Clean Air Technologies

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.