Today in History – September 25, 1974 – Scientists first reported that freon gases released from aerosol spray cans were destroying the ozone layer (Molina, M. j., and F. S. Rowland, “Stratospheric Sink for Chlorofluoromethanes: Chlorine Catalysed Destruction of Ozone”, Nature, 249, 810-814, 1974).
It was not until March 22, 1985 that the Vienna Convention for the Protection of the Ozone Layer was adopted in response to this and other studies documenting the harm caused to the environment and our own health by ozone-depleting substances.
Ozone is a colorless gas, closely related to the oxygen in the air we breathe. The ozone molecule is made up of three oxygen atoms (O3), while normal atmospheric oxygen contains only two (O2). At concentrations above one part per million (1 ppm), ozone is irritating to the skin, eyes, and upper respiratory system. In the lower atmosphere, ozone is a pollutant produced by the action of sunlight on nitrogen oxides and volitile organic compounds present in motor vehicle exhaust and, to a lesser extent, in some industrial emissions.
However in the far upper atmosphere (stratosphere) about 10 to 20 miles above the earth’s surface, a naturally occurring ozone layer performs a highly useful function by filtering out much of the ultraviolet radiation emitted by the sun. By reducing the amount of ultraviolet radiation reaching the surface of the earth, the ozone layer reduces the danger of skin cancer, cataracts, and other negative health and environmental effects.
Scientific studies beginning in the early 1970′s indicated that that the stratopheric ozone layer was becoming depleted by the emission of certain compounds produced on the earth, the most important being the chloroflourocarbons (CFC’s) that had been developed for use in air conditioning and refrigeration systems. Early refrigeration systems had used refrigerants that were flammable (propane), toxic (sulfur dioxide), or both (ammonia, methyl chloride). Joint work by General Motors, Frigidaire, and DuPont in the late 1920′s and 30”s had led to development of the CFC-based Freon refrigerants (see Freon ® – The History of Freon®), which were both non-flammable and non-toxic. These became widely used throughout the world in refrigeration and air conditioning system, as cleaning solvents, and in other applications. Leakage of these substances on earth was carried upward by winds to the stratosphere, where they interacted with ice crystals to cause a breakdown of the ozone molecules.
As evidence of ozone depletion accumulated, governments began taking action to limit emissions of CFC’s and other ozone-depleting substances. International cooperation to address ozone depeletion culminated in the signing of the The Vienna Convention on the Protection of the Ozone Layer on March 22, 1985. Its provisions were further strengthened by the signing of the The Montreal Protocol on Substances that Deplete the Ozone Layer on September 16, 1987.
For more information, see the Engineering Pathway’s educational resources on the ozone layer, global warming or view our Chemical, Biochemical, Biomolecular Engineering Education, Environmental Engineering Education or our Green Design and Sustainable Enginering Education community sites.