Contact: Barbara McGehan IMMEDIATE RELEASE
Stephen Montzka 5/30/96
James Butler
It looks like a brighter future for Earth's stratospheric ozone layer. According to a new study by Commerce Department scientists in Boulder, Colo., the total amount of ozone- destroying chemicals in the troposphere (lower atmosphere) has declined for the first time since humans began producing these substances. This decline is expected to affect the stratosphere, where the ozone layer is found, in a few years.
In findings published in the current issue of Science, Stephen A. Montzka and colleagues from the Climate Monitoring and Diagnostics Laboratory in Boulder, part of Commerce's National Oceanic and Atmospheric Administration, conclude that chlorine and equivalent chlorine (chlorine plus bromine) decreased in the troposphere in 1995. The scientists believe this decline has occurred because many nations have limited the production of materials that cause ozone depletion in the stratosphere. This is good news for the ozone layer, which has been under attack from ozone-depleting chemicals produced by humans for many years.
Limits to ozone-damaging compounds were first set forth in the Montreal Protocol, an international agreement that was originally signed by the United States and 22 other nations in 1987, and subsequently revised and amended.
While the study results do not suggest that ozone depletion is no longer a concern, they do show for the first time that the outlook for stratospheric ozone has improved. The ozone layer was expected to recover in coming decades as a result of restrictions placed on CFCs and other chemicals by the Montreal Protocol, but, before this study, many uncertainties remained regarding the timing for initial recovery.
Unlike other recent measurement studies, this one considers all of the important ozone-depleting substances generated by human activity, and how the total amount of chlorine and bromine (relevant to stratospheric ozone depletion) has changed in recent time. Conclusions drawn by the scientists are based upon their measurements of chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), halons, and chlorinated solvents from tropospheric air samples collected at remote locations across the globe over the past four to five years. Only by considering all of these ozone-depleting substances together does it become possible to draw conclusions regarding amounts of ozone in the future stratosphere.
"Both chlorine and bromine are known ozone-depleting agents that had been increasing steadily in the atmosphere over the 30 years before 1990 because of the use of CFCs, chlorinated solvents, HCFCs, and halons in refrigerators, air conditioners, foams, cleaners and fire extinguishers," says Montzka.
According to the researchers, chlorine in the lower atmosphere was decreasing at about 1 percent per year in mid- 1995, and had dropped approximately 1.5 percent from the observed maximum. "Our data show that the mean global abundance of chlorine in the lower atmosphere peaked in 1994," Montzka continued. "Small yearly increases are still observed for bromine, which destroys ozone more efficiently than chlorine. However, these increases are small enough to be offset by the observed decrease in chlorine, even when the greater ozone- depleting efficiency of bromine is considered."
Montzka and his colleagues believe that ozone-depleting gases in the stratosphere will peak within one to three years, and thereafter begin declining. Changes in the stratosphere lag behind those observed in the troposphere because it takes several years for air in the lower atmosphere to reach the stratosphere. Stratospheric ozone forms an invisible shield around the Earth, protecting it from the biologically damaging ultraviolet rays of the sun.
The scientists warn, however, that this bit of good news is not irreversible. "Decreases in ozone-depleting gases are a direct result of international limits on the production and consumption of ozone-depleting chemicals. Without widespread adherence to restrictions outlined in the revised Montreal Protocol, additional emissions of chlorinated and brominated compounds could slow or reverse the trends we have observed, and delay recovery of stratospheric ozone," asserted Montzka.
The air samples analyzed were from NOAA sites in Point Barrow, Alaska; Mauna Loa, Hawaii; Cape Matatula, American Samoa; and the South Pole. Other stations in the network include the Canadian Atmospheric Environmental Services station at Alert, Canada; the University of Colorado station at Niwot Ridge, Colo., and the Australian Baseline Air Pollution station at Cape Grim, Tasmania.
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Note to Editors: For more information, you can access NOAAžs Climate Monitoring and Diagnostics Lab - Nitrous Oxide and Halocompounds Division home page at: http://www.cmdl.noaa.gov/noah_home/noah.html A color figure can be accessed at: http://www.cmdl.noaa.gov/noah_home/totalcl/totalcl.html Following are some experts in the area of ozone research. Dr. Richard Stolarski NASA/Goddard Prof. Steven Wofsy Harvard University Dr. Michael Kurylo NASA Headquarters