Air Pollution
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How Does lhe Sceni Spread?
1. Choose a place to stand so that you
and your classmates are evenly
spread around the room.
2. Your teacher will open a bottle of
perfume in one corner of the room.
3.
Raise your hand when you first smell
the perfume.
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What causes photochemical
smog?
How is the ozone layer
important?
lWhat
are climate predictions
based on?
Reading Típ As you read,
make a list of different types of
air pollution. Write a sentence
about the effect of each type.
Figure
1 The air supply aboard
the space station Mirwas threatened by a collision during docking.
lnfenüng Describe the
pattern you observed as
people raised their hands.
How do you think the smell
traveled across the room?
dinary day aboard the Russian
FOR, READING
i
Ihink lt Over
iments. Another was exercising. The third cosmonaut was skillfully guiding a supply ship as it dockedwith Min
Suddenly, the crew members heard a frightening sound-the
crumpling of collapsing metal. The space station jolted from side
to side. The pressure gauges indicated an air leak! One crew
member hurried to prepare the emergency evacuation vehicle.
Meanwhile, the other two managed to close the airtight door
between the damaged area and the rest of the space station.
Fortunatel¡ the pressure soon returned to normal. A disaster
had been avoided. There was no need to abandon ship.
Closing the door preserved the most valuable resource on
air. Although you probably don't think about the air
very often, it is just as important on Earth as it is on a space station. Air is a resource you use every minute of your life.
Mir-lhe
What's in the Air?
Though you can't see, taste, or smell it, you are surrounded by
air. Air is a mixture of nitrogen, oxygen, carbon dioxide, water
vapor, and other gases. Almost all living things depend on these
gases to carcy out their life processes.
Nitrogen, oxygen, and carbon dioxide cycle between the
atmosphere and living things. These cycles ensure that the air
supply on Earth will not run out. But they don't guarantee that
the air will always be clean. A change to the atmosphere that has
harmful effects is called air pollution. Substances that cause
pollution are called pollutants. Pollutants can be solid particles,
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such as ash, or gases, such as chlorine. Air pollution can affect
the health of humans and other living things. Pollution can even
impact the climate of the whole planet.
What causes air pollution? If you're like many people, you
probably picture a factory smokestack, belching thick black
smoke into the sky. Until the mid-1900s, factories and power
plants that burned coal produced most of the air pollution in the
United States. Solid particles and gases that are released into the
air are called emissions. Toda¡ there is an even larger source of
emissions that cause air pollution: motor vehicles such as cars,
trucks, and airplanes. The engines of these vehicles release gases
such as carbon monoxide, an invisible toxic gas.
Though most air pollution is the result of human activities,
there are some natural causes as well. For example, an erupting
volcano sends an enormous load of soot, ash, sulfur, and nitrogen oxide gases into the atmosphere.
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La
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Arts
CONN ECTION
People sometimes coin, or
invent
a
word to express
a
specific idea. For example,
Londoners coined the word
smog to describe the hearry
gray air formed when coal
Can you guess the meaning of
these coined words?
I brunch
I
r squinched I
chortle
liger
Try coining a few descriptive
Whøt are some Qxamples of air pollutants?
Smog
Have you ever heard a weather forecaster talk about a "smog
aIert"? A smog alert is a warning about a type of air pollution
called photochemical smog. Photochemical smog is a thick,
brownish haze formed when certain gases in the air react with
sunlight. When the smog level is high, it settles as ahaze over a
city. Smog can niake people's eyes burn and irritate their throats.
The major sources of photochemical smog are the gases
emitted by automobiles and trucks. Burning gasoline in a car
engine releases some gases into the air. These gases include
hydrocarbons (compounds containing hydrogen and carbon)
and nitrogen oxides. The gases react in the sunlight and produce
a form of oxygen called ozone. Ozone, which is toxic, is the
major chemical found in smog.
words of your own. Exchange
your words with a classmate
and see if you can guess the
meanings of the other's words.
Flgure 2 Ahaze of photochemical
smog hangs over this city's skyline.
lnterpreting Photogrophs Whot is
the source of the smog?
Cooler
Figure 3 Normally, pollutants rise
high in the air and blow away (left).
But during a temperature inversion,
a layer of warm air traps pollutants
close to the ground (right).
Worm
Temperature lnvers¡on pollutants usually blow away from
the place where they are produced. Normall¡ air close to the
ground is heated by Earth's surface. As the air warms, it rises into
the cooler air above it. The pollutants are carried higher into the
atmosphere where they blow away. But certain weather conditions cause a condition known as a temperature inversion.
During a temperature inversion, a layer of warm air prevents
the rising air from escaping. The polluted air is trapped and held
close to Earth's surface. The smog becomes more concentrated
and dangerous.
Health Effects of smog The
effects of smog can be more
ozone in smog can cause lung
problems and harm the body's defenses against infection. when
smog levels reach a certain point, a city issues a smog alert.
During a smog alert, you should avoid exercising outdoors.
People who have asthma or other conditions that affect their
breathing should be particularly careful.
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Whøt høppens during a teml)erature inversion?
Acid Rain
Another type of air pollution is caused by power plants and factories that burn coal and oil. These fuels produce nitrogen oxides
and sulfur oxides when they are burned. These gases react with
water vapor in the ait forming nitric acid and sulfuric acid. The
acids return to Earth's surface dissolved in precipitation.
Precipitation that is more acidic than normal is called acid rain.
Acid rain can be in the form of snow sleet, or fog as well as rain.
As you can imagine, acid falling from the sky has some negative effects. when acid rain falls into a pond or lake, it changés
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Gos with pollutants enters
Figure 13 A smokestack scrubber
removes pollutants such as sulfur
dioxide from emissions. The dirtY
gas passes through a tube containing water droplets. Pollutants
dissolve in the water, leaving clean
gas to flow out of the chamber. The
dirty water still must be ProPerlY
disposed of.
Clean
Cleoned gos
exits
water
Water
droplets
Water and
pollutonts
Reducing Air Pollution
The Clean Air Act has resulted in the development of technology to control air pollution. The maior role of technology in
controlling air pollution is to reduce emissions.
Snarpen your
Sft früts
ffirerphåmg
The table below
shows a scientist's predictions
of chlorine levels in the atmosphere with and without the
ban on CFCs. Make a line
graph of the data, using two
different colors. Write a short
paragraph describing the
results.
Chlorine Level
(parts per billion)
Year
w¡th
Without
Ban
Ban
9Bs
2.5
2.5
1990
3.5
4.0
1995
3.8
5.0
2000
3.6
7.5
2005
3.4
10.0
1
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Emissions Controls At one time, industries dealt with emissions by building tall smokestacks. The stacks released wastes
high in the air, where they could blow away. But the pollutants
still ended up somewhere. Now factories place devices in the
stacks to treat emissions. For example, a filter can trap particles
of ash. The device in Figure 13, called a scrubber, removes pollutants from emissions using a stream of water droplets.
Pollutants dissolve in the water and fall into a container.
Cars and trucks now contain pollution control devices. For
example, a catalytic converter is a device that reduces emissions
of carbon monoxide, hydrocarbons, and nitrogen oxides. This
device causes the gases to react, forming less harmful carbon
dioxide and water.
Laws can ensure that people use pollution-control devices.
For example, in many states, cars must pass emissions tests. The
state of California's strict emissions-testing laws have helped
reduce the smog problem in Los Angeles in recent years.
CFC Substitutes 'vVhen a pollutant is banned by laq people
must frnd substitutes for the banned substance. For example, in
1990 many nations agreed to stop using most CFCs by the year
2000. Scientists immediately began to search for substitutes for
these chemicals. Refrigerators and air conditioners were
redesigned to use less harmful substances. Researchers developed
new ways to make products such as plastic foam without using
CFCs. As a result of this work, fewer CFCs should enter the
atmosphere after 2000 than in the past.