Supersonic transports and the ozone layer

The planning and development of a new generation of transport aircraft was well under way in North America, Europe and the USSR by the early 1970s. These were the supersonic transports (or SSTs), designed to fly higher and faster than conventional, subsonic civil airliners, and undoubtedly a major technological achievement. It became clear, however, that they could lead to serious environmental problems, if ever produced in large numbers. Initial concerns included elevated noise levels at airports and the effects of the sonic boom produced when the aircraft passed through the sound barrier, but many scientists and environmentalists saw the impact of these high-flying jets on the structure of the ozone layer as many times more serious, and more universal in its effects.

Supersonic transports received a great deal of attention between 1971 and 1974, as a result of Congressional hearings in the United States into the funding of the Boeing SST, and a subsequent Climatic Impact Assessment Program (CIAP) commissioned by the US Department of Transportation to study the effects of SSTs on the ozone layer. The findings in both cases were extremely controversial, and gave rise to a debate which continued for several years, at times highly emotional and acrimonious. It was fuelled further by a series of legal and legislative battles which ended only in 1977, when the US Supreme Court granted permission for the Anglo-French Concorde to land at New York. The proceedings and findings of the Congressional hearings and the CIAP, plus the debate that followed, have been summarized and evaluated by Schneider and Mesirow (1976) and Dotto and Schiff (1978). The arguments for and against the SSTs were as much political and economic as they were scientific or environmental. They did reveal, however, a society with the advanced technology necessary to build an SST, yet possessing a remarkably incomplete understanding of the environment into which the aircraft was to be introduced.

Like all aircraft, SSTs produce exhaust gases which include water vapour, carbon dioxide, carbon monoxide, oxides of nitrogen and some unburned hydrocarbons. These are injected directly into the ozone layer since SSTs commonly cruise at about 20 km above the surface—just below the zone of maximum stratospheric ozone concentration. Much of the initial concern over the effect of SSTs on ozone centred on the impact of water vapour, which was considered capable of reducing ozone levels through the creation of the hydroxyl radical, a known ozone-destroying catalyst. Later observations, which indicated that a 35 per cent increase in water vapour had been accompanied by a 10 per cent increase in ozone, rather than the expected decrease (Crutzen 1972), caused the role of water vapour to be re-evaluated. It was suggested that water vapour helped to preserve the ozone layer through its interaction with other potential catalysts. It converted NOx to nitric acid, for example, and therefore nullified its ozone-destroying properties (Crutzen 1972; Johnson 1972). By the time this had been confirmed, in 1977, NOx had already replaced HOx as the villain in SST operations (Dotto and Schiff 1978).

In 1970, Crutzen drew attention to the role of NOx in the destruction of ozone through catalytic chain reactions, and in the following year, just as the SST debate was beginning to take off, Johnston (1971) warned that NOx emitted in the exhaust gases of 500 SSTs could reduce ozone levels by as much as 22-50 per cent. Later predictions by (Crutzen 1972) suggested a 3-22 per cent reduction, while Hammond and Maugh reported in 1974 that the net effect of the NOx emissions from a fleet of 500 SSTs would be a 16 per cent reduction in ozone in the northern hemisphere and an 8 per cent reduction in the southern hemisphere.

When all of this was under consideration in the early 1970s, it was estimated that the world's fleet of SSTs would grow to several hundred aircraft by the end of the century and perhaps as many as 5,000 by the year 2025 (Dotto and Schiff 1978). The NOx emissions from such a fleet were considered capable of thinning the ozone layer sufficiently to produce an additional 20,000 to 60,000 cases of skin cancer in the United States alone (Hammond and Maugh 1974). Other predicted environmental impacts included damage to vegetation and changes in the nature and growth of some species as a result of mutation. The extent to which such threats helped to kill SST development is difficult to estimate. At the time, the environmental arguments seemed strong, but the economic conditions were not really right for development, and that, as much as anything else, led to the scrapping of the projected Boeing SST. Development of the Soviet Tupolev-144 and the Anglo-French Concorde went ahead, with the latter being the more successful of the two in terms of production numbers and commercial route development. Less than 10 SSTs are currently in operation, and the effects on the ozone layer are generally considered to be negligible.

The Basic Survival Guide

The Basic Survival Guide

Disasters: Why No ones Really 100 Safe. This is common knowledgethat disaster is everywhere. Its in the streets, its inside your campuses, and it can even be found inside your home. The question is not whether we are safe because no one is really THAT secure anymore but whether we can do something to lessen the odds of ever becoming a victim.

Get My Free Ebook


  • anke
    What is the potential impact of supersonic transports on the ozone layer?
    7 years ago

Post a comment