HUMAN BIOLOGY

hUMaN iMpaCts oN the Biosphere 477

What are impacts of air pollution?

• Air pollution can have local, regional, and global impacts.


• These impacts include smog, acid rain, and thinning of Earth’s
  protective ozone layer as CFCs and other compounds destroy
  ozone molecules.

taKe-Home messaGe

chlorofluorocarbons (CFCs)

Compounds of chlorine,

fluorine, and carbon that are

used as coolants and that

destroy ozone molecules

when they escape into the

atmosphere.

ozone thinning Reduc‑

tion in the usual amount

of ozone (O 3 ) in the

stratosphere.

a series of chemical steps, each of their chlorine molecules

can destroy over 10,000 molecules of ozone. A widely used

fungicide called methyl bromide is even worse. It will

account for 15 percent of ozone thinning in future years

unless production stops.

CFC production in developed countries has been phased

out. Some developing countries have announced plans to

phase it out within the next few years. Methyl bromide pro­

duction may also end soon. Even if these efforts succeed, it

will be decades before ozone thin­

ning is reversed. Current scientific

models project that ozone depletion

over the poles will be severe until

at least 2019. In the meantime we

can expect some ongoing negative

impacts (Table 25.1). One of these

repercussions, the loss of ocean phy­

toplankton (microscopic floating

plantlike organisms), will worsen

global warming, the topic we turn

to next.

Canadian researchers have reported that inhaled soot
particles from a steel mill caused DNA mutations that
showed up in the sperm of male mice and were passed on
to offspring. More study is needed to learn whether such
pollution­spurred mutations can cause disease in mice—or
in humans who also breathe the polluted air.

Air pollution has damaged the ozone layer

Ozone is a molecule of three oxygen atoms (O 3 ). It occurs in
two regions of Earth’s atmosphere. In the troposphere, the
region closest to Earth’s surface, ozone is part of smog and
can damage the respiratory system (as well as other organ­
isms). On the other hand, ozone in the next atmospheric
layer—the stratosphere (17–48 kilometers, or 11–30 miles,
above Earth)—intercepts harmful ultraviolet radiation that
can cause skin cancer and eye cataracts. Ozone thinning
has damaged this protective screen. September through
mid­October, an ozone “hole” appears over the Antarctic,
extending over an area about the size of the continental
United States. Since 1987 the ozone layer over the Ant­
arctic has been thinning by about half every year; a new
hole, over the Arctic, appeared in 2001. Several years later
the Antarctic hole was the biggest ever, covering an area
greater than North America (Figure 25.8).
Chlorofluorocarbons (CFCs) are the main ozone
depleters. These gases (compounds of chlorine, fluorine,
and carbon) are used as coolants in refrigerators and air
conditioners and in solvents and plastic foams. They slowly
escape into the air and do not break down easily. Through

More skin cancers, eye cataracts, and worse sunburns

Increased acid rain and photochemical smog

Reduced ocean phytoplankton, harming ocean food webs and

human seafood supplies

Increased global warming due to CFCs in the troposphere

Table 25.1 Some Predicted Effects of Ozone Depletion

Figure 25.8 Ozone concentrated in the stratosphere helps
shield life on Earth from UV radiation. A The location of the
ozone layer. B Seasonal ozone thinning above Antarctica in 2007.
Darkest blue indicates the area with the lowest ozone level.
(© Cengage Learning)

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10

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mesosphere

stratosphere

troposphere

ozone layer

Altitude (kilometers above sea level)

A B NASA

Antarctica

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