Newsgroups: bit.listserv.biosph-l
Date:         Thu, 17 Dec 1992 21:30:48 +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 :

> In response to requests, private and posted, for more info. on volcanic
> sources of ozone-depleting gases, here is a table from _21st Century_,
> Fall 1991:
>
> SOURCE OF ATMOSPHERIC CHLORINE (millions of tons)

> Seawater                      600
> Volcanoes                      36
> Biomass Burning                 8.4
> Ocean Biota                     5
>
> TOTAL NATURAL SOURCES:        649.4
>
> Total Cl in CFC's                .75
> Total Cl allegedly released
>       by breakup of CFC's        .0075
>
> It must be remembered that this is the atmospheric source, not what
> gets to the stratosphere.  Much of the Cl from sea water, for
> example, is rained out.  Volcanoes, however, inject their gases
> directly to the stratosphere.

These figures do not tell much, not even about  _tropospheric_  chlorine
concentrations. (For those of you who might not know: the troposphere is,
roughly, the lowest 10-15 km of the atmosphere.  The next higher level
is called the stratosphere.  Roughly 90 % of the ozone in the atmosphere
is located in the stratosphere, and that is where ozone depletion takes
part, in particular in high latitudes.)

Firstly, most chlorine contributed by sea water and volcanoes (most of
whom do  _not_  inject their gases into the stratosphere, see below),
is in a reactive form (e.g., HCl) and has a very short tropospheric
lifetime, it is washed out of the troposphere in a matter of days.
Tropospheric chlorine concentrations are presently dominated by manmade
source gases with long tropospheric lifetimes.  Mainly such longlived
gases finally make it up into the stratosphere.


Secondly, most volcanic gases do not reach the stratosphere :

   "As halogen gases catalyse the destruction of ozone in the strato-
   sphere, it is important to quantify the natural emissions of halogens
   from active volcanoes.  ...  Our calculations show that HCl and HF
   are the dominant species in volcanic gases, at least several orders
   of magnitude more abundant than all other species.  We estimate the
   annual global volcanic fluxes of HCl and HF to be 0.4-11 Tg (10^12 g
   [that is, million tonnes]) and 0.06-6 Tg, respectively.  On average,
   < 10 % of these emissions come in large explosive eruptions that
   transmit them effectively to the stratosphere. Although they are
   infrequent, large volcanic eruptions may inject significant amounts
   of HCl and HF into the stratosphere."

          Robert B. Symonds,  William I. Rose  &  Mark H. Reed,
          Contribution of Cl- and F-bearing gases to the atmosphere
          by volcanoes.     Nature 334 (4 August 1988), 415-418

   "Current opinion favors the early removal of halogens  [that is,
   mainly HCl and HF]  from eruption columns by rain flushing and
   adsorption onto tephra particles  [volcanic ash],  but the fate
   of halogens in the atmosphere following very large explosive
   eruptions remains unstudied."  [A 'very large explosive eruption'
   was, for instance, Tambora 1815]

          Haraldur Sigurdsson,  Evidence of volcanic loading of
          the atmosphere and climate response.    Paleogeography,
          Paleoclimatology, Paleoecology 89 (1990), 277-289

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
   Pinatubo    1991   0.01 Tg   or less.  Mankin, Coffey, and Goldman,
                                Geophys.Res.Lett. _19_, 179, 1992

To add to your confusion:  Perhaps, strong volcanic eruptions may
aggravate ozone depletion by putting  _sulphate_  particles into the
stratosphere. These might act similarly to the ice particles in the
(in)famous polar stratospheric clouds:  reactions involving chlorine
and leading to ozone destruction could occur on the surfaces of such
sulphate particles as well.  Note that this, if turning out correct,
means an amplification of the ozone depleting effect of the high
present concentrations of stratospheric chlorine.


Finally, here is an excerpt from
      World Meteorological Organization    [WMO]
      Global Ozone Research and Monitoring Project - Report No. 25
      Scientific Assessment of Ozone Depletion: 1991
      Geneva, WMO 1992 (Case Postale 2300, CH-1211 Gene`ve 2, Switzerland)
compiled by over 100 highly respected researchers from a large number of
countries. Quotations are from chapter 1   "Source gases: concentrations,
emissions, and trends".

*  From the Scientific Summary :

   The major anthropogenic source gases implicated directly in halogen
   induced stratospheric ozone loss, i.e., chlorofluorocarbons (CFCs),
   hydrochlorofluorocarbon-22 (HCFC-22), the halons, methyl chloroform
   and carbon tetrachloride, continue to grow in concentration in the
   background troposphere of both hemispheres. Total tropospheric
   chlorine is increasing by ~0.1 parts per billion by volume (ppbv)
   per year  [ that is, ~100 parts per trillion by volume (pptv) ].
   CFCs contribute approximately  75  percent to this increase,
   methyl chloroform  13  percent, and HCFC-22  ~5  percent.

   The 1989 global mean concentrations and trends of the various source
   gases that can directly or indirectly influence the global abundance
   of stratospheric and tropospheric ozone are given in Table 1-1  ...

*  From Table 1-1 :

   Source gas   Concentration     Increase  1989         Calibration
                 1989 (pptv)    pptv/year  percent/year  uncertainty

   ...
   CCl2F2            453        16.9-18.2*   3.7-4.0       +-  2 %
   CCl3F           255-268       9.3-10.1    3.7-3.8       +-  1 %
   CCl2FCClF2         64         5.4- 6.2      9.1         +- 10 %
   CClF2CClF2       15-20          ~1         ~6
   CCl2FCF3           ~5           ~0.3       ~6
   CClF3              ~5
   CCl4              107         1.0- 1.5      1.2         +- 10 %
   CH3CCl3           135         4.8- 5.1      3.7         +- 15 %
   CHClF2            110          5 - 6       6 - 7        +- 10 %
   CH3Cl             600
   CHCl3             ~10
   CH2Cl2            ~35
   CCl2CCl2          ~30
   CH2ClCH2Cl        ~35
   CHClCCl2          ~10
   ...
   ---------------------------------------------------------------
   Total Cl         3800
   % anthropogenic   ~80
   Total Br           40
   % anthropogenic   ~12  (halons only)
   ---------------------------------------------------------------
   * Data subject to revision; significantly lower trends may result

   [ You get the "total Cl" for a source gas, if you multiply the
     respective pptv by the number of Cl atoms contained in the gas. ]


Jan Schloerer          schloerer@rzmain.rz.uni-ulm.de
Klinische Dokumentation           Uni Ulm
Postfach 3880     DW-7900 Ulm     Germany
Comments: Gated by NETNEWS@AUVM.AMERICAN.EDU