Atmospheric Chemists Win 1995 Nobel Prize in Chemistry

The 1995 Nobel Prize in Chemistry was awarded to three atmospheric chemists, Paul Crutzen (Dutch), Director of the Atmospheric Chemistry Department of the Max Planck Institute for Chemistry, Mainz, Germany; Mario Molina (American), Martin Professor of Environmental Sciences in the Departments of Chemistry and Earth, Atmospheric and Planetary Sciences at the Massachusetts Institute of Technology, Cambridge, MA and F. Sherwood Rowland (American), Bren Professor of Chemistry at the University of California, Irvine, CA, for their work on the forma- tion and decomposition of ozone. Ozone (O₃), a harmful compound at ground level, is scattered thinly throughout the layer of the atmosphere called the stratosphere. This layer is also known as the ozone layer. Ozone is formed when ultra-violet tradiation from the sun splits an oxygen molecule, O₂ , into two atoms which then join with another oxygen molecule to form O₃. Ozone, as well as oxygen, is beneficial because it protects the earth by absorbing much of the sun's ultra-violet radiation. A "hole" in the ozone layer was first discovered in 1985 by Joseph Farman while working at the European Ozone Research Coordination Unit. This "hole" was due to depletion of ozone over the Antarctic where conditions are more favourable for depletion of ozone.

Since then, many scientists have been monitoring the enlargement of the "hole". In 1970, Paul Crutzen showed that nitrogen oxide, NO, catalyses the decomposition of ozone to oxygen. This is a problem because ozone and oxygen are part of an ozone formation/destruction cycle. Damage to the ozone layer will continue to occur at an increasing rate as the nitrogen oxidecontinues to accumulate in the stratosphere. As a result, the cycle becomes unbalanced because the ozone is being destroyed faster than it can be formed and overall depletion of ozone results. The nitrogen oxide is formed primarily from the photochemical decomposition of nitrous oxide, N0₂, in the stratosphere. The nitrous oxide is produced by microbes in the soil and can travel through the air up to the stratosphere.

In 1974, Mario Molina and Sherwood Rowland established that chlorofluorocarbon gases (CFC's/freons) were detrimental to the ozone layer. CFC's present in substances such as aerosols, foams, and refrigerants, could travel up to the ozone layer. When UV radiation hits the molecules it splits them into their individual components yielding chlorine atoms which act as catalysts for the conversion of ozone to oxygen. The chlorine atoms are the main cause of ozone depletion. The work of Crutzen, Molina, and Rowland has increased the understanding of the chemistry of the ozone layer. This knowledge has resulted in regulations being put in place so that the emission of CFC's can be controlled and the depletion of the ozone can be decreased. It is estimated that it will take almost 100 years for the ozone to fully recover if all deleterious gases are prevented from entering the stratosphere!