1. science
2. ecology
3. pollution

Student
text pages
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488–492
SECTION
16.2 Air Quality
SC.912.L.17.11 SC.912.L.17.20
KEY CONCEPT Fossil fuel emissions affect the biosphere.
Pollutants accumulate in the air.
Pollution is the addition of any undesirable material to the air, water,
or soil. A pollutant is any material that causes pollution. Pollutants are
harmful to ecosystems and human health.
Smog and Ozone
Smog is a type of air pollution that forms from the waste products of
burned gas, coal, and oil. One component of smog is particulates,
microscopic bits of dust, metal, and unburned fuel. Breathing air with
particulates can cause many different types of health problems.
Another component of smog is ground-level ozone. The ozone that is
formed from pollution stays near the ground and is harmful to human
health and to ecosystems. Ozone is also found in the upper atmosphere.
There, ozone plays an important role in protecting Earth from ultraviolet rays found in sunlight.
Acid Rain
Chemicals produced from the burning of coal and oil can
become part of Earth’s cycles, including the water cycle.
Acid rain is produced when pollutants in the water cycle
cause the pH of rain to drop below normal.
Recall that pH 7 is neutral. All rain is slightly acidic and
has a pH of around 5.6. When pollutants become part of the
water cycle, they can react with water and oxygen and cause
acid rain, which has a pH lower than 5.6. Acid rain falls in
many areas of the United States. It threatens water supplies
and harms ecosystems.
VISUAL VOCAB
Acid rain is a type of rain produced
when pollutants in the water cycle
cause rain pH to drop below normal
levels.
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How are the effects of ground level ozone different
from the effects of ozone in the upper atmosphere?
Air pollution is changing Earth’s biosphere.
Carbon dioxide is a natural part of Earth’s atmosphere. The levels of
carbon dioxide rise and fall over time as a natural part of Earth’s climate
cycles. Times of high carbon dioxide levels are also times of warmer
global climates. Lower carbon dioxide levels are times of cooler
global climates.
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McDougal Littell Biology
Visual Connection
See figure in student
text, pg. 491
The Greenhouse Effect
It can be cold outside but warm inside a car that is parked in a
sunny place. It can also be warm inside a greenhouse on a cold
day. Like the greenhouse glass that helps to trap heat, Earth’s
atmosphere contains gases that help to slow the loss of heat.
These gases are called greenhouse gases, and the process by
which they slow the loss of heat is called the greenhouse effect.
Carbon dioxide, water vapor, and methane are three of the
most common greenhouse gases. You can think of these gases as
forming a blanket that helps to keep Earth warm. The greenhouse effect keeps Earth warm enough to support life.
carbon dioxide (CO2)
methane (CH4)
water (H2O)
Carbon dioxide, water vapor, and
methane are three of the most
common greenhouse gases.
Global Warming
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Over the last 100 years, the average global
GLOBAL WARMING
temperature has risen. Global temperature
Global Temperature and Carbon
changes are a normal part of Earth’s
Dioxide Levels over Time
climate cycle. But changes in temperature
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Global warming already threatens
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ecosystems around the world. Increased
Source: University of California, Scripps Institute of Oceanography/
flooding, stronger tropical storms, and a
Hadley Centre for Climate Prediction and Research
loss of biodiversity are a few of the threats
As automobile use and industry have grown, so have the
that may be caused by global warming.
levels of carbon dioxide and other greenhouse gases in the
The polar ice cap is melting, and may
atmosphere. This graph shows average global temperature
affect global weather patterns. The future
changes (blue) against atmospheric carbon dioxide levels
of global warming is uncertain, but con(gray) measured at Mauna Loa Observatory in Hawaii.
tinued global warming could greatly
change our planet.
How
has air pollution
contributed
global warming?
How has air
pollution
contributed
to global to
warming?
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Interactive Reader
273
16.2
pollution
smog
particulates
Vocabulary Check
acid rain
greenhouse effect
global warming
Mark It Up
Go back and highlight
each sentence that
has a vocabulary
word in bold.
Match each clue below with the correct term from the list above.
1. one component of smog
2. a trend of increasing global temperatures
3. keeps heat from escaping Earth
4. rain with reduced pH due to pollution
5. a kind of air pollution
16.2
The Big Picture
6. What is one main human activity that causes smog, acid rain, and contributes to global warming?
7. Global weather patterns usually change over tens of thousands of
years. What makes the current global warming trend different from
normal climate cycles of the past?
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McDougal Littell Biology