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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
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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.
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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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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
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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.