1. EARTH’S “OCEAN” OF AIR
Prepared by: Christelle Angelica C. Corpin
BSE- Biological Sciences
OUR ATMOSPHERE IS OUR LIFE

2. The Earth’s Atmosphere
• Earth’s atmosphere differs from those of
other planets in the solar system.
• Venus – usually called “Morning Star” consist
of 97% CO2 with dense clouds containing
sulfuric acid.
• Jupiter and Neptune – consist of Hydrogen
(H2), helium (He) and methane (CH4)

3. COMPOSITION OF AIR
• FACTS:
a. Air is a mixture of many gases.
b. The two most abundant gases in the air are nitrogen
and oxygen.
c. The percentage by volume of gases in table 30 can
change as atmospheric conditions change.
d. except for Carbon Dioxide, the gases in air are
chemical elements.
e. Water vapor, although gaseous & commonly found in
the lower atmosphere, is not listed in table 30.

4. GAS SYMBOL % VOLUME
(at sea level)
Nitrogen Ni 78. 30
Oxygen O2 20. 99
Argon Ar 0.94
Carbon dioxide CO2 0.03
Hydrogen H2 0.01
Neon Ne 0.00123
Helium He 0.0004
Krypton Kr 0.00005
Xenon Xe 0.0006
Radon Rn trace
Humidity – the amount of water vapor in the air that varies from 1- 4% by volume
on the average. It is highest over bodies of water and under high atmospheric
temperature when evaporation is rapid.

5. PROPERTIES OF MATTER
1. Air occupies space.
2. Air consist of molecules of matter – tend to
spread out or diffuse throughout a vessel.
- Air can be compressed where it concentrates
atmospheric gases near the ground.
3. Air has mass – amount of matter in an object.
4. Air has weight – Earth’s gravity pulls down on
the molecules of the gases in the air.

6. ATMOSPHERIC PRESSURE
• Pressure – defined as force exerted on a
surface divided by its area.
- The weight of the upper portion of the
atmosphere presses down, or compresses, the
lower portion and all objects below it. This
compression produces air pressure.
• Evangelista Toricelli – Italian mathematician
discovered the weight of that column of air to
be 14.69 pounds.

7. • He used a mercury barometer - an instrument
that measures changes in atmospheric
pressure, which he himself invented.
• The value 14.7 lb/in2 at sea level became
known as one atmosphere (atm) = 1013. 25
newtons per square cm (N/cm2).
• Weathermen or meteorologists record
atmospheric pressure using another unit of
measurement called millibar (mb): 1 atm=
1013.25 mb or 103mb.

8. • Density – defined as mass per unit volume;
atmospheric density is greatest at the bottom
becoming less and less with altitude or more
height.
• In the same manner, atmospheric pressure is
greatest at the bottom.
• Atmospheric temperature – measure of the
average kinetic energy (or energy of motion) of
the molecules of an object (air mass) indicated by
the rise and fall of the column of mercury in a
thermometer.

9. • A higher temperature of air means that the
molecules have greater kinetic energy. They
are moving faster and bumping each other
with greater force. Thereby throwing them
apart.
• Warmer air is less dense than colder air;
colder air is denser than warmer air.

10. MAJOR DIVISIONS OF THE
ATMOSPHERE
Based on temperature variations

11. 1. TROPOSPHERE
• Is the bottom 16 to 18 km of the atmosphere
where winds, clouds and water vapor are found,
and where weather phenomena occur.
• Temperature varies greatly near the earth’s
surface. It is warmer near the equator and colder
toward the poles.
• Air grows colder as one goes up higher. The
temperature at the top of the troposphere is
around -45*C to -50*C.
• The average depth of the troposphere is 11 km at
the equator and 8 km at the poles.

12. 2. STRATOSPHERE
• Second major division of the atmosphere; lies
above the troposphere.
• It is in this region, the air grows warmer
although not uniformly, as one goes up higher.
• 30 km deep; its outer boundary is around 50
km above sea level. 99.9% of the mass of the
atmosphere is found within this 50 km of air.

13. 3. MESOSPHERE
• 3rd major division of the atmosphere, above the
stratosphere.
• Air grows colder again almost uniformly as one
goes up higher . This is because gases in this
region do not absorb the sun’s rays. The average
rate of temperature decrease is about 3.5*C per
km ascent.
• The average depth of the mesosphere is 30 km
and its outer boundary is around 80 km above
sea level.

14. BASED ON THE DISTRIBUTION
OF GASES IN THE ATMOSPHERE
1. Homosphere – is the bottom 90 km of the
atmosphere where there is continuous
movement of air masses.
- N2 and O2 are well- mixed; comes from the
prefix homo (meaning same), homogeneous
mixture of gases in this region.
- A notable exception is the ozone layer that
envelops the globe at around 30 km above
sea level.

15. 2. Heterosphere
• The outer portion of the atmosphere where
no mixing of gases takes place.
- Gases tend to separate in layers; hetero
meaning different.

16. BASED ON THE DISTRIBUTION OF
OZONE & IONS
1. Ozonosphere – the bottom 70 km of the
atmosphere where ozone is found.
 Stratospheric Ozone – refers to the ozone in the
ozone layer, some 30 km above sea level.
 Ground level ozone – refers to the ozone formed
near the earth’s surface, sometimes due to
photochemical reactions involving air pollutants.
 Ions – electrically charged particles; gas
molecules in the upper atmosphere become
ionized.

17. 2. Ionosphere -the region of the atmosphere
which is sufficiently ionized by solar ultraviolet
radiation.
- This is the outer portion of the atmosphere
where ions and electrons are trapped by
Earth’s magnetic field and form layers referred
to as D, E, F layers.
- They reflect radio waves back to the earth
which plays an important role in radio
transmission.