Air Samples Show Ozone Depletion May Have Other Causes Than Fluorocarbons
HARRY F. ROSENTHAL
Nov. 10, 1995
WASHINGTON (AP) _ The worrisome depletion of the ozone layer may be caused by more than fluorocarbons released by hair spray and Freon, new research indicates. Something happens to the sun's energy when it hits the upper atmosphere.
Air samples brought back from higher altitudes than ever before show a significant amount of the energy is diverted, biochemist Mark Thiemens said. Scientists may have to change the assumption that only manmade gases and light are responsible for ozone depletion, he said.
Ozone is the barrier that shields Earth from deadly doses of the sun's ultraviolet radiation.
Thiemens' research is the subject of an article in today's issue of Science magazine.
A professor of chemistry and biochemistry at the University of California, San Diego, Thiemens said current theories about ozone depletion are not incorrect but need to be updated with new information.
``There is a process going on in the upper atmosphere not known before, a significant amount of energy doing chemistry that otherwise you didn't account for,'' he said. ``We need a good tally where that energy goes.''
How the new findings might affect the life cycle of ozone or other chemical processes in the atmosphere isn't known, Thiemens said. Neither is it known how the process is governed by location or time of year.
Scientists believe the reduction in ozone over the Antarctic and Northern Hemisphere in a four- to six-week period beginning in late September is due to atomic chlorine and chlorine oxide in the atmosphere. Those compounds result from chlorofluorocarbons _ gases used in aerosol spray cans, Styrofoam containers and air-conditioning systems.
Ozone absorbs ultraviolet light, coupling the energy of the sun to the atmosphere.
``In a general sense, the climate of the planet is in large part dictated by this absorption process,'' Thiemens said in an interview.
In a series of small rocket launches in 1992 from White Sands, N.M., an instrument brought back samples of frozen air from an altitude of 27 miles _ halfway through the stratosphere and into the next higher region, the mesosphere.
``We really looked into a region where no one looked with this degree of precision before,'' Thiemens said.
Until now, scientists relied on samples of air trapped by instruments on balloon flights, which climb no higher than about 18 miles.
Thiemens' team focused on an isotope that is characteristic of oxygen found in ozone, a heavyweight cousin of oxygen. They saw an unusual chemical reaction in which stratospheric ozone makes another oxygen atom, which interacts with carbon dioxide and gives off some of its energy.
``You can see a real significant chunk of ozone energetics goes through this process,'' he said. ``No one has ever seen a change in air oxygen in its composition or its isotopes before. ... If the second most abundant molecule in the atmosphere is changed, it takes a big process to do this.''