NetNews Usenet Archive 1992 #31/NN_1992_31.iso/spool/bit/listserv/biosphl/1243

Text File | 1992-12-22 | 6.7 KB | 163 lines

Comments: Gated by [e-mail]
Path: sparky!uunet!zaphod.mps.ohio-state.edu!howland.reston.ans.net!paladin.american.edu!auvm!RZMAIN.RZ.UNI-ULM.DE!SCHLOERER
Message-ID: <[e-mail]>
Newsgroups: bit.listserv.biosph-l
Date:         Mon, 21 Dec 1992 21:10:38 +0100
Reply-To:     Jan Schloerer <[e-mail]>
Sender:       List Owner <[e-mail]>
From:         Jan Schloerer <[e-mail]>
Subject: Re: Ozone - R.Parson's missing messages
Lines: 151

Robert Parson's two messages  on sources of tropospheric and
stratospheric chlorine in general,  and on volcanoes in particular,
still weren't in the email.  I re-mail them below.  Apologies
if some of you see this twice.

Jan Schloerer   ([e-mail])

----------

Subject:      Re: Re: Ozone Layer
From:         [e-mail] (Robert Parson)
Newsgroups:   bit.listserv.biosph-l
Message-ID:   <[e-mail]>
Sender:       [e-mail] (USENET News System)
Nntp-Posting-Host: gold.colorado.edu
Organization: University of Colorado, Boulder
References:   <[e-mail]>
Date:         Fri, 18 Dec 1992 02:20:16 GMT


In article <[e-mail]>,
           Jeremy Whitlock <[e-mail]> writes:

> 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:

 "21st Century" is put out by Lyndon Larouche's organization. It is
 utterly unreliable.  Some of what they say about ozone is distortion,
 some is 100% wrong.

> -------------------------------
> SOURCE OF ATMOSPHERIC CHLORINE (millions of tons)
>
> Seawater                600

  Wrong - 300 Mt, most of which never gets far above the ocean.
  (Ref: Symonds et al, _Nature_ _334_, 415 (1988); R. Cadle, _Rev.
  Geophys. Space Phys. _18_, 746 (1980).)

> Volcanoes               36

  Wrong - total emissions are estimated at 0.3 - 10.0 Mt, most of
  which does  _not_  get into the stratosphere (see below).

> Biomass Burning         8.4

  This could be correct - but only the methyl chloride (which is a
  small fraction of the above) gets into the strat. (and only a
  fraction of that).

> Ocean Biota             5

  This isn't too far off - Symonds et al. give 1.4-3.5 Mt. for the
  _total_ methyl chloride from both ocean biota and biomass burning.
  Most of this is destroyed in the troposphere, but some gets into
  the strat, and this is the principal natural source.

>
> --------------------------------
>
> 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.

 No, only the occasional _explosive_ eruption with a Volcanoc
 Explosivity Index (VEI) greater than 4 (this is a sort of Richter
 scale for volcanic eruptions) injects its gases into the stratosphere.
 These occur about once every 10 years.  Jan Schloerer posted my figures
 for the two most recent such eruptions, El Cichon and Pinatubo, last
 night.  To repeat, El Cichon put out 0.04 Mt, and Pinatubo < 0.02 Mt.
 Low grade sizzlers like Kilauea (VEI 1) or Erebus (VEI 1-2) don't amount
 to much.

 Symonds et. al. collected geophysical estimates of the _total_ amount
 of chlorine put out by historic eruptions, and using this estimated that
 explosive eruptions put 0.1 - 1.0 Mt of chlorine into the stratosphere
 each year. The _upper_ end of this is _comparable_ to the amount of
 chlorine that reaches the stratosphere from CFC's (>0.9 Mt during the
 1980's).  However, subsequent work (Pinto et al., J. Geophys. Res. _94_,
 11165 (1989)) showed that these estimates are too large, by a factor
 of as much as 100.  The present consensus is that volcanoes don't
 contribute much chlorine to the stratosphere, in agreement with the
 _direct_ measurements for El Cichon, the largest eruption of the 80's,
 and Pinatubo, the largest since 1912.

 An _enormous_ amount of work has been done since 1974 to assess the
 sources of stratospheric chlorine. The evidence that CFC's produce
 most of it can be summarized as follows:

 1. Stratospheric chlorine has risen by a factor of 4 since 1958. The
 principal natural source (biologically produced methyl chloride) has
 stayed constant. The frequency of stratosphere-piercine eruptions has
 stayed constant.

 2. The concentrations of CFC's have been measured _as a function of
 altitude_  (see R. P. Wayne, _Chemistry of Atmospheres_. Oxford,
 1991, p. 162). They are nearly constant all the way up to the
 stratosphere, then they drop off rapidly (when the CFC's get high
 enough up to be photolyzed).

 3. The decay products of CFC photolysis (radicals like CF2Cl, CFCl2,
 and products of reactions of these with oxygen and nitrogen) have
 been measured in the stratosphere.

 When this is all put together, the numbers work out - the measured
 flux of CFC's into the stratosphere accounts for the measured
 increase in chlorine in the stratosphere.

 The present consensus is:
 CFC's and related compounds : ~75-85%
 Methyl Chloride: ~10 - 20%
 Everything else: ~10% or less.

 Robert


Newsgroups:    bit.listserv.biosph-l
From:          [e-mail] (Robert Parson)
Subject:       Re:      Re: Ozone Layer
Message-ID:    <[e-mail]>
Sender:        [e-mail] (USENET News System)
Nntp-Posting-Host: gold.colorado.edu
Organization:  University of Colorado, Boulder
References:    <[e-mail]>
               <[e-mail]>
Date:          Fri, 18 Dec 1992 02:40:18 GMT


In article <[e-mail]>, I wrote:

>  No, only the occasional _explosive_ eruption with a Volcanoc
>  Explosivity Index (VEI) greater than 4 (this is a sort of Richter
>  scale for volcanic eruptions) injects its gases into the
>  stratosphere. These occur about once every 10 years. Jan Schloerer
>  posted my figures for the two most recent such eruptions, El Cichon
>  and Pinatubo, last night. To repeat, El Cichon put out 0.04 Mt,
>  and Pinatubo < 0.02 Mt.  Low grade sizzlers like Kilauea (VEI 1)
>  or Erebus (VEI 1-2) don't amount to much.

 I garbled that - sorry. VEI ~4 occurs a little less than once per year.
 The top of the cloud can pierce the stratosphere and put a little
 chlorine in, which can drift up to the ozone layer, but no one has
 ever measured a significant chlorine increase after an eruption
 like this. It's VEI >5 that blasts right into the ozone layer, and
 these come about once a decade.  (The scale is logarithmic. Krakatau
 was a 6, and Tambora in 1816 was a 7, the only one in recorded
 history).

 Robert