Xref: utzoo sci.bio:2413 sci.chem:582 sci.med:13010
Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!ncar!boulder!sunybcs!kitty!larry
From: larry@kitty.UUCP (Larry Lippman)
Newsgroups: sci.bio,sci.chem,sci.med
Subject: Re: PAM propellant
Summary: Ozone layer depletion methods...
Message-ID: <3452@kitty.UUCP>
Date: 17 Oct 89 02:44:41 GMT
References: <1989Oct16.145131.13913@utzoo.uucp> <2122@hudson.acc.virginia.edu> <12860@boulder.Colorado.EDU>
Organization: Recognition Research Corp., Clarence, NY
Lines: 35

In article <12860@boulder.Colorado.EDU>, eesnyder@boulder.Colorado.EDU (Eric E. Snyder) writes:
> What "chlorofluorocarbons" detrimental to the ozone layer?  I thought any
> organic chlorine compound that is volatile enough to get into the upper
> atmosphere was capable of generating chlorine free radicals and this 
> taking out ozone....

	It's much more complex than that.  I don't claim to understand all
of the applicable reaction mechanisms and kinetics, but here are a few
salient points:

1.	The ozone layer is in the stratosphere.

2.	There are various tropospheric processes which are resonsible for
	decomposition of chlorocarbons (CC's), but which do NOT affect
	chlorofluorocarbons (CFC's).

3.	As a result of (2) above, CFC's are not removed in the troposphere
	and diffuse to the stratosphere where they undergo photodissociation
	caused by UV radiation, therefore forming chlorine atoms.  These
	chlorine atoms undergo a "Chlorine Oxide Cycle" where they combine
	with ozone (depleting it) to form chlorine oxide and oxygen, which
	further reacts to again form elemental chlorine plus oxygen.

4.	So the major point is: most CC's never make it to the stratosphere
	to cause the above problem.

5.	The effective "tropospheric lifetime" [tau] for the "problem" CFC's
	is something like 70 years, whereas the tropospheric lifetime
	for a CC such as 1,1,1-trichloroethane is measured in weeks or
	even days.

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