From: parson_r@cubldr.colorado.edu (Robert Parson)
Subject: Re: Steering Clinton onto the right track
Organization: University of Colorado, Boulder
Date: Thu, 19 Nov 1992 04:33:51 GMT

In article <1992Nov18.203503.12198@gn.ecn.purdue.edu>, 
dyrda@gn.ecn.purdue.edu (Richard Dyrda) writes:


> Volcanic eruptions put out 1,000's upon 1,000's more ozone depleting
>chemicals than we humans have ever done. Since volcanoes have erupted
>for 1 billion years I think our ozone level is just fine.

 No. Volcanoes are _not_ a major source of stratospheric chlorine.

 Consider the two most famous eruptions in the past decade: El Cichon and
 Pinatubo. We have direct measurements for these. According to one report 
(Mankin and Coffey, _Science_  _226_, 170, 1983) El Cichon put *0.04* Tg HCl 
 into the stratosphere. Another study found less. Pinatubo, the biggest eruption
 since 1912, coughed up much less  (Mankin, Coffey, and Goldman,
 _Geophys. Res. Lett. _19_, 179, 1992). In fact the effect was so small
 they were unwilling to assign a quantitative figure; they only concluded
 that it was much less than El Cichon (a factor of 4 or more). An eruption
 like El Cichon occurs once a decade or so; an eruption like Pinatubo
 occurs once or twice every century.

 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.

 Volcanoes are not even the principal _natural_ source - that distinction 
 goes to biologically produced CH3Cl. It contributes ~15% of the Cl in the 
 strat., CFC's and related compounds contribute ~75%.

 Sure, volcanoes have been erupting for billions of years, but HCl _does_
 rain out of the stratosphere. Transport across the tropopause is slow, but
 it's not _that_ slow!

> Sun creates ozone, you wanna destroy the ozone layer you gotta destroy
>the sun. How are you gonna do it?
 
 The antarctic stratosphere, between 15 and 20 km, does it very nicely.
 Simply provide a catalytic pathway for ozone loss that is very much faster
 than the rate of creation by the sun. During the mid-antarctic spring,
 the ozone layer in this region of the stratosphere (the region where ClO
 is present) is _>90% depleted_. This depletion _starts_ in the spring,
 when the sun comes up - in fact, solar radiation is necessary for the
 ozone hole to form. In 1990, the ozone hole lasted well into December. 
 It's the flow of warm air in from higher latitudes, not increased 
 solar radiation, that shuts it down.
 
> Not only this, the ozone level
>has been known to be in a sort of cycle. Case in point, look at the
>1964 Air Force study on Ozone Activity, the data they collected matched
>perfectly with the data taken in 1989.

 Sure, ozone levels track the 11-year solar cycle (more or less). 1964 was
 a solar _minimum_. 1989 is well on the way towards the 1991 maximum. 
 You are comparing the low point of one cycle to a point past the middle
 of another. All this shows is that the _net_ ozone depletion (of the order
 of 3-5% per decade) is smaller than the total excursion during the cycle
 (~10%), a result that is well known. To get meaningful numbers you have
 to fit the data to the solar cycle, as well as to the annual and bienniel
 cycles, and extract the net trend. Take a look at Stolarski et al., 
 _Science_ _256_, 343 (1992).

Dyrda replied to Michael Tobis:
> Nope, but there are some things that you need common sense in. This is
>no particular theory either, it is my opnion! Once again why not look
>at some of the true facts instead of second hand info from magazines, who
>usually twist the figures to suit their purposes.

"Second hand opinions from magazines"?  Michael cited a monograph and a 
 technical review article by two of the leading figures in this field,
 Guy Brasseur and Susan Solomon. 

 Robert
Xref: sparky sci.environment:12740 sci.energy:5438