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Date:         Fri, 18 Dec 1992 17:52:13 -0700
Reply-To:     PARSON_R@CUBLDR.COLORADO.EDU
From:         PARSON_R@CUBLDR.COLORADO.EDU
Subject:      chlorine, ozone, volcanoes

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

> 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 figure is completely impossible; I suspect a typo in the encyclopedia
 (I'll check tomorrow, library's closed.) It is far larger than the _total_
 amount of chlorine in the stratophere.

  The _total_ amount of chlorine emitted from Mt. St. Augustine's 1976
 eruption (one of the bigger eruptions of the decade, although I don't
 remember its VEI, I'm no geophysicist either) is estimated at ~0.6 Mt.
 (Johnston, _Science_ _209_, 491, 1980.) Johnston went on to estimate
 that 0.08 - 0.18 Mt of this went into the stratosphere, and these figures
 are included in the compilation of Symonds et al. There were no direct
 stratospheric measurements. Subsequent research (Pinto et al., J. Geophys.
 Res. _94_, 11165, 1989) has shown that this and other geophysical estimates
 are much too large. This is in accordance with the _direct_ stratospheric
 measurements on El Cichon and Pinatubo. It is known that the magma beneath
 El Cichon is very rich in chlorine, thus its comparatively large output
 (0.04 Mt) compared to Pinatubo, a much larger eruption.

> 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 ?

 You need to take the baseline into account. At the equator, the ozone
 layer is about 260 DU thick, almost independent of season. Over central
 Europe it ranges from ~275 to ~360 DU. Over the arctic you get huge swings,
 from ~275 to ~475 DU, since the seasonal variation of sunlight is so large.
 Notice that the _minimum_ ozone value is about the same.
 But nowhere on earth outside the antarctic do you get the behavior seen
 in the ozone hole: starting from a normally low winter value of ~300 DU,
 the ozone concentration plummets in early spring, hitting a monthly average
 of ~150 DU in October with daily lows going as far down as 108 DU.

> 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 ?

 Jan already answered most of this, I'll take another tack. The most
 convincing evidence that the hole is due to ClO was obtained by Anderson
 et al. in the fall of 1987 (unfortunately several of the best general
 references, such as Stolarski's Jan '88 Sci. American article, were written
 before this and thus are out of date.) They found that the ClO and
 ozone concentrations are beautifully anticorrelated, even down to local
 fluctuations - as ClO goes up, Ozone goes down. These figures should be
 in every popular article about the ozone hole. The easiest place to find
 them is in _Science_ _251_, 39, 1991. These are the results that made
 DuPont (who sent their own atmospheric scientist along on the mission)
 agree to phase out CFC's.

 Robert Parson (PARSON_R@cubldr.colorado.edu)
Comments: Gated by NETNEWS@AUVM.AMERICAN.EDU