CHAPTER
15
The Atmosphere
Charging Toward Cleaner Air
in London
• More than 4000 people in London died during a
“killer smog” event in 1952.
• In 2003, London started charging a fee to people
who drove into the city during the week.
• Since the program began, traffic congestion in
London has decreased by 30%, but there is not a lot
of evidence that air quality has improved.
Talk About It What are the pros and cons of a
congestion-charging program?
Lesson 15.1 Earth’s Atmosphere
The air we breathe and all the weather we see is
contained in the lowest 1% of the Earth’s
atmosphere.
Lesson 15.1 Earth’s Atmosphere
Properties of the Atmosphere
• Composition: 78% nitrogen, 21% oxygen, and 1% other
gases
• Temperature: Varies
and location
• Pressure: In general,
air pressure decreases
with altitude; can be
measured using a
barometer.
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Barometer
Lesson 15.1 Earth’s Atmosphere
Relative Humidity
• The ratio of water vapor in
air to the maximum amount
the same air could contain at
the same temperature
• Is affected by temperature
and location; in general,
warm air holds more water.
• When air cools, water vapor
may condense to liquid or to
ice. Water vapor can only
condense on surfaces, such
as a petal or a dust particle.
Hoarfrost on leaves
Lesson 15.1 Earth’s Atmosphere
Did You Know?
The stratosphere and
mesosphere are cold, but the
upper thermosphere can be
hotter than 1500°C.
Layers of
Atmosphere
• Troposphere: 0–11 km;
movement of air, weather
• Stratosphere: 11–50 km;
ozone layer, absorbs and
scatters UV rays
• Mesosphere: 50–80 km;
meteoroids burn up
• Thermosphere: 80+ km;
disturbances produce
aurora borealis
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Lesson 15.1 Earth’s Atmosphere
Heat Transfer in the Troposphere
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• Radiation: The
• Conduction:
transfer of energy
The transfer of
through space,
heat directly
such as heat from
between two
the sun to Earth’s
objects that are
atmosphere
in contact
• Convection: The
transfer of heat by
the movement of
currents within a
fluid (liquid or gas)
Lesson 15.1 Earth’s Atmosphere
Convection Currents
• Warm air is less dense than cool air.
• When air near the surface heats up, it rises; as it rises, it
cools and then sinks.
• Rising and sinking
fluids generate
convection currents.
• Cause wind and
heat to move through
the atmosphere
Lesson 15.1 Earth’s Atmosphere
Air Masses and Fronts
• Air masses: Large bodies of air with similar properties
• Fronts: Boundaries between air masses of different properties
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Warm front
• Boundary along which a mass of warmer,
moister air pushes against a mass of
cooler, drier air
• Can produce light precipitation
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Cold front
• Boundary along which a mass of cooler,
drier air pushes against a mass of
warmer, moister air
• Can produce heavy precipitation
Lesson 15.2 Pollution of the Atmosphere
Air pollution is estimated to cause 2 million
premature deaths worldwide every year.
Lesson 15.2 Biomes
Sources of Air Pollution
•
Natural processes: Windblown dust, particles in volcanic
eruptions, smoke and soot from fire
•
Human sources: Most come directly or indirectly from
the burning of fossil fuels.
Did You Know? Humans can increase
the hazards of natural air pollution.
For example, by removing trees,
humans expose soil, which can dry
out and add to huge dust storms
when picked up by wind.
Dust storm approaching a U.S. farm during the 1930s
Lesson 15.2 Pollution of the Atmosphere
Types of Air Pollutants
• Primary air pollutants:
Released directly into the
atmosphere; example: soot
• Secondary air pollutants:
Formed when primary
pollutants react chemically
with other substances;
example: sulfuric acid
Lesson 15.2 Pollution of the Atmosphere
How Air Pollutants Affect
Your Health
• Lung irritation and respiratory
illnesses, such as asthma
• Carbon monoxide interferes with
body’s ability to use oxygen.
• Trace amounts of some air
pollutants, such as benzene or
soot, may contribute to cancer.
Lesson 15.2 Pollution of the Atmosphere
Smog
• A mix of air pollutants that forms over cities
• “Smog” is a combination of the words smoke and fog.
• Industrial smog (soot, sulfur, and water vapor) comes from
industrial sources.
• Photochemical smog is mostly tropospheric ozone created
when primary pollutants from vehicle exhaust react to
sunlight.
Lesson 15.2 Pollution of the Atmosphere
Temperature Inversions
• Normally, air near Earth’s surface warms and
rises, carrying pollutants with it.
• When a layer of warmer air sits over a layer of
cooler air, it traps pollution near Earth’s surface.
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Did You Know? A
thermal inversion
caused London’s
“killer smog.”
Lesson 15.2 Pollution of the Atmosphere
Acid Deposition
• Sulfur dioxide and nitrogen oxides can react with water,
oxygen, and other chemicals to form acids.
• Acid falls as particles or dissolves in precipitation, lowering the
pH of rain and snow.
• Acid deposition harms forest and lakes and damages human
structures.
Did You Know?
Rainwater is
naturally acidic
(pH 5.6), but
acid precipitation
in some parts of
the U.S. has a
pH as low as 4.
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Lesson 15.3 Controlling Air Pollution
Since the Clean Air Act was
first enacted in 1963,
emissions of the worst
pollutants in the U.S. have
decreased by 57%.
Lesson 15.3 Controlling Air Pollution
The Clean Air Act
•
First passed in 1963 to protect
human and environmental health
by improving air quality; has been
revised several times
•
Limits emissions of pollutants, sets
standards for air quality, establishes
a legal framework for suing
industries that break the rules, and
provides funding for pollution
control
Lesson 15.3 Controlling Air Pollution
Major Accomplishments of the
Clean Air Act
• Catalytic converters, present in all
cars since 1975, have reduced
vehicle emissions.
Did You Know? The removal of lead
from gasoline has led to a 99%
reduction in lead emissions since 1973.
• Lead has been phased out of gasoline.
• Industries and power plants have reduced releases of
pollutants by using scrubbers, which remove or alter
chemicals before they leave factory smokestacks.
Lesson 15.3 Controlling Air Pollution
The Ozone Hole
• Ozone is a pollutant in the troposphere,
but in the stratosphere it creates a
protective barrier against UV radiation.
• Chemicals called chlorofluorocarbons,
which used to be found in everything
from aerosol cans to refrigerators, have
destroyed ozone, causing an “ozone
hole” to form over Antarctica.
• An ozone hole allows more UV radiation
to reach Earth’s surface, potentially
increasing cases of skin cancer.
Aerosol spray can
Lesson 15.3 Controlling Air Pollution
Recovery of the Ozone Layer
• The Montreal Protocol is an international treaty signed in
1987 that has cut CFC production by 95% since the 1980s.
• Ozone levels in the stratosphere have begun to stabilize,
and the ozone hole will likely start to disappear.
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Ozone Hole 1979
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