Air Pollution - Environmental Science - page 346

I thought I saw a blue jay this morning. But the smog was so
bad that it turned out to be a cardinal holding its breath.
M ICHAEL J. C OHEN

15-1 STRUCTURE AND SCIENCE
OF THE ATMOSPHERE

Science: The Troposphere
The atmosphere's innermost layer consists mostly of
nitrogen and oxygen, plus smaller amounts of water
vapor and carbon dioxide.
We live at the bottom of a thin layer of gases surround-
ing the earth, called the atmosphere. It is divided into
several spherical layers (Figure 15-2), each of which is
characterized by abrupt changes in temperature as a
result of differences in the absorption of incoming solar
energy.
About 75-80% of the earth's air mass is found in
the troposphere, the atmospheric layer closest to the
earth's surface. This layer extends only 17 kilometers
(11 miles) above sea level at the equator and 8 kilome-
ters (5 miles) over the poles. If the earth were the size
of an apple, this lower layer containing the air we
breathe would be no thicker than the apple's skin.
Take a deep breath. About 99% of the volume of
the air you inhaled from the troposphere consists of
two gases: nitrogen (78%) and oxygen (21%). The re-
mainder consists of water vapor (varying from 0.01%
at the frigid poles to 4% in the humid tropics), slightly
less than 1% argon (Ar), 0.038% carbon dioxide (CO 2 ),
and trace amounts of several other gases.
The troposphere is also involved in the chemical
cycling of the earth's vital nutrients. In addition, this
thin and turbulent layer of rising and falling air cur-
rents and winds is largely responsible for the planet's
short-term weather and long-term climate.

This chapter discusses the types, sources, and effects
of chemicals that pollute the outdoor and indoor air
that we breathe and presents solutions for reducing
these threats to our health and to ecosystems. It ad-
dresses the following questions:

What layers are found in the atmosphere?

■

What are the major outdoor air pollutants, and
where do they come from?

■

What are two types of smog?

■

What is acid deposition, and how can it be
reduced?

■

What are the harmful effects of air pollutants?

■

How can we prevent and control air pollution?

■

KEY IDEAS
■ Burning fossil fuels in motor vehicles and power
and industrial plants is the major source of air pollu-
tion from human activities.

■ Photochemical smog is a mixture of air pollutants
formed by the reaction of nitrogen oxides and volatile
organic hydrocarbons under the influence of sunlight.

■ Industrial smog is a mixture of sulfur dioxide,
droplets of sulfuric acid, and suspended solid particles
emitted or formed in the atmosphere when coal and
oil are burned.

Science: The Stratosphere
Ozone in the atmosphere's second layer filters out
most of the sun's UV radiation that is harmful to us
and most other species.
The atmosphere's second layer is the stratosphere,
which extends 17-48 kilometers (11-30 miles) above
the earth's surface (Figure 15-2). Although the stratos-
phere contains less matter than the troposphere, its
composition is similar, with two notable exceptions: its
volume of water vapor is about 1/1,000 as much and
its concentration of ozone (O 3 ) is much higher.
Stratospheric ozone is produced when oxygen
molecules there interact with ultraviolet (UV) radiation
emitted

■ Sulfur dioxide, nitrogen oxides, and particulates pro-
duced mostly by burning coal can react in the atmo-
sphere to produce acidic chemicals that can travel
long distances before returning to the earth's surface
as harmful acid deposition.

■ Indoor air pollution usually poses a much greater
threat to human health than outdoor air pollution,
especially for the poor in developing countries.

■ At least 3 million people (most of them in Asia) die
prematurely each year from the effects of air pollu-
tion—mostly from burning wood or coal inside
dwellings in developing countries.

UV 2 O 3 ). This
“global sunscreen” of ozone in the stratosphere pre-
vents 95% of the sun's harmful UV radiation from
reaching the earth's surface.
The UV filter of “good” ozone in the lower stratos-
phere allows us and other forms of life to exist on land
and helps protect us from sunburn, skin and eye can-
cer, cataracts, and damage to our immune systems. It

by the sun (3 O 2

■ The Clean Air Acts in the United States have greatly
reduced outdoor air pollution from six major pollu-
tants but these laws can be made more effective.

■ We need to focus on preventing air pollution, with
emphasis on sharply reducing indoor air pollution in
developing countries.