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Science Bits

University of Colorado at Boulder
Modeling Ozone Hole Chemistry

An exhaustive supercomputer modeling effort at the University of Colorado (CU) at Boulder has shown that hydrochloric acid is broken down on the surface of ice particles found in stratospheric clouds over the Earth's poles. The breakdown of HCl to chlorine atoms is an important step in the cascade of chemical reactions that lead to ozone destruction in the stratosphere over Antarctica each spring.

Although scientists have known that hydrochloric acid molecules which stick to the surface of the ice crystals in the clouds play a pivotal role in ozone depletion, the specific chemical processes have been the subject of much debate, according to CU chemistry and biochemistry professor James Hynes. Some scientists have speculated that the ionization of hydrochloric acid in the ice particles could only occur when the icy surfaces were in a liquid form.

But the modeling project, which used NCAR's supercomputers, indicates that hydrochloric acid molecules trapped at the surface by the ice particles can be broken down while still in the solid phase. The ionization triggers a stream of complex chemical reactions resulting in the eventual release of chlorine atoms, which destroy huge quantities of ozone molecules by stripping away oxygen atoms.

The research indicates the icy surfaces of the cloud particles are "an active player" in the ozone depletion process, said Hynes. "It's almost as if the ice is acting like an enzyme for these chemical reactions."

"This study gives us a stepping stone for making predictions about what may be happening to other molecules in the stratosphere," said postdoctoral research associate Brad Gertner. For example, hydrofluoric acid is also known to adhere slightly to the ice crystals in polar stratospheric clouds. But, according to Hynes, "Our opinion at this point is that hydrofluoric acid does not ionize like hydrochloric acid."

University of Colorado at Boulder
Go fly a kite ...

A research team from the University of Colorado (CU) at Boulder is studying the tropical troposphere. Armed with a large balloon and kite, they are testing the skies over a remote part of the Amazon Basin in northern Peru for greenhouse gas and ozone levels.

According to Detlev Helmig of the university's Cooperative Institute for Research in Environmental Sciences (CIRES), the researchers are measuring the exchange of greenhouse gases between rain forest vegetation and the atmosphere and charting levels of carbon dioxide, methane, and nitrous oxide. Helmig designed the sampling systems, which will be attached to the tethers of the unmanned balloon and parafoil kite. Other members of the research team include John Birks and Cathy Rowlen of the chemistry and biochemistry department, Ben Balsley of CIRES, and several graduate students.

The balloon, which is about 3 meters in diameter and 9 m long, will be floated up by tether more than 1.6 kilometers over the Amazon rain forest. The parafoil will be raised to about the same altitude during initial testing.

The far western edge of the Amazon, which is relatively pristine, will give the team good data on undisturbed jungle. The researchers are particularly interested in charting the emissions and absorption of atmospheric carbon dioxide over the rain forest.

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Edited by Carol Rasmussen, carolr@ucar.edu
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Last revised: Tue Apr 4 10:18:15 MDT 2000