,000 ft; 4.3 mi) [5]
Temperatures range from -51 ° C (-60 ° F; 220
K) near tropopause to -15 ° C (5.0 ° F; 260 K)
near the mesosphere

15. Presence in this layer
• The ozone layer is mainly found in the lower portion of
the stratosphere, approximately 15 to 35 kilometers
above Earth, although its thickness varies seasonally
and geographically.
• Bacterial life survives in the stratosphere, making it a
part of the biosphere.
• Some bird species have been reported to fly at the upper
levels of the troposphere.

16. Mesosphere
• The mesosphere is the third layer of the atmosphere
• Present directly above the stratosphere and directly below the thermosphere.
• In the mesosphere temperature drops as the temperature rises.
The temperature feature is used to define its limits: it begins at the top of the
stratosphere (sometimes called stratopause), and ends at the end of the
period, which is the coldest part of the earth's atmosphere with
temperatures below -143 ° C (-225 ° F; 130 K). The upper and lower limits of
the mesosphere vary in size and season (higher in winter and in tropical,
lower in summer and higher), but lower limits are usually found at altitudes
from 50 to 65 km (31 to 40 mi; 164,000 to 213,000 ft) above the earth's
surface and the upper boundary (mesopause) is usually around 85 to 100 km
(53 to 62 mi; 279,000 to 328,000 ft).

18. Thermosphere
• Thermosphere, a region of increasing temperature in the earth's atmosphere
found above the mesosphere.
• The base of the thermosphere (mesopause) is about 80 km (50 miles) high, and its
surface (thermopause) is about 450 km.
• It has highest temperature
The thermosphere is very important for human health as it contributes greatly to the
protection of the earth, and it has enabled us to explore modern space and
communication systems. It also absorbs water, absorbs solar energy, and generates
moderate heat
Reason of high temperature:
It lies above the mesosphere the middle layer of the atmosphere and directly below
the exosphere which is the upper layer of the atmosphere. It exhibits the highest
temperatures across the atmosphere because it absorbs X-rays and ultraviolet rays
from the sun. These rays increase the temperature of the thermosphere.

19. Exosphere
• Uppermost layer, where atmosphere thins out
• There is no clear boundary between exosphere and space
• Composed of light gases such as helium and hydrogen
• Very fast moving molecules present
• Air density is so low that a fast-moving air molecule is more than 50 percent
likely to escape from the atmosphere instead of hitting other molecules.