The Atmosphere 461
CROWDED TOGETHER, the horses in the parade seem to be fight-
ing for space. The horse in the forefront is rearing, possibly frightened by
the other horses and riders nearby. The rider, in contrast, appears calm as
he looks off into the distance. Thousands of years ago, in ancient Athens,
Greek sculptors created this parade in marble to go at the top of the
Parthenon, a temple that honored the goddess Athena.
Today the parade of warriors no longer graces the Parthenon. Instead,
the sculptures are inside a museum in Athens. The sculptures were moved
to protect them from more damage. One cause of damage was pollutants
in the air. If you look carefully at Figure 10, you can see that some of the
stone has been worn away.
N 2Pollution of the Atmosphere
FIGURE 10 Damage From Air
Pollution Notice that the warriors’
faces have been worn away. The
damage was caused partly by air
• Explain how both natural processes and human
activities can cause air pollution.
• Describe how air pollutants affect human health.
• Explain what causes smog and how temperature
inversions affect it and other forms of air pollution.
• Explain how acid deposition occurs and describe
Reading Strategy Before you read, make a three-column
KWL chart. In the first column, write what you already know
about air pollution. In the second column, write what you want
to learn. After reading, complete the chart by filling in what
you have learned in the third column.
Vocabulary air pollution, emission, fossil fuel,
primary air pollutant, secondary air pollutant, smog,
temperature inversion, acid deposition
Guiding Question: What are the sources of air pollution?
FOCUS Divide the class into small
groups and have each group sit in
a circle. Have one student in each
circle name a source of air pollution.
Then, have the student to his or her
right name another source. Have
them continue around the circle
naming different sources until the
group runs out of ideas.
15.2 LESSON PLAN PREVIEW
Inquiry Students research the
health effects of air pollutants.
Real World Students predict
how increasing public transpor-
tation use might affect a city’s
Less proficient readers organize
information about the sources
and effects of acid deposition.
Scientific Method Lab, Acid Rain and
Seeds • Outdoors Lab, What’s in the
Air? • Lesson 15.2 Worksheets • Lesson
15.2 Assessment • Chapter 15 Over-
462 Lesson 2
Sources of Air Pollution
Air pollution can be caused by natural processes and
The cars, trucks, and industries of modern Athens have released pollut-
ants that have contributed to the damage to the Parthenon. Both human
activities and natural processes cause outdoor air pollution, which is
the release of damaging materials into the atmosphere. The substances
released are called emissions. Some emissions, such as smoke and soot,
consist of tiny particles, or particulate matter. Others are gases such as
sulfur dioxide and carbon monoxide.
Natural Processes Natural processes produce a great deal of the
world’s air pollution. Winds sweeping over dry land can create huge dust
storms, as seen in Figure 11. Winds sometimes blow dust across oceans
from one continent to another. Volcanic eruptions release tiny solid par-
ticles and gases into the atmosphere. Fires in forests and grasslands also
produce smoke, soot, and gases.
Human activities can make some natural pollution worse. For exam-
ple, some farming and grazing practices strip most plants from the soil.
When there are few plant roots to hold soil in place, wind erosion may
occur. Wind erosion can lead to dust storms.
Human Sources People’s activities have influenced air quality. The
way we live—for example, our industries, the cars we drive, and the way
we produce electricity—has introduced many sources of air pollution. Air
pollution can come from point sources or nonpoint sources. In London,
power plants and factories act as point sources of emissions. Millions of
cars and trucks together make up a moving nonpoint source.
Most air pollution comes, directly or indirectly, from the combustion
of fossil fuels. Fossil fuels are carbon-containing fuels that formed mil-
lions of years ago from the remains of living things. Motor vehicles, such
as cars and trucks, run by burning fossil fuels. Motor vehicles release an
enormous amount of pollutants into the air.
FIGURE 11 Dust Storm Over a field
in Africa, wind blows dust particles into
How can we ensure everyone has
clean air to breathe?
Perspective After students have read
about human sources of air pollu-
tion, reread the following sentence:
Most air pollution comes, directly or
indirectly, from the combustion of
fossil fuels. Have students write a
paragraph or two explaining how
this statement affects their answer to
the Big Question.
Primary Air Pollutants
Secondary Air Pollutants
Carbon monoxide (CO)
A colorless, odorless gas
Sulfur dioxide (SO2 )
A colorless gas with a strong, unpleasant odor
Nitrogen dioxide (NO2 )
A foul-smelling, reddish-brown gas that belongs
to a family of compounds called nitrogen oxides
Volatile organic compounds (VOCs)
Carbon-containing chemicals that evaporate
easily, producing fumes. Examples include
methane, propane, butane, and benzene.
Solid or liquid particles that are small enough to
�oat in the atmosphere—soot, dust, tiny bits of
A heavy metal that is one type of particulate
Tropospheric ozone (O3 )
A colorless gas with an unpleasant odor
Sulfuric acid (H2SO4 ) and nitric acid (HNO3 )
Binds to hemoglobin, the oxygen-
carrying chemical in blood; deprives
cells of oxygen
Produces secondary pollutants that
are part of acid precipitation; causes
Can cause serious lung irritation;
contributes to smog and acid
Some can cause cancer; some
interact with other chemicals to
produce ozone in the troposphere.
Can a�ect breathing and damage
Can damage body tissues, including
those in the nervous system
Ozone in the stratosphere protects
humans from radiation, but ozone
in the troposphere can injure living
tissues and cause respiratory
Components of acid precipitation
The incomplete combustion (burning)
of fossil fuels by motor vehicles,
industries, and other sources
Burning of fossil fuels, especially coal,
for electricity generation and industry
A reaction between atmospheric
nitrogen and oxygen in combustion
engines and during the production of
Many sources, including vehicle engines,
household cleaning products, some
industrial processes, and natural
Dust blown by wind; soot and chemicals
produced by �res and combustion
within engines; particles produced
during construction and farming
Industrial re�nement of metals; in
developing nations, gasoline contains
Results from the interaction of sunlight,
heat, nitrogen oxides, and volatile
Produced when sulfur dioxide and
nitrogen oxides combine with water in
The Atmosphere 463
FIGURE 12 Air Pollutants Primary air pollutants are released directly
into the troposphere. Secondary air pollutants, in contrast, are the products
of chemical reactions between primary air pollutants and other substances.
Primary and Secondary Air Pollutants Pollutants
may do harm directly, or they may cause chemical reac-
tions that produce harmful compounds. Primary air
pollutants, such as soot and carbon monoxide, are pol-
lutants released directly into the troposphere. Primary air
pollutants may cause damage themselves, or they may react
with other products to cause damage. Harmful products
produced when primary air pollutants react chemically
with other substances are called secondary air pollutants.
Secondary air pollutants include tropospheric ozone and
sulfuric acid. The table in Figure 12 describes some pri-
mary and secondary air pollutants.
464 Lesson 2
How Air Pollutants Affect Your
Air pollutants can damage the respiratory system, interfere
with the body’s uptake of oxygen, and cause cancer.
Outdoor air pollution is a big health problem. Air pollutants can do seri-
ous harm to the respiratory system, which transports oxygen into your
body and removes carbon dioxide. Some air pollutants can cause cancer.
Respiratory System Problems Have you ever inhaled dust and then
started coughing? Particles in the dust irritated your respiratory system,
making you cough. Similarly, air pollutants irritate people’s air passages
and lungs. If people are exposed over and over to air pollution, they may
develop harmful respiratory conditions. Asthma, bronchitis, and emphy-
sema have all been linked to air pollutants.
The Effect of Carbon Monoxide How do the cells of your body
obtain the oxygen they need? The air that you inhale contains oxygen.
This oxygen passes from the lungs into the bloodstream. There, oxygen
binds to hemoglobin. Hemoglobin is a molecule in red blood cells that
combines chemically with oxygen. The red blood cells then carry the
oxygen to the cells of the body.