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]]]]]]]]]]]]]]]]] OZONE DEPLETION [[[[[[[[[[[[[[[[[[[[[[
[Uploaded by Freeman 10602PANC 9/4/88]
One would expect the question of ozone depletion to have
ballooned into the Great Ozone Controversy, yet the great
surprise of it all is how little controversial it was.
The NASA sponsored Ozone Panel has issued its report,
concluding that indeed, ozone is being depleted by CFCs. DuPont
announces that it will stop producing CFCs. Yet, the layman who
has gone beyond what the newspapers say is left wondering about
the wisdom of those who have decided things for him. I present
the following without comment:
In Science News (19 March 1988) we read
"The [Ozone Trends Panel] based its conclusions on
ground-based instruments called Dobson meters, which
have been measuring ozone levels at certain stations
for 30 years." (Monastersky 1988, p. 20:1)
Richard Kerr, in his article on ozone depletion in Science (10
July 1987), had mentioned some of the limitations of the Dobson
spectrometers. W.F.J. Evans and his associates wrote a letter
(27 November 1987) elaborating on the shortcomings:
"[T]he Dobson spectrometer was not designed for trend
monitoring and there are problems with its maintenance
and calibration. ... Dobson instruments are calibrated
against a particular Dobson spectrometer chosen as a
reference. The procedure is vulnerable because the
reference instrument is subject to drift and because
changes occur during transportation. The precision of
Dobson measurements is not readily calculable from its
instrument characteristics; rather it is established
empirically and with difficulty." (Evans et al. 1987,
p. 1216)
Kerr pointed out that
"Individual sites have been operated by each host
country to their own standards of maintenance and
calibration." (Kerr 1987, p. 131:3).
Again, Evans et al.:
"Checks on performance are intricate, time consuming,
and demand dedicated, trained personnel. In practice
checks are often not adequate and major malfunctions
can go undetected, sometimes for years." (Evans et al.
1987, p. 1216)
Variations of ozone with altitude are mapped using the Umkehr
("reversal" in German) technique: the instrument follows the sun
and the variations in the ozone signal with the sun's height are
recorded.
Also,
"There are far fewer Umkehr sites than standard Dobson
sites and they are far more unevenly distributed around
the world." (Kerr 1987, p. 132:2)
Yet,
"The Dobson record is regarded as the best standard
available for comparison with satellite data." (Kerr
1987, p. 131:3)
Robert Watson, director of the NASA study, said:
"After we took all those known phenomena out from the
data we were still left with a residual trend that we
could account for in no other way than attribute at
least some of that change to the fluorocarbons."
(Watson 1988)
REFERENCES
Evans, W.J.F; Kerr, J.B; Wardle, D.I.; Forester, A.J. (Letter)
"Monitoring of Atmospheric Ozone", 238 Science (27 Nov 1987):
1216 [Elaborating on Kerr 1987].
Kerr, Richard A. "Has Stratospheric Ozone Started to
Disappear?", Science 237 (10 July 1987): 131.
Monastersky, R. "Dramatic Drop in Global Ozone Layer", 133
Science News (19 Mar 1988): 183.
Van Nostrand's Scientific Encyclopedia, Sixth Edition. New York:
Van Nostrand Reinhold Company, 1983.
Watson, Robert. Television interview with Jim Lehrer,
"McNeil-Lehrer News Hour" (PBS), broadcast 25 Mar 1988.
* * *
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