Page 483 - Environment: The Science Behind the Stories

China’s government is now striving to reduce pollu- of brownish haze is estimated to reduce the sunlight reaching
tion. It has closed down some heavily polluting factories and Earth’s surface in southern Asia by 10–20%; promote flooding
mines, phased out some subsidies for polluting industries, in some areas and drought in others by altering the monsoon;
installed pollution controls in power plants, and encouraged decrease rice productivity by 5–10%; speed the melting of
the development of wind, solar, and nuclear power. It subsi- Himalayan glaciers by depositing dark soot that absorbs sun-
dizes people to buy efficient electric heaters for their homes light; and contribute to many thousands of deaths each year.
to replace dirty, inefficient coal stoves. It has mandated
cleaner formulations for gasoline and diesel and has raised Smog poses health risks
standards for fuel efficiency and emissions for cars above
what the United States requires. In Beijing, mass transit is Let’s now examine one of our most prevalent types of air pollu-
being expanded, many buses run on natural gas, and heavily tion: smog. Smog is an unhealthy mixture of air pollutants that
polluting vehicles are restricted from operating in the cen- often forms over urban areas as a result of fossil fuel combustion.
tral city. China is also aggressively developing cleaner wind, Since the onset of the industrial revolution, cities have
solar, and nuclear power to substitute for power produced by suffered a type of smog known as industrial smog. When coal
burning coal. The nation likely will need to accelerate such or oil is burned, some portion is completely combusted, form-
steps, as its 1.35 billion citizens are becoming increasingly ing CO ; some is partially combusted, producing CO; and
2
fed up with air pollution. some remains unburned and is released as soot (particles of
Pollution from autos, industry, agriculture, and wood- carbon). Moreover, coal contains contaminants such as mer-
burning stoves in China, India, and other industrializing cury and sulfur. Sulfur reacts with oxygen to form sulfur diox-
nations of Asia has resulted in a persistent 2-mile-thick layer ide, which can undergo a series of reactions to form sulfuric
of pollution that hangs over southern Asia throughout the acid and ammonium sulfate (Figure 17.21a). These chemicals
dry season each December through April. Dubbed the Asian and others produced by further reactions, along with soot, are
Brown Cloud, or Atmospheric Brown Cloud, this massive layer the main components of industrial smog.

Figure 17.21 Industrial smog results from fossil fuel
combustion. When fossil fuels are burned, sulfur contaminants
give rise to sulfur dioxide, which may react with atmospheric gases
to produce other sulfur compounds (a). Industrial smog also con-
sists of particulate matter, carbon monoxide, and carbon dioxide.
Under certain weather conditions, industrial smog can blanket
whole towns or regions, as it did in Donora, Pennsylvania (b),
shown in the daytime during its deadly 1948 smog episode.

Coal and oil

Sulfur (S) in coal and oil Carbon (C)
Oxygen (O ) Oxygen (O 2 )
2
Burning Burning

Sulfur dioxide Carbon monoxide (CO)
(SO 2 ) and carbon dioxide (CO 2 )
Oxygen (O )
2
Sulfur trioxide
(SO 3 )
Water vapor (H 2 O)

4
Sulfuric acid (H 2 SO )
Ammonia (NH 3 )

Ammonium sulfate
((NH ) SO )
4
4 2
(a) Burning sulfur-rich oil or coal without adequate (b) Donora, Pennsylvania, at midday in the 1948 smog event
482 pollution control technologies

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