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The Atmosphere Notes
Composition
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When the Earth was first formed, its primitive atmosphere was made up of hydrogen and
helium, just like our sun.
 Early volcanic activity and meteorite impacts can inject large quantities of dust and gases into
the early atmosphere:
carbon dioxide, sulfur dioxide, water vapor, and nitrogen.
The dust acts as seeds for clouds.
 The amount of oxygen in the atmosphere increased when early photosynthetic life –
cyanobacteria (blue-green algae) – consumed carbon dioxide and generated oxygen.
 Today’s Earth’s atmosphere is 78% nitrogen, 21% oxygen, and 1% trace gases (carbon dioxide,
argon, hydrogen, etc).
Structure
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Troposphere: Lowest layer of the
atmosphere where temperature
decreases with altitude.
Tropopause: area between troposphere
and stratosphere where the
temperature stops decreasing.
Stratosphere: clear, dry layer above the
tropopause. Upper part of the
stratosphere warms steadily because of
the ozone layer. Ozone absorbs
ultraviolet rays and releases this energy
in the form of heat.
Mesosphere: temperatures again drop
at you move up the mesosphere.
Thermosphere: atmosphere is very thin,
but receives intense solar radiation. A
portion of the thermosphere is called
the ionosphere where the sun’s
radiation knock off electrons in the
gases and causes them to form auroras.
Earth Systems and Effects
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Our atmosphere is stable because of a delicate balance of gases moving between parts of the
Earth system: atmosphere, geosphere, hydrosphere, and biosphere.
The carbon dioxide content of the atmosphere has increased due to human activities, primarily
the burning of fossil fuels: coal, gasoline, and natural gas.
Heat and the Atmosphere
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Energy from the sun heats Earth’s atmosphere and surface.
Heat moves through the atmosphere in three different ways: radiation, conduction, and
convection.
Convection: Transfer of heat energy through motion of liquid or gas caused by differences in density.
Conduction: Transfer of heat energy through collisions of the molecules of a substance.
Radiation: Transfer of energy through space in the form of electromagnetic waves.
• Energy from the sun radiates through space
to heat the atmosphere and Earth’s surface by conduction & convection
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The accumulation of carbon dioxide and water vapor in the atmosphere absorbs and retains
heat so that it can’t escape into space: greenhouse effect.
Insolation: incoming solar radiation
The intensity of insolation depends on the angle at which the sun’s rays strike Earth’s surface.
When the sun is directly overhead, the angle of insolation is 90°, and Earth’s surface receives the
maximum amount of energy.
Energy Transfer
Energy transfer among sun, atmosphere & Earth’s surface produces weather.
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If more energy comes in than leaves, Earth’s temperature will increase
If more energy leaves than comes in, Earth’s temperature will decrease
Local Temperature Variations
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The temperature changes from place to place because solar energy heats the Earth’s surface
unequally.
The intensity of solar energy varies with the time of day, the latitude, and the time of the year.
Human Impact on the Atmosphere
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Ozone Depletion – a hole in the protective ozone layer created by chlorofluorocarbons (CFCs)
Biologic activity, including human activity, may influence global temperature and climate.
Air pollution – harmful particles caused by volcanoes, forest fires, and human activity.
Acid Rain – sulfur dioxide and nitrogen react with water vapor create an acid rain that kills fish
and forests, and damages structures of marble and limestone.
Smog – nitrogen oxides and hydrocarbons (auto exhaust) that, when triggered by solar
radiation, create harmful ground-level ozone.
Global Warming – due to increase in greenhouse gases.
Rising sea levels
Melting polar caps
Stronger storms
More storms and droughts
Relocation of crop areas
Water in the Atmosphere
Humidity- water vapor in the air
o Specific humidity: actual amount of water vapor in the air at a given time & place (grams of
vapor per kilogram of air)
Warmer air can hold more water vapor
As humidity increases, pressure decreases because water molecules are less massive than air.
Measured with a psychrometer
Condensation and Dew Point
Condensation: when water changes from a gas to a liquid
• Fog & clouds form only when there are condensation nuclei (like dust particles) for the water to
condense on
• Air must cool below its dew point
• Warm air rises taking the water vapor along with it. Once it cools, it condenses forming a cloud.
Cloud Types
Types of Precipitation: Any form of water that falls from a cloud to Earth’s surface
o Rain
o Snow
o Sleet: raindrops that refroze on their way to the surface
o Freezing Rain: raindrops that only freeze when they hit the surface
o Hail: when frozen raindrops are bounced up & down in the cloud until they fall in a huge ball of
ice
o depends on the temperature of the atmosphere, both at the surface & on the way down
Two instruments used to measure precipitation:
1. Rain gauge: measures liquid precipitation
2. Measuring stick: measures frozen precipitation
Where is precipitation?
Rain Shadow effect: near a mountain range, the windward side gets lots of rain and the leeward side
gets little/no rain – the rain shadow