Evaluation of
Tetra Ethyl Silicate Dissolved in Aviation Kerosene As a Means of Distributing
Stratospheric Aerosols for Geoenginering.
(Geoenginering in this
context refers to ways of minimising global warming by blocking some sunlight.)
Note:
It is not suggested that the additive would be burnt in a jet engine. It will be assumed that a purpose-built
burner will be developed in a subsequent project.
Part 1 Background.
There is a growing awareness that global warming will not be kept within
acceptable limits by CO2 emissions reductions alone. Dr Chris Field, a co-chair of the IPCC, speaking at
the American Association for the Advancement of Science in February 2009
admitted "We are basically looking now at a future climate that is beyond
anything that we've considered seriously in climate policy."
"
Geoenginering has therefore staged something of a comeback" to quote an
editorial in Nature (Feb 2007) This is exemplified by the special edition of
the Philosophical Transactions of the Royal Society published in September 2008
and also by the hearings of the Parliamentary select committee for Innovation,
Universities, Science and Skills devoted to geoenginering in November 2009
Among
the various geoenginering proposals, one stands out because it has been tested
on a global scale. This is the
injection of aerosols into the stratosphere by volcanic eruptions, which has
occurred 13 times in the last 250 years.
This would lower global temperatures if done artificially. This is confirmed by a recent paper (), which stated, “By 2050, only
stratospheric aerosol injections or sunshades in space have the potential to
cool the climate back toward its pre-industrial state”
In the
case of volcanoes, various sulphurous compounds release sulphur dioxide into
the stratosphere which eventually forms an aerosol of sulphuric acid. Most stratospheric aerosol geoenginering
proposals have therefore discussed SO2 injection.
This
proposal is to investigate the possibilities of submicron silica particles as
the aerosol.
Possible
Advantages of Silica.
Particle
size. At these submicron sizes it is
the size of the particle which defines the wavelength of light which is
reflected/diffracted. There have been
several papers, which have pointed out the difficulty of controlling sulphuric
acid droplet size and the problem of agglomeration of the droplets. (Papers include that by Tilmes/Robock in the
Royal Society's Philosophical Transactions)
It seems
logical that the concentration of Tetra ethyl silicate in aviation fuel would
define the size of silica particles produced on burning. If so, the particle size could be selected
for maximum reduction in net radiation.
There would then be less material and fewer particles/droplets for the
same level of global cooling.
This would
not just be ”economical” in various ways but might be of critical importance
for the following reason:
Ozone. Stratospheric aerosols will affect the ozone
layer. This is because the particles
act as nuclei for the remaining CFCs to concentrate and react with the ozone.
It is
not clear whether this is a small and acceptable loss as suggested by Paul
Crutzen “Compensating for a CO2 doubling would lead to-- ozone loss -- not as large
as after Mount Pinatubo--(where) --
ozone loss was about 2.5% Furthermore,-- (CFC’s)--are now declining by
international regulation, so that ozone will significantly recover by the
middle of this century.”(Paul Crutzen got his Nobel Prize for work on the ozone
layer) or whether the loss will be much greater as suggested by Tilmes
Whichever
is correct, the effect on the ozone layer is likely to be the limiting factor
in the use of stratospheric aerosols.
There would therefore be great advantage in achieving the maximum net
radiation reduction for the minimum number of aerosol particles. This is the most important reason for
investigating the possible use of silica particles.
Inert -- Non Acid.
Sulphur dioxide
will add to global acid rain whereas silica particles will avoid this
completely. This is not however a major
factor as the quantity of sulphur dioxide in the stratosphere would only be of
the order of 1% of the sulphur dioxide released into the lower atmosphere by
industrial processes.
Delivery to
Stratosphere.
It is not clear
how sulphur dioxide would-be delivered but aircraft would almost certainly be
used for any early experimental phase.
Storage of the gas safely on board an aircraft would not be easy.
If Tetra ethyl
silicate could be mixed with the fuel in some of the tanks of the aircraft; and
if the mixture could be pumped and piped by the normal aircraft equipment, most
of the problems of storage and delivery would-be solved. A burner would still have to be developed.
Ultraviolet.
By careful
selection of particle size it might be possible to selectively block some
ultraviolet light thus compensating to some extent for slight loss of ozone.
Patr
2 Experimental Project.
Note: preliminary
tests using a paraffin blow lamp have shown :
-- that Tetra
ethyl silicate mixes with kerosene in any proportion.
-- that the
mixture burns in the blow lamp just as kerosene does.
-- that a
"mist" of some kind is produced when the additive is present.
Phase 1.
Check that the
mixture can be stored and pumped by normal aircraft components. (If this fails, then much of the simplicity
of the idea is lost.) This would not be an exhaustive test. Maybe a week of storage and pumping with
examination of components afterwards.
Phase 2.
The object during
this phase would be to burn the mixture at various concentrations, to confirm
that silica particles are produced and to determine the size and other details
of the particles.
It might be
possible to use a domestic central heating boiler for this purpose. This would not be realistic in terms of the
speed of air flow but might be quite adequate initially. To have a high-speed airflow simulating a
burner attached to an aircraft would make project much more difficult.
Particles would be
filtered from the exhaust and examined both microscopically and
chemically. The way in which particle
size varied with additive concentration would be evaluated.
Experiments with
light beams could also be done to evaluate the reflection of light of various
wavelengths by the "mist" of particles. (It was observed in the preliminary experiments that the mist
persisted at least an hour.)
Part
3 The Burner.
(Note: this is not
a part of this proposed project.)
A burner which
could be attached to an aircraft would obviously have safety implications and
could only be designed by a suitable organisation.
Various other
forms of burner should also be considered.
-- it is unlikely
to be possible to burn the mixture in a normal jet engine because of the
probable effects on the turbine of the silica particles. However it might be possible to inject the
mixture into an afterburner.
-- burning the
fuel in a ramjet might be possible and might have the advantage of providing
the propulsion at altitude as well as the burning function. It is also possible that a ramjet might be
used at a higher altitude than a conventional turbojet.
Part4 Atmospheric
Implementation.
4.1 It does seem sensible to have an
application in mind in order to justify preliminary experiments.
4.2 Even among those proposing stratospheric
aerosols there is scepticism as to whether aircraft fuel additives could be a
distribution system. The doubts
expressed include:
1)
Aeroplanes don't fly high enough in the stratosphere.
2)
Aerosols will fall out of the atmosphere too quickly.
3)
Sulphur dioxide, which becomes sulphuric acid, will damage the ozone layer.
4)
Acid rain.
5)
Ozone layer damage will be particularly high in winter. (Recent Simone Tilmes paper)
6)
Aerosols will tend to cause high latitude warming in winter because of
reflection of outgoing radiation during the longer nights relative to daytime.
7)
Damage to the jet engine.
4.3 The most likely first application of a
stratospheric aerosol sunscreen is that proposed by Gregory Benfold, a
planetary atmospheric scientist at the University of California. The title was "Saving
the Arctic".Ref4
4.4 Combined with the aircraft distribution
system, the proposal would be to spread the aerosol by aircraft flying between
40 and 60,000 ft. from the time of first Arctic daylight (April approximately)
until late July approximately.
4.5 I believe that this would “slip” neatly
between the various disadvantages mentioned above, in the following way:
4.5.1 Doubts 1 and 2. Ideally for very long stratospheric life,
aerosols need to be injected at about 80,000 ft. If they are only injected at
50,000 ft. they will fall out of the atmosphere in about three months. (Ken Caldera's lecture available on U
tube). In this case that is exactly
what we want so that they would fall out by the end of the Arctic summer and
would not be present during the winter -- solving 6. The aerosols will probably also be more effective, weight for
weight, in the Arctic since there is no night during the summer when the
night-time blanketing effect has to be subtracted from the daytime screening.
4.5.2 Most of the arguments that aerosols will
damage the ozone layer assume that the aerosols are injected high in the
stratosphere for long life. In this
case most of the injection would not reach the ozone layer. In addition the aerosols would no longer be
present in winter when the effect is greatest.
(The damage to the ozone layer is not directly caused by the aerosols
but by the aerosol droplets or particles forming nuclei on which the remaining
CFCs have their chemical effect on the ozone.
The level of CFCs in the atmosphere is dropping steadily now that
controls are in place.)
4.5.3 The problem of acid rain, 4 above, has always
been a bit of a red herring because the quantity of sulphur dioxide needed is
only of the order of one per cent of that produced by industrial processes
worldwide. It could however be eliminated
if the silica particle version was used.
4.6 It seems very likely that implementation
of this type would succeed in "saving the Arctic". In particular the target would be to
eliminate significant melting of the Greenland ice sheet or sudden loss of
parts of it. The same principle could then be applied to Antarctica.
4.7 The target should be zero sea level
rise. If this could be achieved the
saving in costs of construction, relocating populations and lives lost in flood
disasters would be absolutely enormous.
John Gorman May 09