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Chapter 9 from: J.J. Ray (Ed.) "Conservatism as Heresy". Sydney: A.N.Z. Book Co., 1974


Concorde and the Destruction of Ozone



By S. T. BUTLER

Recent publications by two physicists from Columbia University, U.S.A., are of vital significance with regard to the question of pollution of the upper atmosphere by the exhaust gases of supersonic transports such as the Concorde.

The possible depletion of the ozone layer in the stratosphere by oxides of nitrogen in the exhaust gases of supersonic aircraft made headlines last year.

Ozone is a type of oxygen which resides in the atmosphere at high altitudes - primarily between 60,000 to 150,000 feet. The molecules of ozone consist of three oxygen atoms joined together, so that ozone is described by the symbol 03. Normal oxygen as we know it consists of two oxygen atoms combined - and has the symbol 02.

Ozone is formed in the first instance by ultraviolet rays in the solar radiation splitting the normal 02 molecules into their separate oxygen atoms. Each one of these, through a series of collisions, may become attached to normal (O2) molecules to produce the ozone (03) molecules.

Ozone molecules are in turn destroyed by being broken up by ultraviolet radiation, or by undergoing chemical reactions with other molecules which exist naturally in the atmosphere - the oxides of nitrogen providing one example.

Thus there is a continuous formation of ozone in the upper atmosphere and a continuous destruction of it. An analogy is that of water flowing into a tank but also running out through holes at the bottom. The water in the tank reaches a certain level, which stays constant when the rate of input is equal to the rate of output. The equilibrium 'level' of ozone in the upper reaches of the atmosphere is determined by the production rate of ozone being balanced by its destruction rate.

In terms of the atmosphere at ground level, the ozone is extremely small in quantity. If all the ozone were compressed to normal atmospheric pressure, it would form a spherical shell around the earth only about 0.3 centimetres thick (a little more than one-tenth of an inch).

Small as this effective thickness of ozone is, it is a highly efficient absorbent of ultraviolet radiation, and evolution on earth has evolved below this absorbing layer.

The ozone is responsible for strongly absorbing ultraviolet radiation of wavelengths which are highly 'biologically active'. These wavelengths are known to be most effective in producing skin cancer and skin inflammations (erythema), and can be damaging to the eyes. If the quantity of ozone were halved, the effects to human and plant life could be disastrous.

This is the crux of the concern about supersonic aircraft flying at high altitudes above about 50,000 feet. Their exhaust gases will inject additional oxides of nitrogen into the atmosphere which will, in effect, put another hole in the tank, so that the average level of ozone in the stratosphere may drop.

In 1971 Professor H. Johnston, of Berkeley Uuiversity, California, calculated that 500 supersonic aircraft, each flying about seven hours a day, might eventually produce a reduction in the quantity of ozone to one-half its present value. Such predictions could not be certain because of unknowns in the rates of the chemical amounts involved, and indeed the quantities of natural oxides of nitrogen which occur in the stratosphere anyway.

Committees were set up in several countries to report on the issue; these included one appointed by the Australian Academy of Science, which expressed the opinion that, on data presently available, it would not expect significant adverse effects to the ozone level from the flying of supersonic aircraft. However, uncertainties remained.

Professor Henry M. Foley, chairman of the Physics Department of the Columbia University, and Professor M. A. Ruderman, visiting Columbia University from the Institute of Advanced Studies at Princeton, have now pointed out that man has already injected into the stratosphere more oxides of nitrogen than would result from the flying of 500 Concordes seven hours a day for nearly ten years. Thus mankind has, albeit unwillingly, already exposed himself to the ozone reduction risk.

Foley and Ruderman point out that oxides of nitrogen are not only products of jet engine exhausts but will automatically be produced at high temperatures as a result of combining of naturally occurring nitrogen and oxygen in the air. This occurs in the 'fireball' of a nuclear explosion, and most of the products of this explosion are injected upwards into the stratosphere.

During one peak period between October 1961 and December 1962, the United States and Russia jointly exploded 340 megatons of nuclear bombs.

Foley and Ruderman calculate that these tests alone injected more oxides of nitrogen into the stratosphere than the flying of 500 Concordes seven hours a day for some five years.

If drastic ozone reduction had occurred, the world would already have felt the consequences. Yet detailed measurements of ozone concentrations over the world-wide system of monitoring stations has shown that in the last ten years the concentration of ozone has in fact slightly increased -- in some latitudes by as much as ten per cent.

The analysis by Foley and Ruderman seems unambiguous and undeniable. Whatever other problems the Anglo-French aircraft may be meeting, it seems that it can be freed from the charge of destruction of the earth's ozone layer.



This chapter originally appeared as an article in "The Sydney Morning Herald", 16 July 1973, p. 7.




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