Ozone hole myths (was: Kyoto, Driving our car)

Hal Finney (hal@rain.org)
Tue, 9 Dec 1997 07:31:01 -0800

I didn't know much about this issue, but I've just browsed the web a bit
to find some information about the ozone problem.

"Warrl kyree Tale'sedrin" <warrl@blarg.net> wrote:

> (1) What is the primary source of chlorine in the atmosphere?
> (2) More specifically, what is the primary source of chlorine in the
> upper atmosphere over Antarctica?
> (Surprisingly enough, the answers to the two questions are
> different).
> (3) How do human (industrial and other) emissions of chlorine into
> the atmosphere relate or compare to either of these?
> (4) How much human-source chlorine is specifically in the upper
> atmosphere over Antarctica?
> (Answers: oceans, a volcano, infinitesmal, and essentially none.)

Here is a page on "ozone myths" from the EPA:

Following the link about sources of chlorine, we find:

> Myth: Volcanoes and the Oceans are Causing Ozone Depletion
> Volcanic eruptions are powerful events, and they are capable of
> injecting hydrogen chloride (HCl) high into the atmosphere. Similarly,
> oceans produce large volumes of sea salt, which contains chlorine, on a
> daily basis. If these compounds accumulated in large quantities in the
> stratosphere, they might produce ozone depletion. However, for several
> reasons, we know that CFCs and other substances used in human activities
> are the primary sources of chlorine in the stratosphere.
> First, the vast majority of volcanic eruptions are too weak to reach
> the stratosphere, around 10 km above the surface. Thus, any HCl emitted
> in the eruption begins in the troposphere. Sea salt from the oceans is
> also released very low in the atmosphere. These compounds would have to
> remain airborne for 2-5 years to be carried to the stratosphere. However,
> both sea salt and HCl are extremely soluble in water, as opposed to CFCs
> which do not dissolve in water. Rain effectively scrubs the troposphere,
> removing both of these forms of chlorine. Steam in volcanic plumes
> can act the same way, removing HCl long before it reaches the ozone
> layer. Measurements have shown that concentrations of these substances
> vanish very rapidly as altitude increases. Neither sea salt from the
> oceans nor tropospheric-level volcanic eruptions (like Mt. Erebus
> in Antarctica) contribute significantly to stratospheric chlorine
> levels. Some sea life does produce methyl chloride, a more stable form of
> chlorine than sea salt, but its contribution is small, as explained below.
> CFCs, on the other hand, do not dissolve in rain. In addition, no
> chemical processes have been found that aggressively remove them from
> the troposphere. In fact, one of the advantages of the CFCs was their
> stability. However, it is this very stability that poses a threat to
> the ozone layer.

Another source is:

Reading the section on chlorine, we find:

> 1.1) Where does the Chlorine in the stratosphere come from?
> ~80% from CFC's and related manmade organic chlorine compounds,
> such as carbon tetrachloride and methyl chloroform
> ~15-20% from methyl chloride (CH3Cl), most of which is natural.
> A few % from inorganic sources, such as volcanic eruptions.
> [Russell et al. 1996] [WMO 1991, 1994] [Solomon] [AASE]
> [Rowland 1989,1991] [Wayne]
> These estimates are based upon >20 years' worth of measurements of
> organic and inorganic chlorine-containing compounds in the earth's
> troposphere and stratosphere. Particularly informative is the
> dependence of these compounds' concentrations on altitude and
> their increase with time. The evidence is summarized in section 2
> of this FAQ.

Maybe things are different down in the Antarctic? This seems to
indicate otherwise:

> 4.2) CFCs are produced in the Northern Hemisphere, so how do they get down to
> the Antarctic?
> Vertical transport into and within the stratosphere is slow. It
> takes more than 5 years for a CFC molecule released at sea level to
> rise high enough in the stratosphere to be photolyzed. North-South
> transport, in both troposphere and stratosphere, is faster - there is
> a bottleneck in the tropics (it can take a year or two to get across
> the equator) but there is still plenty of time. CFC's are distributed
> almost uniformly as a function of latitude, with a gradient of ~10%
> from Northern to Southern Hemispheres.
> [Singh et al. 1979] [Elkins et al. 1993]

I hope Warrl will respond to this. On the face of it it appears that
his (1) was technically correct but irrelevant (since he referred to the
atmosphere rather than the stratosphere where depletion occurs), and his
(2) is incorrect. Likewise (3) is irrelevant since it does not refer
to the stratosphere, and (4) appears to be contradicted.