Environmental Engineering Reference
In-Depth Information
progressively over a thirty-five-year period ending
in 2030. Methyl bromide was added to the list
of banned substances, with emissions to be frozen
at the 1991 level by 1995 (MacKenzie 1992).
In contrast to their attitudes in the 1970s, the
CFC manufacturers responded positively after
Montreal to the call for a reduction in the
manufacture of the chemical. The DuPont
Company, for example, pledged to reduce its
output by 95 per cent by the year 2000 (the
original EPA suggestion), although the initial
search for appropriate substitutes—which
included testing for health and environmental
effects—was estimated to take up to five years
(Climate Institute 1988c). The market for
substitutes is large, particularly in Europe,
where CFCs were not banned in the 1970s.
Although the concern for the supply of energy is
no longer at crisis levels, the demand for
residential and industrial building insulation
remains high, and will undoubtedly rise if
energy supplies are again threatened. Since the
manufacture of insulating materials accounts
for 28 per cent of worldwide CFC production,
the search for alternatives received urgent
attention. Results have been mixed. DuPont has
developed hydrochlorofluorocarbons (HCFCs)
as potential replacements for CFCs in the
production of polystyrene sheet, which has been
used successfully in food packaging, but is not
suitable for other forms of insulation since the
product loses its insulating ability as the HCFCs
break down (Webster 1988). HCFCs are 95 per
cent less damaging to ozone than normal CFCs
because they are less stable and tend to break
down in the troposphere before they can diffuse
into the ozone layer. Although they are less
harmful, they do have a negative impact on the
ozone layer, and, as a result, they too will
ultimately need to be replaced. An isocyanate-
based insulation foam, in which carbon dioxide
is the foaming agent, has produced promising
results. It cannot be produced in sheet form,
however, and, as a result, its use remains limited
to situations where spray-on or foam-in
application is possible.
Substitutes are being sought in other areas
also. For example a German company has
developed a so-called 'green' refrigerator, in
which the normal CFC refrigerant is replaced by
a propane/butane mixture. Although the mixture
has a greater cooling capacity than the CFCs
currently used, inefficiencies in the compressor
system require attention before the refrigerator
can compete with conventional units. Bans on
the use of hydrocarbons in domestic refrigerators
in some countries will also limit its adoption
(Toro 1992). More damaging to the ozone than
most CFCs are the halons used in fire-fighting—
Halon 1301, for example is ten times more
destructive than CFC-11—and replacements are
required to meet the 1994 ban on halon
production agreed at Copenhagen in 1992. To
meet that need, a new gas mixture consisting of
nitrogen, argon and carbon dioxide has been
developed in Britain. None of these gases
damages ozone, and existing fire extinguishing
systems can be modified to use the mixture
(Tickell 1992). Clearly, CFC manufacturing
companies, and those utilizing gases hazardous
to ozone, are committed to the search for
alternatives, but it may be some time before their
good intentions are translated into a suitable
product.
SUMMARY
There is an ever-increasing amount of evidence
that the earth's ozone layer is being depleted,
allowing a higher proportion of ultraviolet
radiation to reach the earth's surface. If allowed
to continue, this would cause a serious increase
in skin cancer cases, produce more eye disease
and change the genetic make-up of terrestrial
organisms. In addition, since ultraviolet radiation
is an integral part of the earth's energy budget,
any increase in its penetration to the lower
atmosphere could lead to climatic change. The
effects of a depleted ozone layer are widely
accepted, but the extent of the depletion and its
cause are still not completely understood. This
reflects society's inadequate knowledge of the
workings of the earth/atmosphere system in
general, and the photochemistry of the
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