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Understanding Ozone
The following timeline is a combination of material quoted from Sharon Roan's book entitled "Ozone Crisis; The 15 Year Evolution of a Sudden Global Emergency", and up-to-date information from current research scientists. It demonstrates the course of events that have taken place since the first ozone destroying pollutants were identified more than 20 years ago.
1973 Rowland and Molina first discover that chlorofluorocarbons (CFCs) can destroy stratospheric ozone.
1974 First government hearings are held on the CFC-ozone theory.
1975 Natural Resources Defense Council sues Consumer Product Safety Commission for a ban on CFCs used in aerosol spray cans. Lawsuit is rejected due to insufficient evidence that CFCs harm the ozone layer.
1976 National Academy of Sciences releases report verifying Rowland-Molina hypothesis, but recommends postponing government action.
1977 The United Nations Environmental Programme holds first international meeting to discuss ozone depletion.

United States bans CFCs used in aerosols.

Total Ozone Mapping Spectrometer (TOMS) is launched aboard the NIMBUS-7 spacecraft.

1984 Ozone loss of 40% is detected over Antarctica during austral spring.

Vienna Convention, calling for additional research, is signed.

Satellite images show existence of an Antarctic ozone hole.

1986 International negotiations resume in Geneva. United States requests global CFC reductions of 95% over the next 10 years.

Montreal Protocol, for CFC reductions of 50% by 1999, is signed.

Antarctic studies find chlorine to be primary cause of ozone depletion.

1988 Ozone losses of 1.7 to 3% are measured over Northern Hemisphere.
1990 International delegates meet in London to strengthen the Montreal Protocol and agree to a complete phaseout of CFCs by 2000.

Upper Atmospheric Research Satellite (UARS) is launched.

Meteor-3 TOMS is launched.

Mt. Pinatubo erupts, increasing natural levels of atmospheric chlorine.

Airborne Arctic Stratospheric Expedition (AASE I) studies northern vortex.


Record levels of ClO, 1.5 parts per billion, are measured over Bangor, Maine. Ozone depletion rates of up to 20% are found in the Northern Hemisphere. Maximum losses of 40 to 45% discovered over Russia.

Parties to the Montreal Protocol meet in Geneva and agree to a 75%reduction in CFCs by 1994 and overall phaseout by January of 1996.

Production grace period, to supply CFCs for essential purposes and the needs of developing countries, is extended to 2006.

1993 The TOMS aboard Nimbus 7 fails on May 6.
1994 The Meteor-3 TOMS fails on December 27.
1995 Professor Paul Crutzen, Professor Mario Molina, and Professor F. Sherwood Rowland receive the Nobel Prize in Chemistry.

(Click to return to Understanding Ozone.)

Text, images and videos courtesy of Distributed Active Archive Center at NASA's Goddard Space Flight Center.

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