Re: [asa] Level of certainty in science

From: PvM <pvm.pandas@gmail.com>
Date: Tue Feb 06 2007 - 12:40:05 EST

I now realize that there is not just the global warming myth but that
people are also under false impressions about DDT and Ozone.

For instance, DDT is still recommended for use but rather that use it
for indiscriminate crop dusting which was a major cause for mosquitos
gaining immunity against DDT, the policies ask for a more careful use
of DDT. The myth that DDT was banned and caused millions of deaths in
the form of malaria seems to be a persistent one.

As far as ozone is concerned, the scientific evidence, once again, was
extremely strong in that we had observations, mechanisms and
predictions, all of which led to the inevitable conclusion that human
contributions to the widening and deepening of the ozone hole were
significant.

CFC's only have manmade origins, yes, HCL and HF do have natural
origins but that does nothing to undermine the ozone findings, it
merely shows that there are additional factors which can affect ozone
(and global warming for that matter).

Most of the HCL and HF emitted by volcanos is quickly rained out unlike CFC's

<quote>However, in the Earth's stratosphere, fluorine atoms react
rapidly with water and methane to form strongly-bound HF, while
organic molecules which contain iodine react so rapidly in the lower
atmosphere that they do not reach the stratosphere in significant
quantities.</quote>

Researchers, aware of the potential confusion, decided to do
experiments to determine the origin of these ozone depleting chemicals
and by making atmospheric measurements they determined, quite
convincingly, that it was CFC's that were the 'bad guys'. Since
science had established the various chemical reactions involved, it
was a simple matter of book keeping once the chemical concentrations
had been measured as function of altitude.

<quote>
the concentrations of the source gases (CFC's and related compounds)
and the chlorine reservoir species (HCl and ClONO2) were measured
throughout the stratosphere, and demonstrated that CFCs were indeed
the major source of stratospheric chlorine, and that nearly all of the
CFCs emitted would eventually reach the stratosphere. Even more
convincing was the measurement, by James G. Anderson and
collaborators, of chlorine monoxide (ClO) in the stratosphere. ClO is
produced by the reaction of Cl with ozone its observation thus
demonstrated that Cl radicals not only were present in the
stratosphere but also were actually involved in destroying ozone.
</quote>

See for instance http://en.wikipedia.org/wiki/Ozone_depletion for some
common objections to the Ozone science.

Yes, there are natural sources of HF, and they have some impact on
ozone but again, they typically are much smaller than the human
contributions. I am not sure why you believe that NASA was surprised
nor what the relevance of this surprise was to Ozone science.

The Union of Concerned Scientists has an excellent Ozone FAQ, but for
those suspicious of concerned scientists, there are many easy
accesible resources on the internet.
The best FAQ is the one by Robert Parson and is known as the usenet
Ozone depletion FAQ

While old, it addresses many of the issues related to ozone depletion,
including the impact of volcanoes and much more

http://www.faqs.org/faqs/ozone-depletion/

Ozone Depletion FAQ Part I: Introduction to the Ozone Layer
Ozone Depletion FAQ Part II: Stratospheric Chlorine and Bromine
Ozone Depletion FAQ Part III: The Antarctic Ozone Hole
Ozone Depletion FAQ Part IV: UV Radiation and its Effects

The important data are the vertical profiles of the various
intermediate products

<quote>Let us now look at the organic source gases. Here, the data show
that the mixing ratios of the CFC's and CCl4 are _nearly independent
of altitude_ in the troposphere, and _decrease rapidly with altitude_
in the stratosphere. The mixing ratios of the more reactive
hydrogenated compounds such as CH3CCl3 and CH3Cl drop off somewhat
in the troposphere, but also show a much more rapid decrease in
the stratosphere. The turnover in organic chlorine correlates
nicely with the increase in inorganic chlorine, confirming the
hypothesis that CFC's are being photolyzed as they rise high enough
in the stratosphere to experience enough short-wavelength UV. At
the bottom of the stratosphere almost all of the chlorine is
organic, and at the top it is all inorganic. [Fabian et al. ]
[Zander et al. 1987] [Zander et al. 1992] [Penkett et al.]

Finally, there are the stable reaction intermediates, COFCl and
COF2. These show up in the middle stratosphere, exactly where one
expects to find them if they are produced from organic source gases
and eventually react to give inorganic chlorine.

For example, the following is extracted from Tables II and III of
[Zander et al. 1992]; they refer to 30 degrees N Latitude in 1985.
I have rearranged the tables and rounded some of the numbers, and
the arithmetic in the second table is my own.

   Organic Chlorine and Intermediates, Mixing ratios in ppbv

Alt., CH3Cl CCl4 CCl2F2 CCl3F CHClF2 CH3CCl3 C3F3Cl3 || COFCl
km
12.5 .580 .100 .310 .205 .066 0.096 0.021 || 0.004
15 .515 .085 .313 .190 .066 0.084 0.019 || 0.010
20 .350 .035 .300 .137 .061 0.047 0.013 || 0.035
30 - - .030 - .042 - - || 0.029
40 - - - - - - - || -

     Inorganic Chlorine and Totals, Mixing ratios in ppbv

Alt., HCl ClONO2 ClO HOCl || Total Cl, Total Cl, Total Cl
                                || Inorganic Organic
km ||
12.5 - - - - || - 2.63 2.63
15 .065 - - - || 0.065 2.50 2.56
20 .566 .212 - - || 0.778 1.78 2.56
30 1.452 1.016 .107 .077 || 2.652 0.131 2.78
40 2.213 0.010 .234 .142 || 2.607 - 2.61

(I have included the intermediate COFCl in the Total Organic column.)

This is just an excerpt. The original tables give results every 2.5km
from 12.5 to 55km, together with a similar inventory for Fluorine.
Standard errors on total Cl were estimated to be 0.02-0.04 ppbv.

Notice that the _total_ chlorine at any altitude is nearly constant
at ~2.5-2.8 ppbv. This is what we would expect if the sequence of
reactions that leads from organic sources to inorganic reservoirs
was fast compared to vertical transport. Our picture, then, would be
of a swarm of organic chlorine molecules slowly spreading upwards
through the stratosphere, being converted into inorganic reservoir
molecules as they climb. In fact this oversimplifies things -
photolysis pops off a single Cl atom which does reach its final
destination quickly, but the remaining Cl atoms are removed by a
sequence of slower reactions. Some of these reactions involve
compounds, such as NOx, which are not well-mixed; moreover,
"horizontal" transport does not really take place along surfaces of
constant altitude, so chemistry and atmospheric dynamics are in fact
coupled together in a complicated way. These are the sorts of issues
that are addressed in atmospheric models. Nevertheless, this simple
picture helps us to understand the qualitative trends, and
quantitative models confirm the conclusions [McElroy and Salawich].

We conclude that most of the inorganic chlorine in the stratosphere
is _produced_ there, as the end product of photolysis of the organic
chlorine compounds.</quote>

It may be ironic that it was the detection of HF which set in motion
the whole ozone debate even though there were (at that time unknown)
natural contributors to HF. However, that NASA may have been wrong
about HF does not undermine the anthropogenic component to ozone
depletion. It's a red herring at most.
Btw HF is also not an ozone destroying chemical, although some seem to
have reached this conclusion erroneously.

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Received on Tue Feb 6 12:41:10 2007

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