When it comes to air pollution, there is good news, there is bad news, and
there is reality. The good news is that during the past three decades,
environmental measures and new technologies have helped reduce air pollution
dramatically, by almost 50 percent. The bad news is that worldwide, the
atmosphere over our cities is still smoggy, more areas are urbanizing, and the
number of cars on the road is increasing. The reality is that engineers have
developed dozens of creative methods to curb pollution, and although there is
no magic bullet, some combination of these approaches may hold the answer. In
this slide show, get to know a handful of tools for reducing and preventing
air pollution.—Lexi Krock
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Scrubbers
Toxic exhaust from power plants accounts for much of the nation's air
pollution. Congress's 1990 Clean Air Act required that all electric generating
plants in the U.S. reduce their emissions by 2010. In response, many plants
have already added scrubbers to their chimneys. These industrial pollution
control devices can remove toxic substances from exhaust streams, or neutralize
them so that they are harmless or even recyclable. Ironically, the more robust
the plume of smoke rising from a smokestack, the more likely it is "scrubbed"
exhaust. So-called "wet" scrubbers can increase the proportion of water in
waste gases, plumping up smoke plumes.
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Baghouses
Power plants often use more than one device to stop pollutants from escaping
smokestacks. Baghouses are filtration structures such as the one seen here that
have been retrofitted to many power plants nationwide. They work by catching
fine particulates—tiny clumps of soot, dirt, and chemicals that can
damage lungs and collect in the atmosphere, creating smog. Baghouses function
as massive vacuum cleaners. They are lined with many fabric filter "bags,"
which plant engineers periodically clean or replace, carting away the
particulates they collect.
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Bioreactors
While most antipollution technologies involve massive, complex equipment, some
scientists are experimenting with tiny, simple living organisms called
cyanobacteria that eat polluting carbon dioxide (CO2). These algae can flourish in the blistering temperatures of chimneys. Researchers have
designed "bioreactors," window-screen-like membranes teeming with
cyanobacteria, for future installation into power plant smokestacks. Fiber-
optic cables would focus life-sustaining light across the membranes, allowing
the algae to grow inside chimneys while feasting on a diet of CO2 exhaust. This technology has already proved itself in small-scale
demonstrations. A test on a fully operational power plant is about five years
away, and scientists are also studying the same algae as a potential source of
hydrogen energy.
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Catalytic Converters
Most cars are sources of pollution, and to keep up with emissions laws
automakers began refining car engines and fuel systems in the 1970s. These
modifications culminated in catalytic converters, which treat exhaust before it
leaves a car's tailpipe, converting toxic combustion by-products such as carbon
and nitrogen monoxides to less-toxic gases. Catalytic converters have been
highly successful in reducing emissions, but substantial increases in the
distances cars and trucks travel on average and in the overall number of
vehicles in use have made up the difference, and cars are still a major cause
of pollution.
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Wind Energy
Wind is a renewable energy source that emits no pollution. It is the
fastest-growing "green" energy in the U.S. and provides light to the Statue of
Liberty. Wind farms—clusters of huge windmills—produce electricity by
using the motion of their blades to spin a shaft connected to a generator.
Experts estimate that the electricity created in 2006 by America's wind farms
will displace some 15 million tons of carbon dioxide. Over five million acres
of forest would be needed to absorb that much CO2. Some people
oppose wind farms because they occupy large tracts of land and can sometimes
harm birds, but most agree that their environmental costs are much lower than
those of fossil fuels.
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Hybrid Cars
Celebrity owners have made them famous, and drivers' concerns about
skyrocketing gas prices and the environment have made them a popular new
choice. Sales in the U.S. of hybrid cars such as Toyota's Prius, seen here,
doubled in January 2006 compared to the year before, with nearly 16,000 cars
sold. Hybrids get their power from small gasoline engines combined with
electric motors and rechargeable batteries. Their compact engines deliver
excellent gas mileage and cause much less pollution than those in conventional
cars. Experts estimate that driving a hybrid for 100,000 miles would
barely fill a teacup with pollutants.
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Ethanol
Ethanol is a clean-burning alcohol produced by bacteria that ferment the sugars
in corn and cornstalks. Some environmentalists tout ethanol as a potential
alternative to gasoline. In the U.S., about five million vehicles already drive
on "flex-fuel." They can use traditional gas or E85, a mix of 85 percent
ethanol and 15 percent gasoline. Converting an automobile to flex-fuel is
inexpensive, but there are few ethanol pumps in the U.S. In Brazil, nearly all
cars run on a 96 percent ethanol fuel produced from sugarcane, which is readily
available. Brazilians have seen benefits: not only is it cleaner burning, it is
half the price of imported gasoline.
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Fuel Cell Cars
Imagine a car that only had one waste product: water. That is the tantalizing
promise of fuel cell cars, which have not yet arrived in the commercial
marketplace. If it sounds too good to be true, that's because it might be. Fuel
cell cars produce electricity by chemically breaking down hydrogen fuel. When
pure hydrogen is used, the only by-product is water, but pollution is produced
in creating the fuel itself. Also, because hydrogen is a flammable gas, safety is an
issue. Fuel distribution stations, such as this proposed northern California
hydrogen pump, and storage solutions are under development but still rife with
kinks. It could be two or more decades before fuel cell cars are widely
available and adopted by drivers.
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Solar Power
The sunlight that reaches Earth's surface delivers 10,000 times more energy
than we consume, and solar power aims to harness this force. Solar technologies
use sunlight to provide heat, electricity, and even cooling for homes,
businesses, and industry by conducting electrons across an array like the one
at right or like the tiny solar cell in your calculator. Researchers have
optimistically proposed that if they could cover just 0.1 percent of the
Earth's surface with highly efficient solar cells they could in theory replace
all other forms of energy. At universities around the world, efforts are under
way to develop the kinds of advanced solar arrays using nanotechnology and
other cutting-edge science that could perhaps accomplish this goal in the
future.
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Biodiesel
This relatively new type of alternative fuel is processed from any vegetable
oil—including used oil from fast-food restaurants—and can power
most diesel-engine vehicles without modification. Sales of biodiesel are
gradually increasing—75 million gallons were sold in the U.S. in
2005—and many government vehicles like these from the USDA use it to fill
up. Though it burns 78 percent cleaner than petroleum diesel and comes from a
renewable source, it is double the cost and fueling stations are scattered.
Furthermore, only a fraction of vehicles in the U.S. have diesel engines,
though new fuel-efficient models on the market have recently gained in
popularity.
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Nuclear Power
Nuclear power plants provide about 17 percent of the world's electricity and
about 20 percent of the electricity in the U.S. They are extremely clean
compared to coal-fired plants, which, perhaps surprisingly, release more
radioactivity than a properly functioning nuclear power plant. Many experts
believe nuclear power such as that being developed in this Sandia National
Laboratory experiment is an important option for the U.S. and the world to meet
pollution-free energy needs. But others cite significant problems with nuclear
power. For example, mining and purifying the uranium that fuels nuclear plants
is not a clean process; improperly functioning nuclear plants present
environmental and terrorism risks; spent nuclear fuel remains toxic for
centuries and must be stored; and transporting nuclear fuel to and from plants
can be hazardous.
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