]]]]]]]]]]]]]]]]]       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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