Unit 2: Surface Processes and the
Hydrosphere
Lesson 1: Characteristics and Significance of the Atmosphere
(Heath Earth Science – Pg. 480-487)
Today’s Objectives
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Explain the characteristics and significance of the atmosphere,
including:
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Demonstrate and explain the relationships among air volume, density,
pressure, and temperature
Describe the effects of the sun’s radiation on the atmosphere,
including the greenhouse effect, conduction, convection, and radiation
Describe the structure of the atmosphere and the abundance of
various substances in it
Predict the effects of changing the composition of the atmosphere
(e.g., ozone depletion, adding water vapour, greenhouse gases, and
pollutants)
The Atmosphere
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The Earth is surrounded by a life-giving gaseous
envelope called the Atmosphere
The atmosphere extends from the Earth’s surface to an
altitude of a few hundred kilometers
The Atmosphere provides us with the air that we breath
as well as protection from the Sun’s dangerous radiation
The atmosphere is also responsible for our weather and
our climate
Bill Nye Video – The Atmosphere
Did you know?
 If
we could gather all of the gases
that make up our atmosphere, and
weigh them on a scale, the mass
would be about 5 x 1018 kg!
Layers of the Atmosphere
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Our atmosphere has 4 main layers and a transitional layer
that have varying characteristics:
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Troposphere ~ 0-18 km above surface
Stratosphere ~ 18-50 km above surface
Mesosphere ~ 50-80 km above surface
Thermosphere ~ 80-500 km above surface
*Exosphere ~ 500~10,000 km above surface
*Exosphere is a transitional zone between atmosphere
and outer space
A further sub-layer extends from about 65-500 km above
surface known as the ionosphere
Layers of the Atmosphere
• The layers are
based on
temperature
changes
• Each layer is
separated by a
zone called a “pause”
• At each “-pause”
the temperature
remains
relatively
unchanged
Characteristics of Atmospheric Layers
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Troposphere (0~18 km)
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Thickness depends on latitude: at equator ~18km thick; at poles~8
km thick
Atmosphere is most dense in troposphere
The gases of the troposphere are essential to life on Earth
Earth’s weather occurs in the troposphere
Temperatures gradually decrease with altitude
Stratosphere (18~50 km)
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Ozone layer found in stratosphere
Clear and dry
Strong steady winds
Steady weather conditions make stratosphere ideal for flights
Temperature steadily increases due to ozone absorption of sunlight
Characteristics of Atmospheric Layers
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Mesosphere (50~80 km)
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Thermosphere (80~500 km)
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Steadily dropping temperature with increasing altitude due to
lack of ozone
Steadily rising temperature with increasing altitude due to
nitrogen and oxygen atoms absorbing solar energy
*Exosphere (500~10000 km)
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Exosphere has very low density as distance from earth makes
gravitational pull very weak
No clear boundary between exosphere and outer space
Ionosphere
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Ionosphere (65~500 km)
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Air is highly ionized
Ions formed when ultraviolet (UV) rays from the sun knock
electrons off oxygen atoms
Stretches from lower mesosphere to top of thermosphere
These ions are responsible for reflecting radio waves, making
broadcasting and cell phones possible
Also responsible for the aurora borealis and aurora australis, also
known as the northern and southern lights
Practice
 Topic
Questions, pg. 483 #5, 6ab
Atmospheric composition
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Our atmosphere is not just made of oxygen!
Atmospheric composition:
Atmospheric Composition
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Air thins out quickly with increasing altitude
Composition remains the same by percentage to about
80 km
Above this altitude, gases form layers
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Oxygen up to 1000 km
Helium up to 2400 km
Hydrogen above this gradually thinning out into space
Gas molecules at the bottom of the atmosphere are
squeezed together by the gases above
As a result, 99% of atmospheric mass is within 32 km of
Earth’s surface
Water Vapour, Ozone, and Dust
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Water Vapour:
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Air always contains some water vapour due to evaporation from
oceans, and plants
Amount varies with location, season, and time of day
Most is near the surface, decreasing with height
Ozone:
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Ozone is a form of oxygen gas, each molecule contains 3 oxygen
atoms compared with 2 in oxygen gas
Ozone forms when UV rays from sun act on oxygen in upper
atmosphere
Most concentrated at 10~50 km above surface to form ozone layer
Absorbs 99% of harmful UV rays
What are the consequences of ozone depletion?
Dust
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Dust is another part of the air
includes tiny grains of rock, dirt,
pollen, salt crystals from sea spray,
soot from fires, chemicals from
factories, and bacteria
Dust helps form fog and rain: water
vapour condenses around dust
particles, forming tiny water droplets
*The Chinese government sometimes
uses a method called “cloud seeding”
before important holidays to reduce
the chance of rain
Cloud Seeding
Ozone Depletion
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Ozone thinning occurs
from release of gases
called
chlorofluorocarbons
(CFC’s) into the
atmosphere
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Used as coolants in air
conditioners, cleaners, and
foam products
Do not break apart easily;
chlorine atoms break
down ozone layer in
presence of sunlight
Ozone Depletion
• The ozone layer decreased
by as much as 50% with
increased use of CFC’s in
the 80’s and 90’s
• Most noticeable at the
poles where cold weather
allows clouds to form in the
mesosphere: ice crystals in
these clouds provide
places for ozone
destruction
• Global CFC policies have
reduced this depletion, but
ozone won’t fully recover
until approx. 2050 at the
earliest
Practice
 Topic
Questions, pg. 483 #3, 4
Heat Transfer in the Atmosphere
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The sun provides most of the thermal (heat) energy in our
atmosphere
This heat is transferred in 3 ways:
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1) Radiation
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Sun radiates energy in the form of waves
These short waves are seen as visible light
2) Conduction
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Conduction occurs when heat is transferred from a hot object to a cooler
object by physical contact
Ex. Air warms as it passes over the warm ocean
Heat Transfer in the Atmosphere
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3) Convection
 Most effective form of heat transfer in liquids and gases,
therefor most effective in atmosphere
 Molecules nearest heat source gain kinetic energy and
move farther apart, becoming less dense
 Cooler, more dense gas/liquid above sinks, forcing up the
warmer, less dense gas/liquid – this flow is called a
convection current
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*If water were heated from the top, why wouldn’t
convection occur?
Heat Transfer in the Atmosphere
• Transfer of
warm or cold
air by
horizontal
winds is
called
advection
Temperature Drops with Altitude
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In the troposphere, the temperature drops about 1°C for
every 160 meters gained in altitude
This is called the normal lapse rate
Why?
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Most of suns radiation is absorbed by the earths surface
Heat is transferred to the air by conduction and carried aloft by
convection
The rising air cools from expansion due to lower pressure
Lower pressure allows air molecules to move farther apart
As molecules move farther apart, they collide less often, so less
energy is transferred
Less energy = lower temperatures
The Greenhouse Effect
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The Earth’s surface radiates infrared waves
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These waves warm the atmosphere because they are absorbed
by water vapour and carbon dioxide in the air
These gases are known as “greenhouse gases”
Just like in a greenhouse, these gases allow the suns short wave
UV radiation to enter, but trap the Earth’s long wave infrared
radiation, thus heating the atmosphere
The greenhouse effect is necessary for life on earth,
without it, our planet would be too cold
However, the burning of fossil fuels is constantly adding
CO2 to the air, increasing the greenhouse effect, and
consequently raising temperatures
What are the consequences?
Earth’s Energy Budget
Practice
 Topic
Questions, pg. 486 #7-9
Air Pollution - Activity
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Next class: we will measure the particulate air pollution in
Shanghai
We will place several microscope slides with scotch tape
attached to them in various locations around the school
campus
We will leave these slides in place for several days, then
view them under microscopes
We can count the number of particles on the tape per
unit of area to determine the particulate air pollution