Properties of the
Atmosphere
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Composition of the Atmosphere
• If your class is doing the “Composition of the
Atmosphere STEM Lab”, please complete it
before continuing this presentation.
• Answers to lab follow.
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Composition of the Atmosphere
• The atmosphere is a thin layer of gases
surrounding Earth. It protects us from
harmful radiation, meteors, and temperature
extremes.
• We simply call the gases in this atmosphere
“air”. Air, however, is composed of many
different gases.
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Our “Air”:
• 78% Nitrogen gas
• 21% Oxygen gas
• Remaining 1% is
made of trace
gases:
•
•
•
•
•
•
•
Argon
Carbon dioxide
Neon
Helium
Methane
Krypton
Helium
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Layers of the Atmosphere
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• Pressure is a force that
acts over a certain area.
• Liquids and gases are
fluids. Fluids are any
material that is able to
flow. Fluids exert pressure
because of the motion of
their particles.
• Pressure will always move
from a high pressure to a
low pressure area. The
pressure will always try to
equalize. You see this when
you get a hole in your
bicycle tire.
Pressure
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• Air inside
a ball pushes
against
Inflating
example
the sides. The more air we put in
a ball, the more the molecules
push. So the pressure increases
as we add air.
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• Air pressure Air
is thePressure
result of the column
of air that is above
you.
• There is so much air
above you that at
sea level you have
14.7 lbs/in2 pushing
on you.
• Gravity causes most
of the air to be
pulled down to the
surface.
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Why
we not crushed
• Why
don’tare
we feel
this pressure? pressure?
• Air pressure is
equal in all
directions.
• So air pushes
equally in all sides
of us. The forces
are balanced!
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by air
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Units of Air Pressure
• TV weather stations and aviation use
inches of mercury.
• Meteorologists (and the NWS) use
millibars, an SI unit.
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Altitude and Density
• As the air pressure decreases, the density of the air
decreases. The air particles are not squashed together as
tightly the higher one goes. This is caused by gravity!
• The air at sea level and at 6km has the same 21% oxygen, but
at 6km there are fewer molecules, so you take in less oxygen
with each breath.
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Layers of the
Atmosphere
• The atmosphere is
divided into imaginary
layers based on
temperature trends as
you move further from
the Earth’s surface.
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Temperature and the Troposphere
• Troposphere:
temperature at surface is
warmed by the earth
absorbing energy from
the sun.
• Convection currents
carry the heat upward,
so the air cools as it rises.
• The air cools by about
6.5°C for every 1-km
above the ground.
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If your class is doing the “Layers of
the Atmosphere Graphing: An
Inquiry Activity”
STOP HERE AND DO IT NOW.
Answers follow.
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Temperature
and the
Stratosphere
• Ozone absorbs
ultraviolet radiation
from the sun, causing
the temperature to
increase.
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Temperature
and the
Mesosphere
• This layer does
not absorb energy
from the sun, so it
starts to cool
again.
• Without
greenhouse gases,
energy pretty
much passes
straight through!
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Temperature and
the
Thermosphere
• Solar radiation first hits
this layer, so the few
particles that are here can
gain lots of energy. They
move rapidly, so they have a
very high temperature.
• But the air is so thin here
that it takes special
instruments to measure the
temperature accurately.
• So even though it is very
hot (over 1000°C), it would
feel cold because there are
so few particles to transfer
heat to you.
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The Troposphere
Lowest (inner) layer
weather occurs here
we live in it.
“tropo” means turning or
changing conditions
• depth varies from 9km
above the poles to 16km
at the equator
• shallowest (least thick)
layer, but contains most
of the mass (90%).
•
•
•
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The Stratosphere
• “strato” means layer or
spreading out
• Contains the ozone layer
which absorbs energy
and causes the
temperature to rise
• The ozone layer protects
the surface from
dangerous UV rays
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The Mesosphere
• Drop in
temperature
marks beginning of
mesosphere
• “Meso” means
middle
• Most meteors burn
up here
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The Thermosphere
• Very top layer
• Air is very, very thin, about
1/1000th as dense as the air at
sea level
• “Thermo” means heat
• Extends from 80km to space
• No definite outer edge
• Very hot (over 1000°C), but
since air is so thin it would not
feel warm at all.
• Divided into two parts, the
ionosphere and the exosphere
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The Ionosphere
• Energy from sun strips the electrons from the gas
molecules creating charged particles called ions.
• Radio waves can bounce off of ions, allowing radio
waves to travel great distances.
• The aurora borealis (Northern Lights) occur here
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The Exosphere
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“Exo” means outer
Extends for 1000’s of miles
Satellites orbit here
No definite edge
Molecules gradually escape out
into space
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Sources:
• All images used in this presentation are in
public domain. They may be used by anyone,
for any purpose.
• Information and content provided in this
presentation are property of Gnature with
Gnat and should not be copied or posted on
the internet without specific permission.
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