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16 Can the hole be "plugged"? (Ozone Depletion: The Antarctic Ozone Hole)




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This article is from the Ozone Depletion: The Antarctic Ozone Hole FAQ, by Robert Parson rparson@spot.colorado.edu with numerous contributions by others.

16 Can the hole be "plugged"? (Ozone Depletion: The Antarctic Ozone Hole)

The present ozone hole, while serious, is not in itself
catastrophic. UV radiation is always low in polar regions since the
sun takes a long path through the atmosphere and hence through the
ozone layer. There may be serious consequences for marine life in
the antarctic ocean, which is adapted to the normally low UV
levels. When the hole breaks up in summer, there may be temporary
increases in UV-b at high latitudes of the southern hemisphere as
air that is poor in ozone and rich in "active", ozone-destroying
forms of chlorine mixes with the air outside.

Nevertheless it looks like we are stuck with the hole for the
next 50 years at least, and we don't know what new surprises the
atmosphere has in store for us. Thus, some atmospheric scientists
have been exploring the possibility of fixing the hole by
technological means. All such schemes proposed so far are highly
tentative, and there are no plans to carry any of them out
until the chemistry and dynamics of the stratosphere are much
better understood than they are at present.

It should be made clear at the beginning that there is no
point in trying to replace the ozone directly. The amounts are far
too large to be transported to the stratosphere, and the antarctic
mechanisms are so fiendishly efficient that they will easily
destroy added ozone (recall that where the catalytic cycles
operate, ~95% of the ozone is gone, in spite of the fact that the
sun is generating it all the time.) It is far better to try to
remove the halogen catalysts. One suggestion made a few years ago
was to release sodium metal into the stratosphere, in hopes that it
would form sodium chloride crystals which would settle out. The
problem is that the microcrystals remain suspended as long as they
are small, and can play the same role as clouds and aerosols in
converting reservoir chlorine to active chlorine.

A second suggestion is to destroy the CFC's while they are
still in the troposphere, by photolyzing them with high-powered
infrared lasers installed on mountainsides. (CFC's and similar
molecules can absorb as many as 30 infrared photons
from a single laser pulse, a phenomonon known as infrared
multiphoton dissociation). The chlorine atoms released would
quickly be converted to HCl and rained out. The power requirements
of such a project are daunting, however, and it appears that much
of the laser radiation would be shifted out of the desired
frequency range by stimulated raman scattering. [Stix]

A more serious possibility is being explored by one of the
discoverers of chlorine-catalyzed ozone depletion, Ralph Cicerone,
together with Scott Elliot and Richard Turco [Cicerone et al.
1991,1992]. They considered the effects of dumping ~50,000 tons of
ethane or propane, several hundred planeloads, into the antarctic
stratosphere every spring. The hydrocarbons would react rapidly
with the Cl-containing radicals to give back the reservoir HCl. The
hydrocarbons themselves are fairly reactive and would decompose by
the end of a year, so the treatment would have to be repeated
annually. The chlorine would not actually be removed from the
stratosphere, but it would be bound up in an inert form - in other
words, the catalyst would be "poisoned". There are
no plans to carry this or any other scheme out in the near future;
to quote from Cicerone et al. (1991), "Before any actual injection
experiment is undertaken there are many scientific, technical,
legal and ethical questions to be faced, not the least of which is
the issue of unintended side effects."

 

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