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Hydrogen levels increasing in atmosphere.

Hydrogen levels increasing in atmosphere

Analyses of air samples from around the globe reveal that atmospheric levels of molecular hydrogen have climbed over the last five years, apparently because of human activities, two atmospheric scientists report. Over many decades, rising levels of this gas could stimulate greater loss of protective ozone above Earth's polar regions, they suggest.

M.A.K. Khalil and R.A. Rasmussen of the Oregon Graduate Institute in Beaverton measured air samples collected from six sites in the northern and southern hemispheres. Technicians at these locations take weekly samples and send them in stainless steel canisters to the Beaverton lab for analysis.

Examining 3,500 air samples taken from October 1985 through April 1989, Khalil and Rasmussen found molecular hydrogen ([H.sub.2]) rising at an average annual rate of 0.6 percent, or 3.2 [+ or -] 0.5 parts per billion, they report in the Oct. 25 NATURE. The current level of hydrogen in the atmosphere measures just over 500 parts per billion.

The researchers attribute the hydrogen buildup to various human activities, including the burning of vegetation and emissions of the greenhouse gas methane -- which reacts with other gases to produce hydrogen -- arising primarily from rice cultivation and cattle raising. They estimate hydrogen levels were 200 parts per billion before the industrial era began. Future studies of air bubbles trapped in glacial ice might help determine the preindustrial level, Khalil suggests.

Hydrogen accumulating in the lower atmosphere can leak up into the stratosphere, where it oxidizes to form water vapor. The addition of water vapor to the extremely dry stratosphere could increase the number of clouds over Earth's coldest regions -- an effect that might accelerate the destruction of ozone molecules in the polar stratosphere (SN: 10/15/88, p.249), Khalil says. In this way, a hydrogen buildup could enhance ozone loss near the poles, he says.

Because the observed hydrogen increase is right at the margin of detectability, researchers must confirm the trend by gathering several more years' worth of data, says chemist F. Sherwood Rowland of the University of California, Irvine. He contends that rising levels of methane should add significantly more water vapor to the stratosphere than would increasing levels of hydrogen, posing an even greater threat to the ozone layer. Researchers believe methane concentrations are currently rising by about 1 percent per year.
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Author:Monastersky, Richard
Publication:Science News
Date:Oct 27, 1990
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