1. UNIVERSITATEA DE STAT DE MEDICINA SI FARMACIE NICOLAE
TESTEMITANU
BIVOL NATALIA

2. LIST OF CONTENTS
1) ATMOSPHERIC AIR
2) PRINCIPAL LAYERS
3) ATMOSPHERE GASES
4) TROPOSPHERE
5) STRATOSPHERE
6) MESOSPHERE
7) THERMOSPHERE (IONOSPHERE AND
EXOSPHERE)
8) COMPOSITION OF AIR
9) CHEMICAL COMPOSITION OF AIR
10) OXYGEN
11) CARBON DIOXIDE

3. ATMOSPHERIC AIR
The atmosphere of Earth is the layer of gases, commonly known as air
that surrounds the planet Earth and is retained by Earth gravity. The
atmosphere protects life on Earth by absorbing ultraviolet solar
radiation, warming the surface through heat retention (greenhouse
effect), and reducing temperature extremes between day and night
(the diurnal temperature variations). By volume, dry air contains
78.09% of nitrogen, 20.95% of oxygen, 0.93% of argon, 0.039% of
carbon dioxide, and 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. Air content and atmospheric
pressure vary at different layers, and air suitable for use in
photosynthesis by terrestrial plants and breathing of terrestrial
animals is found only in the Earth's troposphere and in artificial
atmospheres.

4. PRINCIPAL LAYERS
In general, air pressure and density decrease with altitude in the
atmosphere. However, temperature has a more complicated profile with
altitude, and may remain relatively constant or even increase with
altitude in some regions. Because the general pattern of the
temperature/altitude profile is constant and measurable by means of
instrumented balloon soundings, the temperature behavior provides a
useful metric to distinguish atmospheric layers. 6 In this way, Earth
atmosphere can be divided (it is called atmospheric stratification) into
five main layers. Excluding the exosphere, Earth has four primary
layers, which are the troposphere, stratosphere, mesosphere, and
thermosphere. From the highest to the lowest, the five main layers
are: • Exosphere: 700 to 10,000 km (440 to 6,200 miles) •
Thermosphere: 80 to 700 km (50 to 440 miles) • Mesosphere: 50 to
80 km (31 to 50 miles) • Stratosphere: 12 to 50 km (7 to 31 miles) •
Troposphere: 0 to 18 km (0 to 7 miles)

6. ATMOSPHERE GASES
The concentration of atmosphere gases varies
depending on the atmosphere layers. The troposphere
contains primarily nitrogen (78%) and oxygen (21%).
The remaining 1% of the atmosphere is trace gases.
The stratosphere contains a layer of relatively high
concentrations of 7 ozone. The lower part of the
thermosphere is the ionosphere. This layer has free
ions and electrons that are the result of ionization of
gas molecules. As the distance increases from Earth
the atmosphere becomes thinner as the molecules
move further and further apart.

7. TROPOSPHERE
The lower boundary is the surface of the Earth. The upper boundary
varies between 7 km (23,000 ft.) above the poles and 14 km (56.000
ft.) above the equator. This is the layer of the atmosphere where we
live. The troposphere contains 75% of the total mass of the
atmosphere. The air cools 6.5°C for each kilometer above sea level.
Most of the energy from the sun travels through the atmosphere and
is absorbed by the ground. The ground heats up warming the air above
creating air currents. The rising of warm air and falling of cooler air
creates convection currents that cause air circulation in this layer of
the atmosphere

8. STRATOSPHERE
The lower boundary is the tropopause which separates the stratosphere
from the troposphere. The upper boundary of the stratosphere is 50
km (32 miles; 170,000 feet). The bottom layer of the stratosphere
remains constantly at approximately 60°C. Jet streams are formed
here as cold air from the poles meets the warmer air rising from the
equator. It is a strong eastward moving wind that blows horizontally
around the Earth. The stratosphere contains the ozone layer. Ozone is
created when radiation from the sun splits two-atom oxygen molecules
into separate atoms. They combine with other two-atom molecules to
form a three atom molecule. The layer acts as a shield from ultraviolet
radiation from the sun. The upper part of the stratosphere warms up
to approximately 18°C as the ozone reacts with ultraviolet radiation
giving off enough heat to warm this layer.

9. MESOSPHERE
The mesosphere is the third layer of the atmosphere. It extends from
the top of the stratopause to an altitude between 80 and 85 km. The
temperature begins to drop in this layer until it reaches minus 90°C.
The upper region of the mesosphere is the coldest region of the Earths
atmosphere layers. Water vapor is sometimes present in this layer and
it can be seen from Earth as thin feathery clouds of ice crystals.
Many meteors entering the atmosphere burn up in this layer. The heat
causes 8 enough friction between a meteoroid and gas particles in the
mesosphere to burn them up. Shooting stars are the trail of hot
glowing gases as a meteoroid burns

10. THERMOSPHERE (IONOSPHERE AND
EXOSPHERE)
Location of layer above Earth: 640 kilometers (400 miles; 2.100.000 feet).The
thermosphere has two layers of Earths atmosphere layers. The atmosphere is
very thin in the thermosphere. The space shuttles orbit in the thermosphere.
The layer has free ions and electrons that are the result of ionization of gas
particles. Radio waves bounce off the ionosphere allowing communication with
countries overseas. The aurora borealis, (northern lights) is formed when
electrically charged particles from the sun collide with particles in the
ionosphere producing multicolored lights. The temperature in this region can
reach 1500°C (2.730 degrees F). The air particles are so far apart that a
person would not feel warmth because of the low density of the particles. The
exosphere is the highest layer of the atmosphere. It extends up to 10.000 km
(6.200 miles; 33.000.000 feet.) above the Earth. Satellites orbit the Earth in
the exosphere. The atmosphere in this layer is extremely thin and atoms and
molecules of air are constantly escaping into the outer space. Free-moving
particles move in and out of the solar wind in the exosphere

12. COMPOSITION OF AIR
Air contains different gases such as nitrogen, oxygen, carbon dioxide
and other gases (It includes water vapour, trace gases like argon and
helium, hydrogen, smoke and dust particles, etc.) The below diagram
gives an idea about the main components of air.
The composition of air varies from place to place. For example, the air
is thinner on mountains as compared to plains. This is the reason why
mountaineers always carry oxygen cylinders with them. Also, the
percentage of oxygen in the air may be higher in areas where there is
more greenery. In the desert areas, the water vapour content will be
significantly lower than the regular areas because of the lack of water
in desert areas.

13. CHEMICAL COMPOSITION OF AIR
NITROGEN
It is the major component found in the air. It is the
most abundant gas on the earth’s planet too. It is
required by plants and animals for their growth. The
circulation of nitrogen between these organisms and
the atmosphere is called the nitrogen cycle.
The nitrogen cycle is essential for maintaining
productive and healthy ecosystems. Nitrogen present
in the air is also used to manufacture fertilisers
which helps in the healthy growth of plants.

14. OXYGEN
Air contains around 21% of oxygen.
It is called the life-supporting gas. Oxygen is necessary
for all living organisms because they derive energy from
food with the help of oxygen. Respiration is the process
of taking in oxygen, using it to make energy (by breaking
down food), and then exhaling carbon dioxide.
Besides breathing, the presence of oxygen is required for
combustion (that is, burning of fuels and other
substances). Both respiration and combustion processes
utilise oxygen and release carbon dioxide in the
atmosphere.

15. CARBON DIOXIDE
Carbon dioxide makes up a small component of the air
around us. It is an important gas for plants as well
as animals. Plants use carbon dioxide for making food
during the process of photosynthesis. Carbon dioxide
is known as a greenhouse gas as it helps to trap
heat. The property of trapping heat on the earth’s
atmosphere and thus maintaining a comfortably warm
temperature is known as the greenhouse effect. The
percentage of carbon dioxide in the atmosphere
keeps on changing from one place to another. It will
be more in polluted areas.

16. MEDICAL IMPORTANCE OF AIR
HYGIENE
It has thermolytic influence.
It has unfavorable effects when it drops
below some limits, which are considered to be
physiological, or when it exceeds some
superior limits.
It influences air pollution.
It influences the other physical air factors
(humidity, air currents, pressure).

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