The Atmosphere
In this chapter you will investigate the structure and composition of the
atmosphere and its influence on physical systems of the Earth. Our atmosphere
is a dynamic mixture of gases that envelop the Earth
Permanent Gases .
Nitrogen and oxygen
 They are indeed important for maintaining life and driving a number of processes
near the surface of the Earth.
 The permanent gases that make up the atmosphere by volume are:
 Nitrogen (78%),
 Oxygen (21%) and
 Argon (0.93%).
 Physical geographers often refer to these gases as the "permanent gases"
because their concentration has remained virtually the same for much of recent
earth history.
 Nitrogen is a relatively inert gas produced primarily by volcanic activity. It is an
important component of protein in meat, milk, eggs and the tissues of plants,
especially grains and members of the pea family.
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Oxygen is important for human, plant and animal respiratory processes.
It is also important to chemical reactions (oxidation) that breakdown rock
materials (chemical weathering).
Without oxygen, things cannot burn either.
Free oxygen in the atmosphere is a product of plant photosynthesis.
Plants take up carbon dioxide and in the process of photosynthesis release
oxygen.
Variable Gases
Even though they represent a tiny portion of the atmosphere as a whole, they exert
a great control over our environment
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Carbon dioxide
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Methane
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Ozone
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Water vapor
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Particulates
Carbon dioxide(CO2 ) makes up only .036% of the atmosphere by volume.
Carbon dioxide is essential to photosynthetic processes of plants.
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Huge quantities of carbon are stored in plant tissue, deposits of coal, peat,
oil, and gas.
Carbon dioxide is taken in by plants and during photosynthesis is combined
with water and energy to form oxygen and carbohydrates.
The stored carbohydrates are used to fuel plant respiration and growth.
Because vegetation takes in so much carbon dioxide, we often refer to plants as
a "sink" for it.
Carbon dioxide varies throughout the year, decreasing slightly during the
summer as plants leaf out,
Increases during the winter as plants go dormant and photosynthesis decreases
Methane
Methane (CH4) is a greenhouse gas contributing to about 18% of global warming and has been
on the rise over the last several decades.
Though methane makes up far less of the atmosphere (.0002%) than carbon doxide, it is 20 times
more potent than CO2 as a greenhouse gas.
Methane is a product of the decomposition of organic matter, with major natural sources being
that which occurs from wetlands, termites, the oceans, and hydrates.
Figure TA.2 Natural Sources of Methane
(Courtesy US EPA: Source)
Ozone
Ozone (O3) is both beneficial and harmful to life on Earth.
Much of the ozone in the atmosphere is found in the stratosphere . Here, ozone absorbs UV
light from the Sun preventing it from reaching the surface.
Without this blanket, humans would be exposed to serious sun burn and potential risk of
skin cancer.
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Ozone is also found in the lowest layer of the atmosphere, the troposphere . Here ozone
can act as an eye and respiratory irritant. Ozone also causes cellular damage inside
the leaves of plants causing brown splotches, impairing carbon dioxide uptake and
disrupting the photosyntheitic apparatus.
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leaving more carbon dioxide in the atmosphere to enhance the greenhouse effect and
potential global warming.
Human-produced compounds such as chloroflourocarbons and halides containing chlorine
and bromine destroy ozone, and have disrupted the fragile stratospheric ozone layer over
Antarctica and the Arctic.
Water vapor
is an extremely important gas found in the atmosphere. It can vary from 4% in the
steamy tropics to nearly nonexistent in the cold dry regions of the Antarctic. Water vapor
is a good absorber of Earth's outgoing radiation and thus is considered a greenhouse
gas.
Particulates
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Particulates play several important roles in atmospheric processes.
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Particulate matter includes dust, dirt, soot, smoke, and tiny particles of
pollutants. Major natural sources of particulates are volcanoes, fires, windblown soil and sand, sea salt, and pollen.
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Human sources such as factories, power plants, trash incinerators, motor
vehicles, and construction activity also contribute particulates to the atmosphere.
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The most spectacular sunrises and sunsets are a result of light being refracted from
particulates in the atmosphere.
ATMOSPHERIC STRUCTURE
Troposphere
Stratosphere
Mesosphere and beyond
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It is the properties of the previously discussed layers that affect most of what we
study in physical geography.
Layers above the stratopause have relatively little impact on our elemental study
of Earth.
In the mesosphere air temperatures begin to decrease with increasing altitude.
99.9 percent of the gases that comprise the atmosphere lie below this level.
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The air of the mesosphere is thus extremely thin and air pressure very small.
The mesopause separates the mesosphere from the thermosphere above.
Figure TA 9 shows air temperature increasing with increasing altitude in the
thermosphere. Even though the temperatures are quite high in the
thermosphere, the heat content of the layer is very low due the low density of air
at this level.
Functional layers
Two layers, the ionosphere and ozonosphere are identified when using function as
the criterion for subdivision. The ionosphere is not really a layer of the atmosphere, but
an electrified field of ions and free electrons. The ionosphere absorbs cosmic rays,
gamma rays, X-rays, and shorter wavelengths of ultraviolet radiation. The spectacular
display of auroral lights are generally found in this region.
The ozonosphere is the concentrated layer of ozone found in the stratosphere. Ozone
(O3) absorbs ultraviolet light between 0.1 - 0.3µm. Though relatively constant through
millions of years, seasonal fluctuations of ozone especially over the Arctic and Antarctic
are common.
Review material you've just read by watching "Atmosphere" from the "Earth: The
Biography" series courtesy of National Geographic.
Greenhouses
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In order to understand the Greenhouse Effect one must first understand what a
greenhouse is and how it works.
Greenhouses keep the temperature inside warmer than outside.
Sunlight (shortwave radiation) passes through the panes of glass.
Materials within the greenhouse (plants, floors, walls, benches, etc.) absorb this
energy.
Absorbed radiation is reradiated as heat (longwave radiation).
The glass panes block the longwave radiation, thus trapping the heat, keeping
the air warm inside the greenhouse.
The Greenhouse Effect can be defined as a system in which shortwave radiation
is allowed to enter freely and is absorbed, then is reradiated as longwave
radiation. The longwave radiation is then retained within the system
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Does the greenhouse effect in the greenhouse continue to work if the panes of glass are
removed?
Earth as a Greenhouse
The gases within the Earth's atmosphere allow shortwave radiation to enter.
Some of the gases, liquids and particles absorb outgoing longwave radiation better
than shortwave radiation.
Greenhouse Gases In The Atmosphere
1. Water Vapor (H2O)
2. Carbon Dioxide (CO2)
3. Methane (CH4)
30 times more efficient at trapping longwave radiation than carbon dioxide
much less abundant than carbon dioxide
4. Chlorofluorocarbons (CFCs) - freon
5. Ozone (O3)
- Sources - naturally produced in upper atmosphere,
6. Pollutants, Greenhouse Particles
Any solid or liquid particles within the atmosphere can absorb longwave radiation
and re radiate it.
CRITICAL THINKING
Consequences of the Greenhouse Effect
 Is the Greenhouse Effect a bad thing?
How can the Greenhouse Effect be harmful?
 Rising levels of greenhouse gases is thought to cause a rise in
global air temperatures.
 Global mean surface temperatures have increased by .5 - 1.0 F
since the latter part of the 19th century.
 Rising temperatures have caused a decrease in snow cover and
sea ice in the Northern Hemisphere.
 Global sea level has risen by 4-8 inches over the past hundred
years. Additional sea level rise and inundation of coastal regions
is feared as Antarctic ice sheets and shelves, and smaller alpine
glaciers melt.
 The frequency of extreme precipitation events has increased
throughout much of the United States.
Watch "Global Warming 101" Courtesy of National Geographic