posted 02-12-2001 07:14 PM            

SCIENTISTS DISCOVER NEW KEYS TO ARCTIC OZONE LOSS

WASHINGTON, DC, February 9, 2001 (ENS) - Scientists have discovered a new class of particles present in the Arctic's winter stratosphere that may play an important role in ozone loss in that region, the National Oceanic and Atmospheric Administration (NOAA) said Thursday.

These findings give scientists a better understanding of the processes that set the stage for ozone depletion in the stratosphere above the Arctic.

An international team of scientists published their findings in today's issue of "Science" magazine. Lead author David Fahey, a scientist at NOAA's Aeronomy Laboratory, and his colleagues discovered a new class of very large polar stratospheric cloud (PSC) particles that had never before been detected.

Scientists have known for some time that during the cold Arctic winter, icy, polar stratospheric cloud particles containing nitric acid are formed, which increase the destruction of ozone by human emissions of chlorine and bromine.

The new particles have diameters of 10 to 20 microns (millionths of a meter), which is about 10 to 20 times larger in diameter than typical particles in PSCs. These particles have eluded detection to date because of their large size and their very small abundance in the atmosphere.

PSCs serve as reservoirs for nitrogen in the polar stratosphere. As the particles fall out of the atmosphere, the stratosphere becomes "denitrified" or depleted of nitrogen.

The discovery of this new class of large PSCs helps to explain a longstanding mystery - that the extent of denitrification observed in the polar stratosphere could not be accounted for by the smaller PSCs.

The researchers say the loss of nitrogen has important consequences for the ozone because ozone destroying forms of chlorine and bromine survive longer in a denitrified stratosphere.

"Our findings suggest that we still need to learn more about how these large PSCs are formed, so that we'll have a better understanding of how the ozone layer will recover in the future," Fahey said.
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Once again, the problem of residual chlorine and bromine in the upper atmosphere. Since these are long-lived catalyts in ozone depleting reactions, what can, will, be done to limit their impacts on our protective ozone layer?