]]]]  Volcanic Introduction of Chlorine into the Stratosphere  [[[[[
                                                        (1/14/1990)
[Excerpt  from  article  on volcanoes  in  Douglas  M. Considine,
editor, Van Nostrand's Scientific  Encyclopedia, 7th Edition (New
York: Van Nostrand Reinhold, 1989), p. 2973:1]

          [Kindly uploaded by Freeman 10602PANC]

   ``Volcanic  Introduction  of Chlorine  into  the Stratosphere.
Some researchers  (Johnston, 1980) now  suspect that considerably
more hydrogen chloride (HCl) is injected into the stratosphere by
certain volcanic  eruptions than previously  estimated.  In fact,
this  could  amount  to  as  much  as  17-36%  of  the  worldwide
production of industrial production  of chlorine in fluorocarbons
--  as of  1975  prior to  severe  reductions is  such production
brought about by concern with degradation of the protective ozone
layer  in the  stratosphere.   Under normal  conditions, hydrogen
chloride emanating from anthropogenic sources  is not a threat to
the ozone layer  simply because the  HCl is soluble  in water and
thus  is  removed in  rain  prior to  reaching  the stratosphere.
Large   volcanic   eruptions  inject   HCl   directly   into  the
stratosphere forcefully  and in  significant quantities  and thus
bypass the  absorptive effects of  the lower  atmosphere.  It has
been estimated that eruptions of  this nature occur at least once
per year.  As  pointed out by Johnston,  the moderately to highly
silicic  magmas of  volcanoes  along the  continental  and island
arcs,   because   of  their   high   chlorine   content,  extreme
explosivity,  and  frequent  eruptions  are  likely  to  have the
greatest atmospheric impact.  These observations suggest that the
impact of  anthropogenic production of  chlorine in fluorocarbons
should once again be reviewed against the backdrop of disturbance
of the ozone layer that  may arise from natural, volcanic causes.
Researchers  have  observed,  for  example,  that  the  Augustine
Volcano (Alaska), which erupted in  1976, may have injected 289 x
10E9 kilograms  (289,000,000,000 kg) of HCl  into the  stratosphere.
This  quantity is about 570 times the 1975  world industrial
production of chlorine and fluorocarbons.''

(Johnston, 1980) refers to

Johnston,  D.A.  ``Volcanic  Contributions  of  Chlorine  to  the
   Stratosphere:  More  Significant   to  Ozone  than  Previously
   Estimated?'', Science 209:491-493 (1980).

Thanks  to  AtE  subscriber J.W.  of  Tempe,  Ariz.,  for drawing
attention to this  reference (mentioned in  the October 1989 AtE,
p. 3:2, bottom).

How  many  active  volcanoes  are  there  in  the  world?   Three
references at  hand give  three answers:  500, 600  and 850.  The
important point is that active volcanoes are not rare.

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