LESSON
Pollution of the Atmosphere
Guiding Question: What are the sources of air pollution?
• 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
its effects.
2
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
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.
15.2 LESSON PLAN PREVIEW
Inquiry Students research the
health effects of air pollutants.
Real World Students predict
how increasing public transportation use might affect a city’s
smog levels.
Differentiated Instruction
Less proficient readers organize
information about the sources
and effects of acid deposition.
15.2 RESOURCES
Scientific Method Lab, Acid Rain and
Seeds • Outdoors Lab, What’s in the
Air? • Lesson 15.2 Worksheets • Lesson
15.2 Assessment • Chapter 15 Overview Presentation
GUIDING QUESTION
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.
FIGURE 10 Damage From Air
Pollution Notice that the warriors’
faces have been worn away. The
damage was caused partly by air
pollution.
The Atmosphere 461
FIGURE 11 Dust Storm Over a field
in Africa, wind blows dust particles into
the air.
Sources of Air Pollution
Air pollution can be caused by natural processes and
human activities.
The cars, trucks, and industries of modern Athens have released pollutants 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 particles 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 example, 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.
BIG QUESTION
How can we ensure everyone has
clean air to breathe?
Perspective After students have read
about human sources of air pollution, 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.
462 Lesson 2
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 millions 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.
Primary and Secondary Air Pollutants Pollutants
may do harm directly, or they may cause chemical reactions that produce harmful compounds. Primary air
pollutants, such as soot and carbon monoxide, are pollutants 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 primary and secondary air pollutants.
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 Air Pollutants
Pollutant
Source
Effect
Carbon monoxide (CO)
A colorless, odorless gas
The incomplete combustion (burning)
of fossil fuels by motor vehicles,
industries, and other sources
Binds to hemoglobin, the oxygencarrying chemical in blood; deprives
cells of oxygen
Sulfur dioxide (SO2 )
A colorless gas with a strong, unpleasant odor
Burning of fossil fuels, especially coal,
for electricity generation and industry
Produces secondary pollutants that
are part of acid precipitation; causes
lung irritation
Nitrogen dioxide (NO2 )
A foul-smelling, reddish-brown gas that belongs
to a family of compounds called nitrogen oxides
A reaction between atmospheric
nitrogen and oxygen in combustion
engines and during the production of
electricity
Can cause serious lung irritation;
contributes to smog and acid
precipitation
Volatile organic compounds (VOCs)
Carbon-containing chemicals that evaporate
easily, producing fumes. Examples include
methane, propane, butane, and benzene.
Many sources, including vehicle engines,
household cleaning products, some
industrial processes, and natural
processes
Some can cause cancer; some
interact with other chemicals to
produce ozone in the troposphere.
Particulate matter
Solid or liquid particles that are small enough to
float in the atmosphere—soot, dust, tiny bits of
metals
Dust blown by wind; soot and chemicals
produced by fires and combustion
within engines; particles produced
during construction and farming
Can affect breathing and damage
lungs
Lead
A heavy metal that is one type of particulate
matter
Industrial refinement of metals; in
developing nations, gasoline contains
lead
Can damage body tissues, including
those in the nervous system
Secondary Air Pollutants
Pollutant
Source
Effect
Tropospheric ozone (O3 )
A colorless gas with an unpleasant odor
Results from the interaction of sunlight,
heat, nitrogen oxides, and volatile
organic compounds
Ozone in the stratosphere protects
humans from radiation, but ozone
in the troposphere can injure living
tissues and cause respiratory
problems.
Sulfuric acid (H2SO4 ) and nitric acid (HNO3 )
Produced when sulfur dioxide and
nitrogen oxides combine with water in
the atmosphere
Components of acid precipitation
The Atmosphere 463
FIGURE 13 Effects of Air
Pollution A runner in the Beijing
Olympic Games wears a mask to
protect his respiratory system from
air pollution. Beijing has severe air
pollution. Before the 2008 Olympic
Games, the city made a major effort to
clean its air.
How Air Pollutants Affect Your
Health
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 serious 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 emphysema 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.
However, if there is carbon monoxide in the air, the carbon monoxide
will bind to hemoglobin, replacing some of the oxygen that the blood
would normally carry. Therefore, carbon monoxide interferes with your
body’s ability to deliver oxygen to cells. This can cause headaches, tiredness, and nausea. Over time, carbon monoxide can damage the heart
because the heart muscle has to work harder than normal to deliver oxygen to cells. In high concentrations, carbon monoxide can be fatal.
Cancer Trace amounts of some air pollutants may contribute to cancer.
Soot, for example, can cause cancer if it is inhaled frequently. Benzene,
which is a volatile organic compound in gasoline, has also been linked to
cancer. Exhaust from cars and trucks contains benzene.
464 Lesson 2
Smog and Temperature Inversions
Temperature inversions may trap smog close to the surface of
Earth, preventing the pollutants from dispersing.
If you combine the words smoke and fog, you get the word smog. Smog
is an unhealthy mixture of air pollutants that may form over cities and
nearby areas.
Industrial Smog The smog that covered London in 1952 was indus-
trial smog. Industrial smog is produced when soot combines with sulfur
compounds and water droplets in air. Because of government regulation,
this type of smog is far less common in developed nations than it was
50–100 years ago. However, the situation is different in developing nations,
such as China and the nations of Eastern Europe. Industrial technologies
in these nations are often older than those in developed nations, and have
less ability to control pollution than do newer technologies. Also, there
is less government regulation of air quality in these nations. Therefore,
industrial smog continues to create health problems in many areas.
Photochemical Smog A photochemical process is one that needs
light. Photochemical smog is a thick, brownish haze that forms when
sunlight acts on certain air pollutants, such as nitrogen oxides and chemicals called hydrocarbons. Tropospheric ozone is often the most abundant
pollutant in photochemical smog. Ozone in the troposphere is chemically identical to ozone in the stratosphere. However, unlike ozone in the
stratosphere, which protects living things by filtering ultraviolet light,
tropospheric ozone can damage living tissue—especially eye and lung tissues and plant leaves—as well as other materials.
The main source of the pollutants in photochemical smog is the
exhaust released by cars and trucks. Governments are acting to reduce
motor-vehicle emissions, which will reduce photochemical smog. For
example, vehicle inspection programs make drivers fix cars and trucks
that release high levels of pollutants.
Reading
Checkpoint
What Do
you think?
Should your city, or a city near
you, start a congestion-charging
program like London’s? What are
some of the pros and cons of such
a program?
ANSWERS
What Do You Think? Answers will
vary. Students should identify logical
pros and cons.
Reading Checkpoint For photochemical smog to form, light is
necessary. Industrial smog can form
without light.
Figure 14 Burning coal
FIGURE 14 Photochemical
Smog Smog shrouds the borough of
Manhattan in New York City. Relate
Cause and Effect What was the main
source of the pollutants that caused
London’s “killer smog” in 1952?
hat is the difference between industrial smog and
W
photochemical smog?
The Atmosphere 465
Low
Altitude
Figure 15 A temperature inversion
can trap pollutants, including those
in smog, near the ground.
Reading
Checkpoint
uring a temperature inversion, why doesn’t air at Earth’s
D
surface rise?
Cool
Temperature
Reading Checkpoint During a temperature inversion, the air at Earth’s
surface is colder than the air above
it. Cold air has a greater density than
warm air, so the cold air does not rise
and mix with the air above it.
High
ANSWERS
Temperature Inversions Recall that in the troposphere, air temperature usually decreases as altitude increases. Earth’s surface warms the
air at low altitudes. Since warm air rises, any pollutants in the air are carried away from the surface and higher into the troposphere. This process
removes pollutants from low altitudes and helps them disperse.
The situation is different, however, when a temperature inversion
occurs. A temperature inversion, or thermal inversion, is the condition
in the troposphere in which a layer of cooler air is located beneath a layer
of warmer air. Since cold air has a greater density than warm air, the air
at Earth’s surface does not rise and mix with the air higher up. Therefore,
temperature inversions can keep air pollutants, including those found in
smog, from going away. Figure 15 shows how a temperature inversion
can worsen air pollution. It was a thermal inversion that caused London’s
“killer smog” of 1952. Inversions regularly cause smog buildup in some
cities, such as Los Angeles and Mexico City.
Surface
warmed
by sun
Vertical
mixing
Warm
High
(a) Normal Conditions
Cool
466 Lesson 2
Temperature
Low
FIGURE 15 Temperature Inversion
Normally, tropospheric temperature
decreases with height above the ground (a),
and air at the surface mixes with air above it.
In a temperature inversion (b), cool air stays
near the ground, under a layer of warmer air,
and little mixing occurs. Relate Cause and
Effect Why can a temperature inversion,
such as the one that occurred in London in
1952, make air pollution worse?
Altitude
Warm
Inversion layer
Pollution
trapped
Cool
(b) Thermal Inversion
Primary pollutants
Secondary pollutants
Water (H2O),
oxygen (O2), and
other substances
Sulfur dioxide (SO2)
Sulfuric acid (H2SO4)
Nitric oxide (NO)
Nitric acid (HNO3)
Acid precipitation
Acid Deposition
Acid deposition results when products of combustion combine
with water, oxygen, and other substances in the atmosphere.
When some pollutants combine with water, oxygen, and other chemicals
in the atmosphere, they form compounds called acids. These acids may
settle to the surface of Earth as acid deposition. Acid deposition may
consist of solid or gaseous particles, or the acids may dissolve in fog or
precipitation. Acid precipitation is sometimes called acid rain, but any
kind of precipitation, such as snow or sleet, can contain acidic pollutants.
FIGURE 16 Formation of Acid
Precipitation Acid precipitation
starts when sulfur dioxide and
nitrogen oxides such as nitric oxide
combine with water, oxygen, and
other substances. Acid precipitation
can affect areas a long way from the
original source.
The pH Scale and Precipitation The pH scale is used to measure
whether solutions are acidic or alkaline. The values on the scale range
from 0 to 14. A pH of 7 is neutral, that is, it is neither acidic nor alkaline.
If a solution has a pH that is higher than 7, it is alkaline, or basic. An acid
is a solution whose pH is lower than 7. The lower the pH number, the
higher the acidity.
The pH of precipitation varies. Normal precipitation is slightly acidic,
with a pH of about 5.6. Acid precipitation has a lower pH. Some areas in
the United States have precipitation with a pH as low as 4.3.
Go Outside
Is the Rainwater Acidic?
7 plastic
8 9cup outside
1 On
2 a rainy
3 4day, 5put a6 clean
1
1
2
where it will collect rainwater.
5 6 rainwater
7 8 9indoors. Then use
2 Bring
3 4the collected
pH paper to measure the pH of the water.
6 results
7 8 to9those of other students.
3 Compare
4 5 your
ANSWERS
Go Outside
1. Answers will vary. Students should
classify rainwater as acidic if its pH
is lower than 5.6, the pH of normal
precipitation.
2. Answers will vary.
Analyze and Conclude
1. Analyze Data Is rainwater in your area more
acidic than normal rainwater? Explain your
answer.
2. Perform Error Analysis If other students
obtained different results from yours, try to figure
out why.
The Atmosphere 467
Figure 17 Effects of Acid
Deposition Notice that many trees no
longer have any needles—a result of
acid deposition.
Sources of Acid Deposition Acid deposition starts mainly with
ANSWERS
Lesson 2 Assessment
1. Sulfur dioxide: primary pollutant;
sulfuric acid: secondary pollutant.
Sulfuric acid is the product of a
reaction between sulfur dioxide
and water.
2. To protect their respiratory system
3. In a temperature inversion, cooler,
dense air is trapped near the
ground. Since the air does not
move, the pollutants that the
air contains cannot mix with air
higher up.
4. No; normal precipitation has a pH
of about 5.6; acid precipitation has
a pH lower than 5.6.
5. Developing nations are trying to
industrialize. By restricting processes that produce smog, they
might also slow economic progress.
sulfur dioxide and nitrogen oxides. These pollutants are produced largely
through the burning of fossil fuels by automobiles, electric power plants,
and industries. In the troposphere, these compounds can react with water,
oxygen, and other substances to produce acids such as sulfuric acid and
nitric acid.
Wind can carry pollutants over long distances. Therefore, acid deposition may fall on areas that are far from where the pollutants were
produced. For example, much of the pollution that is produced in Pennsylvania, Ohio, and Illinois falls out in states to the east, including New
York, Vermont, and New Hampshire.
Effects of Acid Deposition Acid deposition can harm ecosystems
and structures that humans have built. For example, if the pH in lakes
becomes too low, neither plants nor fishes can survive. Acid deposition
can kill trees and destroy whole forests (Figure 17). When acid gets into
the soil, harmful chemicals can be released. These chemicals can poison
plants growing in the soil. Acid deposition can erode the surfaces of stone
buildings and statues, such as the Parthenon sculptures. In addition, acid
deposition can increase the acidity of the water that comes into your
home. Water with increased acidity can pick up harmful chemicals from
metal pipes and contaminate drinking water.
Acid deposition is a problem, but it can be solved. People and governments have taken steps to eliminate or reduce air pollutants that cause acid
deposition. The next lesson describes some of those steps.
2
1. Interpret Tables Sulfuric acid and sulfur dioxide
are both air pollutants. Use Figure 12 to determine
which is a primary pollutant and which is a secondary pollutant. What is the relationship between
these two types of pollutants?
2. Infer When people work with volatile organic
compounds, why should they wear special masks
that cover their noses and mouths?
468 Lesson 2
3. Relate Cause and Effect Why does a temperature
inversion trap smog and prevent it from dispersing?
4. Apply Concepts The rain that falls in an area has
a pH of 5.8. Is this acid precipitation? Explain your
answer.
5. Explore the BIGQUESTION Why might developing
nations be more reluctant than developed nations to
take measures to control industrial smog?