According to conventional wisdom,
hydrogen-fueled cars are environmentally friendly because they emit only water
vapor — a naturally abundant atmospheric gas. But leakage of the hydrogen gas
that can fuel such cars could cause problems for the upper atmosphere, new
research shows.

In an article appearing this week in the
journal Science, researchers from the California Institute of Technology report
that the leaked hydrogen gas that would inevitably result from a hydrogen
economy, if it accumulates, could indirectly cause as much as a 10-percent
decrease in atmospheric ozone. The researchers are physics research scientist
Tracey Tromp, Assistant Professor of Geochemistry John Eiler, planetary science
professor Yuk Yung, planetary science research scientist Run-Lie Shia, and Jet
Propulsion Laboratory scientist Mark Allen.

If hydrogen were to replace fossil fuel
entirely, the researchers estimate that 60 to 120 trillion grams of hydrogen
would be released each year into the atmosphere, assuming a 10-to-20-percent
loss rate due to leakage. This is four to eight times as much hydrogen as is
currently released into the atmosphere by human activity, and would result in
doubling or tripling of inputs to the atmosphere from all sources, natural or

Because molecular hydrogen freely moves up and
mixes with stratospheric air, the result would be the creation of additional
water at high altitudes and, consequently, an increased dampening of the
stratosphere. This in turn would result in cooling of the lower stratosphere and
disturbance of ozone chemistry, which depends on a chain of chemical reactions
involving hydrochloric acid and chlorine nitrate on water ice.

The estimates of potential damage to
stratospheric ozone levels are based on an atmospheric modeling program that
tests the various scenarios that might result, depending on how much hydrogen
ends up in the stratosphere from all sources, both natural and anthropogenic.

Ideally, a hydrogen fuel-cell vehicle has no
environmental impact. Energy is produced by combining hydrogen with oxygen
pulled from the atmosphere, and the tailpipe emission is water. The hydrogen
fuel could come from a number of sources (Iceland recently started pulling it
out of the ground). Nuclear power could be used to generate the electricity
needed to split water, and in principle, the electricity needed could also be
derived from renewable sources such as solar of wind power.

By comparison, the internal combustion engine
uses fossil fuels and produces many pollutants, including soot, noxious nitrogen
and sulfur gases, and the “greenhouse gas” carbon dioxide. While a hydrogen
fuel-cell economy would almost certainly improve urban air quality, it has the
potential unexpected consequences due to the inevitable leakage of hydrogen from
cars, hydrogen production facilities, the transportation of the fuel.

Uncertainty remains about the effects on the
atmosphere because scientists still have a limited understanding of the hydrogen
cycle. At present, it seems likely such emissions could accumulate in the air.
Such a build-up would have several consequences, chief of which would be a
moistening and cooling of the upper atmosphere and, indirectly, destruction of

In this respect, hydrogen would be similar to
the chlorofluorocarbons (once the standard substance used for air conditioning
and refrigeration), which were intended to be contained within their devices,
but which in practice leaked into the atmosphere and attacked the stratospheric
ozone layer.

The authors of the Science article say that
the current situation is unique in that society has the opportunity to
understand the potential environmental impact well ahead of the growth of a
hydrogen economy. This contrasts with the cases of atmospheric carbon dioxide,
methyl bromide, CFCs, and lead, all of which were released into the environment
by humans long before their consequences were understood.

“We have an unprecedented opportunity this
time to understand what we’re getting into before we even switch to the new
technology,” says Tromp, the lead author. “It won’t be like the case with the
internal-combustion engine, when we started learning the effects of carbon
dioxide decades later.”

The question of whether or not hydrogen is bad
for the environment hinges on whether the planet has the ability to consume
excess anthropogenic hydrogen, explains Eiler. “This man-made hydrogen will
either be absorbed in the soil — a process that is still poorly understood but
likely free of environmental consequences — or react with other compounds in
the atmosphere.

“The balance of these two processes will be
key to the outcome,” says Eiler. “If soils dominate, a hydrogen economy might
have little effect on the environment. But if the atmosphere is the big player,
the stratospheric cooling and destruction of ozone modeled in this Science paper
are more likely to occur.

“Determining which of these two processes
dominates should be a solvable problem,” states Eiler, whose research group is
currently exploring the natural budget of hydrogen using new isotopic

“Understanding the effects of hydrogen on the
environment now should help direct the technologies that will be the basis of a
hydrogen economy,” Tromp adds. “If hydrogen emissions present an environmental
hazard, then recognizing that hazard now can help guide investments in
technologies to favor designs that minimize leakage.

“On the other hand, if hydrogen is shown to be
environmentally friendly in every respect, then designers could pursue the most
cost-effective technologies and potentially save billions in needless

“Either way, it’s good for society that we
have an emission scenario at this stage,” says Eiler. “In past cases — with
chlorofluorocarbons, nitrogen oxides, methane, methyl bromide, carbon dioxide,
and carbon monoxide — we always found out that there were problems long after
they were in common use. But this time, we have a unique opportunity to study
the anthropogenic implications of a new technology before it’s even a problem.”

If hydrogen indeed turns out to be bad for the
ozone layer, should the transition to hydrogen-fueled cars be abandoned? Not
necessarily, Tromp and Eiler claim.

“If it’s the best way to provide a new energy
source for our needs, then we can, and probably should, do it,” Tromp says.

Eiler adds, “If we had had perfect
foreknowledge of the effects of carbon dioxide a hundred years ago, would we
have abandoned the internal combustion engine? Probably not. But we might have
begun the process of controlling CO2 emissions earlier.”


Contact: Robert Tindol (626) 395-3631