The Earth’s Atmosphere
Earth’s Atmosphere
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Atmosphere is the gaseous layer that surrounds the earth

Is a mixture of gases that is naturally odorless, colourless,
tasteless and formless

Air is blended so thoroughly that it behaves as if it were a
single gas
The Atmosphere
Air is held to the earth by the force of gravity:
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The further away from the source of gravitational attraction
(earth) the lower the attractional force
More air molecules are held closer to the earth than at
higher elevations
Atmosphere is more dense near the surface than at higher
elevations
The Atmosphere

No real “top” – atmosphere drifts off to nothingness above
about 100 km

97% of the weight and 100% of the water vapor reside in
the bottom 30 km
Density
The density (mass per unit volume) of the atmosphere quickly
decreases with increasing elevation above sea level
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Density of the atmos can be measured as it exerts its
weight as a pressure (force per unit area)
The pressure the atmos exerts on the surface is know as
air pressure
 Air pressure at sea level = 1013 mb
 Air pressure at the top of the stratosphere (50km) = 0.78 mb
Composition of the atmosphere
Proportion of Elements in Dry Air (by volume)

Nitrogen – N2
78%
Plants
Proportion of Elements in Dry Air (by volume)

Nitrogen – N2
78%
Plants

Oxygen – O2
21%
Animals
Together, Nitrogen and Oxygen account for
99% of the atmosphere, by volume!
Proportion of Elements in Dry Air (by volume)

Nitrogen – N2
78%
Plants

Oxygen – O2
21%
Animals
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Argon – Ar
0.93%
Inert Gas
93% of the remaining 1% is Argon, an inert gas!
Proportion of Elements in Dry Air (by volume)
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Nitrogen – N2
Oxygen – O2
Argon – Ar
Carbon Dioxide – CO2
78%
21%
0.93%
0.0325%
Plants
Animals
Inert Gas
Plants
Proportion of Elements in Dry Air (by volume)
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Nitrogen – N2
Oxygen – O2
Argon – Ar
Carbon Dioxide – CO2
Neon – Ne
78%
21%
0.93%
0.0325%
0.0005%
Plants
Animals
Inert Gas
Plants
Inert Gas
Proportion of Elements in Dry Air (by volume)
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Nitrogen – N2
Oxygen – O2
Argon – Ar
Carbon Dioxide – CO2
Neon – Ne
Krypton – Kr
78%
21%
0.93%
0.0325%
0.0005%
0.0001%
Plants
Animals
Inert Gas
Plants
Inert Gas
Inert Gas
Proportion of Elements in Dry Air (by volume)
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Nitrogen – N2
Oxygen – O2
Argon – Ar
Carbon Dioxide – CO2
Neon – Ne
Krypton – Kr
Hydrogen – H2
Helium – He
Xenon – Xe
Methane – CH4
78%
21%
0.93%
0.0325%
0.0005%
0.0001%
0.00005%
<0.00001%
<0.00001%
<0.00001%
Plants
Animals
Inert Gas
Plants
Inert Gas
Inert Gas
Inert Gas
Inert Gas
The Atmosphere

Water Vapor

Ozone

Chlorofluorcarbons – CFCs (e.g., Freon)
Changing Concentrations of:
 Ozone
 Carbon Dioxide
 Methane
 Water Vapor
Climate

H2O
O3
0 to 4%
0.0 to 0.0012%
Change!
Important Roles Played by Trace Gases
Carbon Dioxide
 An important absorber of outgoing terrestrial radiation
 It, along with water vapor, serve as the primary means
of preventing rapid heat loss from the earth and
atmosphere back into space
Important Roles Played by Trace Gases
Water Vapor  An important absorber of outgoing terrestrial energy
 Amounts vary from 0 to 4% depending on of
evaporating water available and distance that source
 This can cause tremendous differences in temperatures
within the atmosphere
http://weather.unisys.com/satellite/sat_wv_us.html
Important Roles Played by Trace Gases
Liquid Water –
 Causes clouds to form… this affects the amount of heat
absorbed by the earth and atmosphere
 Can vary tremendously within the atmosphere
Insolation losses in the atmosphere
Dust - Gas molecules, dust, and other particulates are
important because they can cause the sun’s rays to be
scattered or absorbed
Scattering - visible light rays to be turned aside in all
possible directions. Under clear sky conditions, scattering
sends about 5% of the incoming solar radiation back to
space.
Absorption - Solar rays strike gas molecules and dust, and
their energy is absorbed and temperatures rise. This
accounts for about a 15% decrease in solar radiation.
Both carbon dioxide and water vapor are capable of directly
absorbing some wavelengths of solar radiation.
Electromagnetic Radiation
Electromagnetic radiation can be:
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Absorbed – increases the energy content of the object,
like a black car in the summer
Reflected – bounce the energy back toward the source,
like a mirror
Transmitted – pass through without absorption or
reflection, like a pane of glass
Electromagnetic Radiation

Albedo – percent of solar/shortwave radiation that is
reflected from a surface.
New snow:
Clouds:
Dark, wet soil:
Asphalt:
Grass:
80%
50%
5%
5%
20%
Old Snow:
Ice:
Light, dry soil:
Forest:
Crops:
Water – high incident angle
Water – low incident angle

50%
35%
40%
15%
20%
50%
5%
Average albedo of the earth’s surface:
7%
Electromagnetic Radiation

The atmosphere is generally transparent to
shortwave radiation and opaque to longwave
THE GREENHOUSE EFFECT
Vertical Distribution of the Atmosphere
The Troposphere
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Layer of the atmosphere in contact with the surface
Temperature decreases with height because the
troposphere is heated from below (atmosphere is
generally transparent to shortwave radiation)
Layer that contains all weather and all clouds
Extends to about 12 to 15 km; actual height varies with
latitude and season (thicker as temperature increases)
Much water vapor and dust – from interactions with
the surface
Contains about 80% of the mass of the atmosphere
Vertical Distribution of the Atmosphere
The Tropopause

Small, isothermal layer above the troposphere
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Isothermal – no temperature change with height
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About 12 to 15 km in height – actual height varies with
latitude and season
Vertical Distribution of the Atmosphere
The Stratosphere
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Layer of the atmosphere above the troposphere
Temperature increases with height because of
absorption of ultraviolet light by ozone (O3)
Extends up to about 50 km in height
Little exchange of air between troposphere and
stratosphere – little dust or water vapor
Stable air layer – little vertical motions because of the
increasing temperature with height -- inversion
Vertical Distribution of the Atmosphere
The Stratopause
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Small, isothermal layer above the stratosphere
Isothermal – no temperature change with
height

About 50 km in height
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Vertical Distribution of the Atmosphere
The Mesosphere

Layer of the atmosphere above the stratosphere

Temperature decreases with height because of a lack
of contact with the ground and a lack of ozone

Extends up to about 80 km in height
Vertical Distribution of the Atmosphere
The Mesopause

Small, isothermal layer above the mesosphere

Isothermal – no temperature change with height

About 80 km in height
Vertical Distribution of the Atmosphere
The Thermosphere
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Layer of the atmosphere above the mesosphere
Temperature increases with height because of energy
from gamma and x-ray absorption due to the earth’s
magnetic field (van Allen radiation belt)
Density of air at this altitude is very thin and the
thermosphere holds little heat
Thermosphere essentially drifts off to nothingness
above about 120 km
Lapse Rates:
Temperature decreases with increasing altitude within the
troposphere at an average rate of 6.4 C/km
6.4 C/km = Normal Lapse Rate
The actual decrease in temp, or actual lapse rate may vary
considerably from the normal lapse: environmental lapse
rate
Pollution
The atmosphere is made up of two zones based in function:
to remove harmful wavelengths of solar radiation and charged
particles
Ionosphere
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Extends throughout the
thermopause and into
underlying mesosphere
Absorbs cosmic rays, gamma
rays, x-rays, and shorter
wavelengths of UV rad
Absorption changes atoms to
+ve charged ions ~ ionosphere
Ozonosphere

ozone layer that is within the
stratosphere that contains O3

Highly reactive to oxygen
molecules
Ozone is harmful to living
creatures when present near the
surface
Is necessary as absorbs harmful
wavelengths of UV rad and
reradiates it as safer LW rad
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Ozone Depletion
CFC’s- Chloroflurocarbons
-became widely used in the 1920s for industry
-valuable as propellants for aerosol sprays and as refrigerants
-also used in industry as solvents and foaming agents
Good for industry as were not flammable
 Cannot be broken down by atmospheric processes near the earth’s
surface
 Not water soluble and do not break down by biologic processes
 Can be broken down by UV radiation within the stratosphere

-CFC’s migrate to the stratosphere over time
Breakdown of CFCs from UV radiation

Separates single Cl atoms or chlorine monoxide (ClO)
molecules from the CFC components
Ozone is an unstable molecule (O2 or O3)

Chlorine is a catalyst for the destruction of ozone

One Cl atom can decompose 100,000 ozone molecules
 Cl atoms have a residence time within the ozone layer of 40-100yrs.

Example of ozone breakdown……
1970s – noticed depletion in levels of ozone, studies into the
effect of chemicals on ozone depletion
1978 – US banned CFC’s in aerosols but was still used in
refrigerants and polyurethane foam
1981 – banned CFC products still allowed to be exported
1985 – British Ant Survey reported ozone hole over Antarctica
1987 – peak in CFC sales since aerosol ban (1.32 million
tons)
1990 (1992 & 1997) – Montreal Protocol to reduce use of
CFC’s globally
1998 – production of CFC’s declined to 1/4th that of the 1987
peak
Pollution
Air Pollution – an unwanted substance injected into the
atmosphere from the earth’s surface by either natural or
human activities
 Come as aerosols, gases or particulates
Aerosols – small bits of matter in the air that move freely with normal air
movements
Gases – molecular compounds mixed together to form air
Particulates – larger, heavier particles that sooner or later fall back to the
surface (haze, smoke, dust)
Sources of Air Pollution
Natural – produce great quantities of pollutants than human
sources
Volcanoes, forest fires, plants, soil, and ocean
 Produce NOx, CO, HCx and CO2

Anthropogenic – although less than natural sources, humans
have yet to adapt to anthropogenic pollution as for natural
Sources include every day activities by large numbers of people (cars!)
 Industrial burning of fossil fuels and ore smelting

Carbon Monoxide - consists of one carbon and one oxygen
atom
 incomplete combustion of fossil fuels
 90% produced by natural sources (decay of carbon
sources – wood)
 10% anthropogenic, mainly cars

Source of CO for individuals is first and second hand tobacco and
smoke
Photochemical Smog – interactions of sunlight and
combustion products in automobile exhaust (NOx and
VOC’s)
 Result of increased automobile usage over the past century
Smog – combination of smoke and fog
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Aerosols and gas pollutants in urban areas
Lets in light but can obscure objects in the sky
Irritates eyes and throat – difficult to breathe
Corrodes structures over time
Acid Precipitation – atmospheric acids brought to the surface
by precipitation (rain, snow) or by dry dust
 Major source of SOx from industrial emissions
 Acid rain = rain/snow polluted with SO2 or NO2
 Acid dust = sulfuric and nitric nuclei cling to dust particles
Fall to earth and coat surface
 Increase the acidity of soil with wet
 Accumulate with snow and melt in spring as surge of acid water
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Haze – humid air causes a film of water to attach to aerosol
particles making them large enough to scatter light and
reduce visibility
 Natural and anthropogenic sources
 Soil dust, salt crystals, pollen, smoke
Natural Factors Affecting Pollution
Wind – move pollutants from one area to another
 Pollution Dome – dome of pollution over an urban area under calm,
stable atmospheric conditions
 Pollution Plume – plume of pollution originating over an urban area
that is transported downwind from its urban source
But it’s not all bad!
Clean Air Act (1970) – lead to decrease in pollutants and
increase in human health
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Decrease in cancer rates
Less acid rain
206,000 fewer deaths from air pollution in 1990