The news earlier this month that several European countries and the U.S. have agreed to phase out the use of chlorofluorocarbons (CFCs) by the year 2000 brings before us yet again the questionable theory that CFCs cause depletion of the ozone layer.
Atmospheric chemist F. Sherwood Rowland , of the University of California, Irvine, formulated the theory in the early 1970s. His speculations, quoted widely in reports about this month's international conference hosted by Margaret Thatcher in London, have gained so much momentum over the years that they have now become the basis for decisions that would deprive us of the only inexpensive and effective refrigerants we have for refrigeration and air conditioning. This is not because of scientific proof, but the result of the constant reiteration of disaster scenarios that range from skin cancer to DNA damage.
Pronouncements in the past few weeks give the impression that all atmospheric scientists are believers, which is far from true. Many of us are still skeptical because of incompatibilities between the theory and what we know about the ozone layer:
1. The Rowland theory ignores the equilibrium nature of ozone in the layer. The ozone molecules are constantly being created and destroyed— both quite naturally— by the very short wavelengths of ultraviolet light from the sun. The amount of ozone in the layer depends upon an equilibrium between the two processes. This equilibrium varies markedly both over the globe and throughout the year.
At very high altitudes a disrupted equilibrium is restored in a matter of minutes; at lower levels in the stratosphere, in a matter of weeks or months. In any event, repair takes place rather quickly. Depletion of ozone can occur only by reducing the equilibrium density of ozone molecules. This makes for relatively insignificant depletions. No doubt many CFC molecules have reached the ozone layer, but it is unlikely both that they are depleting the ozone to the extent the activists say, and that such damage, even if it existed, would take centuries to repair.
2. Since the same narrow band of ultraviolet light breaks down both CFCs, releasing their ozone-destroying chlorine, as well as oxygen, creating ozone, there is a 'competition' between the two processes for this necessary solar energy. The probability that an oxygen molecule will be broken apart, rather than a CFC molecule, depends upon the relative abundance of the two gases in the ozone layer. Calculations based on high-altitude CFC samplings and data supplied by the National Oceanic and Atmospheric Administration show 60,000 ozone molecules are created for every chlorine atom released from a CFC molecule.
With this probability, how can the equilibrium density of the ozone layer be materially reduced? In other words, the paucity of measurable proof of depletion may be because depletion is not actually occurring. It is of interest to note that surface measurements by the National Oceanic and Atmospheric Administration indicate that the total amount of ozone above the U.S. is actually increasing.
3. Unable to measure depletion in an unambiguous manner, advocates of the theory have taken the `hole' in the layer over Antarctica as indirect proof of loss of the layer over mid-latitudes. However, papers at last summer's international ozone conference at Snowmass, Colo., cast doubt that this phenomenon is a mirror of global ozone decline. Perhaps the erosion of this ozone during the polar night is due to the same interaction of the solar wind with the Earth magnetic field that causes the auroras. It has been observed that this combination can destroy the ozone. Solar wind is the product of solar flares, which are becoming more frequent as sunspot activity waxes.
Let us not blindly follow those environmental activists who cry, 'The sky is falling', but let's continue to study the sky until we know enough to make a sound decision regarding the phasing out of our best refrigerants. Remember, before CFCs, toxic ammonia and sulfur dioxide were used in our home refrigerators.
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