Download Ch. 23 The Atmosphere

Ch. 23 The Atmosphere
Ch. 23.1 Characteristics of the
Atmosphere
Composition of the Atmosphere
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Most abundant elements—nitrogen, oxygen,
and argon.
Most abundant compounds—carbon dioxide
and water vapor.
Water vapor is added through evaporation and
transpiration, and removed through
condensation and precipitation. Its
concentration varies from 4% to less than 1%.
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Ozone—a form of oxygen (O3 instead of O2)
that exists in the upper atmosphere—important
because it absorbs harmful ultraviolet rays.
Ozone can be destroyed by human pollutants
such as chlorofluorocarbons (CFC’s).
Also present is atmospheric dust—suspended
mineral particles from the land and salt
crystals from the ocean.
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78% Nitrogen
21% Oxygen
0.9% Argon
0.1% other (including carbon dioxide)
Oxygen in the Atmosphere
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Oxygen is both removed and replaced in the
atmosphere at a constant rate, so the
percentage of oxygen remains in a state of
balance.
Removed by: animals, bacteria, plants,
burning of fuels and forests, and the
weathering of rocks.
Replaced by: land and ocean plants through
photosynthesis.
Nitrogen in the Atmosphere
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The nitrogen cycle maintains a constant
amount of nitrogen in the atmosphere.
Nitrogen moves from the air, to the soil, to
plants and animals, and again back to the air.
Nitrogen-fixing bacteria convert atmospheric
nitrogen into useful nitrogen compounds taken
up by plants, which are then eaten by animals.
Denitrifying bacteria release nitrogen back to
the air when plants and animals decay or
excrete waste.
Atmospheric Pressure
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Atmosphere is held by Earth’s gravity.
99% of atmosphere’s mass is within 32 km of
the surface.
Remainder extends upwards towards space for
hundreds of kilometers, getting thinner with
increasing altitude.
Weight of the atmosphere presses on the
surface.
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A column of air one square inch at its base, at
sea level, and extending upward to the upper
edge of the atmosphere, weighs 14.7 pounds.
Force of the air on the surface can be
expressed in newtons (101,325 N).
Atmospheric pressure is the ratio of the force
of the air to the area of the surface on which it
presses.
Atm. press. decreases with increasing altitude.
Mercurial Barometer
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Barometers are instruments that measure
atmospheric pressure.
In a mercurial barometer, the atmospheric
pressure presses on a bowl of mercury and
forces it up a tube.
At sea level, mercury would be forced up the
tube to an average height of 760 mm.
Aneroid Barometer
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Aneriod—without liquid.
Contains sealed metal container at a vacuum.
Sides of container flex inwards or outwards
depending on air pressure.
Pointer attached to container. It moves along a
scale, and indicates the atmospheric pressure.
Layers of the Atmosphere
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Pressure gradually decreases with increasing
altitude, but temperature shows distinct
differences with increasing altitude.
Temp. differences are due to the way solar
energy is absorbed as it moves downward
through the atmosphere.
Four distinct layers based on temperature
differences.
The Troposphere
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Layer closest to the earth, in which nearly all
weather occurs.
Almost all water vapor and carbon dioxide
found in the troposphere.
Temp. decreases with increasing altitude, due
to increasing distance from earth’s surface
(and distance from the warming effect of
sunlight absorbed by earth’s surface).
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Rate of temperature decrease is about 6.5° C
per km.
The Stratosphere
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Extends upward from the troposphere to a
height of about 50 km.
Contains most of the ozone in the atmosphere
(the ozone layer).
About -60° C at its base, but temp. begins
rising in upper stratosphere as altitude
increases…due to direct absorption of solar
energy by ozone.
The Mesosphere
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Layer above the stratosphere, extending to an
altitude of about 80 km.
Temperature decrease as altitude
increases…the coldest layer, dropping to about
-90° C.
Very thin air, but thick enough to burn up most
meteors.
The Thermosphere
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Layer above the mesosphere. Temperature
increases steadily with altitude, due to
absorption of short wavelength solar energy by
oxygen and nitrogen.
Although very high temperatures
(over 2000°C recorded), air is so thin and its
molecules so far apart that little heat is
transferred.
Upper boundary of thermosphere not
accurately determined.
The Ionosphere
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Within lower region of thermosphere (80 – 550
km).
Solar rays strip electrons from gas molecules,
forming ions and free electrons.
There are four layers of the ionosphere.
Free electrons can reflect radio waves back to
earth.
The Exosphere
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Region of atmosphere where it blends into the
vacuum of interplanetary space.
Extends thousands of km above the surface.
Air Pollution
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Substances in the atmosphere harmful to
people, animals, plants, or property.
Results mainly from the burning of fossil fuels.
Gases from fossil fuels combine with water to
form acid rain, which kills plants and fish.
Sometimes, cold air becomes trapped under
warm air…this condition is a temperature
inversion. The air is unable to disperse, and
pollutants build up (common in Los Angeles).
The result is smog (smoke and fog).