The study — published today in the journal Nature by Thom Rahn, a Frederick Reines Postdoctoral Fellow at Los Alamos, and colleagues — indicates that molecular hydrogen in the atmosphere tends to accumulate deuterium in the stratosphere, the second layer of Earth's atmosphere located approximately 10 miles above the surface. The stratosphere is home to Earth's ozone layer, which stops potentially lethal amounts of ultraviolet radiation from reaching Earth's surface.
Rahn collaborated with researchers from the California Institute of Technology, the University of California at Berkeley, the University of California at Irvine and the National Center for Atmospheric Research in Boulder, Colo., in looking at deuterium levels in molecular hydrogen in the stratosphere. Since deuterium's chemical behavior is virtually identical to hydrogen, it can substitute itself for a hydrogen atom in H2. Extremely small concentrations of naturally occurring deuterium exist in known concentrations throughout the universe and were produced during the first few minutes of the formation of the universe.
Since the overall concentration of H2 in the stratosphere does not change, Rahn and his colleagues were surprised to find that deuterium levels were nearly one and a half times as high in the stratosphere as they are in seawater — Earth's most abundant reservoir of elemental hydrogen, and hence an excellent reference point. The finding indicated that deuterium is being concentrated in the stratosphere. Rahn and colleagues showed that deuterium enrichment was due to a series of atmospheric chemical reactions.
Deuterium levels in molecular hydrogen act as a fingerprint of the deuterium source. Consequently, Rahn and his colleague's findings have ramifications for the use of molecular hydrogen for fuel cells. These findings will enhance capabilities to identify the unavoidable escape of H2 from production, storage and transfer facilities associated with fuel cell technologies that could lead to increased concentrations of molecular hydrogen in the atmosphere.
Increased atmospheric hydrogen would produce more water in the stratosphere, which could facilitate ozone destruction by chlorofluorocarbons. In addition, in the troposphere, the lowest level of Earth's atmosphere, increased molecular hydrogen could reduce the amount of hydroxyl radicals — chemicals that are available to help scrub greenhouse gases such as methane from the atmosphere.
Finally, the formation of water in the stratosphere could form extremely thin clouds that would not allow sunlight striking Earth's surface to be reflected back into space — a phenomenon that could potentially increase the atmospheric "Greenhouse Effect" and lead to rising global temperatures.
On the other hand, use of fuel cells as an energy source would reduce the amount of nitrogen oxides, the precursors of urban smog, that result from combustion of fossil fuels. This would improve urban air quality.
"Our study gives us a tool in looking ahead at potential consequences if a hydrogen-based energy economy is not properly managed," said Rahn. "This is an opportunity that is somewhat analogous to chlorofluorocarbon usage in the past. No one foresaw what CFCs would do to the stratosphere when they were being developed. But now we have a chance to be proactive in saying what we need to consider when moving to a hydrogen economy."
Building on Los Alamos's growing expertise and interest in hydrogen research, Manvendra Dubey, Rahn's colleague and mentor, in collaboration with Larry Horowitz of NOAA and Doug Kinnison of the National Center for Atmospheric Research is currently applying models to study the effects of potential hydrogen leakage from various hydrogen production and transport methods. The models will examine hydrogen's effects on stratospheric ozone, climate, air-quality and tropospheric chemistry in a global hydrogen economy.
The simulations will help assess potential benefits and risks of the use of hydrogen for energy and ensure that this can be accomplished in an environmentally responsible manner. Continuous measurements of atmospheric hydrogen and deuterium are needed to establish a baseline in anticipation of a transition to a hydrogen economy, an area that Los Alamos is keenly interested in pursuing.
from the Earth and Environmental Science (
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