Afternoon traffic flows along smog-filled Beijing streets on July 14, 2008. Is it possible for vehicles powered by hydrogen fuel cells to reduce the pollution in the air?

FREDERIC J. BROWN/AFP/Getty Images

No more pollution?

One of the most important benefits of a hydrogen economy is that fuel cells are nonpolluting. No carbon emissions are produced when electricity is generated in a fuel cell. A hydrogen fuel cell produces two byproducts -- heat and water. If every vehicle on the road were powered by a hydrogen fuel cell, the familiar clouds of smog that hang over many U.S. cities, most of which comes from vehicle exhaust, would largely disappear. According to the Environmental Protection Agency, half of all Americans live in areas where there's enough pollution to produce a negative effect on human health, so reducing smog would be a significant benefit.

Internal combustion engines, which burn fuels derived from the element carbon, produce several byproducts, primarily carbon dioxide, water, and the tiny particles of matter that we refer to as soot. The soot, when ejected into air breathed by humans, can cause asthma, lung cancer, and other diseases. In addition, most scientists believe that increased amounts of carbon dioxide in the atmosphere contribute to global warming, which could eventually cause damaging climatic changes over much of our planet.

Converting from­ internal combustion engines to nonpolluting fuel sources such as hydrogen will be important for reducing these problems in the 21st century. But with more than 130 million gasoline-powered vehicles on the road today, it's unlikely that fuel cell cars will make enough of a difference in the near future to produce significant environmental improvements. It's estimated that early fuel cell cars will cost at least $100,000, which will put them out of the reach of the ordinary driver. Another point to make is that the infrastructure needed to make these cars practical, including hydrogen production plants and refueling stations, is not yet available. Some observers believe that, in the short term, environmental changes will come through the combined use of hydrogen cars and other types of vehicles, including battery-powered electric cars and cars that use other alternative forms of fuel.

Existing atmospheric pollution isn't going to go away soon. Soot settles out of the atmosphere in a matter of weeks or months, but carbon dioxide remains for a considerably longer time. Even if all sources of carbon emissions were eliminated today, it could still take decades for atmospheric carbon levels to return to normal. Furthermore, automobiles are only one source of carbon emissions. Others, such as coal-burning power plants, would also have to be greatly curtailed in order to prevent global warming.