New Study Looks At Movement of Ozone-Depleting Chemicals in Stratosphere

June 20, 1996



A new study by government and university researchers shows how air moves chemicals between different regions of the stratosphere, which may help scientists better understand the depletion of the ozone layer, the Commerce Department's National Oceanic and Atmospheric Administration announced. The findings could also affect assessment of the environmental impact of a proposed fleet of supersonic aircraft and the possible ozone-depleting pollutants they emit.

In the current issue of Science, researchers from NOAA's Climate Monitoring and Diagnostics Laboratory (CMDL) and Aeronomy Laboratory (AL) in Boulder, Colo., the Cooperative Institute for Research in Environmental Science (CIRES) at the University of Colorado, NASA, the California Institute of Technology, and the New Mexico Institute of Mining and Technology, report on a study that looks at the rate of exchange of air between the tropical (within 20 degrees latitude of the equator) and mid-latitude (30-50 degrees latitude in both hemispheres) regions of the stratosphere. These air motions are critical to understanding the thinning of the stratospheric ozone layer that protects the Earth's surface from the sun's harmful ultraviolet radiation.

The exchange of air between mid-latitudes and the tropics is particularly important because in the tropics, the atmospheric air motion transports natural and human-made gases upward to higher altitudes in the stratosphere, somewhat like a vertical "pipe." Some chemicals, such as CFCs, decompose at these higher altitudes, releasing by-products that destroy ozone. How fast the ozone-damaging by-products are released, how they are distributed throughout the stratosphere, and how fast ozone is depleted over populated regions at mid-latitudes, depends, among other things, on how fast air is exchanged between this tropical "pipe" and the mid-latitudes.

To investigate the air motions, researchers used a new instrument developed by scientists at CMDL and AL in Boulder. The instrument was designed to measure several "tracer" gases that can be used to track air motions. It flew aboard a high-altitude "ER-2" stratospheric research plane, operated by NASA, in wide-ranging flights in the tropics and in both hemispheres during 1994.

The researchers observed the tropical "pipe" in action, and found that mid-latitude air gets to the tropics more slowly than previously thought. "Many current computer models that quantify and predict ozone depletion assume very rapid mixing of tropical and mid-latitude air, but our measurements demonstrate that the actual rate of exchange is rather slow," said lead author Michael Volk.

"We suggest that this might be one of the reasons why models tend to underestimate the observed decline in ozone at mid-latitudes during the past two decades," said James Elkins, co-author of the paper and one of the lead developers of the instrument that made the key measurements. The findings should improve the ability of computer models to represent the amount of ozone depletion that is observed in the atmosphere and to predict future losses of ozone.

The study also has implications for the investigation of the environmental impact of a proposed fleet of civil supersonic aircraft that would emit gases and particles directly into the lower stratosphere at heights between 55,000 and 75,000 feet. The researchers found that nearly half of the air in the tropical stratosphere at 70,000 feet actually originated at mid-latitudes, where most of the aircraft emissions would occur. Emissions that enter the tropics can be carried to higher altitudes where increased amounts of some aircraft pollutants could contribute to ozone loss.

"This study has helped us to understand how much and how quickly the air from mid-latitude flight corridors would reach the upwelling region of the tropics," said co-author David Fahey. "The atmospheric models will be able to make better estimates of the potential effects of supersonic aircraft on the ozone layer."

This research is supported in part by the Atmospheric Effects of Stratospheric Aircraft component of NASA's High Speed Research Program, NASA's Upper Atmosphere Research Program, and the Atmospheric Chemistry Project of NOAA's Climate and Global Change Program.

NOTE: The following are experts in the field that may be contacted for additional information:
Dr. Randy Friedl, NASA Headquarters, 202-554-6477
Dr. Michael Kurlyo, NASA Headquarters, 202-358-0237
Dr. Paul Newman, NASA Goddard SFC,301-286-3806
Dr. Jose Rodriguez, AER Inc.,510-422-1845

National Oceanic and Atmospheric Administration

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