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Widespread use of hydrogen fuel cells might not be as environmentally friendly as many believe.

Scientists say the new technology could lead to greater destruction of the ozone layer that protects Earth from cancer-causing ultraviolet rays.

Researchers believe that if hydrogen replaced fossil fuels to run everything from cars to power plants, large amounts of hydrogen would drift into the stratosphere as a result of leakage and indirectly cause increased depletion of the ozone layer.

They acknowledged that much is still unknown about the hydrogen cycle and that technologies could be developed to curtail hydrogen releases, mitigating the problem. But they say hydrogen's impact on ozone destruction should be considered when gauging the potential environmental downsides of a hydrogen-fuel economy.

Ever since US President George W. Bush this year singled out hydrogen development as an energy priority, the fuel has been the buzzword in energy debates. The US Congress plans to pump more than US$3 billion into hydrogen research over the next five years in hopes of putting fuel-cell-powered cars into showrooms by 2020. Industry is spending billions more to develop fuel cells, although their widespread use is probably still decades away.

Fossil fuels - coal, oil or natural gas - produce chemicals that pollute the air as well as the greenhouse gas carbon dioxide. A hydrogen fuel cell, when making energy, releases only water as a byproduct.

In an article in this week's edition of Science magazine, researchers at the California Institute of Technology raised the possibility that if hydrogen fuel replaced fossil fuels entirely, it could be expected that 10 per cent to 20 per cent of the hydrogen would leak from pipelines, storage facilities, processing plants and fuel cells in cars and at power plants.

Because hydrogen readily travels skyward, the researchers estimated that its increased use could lead to as much as a tripling of hydrogen molecules - both manmade and from natural sources - going into the stratosphere, where it would oxidize and form water.

"This would result in cooling of the lower stratosphere and the disturbance of ozone chemistry," the researchers wrote. It would mean bigger and longer-lasting ozone holes in both the Arctic and Antarctic regions, where drops in ozone levels have been recorded over the past 20 years. They estimated that ozone depletion could be as much as 8 per cent.

Nejat Veziroglu, president of the International Association for Hydrogen Energy and director of the Clean Energy Research Institute at the University of Miami, expressed scepticism about the Cal Tech findings.

"Leakage will be much less than what they are considering," he said.

An Energy Department spokeswoman, Jeanne Lopatto, said the Cal Tech study will influence some of the government's fuel cell research, especially in areas of hydrogen transport and storage. She said the administration "welcomes new scientific knowledge on the potential effects of hydrogen production, storage and use."

The loss of some of the Earth's ozone layer is of concern because ozone blocks much of the sun's ultraviolet light, which over time can lead to skin cancer, cataracts and other problems in humans.

Ozone depletion has been contained with international treaties banning and phasing out ozone-killing chlorofluorocarbons, or CFCs. But the Cal Tech researchers said huge increases in the concentration of hydrogen in the stratosphere "could substantially delay the recovery of the ozone layer," even if a hydrogen economy is still decades away.

John Eiler, an assistant professor of geochemistry at Cal Tech and one of the article's authors, acknowledged that the concerns raised in the study might eventually be resolved when more is learned about the hydrogen fuel cycle.

For example, much of the leaking hydrogen might become absorbed in the soil instead of drifting into the sky, he said. "If soils dominate, a hydrogen economy might have little effect on the environment. But if the atmosphere is the big player, stratospheric cooling and destruction of the ozone layer is more likely to occur."

Cal Tech scientist Tracey Tromp, another of the authors, said that with advanced warnings of a problem, a hydrogen energy infrastructure could be fashioned to allow more control of leaks and reduce the adverse environmental impact.

(Agencies via Xinhua June 17, 2003)