Newsgroups: bit.listserv.biosph-l
Date:         Fri, 18 Dec 1992 22:24:54 +0100
Reply-To:     Jan Schloerer <schloerer@RZMAIN.RZ.UNI-ULM.DE>
From:         Jan Schloerer <schloerer@RZMAIN.RZ.UNI-ULM.DE>
Subject:      Re: Ozone Layer

Jeremy Whitlock  (WHITLOCK@MCMASTER.CA)  wrote   on 18-DEC-1992

> It is clear that I am no geophysicist.

I am neither a geophycicist nor an atmospheric scientist, too :-)

>  Jan Schloerer  (schloerer@rzmain.rz.uni-ulm.de)  ...  writes:
>
>> From Robert Parson's article, reposted yesterday, you may recall that
>> the two most famous volcanic eruptions in the last decade coughed up
>> almost negligible amounts of Cl into the stratosphere, as determined
>> by direct measurements :
>>
>>  El Chicho'n 1982   0.04 Tg   That is, 40 000 t.  Mankin and Coffey,
>>                               Science _226_, 170, 1983
>
> Yet this reference goes on to add that 0.04 Tg is about 9% of the
> global statospheric HCl burden, and to me a _single_ stratospheric
> injection of this relative size is not "negligible".

This was, to my knowledge, by far the most 'successful' eruption during
the 1980's with regard to chlorine injection into the stratosphere.
Perhaps the 19-Nov-sci.env article by Robert Parson I sent to biosph-l
on 16-Dec didn't reach you ?      [While not an atmospheric chemist,
Robert Parson is a physical chemist. Some of his research has relevance
for atmospheric chemical processes. His knowledge of the topic is
considerably deeper than mine.]   In that article he stated :

   "Chlorine emissions from CFC's and related manmade compounds came to
   more than *1.2* Tg/yr during the 1980's, of which 0.9 Tg reached the
   stratosphere (Prather et al., J. Geophys. Res. _95_, 18583, 1990).
   These numbers do not include unknown amounts of emissions from the
   Soviet Bloc and China."

So the comparison is between 0.04 Tg for El Chicho'n (and probably
not much more from volcanoes during the 1980s)  and an annual 0.9 Tg
of manmade chlorine compounds reaching the stratosphere.

> Mankin and Coffey conclude with:
>
>   "The observation that a single, large volcanic event can increase
>    the stratospheric HCl burden by 40 percent over a large part of
>    the globe should lead to a reassessment of the role of volcanoes
>    in stratospheric chlorine chemistry."  [Mankin and Coffey, above
>    reference, p.172]

The article by Symonds, Rose & Reed (Nature 334, 4 August 1988, 415-418)
quoted by me yesterday is a part of this reassessment.  Meanwhile Robert
Parson has dug out another reference:  J.P.Pinto, R.P.Turco & O.B.Toon,
Self-limiting physical and chemical effects in volcanic eruption clouds,
J. Geophys. Res. 94 (1989), 11165-11174.    These authors estimate that
as much as 99 % of the ejected HCl comes right back down, so that even
figures for volcanic chlorine contributions to the stratosphere like
those of Symonds et al may be too high   [ Robert sent this to biosph-l.
It reached the usenet newsgroup bit.listserv.biosph-l, but apparently
not yet the actual mailing list. If it is still missing on Monday,
I shall re-mail it. ]

> I also read from Von Nostrand's Scientific Encylopaedia, p.2973,
> in an article on volcanoes, that researchers have shown that the
> Augustine volcano (Alaska, 1976) may have injected 289 billion kg
> (289 Tg) of HCl directly into the stratosphere

This sounds indeed interesting.  However, it would also be interesting
to have a reappraisal of this figure using more recent knowledge.

> Question:  I've read that ozone variation with latitude and season
> are on the same order as that defining the ozone "hole".  How does
> this affect the belief that the ozone "hole" presents an unprece-
> dented danger ?

A measure for the size of the Antarctic ozone hole is the area for
which the total ozone column falls below 200 Dobson units (DU)  =  2mm
thickness of the ozone layer in the atmosphere (if you were to compress
it to 1 at. pressure and heat it to 0 degrees C).  This area has been
about 14 million square kilometers in 1987, 1989, 1990 and 1991; within
the hole, regions with less than 150 DU have already been observed
(e.g., Richard Stolarski et al, Measured trends in stratospheric ozone,
Science 256, 17 April 1992, 342-349).  There is indeed strong seasonal
variation of the ozone column in middle and high latitudes, but nowhere
it falls as low as in the Antarctic ozone hole. For instance, for 30-59
degrees N, the total ozone fell rarely below 280 DU between 1957 and
1987  (K.Towe/R. Stolarski, letters to Science 257, 7 August 1992,
727-728).  Near the equator, ozone is about 265 DU with very little
seasonal variation.

> Question:  What is the scientific consensus regarding man-made
> ozone depletion?  If the "hole" was discovered the same year they
> started making observations, and has fluctuated since then, what kind
> of cause-and-effect relationships can we have observed ?

That the ozone hole was "discovered the same year they started making
observations" is another of 'those' stories, which was investigated,
you guess it, by Robert Parson. Observations of Antarctic ozone go back
to 1956. For the years 1956-58, an ozone level of ~275-300 DU for winter
and early spring, followed by a rapid rise to ~400 DU in November was
observed:  nothing like 200 or even 150 DU  [G.M.B.Dobson, _Applied
Optics_ _7_, 387 (1968); info taken from R.Parson].  The ozone hole was
detected in 1985 by Farman et al.  With the help of archived but up to
that time ignored satellite data the beginnings of the ozone hole could
be traced back to about 1970  [Susan Solomon, Nature 347, 27 Sept 1990,
347-354, figure 1].

The story that the ozone hole was already in place in 1956 is entirely
erroneous. It has a complicated history itself, in which the University
of Virginia Professor Fred Singer plays a major role.  Robert Parson
unearthed this in a (long !) post to sci.env on 9 May 1992 which I can
repost if so desired.


Jan Schloerer          schloerer@rzmain.rz.uni-ulm.de
Klinische Dokumentation           Uni Ulm
Postfach 3880     DW-7900 Ulm     Germany
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