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 (The radiative forcing potential of different climate geoengineering options. Lenton/Vaughan), 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