From: dean@vexcel.com (dean alaska)
Newsgroups: talk.environment
Subject: more on ozone (and why the hole is in the south)
Date: 13 Apr 92 19:07:12 GMT
Organization: VEXCEL Corporation, Boulder, CO


The reason for the ozone hole being over the south pole
from "Back from Beyond the Limits" by Donella H. Meadows Ph.D., 
	Dennis L. Meadows Ph.D.  and Jorgen Randers Ph.D. p. 153-154

This book is not specifically about ozone depletion, but it uses it as an
example of carrying capacity and the response to it.

begin excerpt

Since Antarctica is surrounded by oceans, winds can circle around the
continent uninterrupted by land masses.  In the southern winter they create
a circumpolar vortex, a whirl of wind that traps air over Antarctica and 
keeps it from mixing with the rest of the atmosphere.  The vortex sets up an
isolated "reaction vessel" of polar atmospheric chemicals.  (There is not
such a strong vortex around the North Pole, so the northern ozone hole is
much less pronouned.)

In winter the Antarctic atmosphere is the coldest place on earth (down to
-90 degrees C).  In that extreme cold water vapor hovers as a fog of minute
ice crystals high up where the ozone layer is.  The surfaces of these
innumerable ice crystals enhance the chemical reactions that release
ozone-destroying chlorine.

The chlorine atoms formed in the dark of the Antarctic winter do not
immediately enter the chain reaction of ozone desctruction.  Instead
they react just once with ozone to form ClO.  The ClO molecules come
together to form a relatively stable ClOOCl dimer.  An accumulation
of ClOOCl builds up, poised and waiting for the return of the sun.

When the light returns in the Antarctic spring, solar radiation breaks up
the ClOOCl dimer to releasae enormous bursts of Cl, which goes to work
on the ozone.  Ozone concentration drops precipitously within a few weeks.
At some altutudes, more than 97% of the ozone vanishes.

The returning sunlight gradually dissipates the circumpolar vortex,
allowing south polar air to mix again.  Ozone depleted air is dispersed
over the rest of the globe, as ozone levels over Antarctica return 
nearly to normal.

Lesser holes have been observed over the north pole in the northern spring.
Discrete holes are not expected to be found elsewhere.  But as the gases
in the atmosphere mix, the concentration of ozone in the stratosphere
over the whole earth is decreasing measurably.  Because of the long delays
in CFC's reaching the stratosphere, more ozone depletion is inevitable. 
Because of the long lifetime of CFC's and Cl in the atmosphere, the
depletion will last for at least a century, even if all CFC releases stop
immediately.

end of excerpt

The book includes figures of measurements which show Cl concentrations as
inversely proportional to ozone in the southern polar regions during the
southern spring and also of long term measurements which show decreasing
ozone in the south since the late 60's or early 70's.
It also describes the "smoking gun" evidence which has
been discovered in recent years.  CFC is not a tracer bullet.  It doesn't
leave streaks in the atmosphere showing where it came from nor are they
tagged with serial numbers, making absolute positive proof of cause and
effect essentially impossible.  Nevertheless, the overwhelming
preponderence of evidence and scientific thought supports the CFC-ozone
connection.  The knee-jerk reaction that environmentalists are accused
of (occasionally correctly) in this case apples to those who deny this
relationship and call for yet more study BEFORE anything is done.

Rather than accusing NASA scientists of pandering for research dollars,
maybe we should look at who pays the salaries of scientists who deny
this relationship.
-- 

		dingo in boulder	(dean@vexcel.com)