Environmental Engineering Reference
In-Depth Information
production and use of CFCs by the end of the
century.
The CFC controversy had ceased to make
headlines by the late 1970s, and the level of public
concern had fallen away. Monitoring of the ozone
layer showed little change. Ozone levels were not
increasing despite the ban on aerosol sprays,
which was only to be expected given the slow
rate of decay of the existing CFCs, but the
situation did not seem to be worsening. Quite
unexpectedly, in 1985, scientists working in the
Antarctic announced that they had discovered a
'hole' in the ozone layer, and all of the fears
suddenly returned.
most of that time, and included a thinning of the
ozone above the Antarctic during the southern
spring, which was considered part of the normal
variability of the atmosphere (Schoeberl and
Krueger 1986). This regular minimum in the total
ozone level began to intensify in the early 1980s,
however (see Figure 6.6). Farman et al. (1985)
reported that it commonly became evident in late
August, and got progressively worse until, by
mid-October, as much as 40 per cent of the ozone
layer above the Antarctic had been destroyed.
Usually the hole would fill by November, but
during the 1980s it began to persist into
December. The intensity of the thinning and its
geographical extent were originally established
by ground based measurements, and later
confirmed by remote sensing from the Nimbus-
7 polar orbiting satellite (Stolarski et al. 1986).
As was only to be expected after the
aerosolspray-can experience in the 1970s, the
immediate response was to implicate CFCs.
The Antarctic ozone hole
Total ozone levels have been measured at the
Halley Bay base of the British Antarctic Survey
for more than thirty years beginning in the late
1950s. Seasonal fluctuations were observed for
Figure 6.6 Changing ozone levels at the South Pole (1964-85) for the months of October, November and
December
Source: After Komhyr et al. 1986
Note: Dobson units (DU) are used to represent the thickness of the ozone layer at standard (sea-level)
temperature and pressure (1 DU is equivalent to 0.01 mm)
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