Contact: Barbara McGehan FOR IMMEDIATE RELEASE
Susan Solomon 3/29/96
Many of the year-to-year fluctuations in human-caused ozone depletion over the northern mid-latitudes in the past 15 years are related to volcanic activity, government and university scientists said in a new study of the stratosphere. The study is the first to explain many of the "ups and downs" of year-to-year stratospheric ozone loss, which is caused by human-made chlorine and bromine compounds and accelerated by volcanic particles.
Using a state of the art dynamical-chemical model of the stratosphere, satellite observations of atmospheric particles and atmospheric measurements of ozone and related gases, the scientists helped show why the amount of ozone destruction varies from year to year over populated regions in the northern hemisphere.
The findings are published in the current issue of the Journal of Geophysical Research by principal author and National Oceanic and Atmospheric Administration scientist, Susan Solomon, and scientists from the National Center for Atmospheric Research (NCAR), the University of Colorado's Cooperative Institute for Research in Environmental Sciences, and the National Aeronautics and Space Administration.
Researchers found that by taking the effects of volcanic particles into consideration, their state-of-the-art stratospheric model also came closer to explaining how ozone losses varied with altitude in the atmosphere above the northern mid-latitudes. The particles, or aerosols, occur naturally as a result of major volcanic eruptions, such as the Mt. Pinatubo eruption in 1991. During these periods of volcanic activity, the particles accelerate ozone destruction.
In the stratosphere, the particles interact with chlorine- and bromine-containing compounds produced from human-made substances such as chlorofluorocarbons (CFCs) that cause destructive changes in the upper atmospheric ozone layer of the Earth.
Solomon stressed that while particles can contribute to the features and fluctuations of the stratospheric ozone depletion, the particles alone do not destroy ozone. "Chlorine- and bromine-containing compounds caused by human activity are the real culprits in destroying ozone," she said. "The particles influence the ozone loss because they provide a surface upon which chemical reactions that enhance chlorine-driven ozone depletion can take place."
The findings of this study also underscore the importance of current efforts to assess the effects of subsonic and supersonic aircraft, whose emissions include particles and gases, on the atmosphere. According to the scientists, any human activities that would increase particle abundances in the stratosphere could influence the ozone layer.
The ozone layer is expected to recover in the coming decades as a result of restrictions on CFCs and other ozone-depleting chemicals required by the United Nations Montreal Protocol on Substances that Deplete the Ozone Layer. This study indicates that future major volcanic eruptions will cause fluctuations during the recovery process that are both expected and temporary. Scientists will be better equipped to predict those fluctuations as they continue to monitor and measure the on-going recovery of the ozone layer along with measurements of volcanic particles.
Authors of the research paper, entitled "The Role of Aerosol Variations in Anthropogenic Ozone Depletion at Northern Mid-Latitudes," are Solomon of NOAA's Aeronomy Laboratory, (currently on sabbatical at NCAR), R.W. Portmann of the Cooperative Institute for Research in the Environmental Sciences at the University of Colorado, R.R. Garcia of NCAR, and L. W. Thomason, L.R. Poole and M. P. McCormick of NASA's Langley Research Center.
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