Stratospheric Aerosol Injection by Coulombic Hoist

Reprinted from “My Pages,” Hackaday.io

An exploration of possible modern uses of clear-weather atmospheric electricity.

The idea

On clear, calm days, release tiny, negatively charged sulfur particles near ground level (but no lower than 25 cm) and wait for them to rise into the stratosphere on the sky voltage. They should then oxidize to a sulfuric acid aerosol, which is a powerful climate cooling agent if present in the stratosphere. The stratosphere begins 8 km above the surface in the arctic and 16 km above the surface in the tropics (mode = 12 km). At the surface, the electric field of the sky voltage has an intensity of 100 to 200 volts/m, earth negative, with the maximum occurring at 18:00 UTC, no matter where you are. It is part of the global atmospheric electric circuit, which is powered by thunderstorms and other electrified clouds. Solid sulfur can be negatively charged by friction, a process called tribocharging. Tribocharging is already used in one type of powder coating technology. 

Chemical  Issues

A network of photochemical reactions given here  https://doi.org/10.1073/pnas.1620870114 [1] (scheme 1) suggests that elemental sulfur will change into sulfuric acid aerosols in the atmosphere. (The scheme is presented as applying to anoxic conditions, but in the text, it is presented as describing current knowledge of atmospheric sulfur chemistry.) A fly in the ointment is that an irreversible step is shown going from gaseous S8 to solid S8, and I want reversible, so I am still searching for a rigorous chemical precedent for the supposed transformation. DOI:10.1126/sciadv.abc3687 [2] figures 5B and S4, shows that when suspended in an aqueous solution at pH 6, solid sulfur generates sulfate when irradiated at 280 nm (shortest-wavelength end of the UVB range). That precedent isn’t rigorous either but it is helpful in addressing the question of providing sulfur in solid elemental form.

If stratospheric temperatures are too low to permit useable oxidation rates, microwave heating using ground-based projectors could be tried. (Such projectors could also be used for in-flight recharging of high-flying drones that deliver substances into the upper atmosphere.)

Electrical Issues

To charge negatively, the Teflon tube that is standard on a triboelectric gun will have to be replaced by a tube made with an electron donor, or else corona charging used instead of triboelectric charging. I calculate that to rise in the atmospheric electric field, a particle needs a charge to mass ratio ("specific charge") greater than 75.5 milliCoulomb/kilogram, which may be another factor requiring corona charging.

The figure of 75.5 mC/kg was derived by dividing g, the gravitational acceleration at the Earth's surface (9.81 m/s²), by 130 V/m ([4], section 20.1.2),  and multiplying by 1000 to get the units used in studies of powder-coating physics. 

Extrapolating from data in Meng et al., 2008, http://dx.doi.org/10.1088/0022-3727/41/19/195207 [3] , 2.6-micron-diameter sulfur particles corona charged at 90 kV should fly. However, a ten-fold smaller sulfur particle will have a ten-fold greater specific charge, giving some margin to allow for discharging on the way up. (Meng et al. found 5.5 mC/kg for 35-micron diameter particles charged at 90 kV with 10 seconds of spraying, and charging efficiency as specific charge was stated to be inversely proportional to particle radius (their equation 3), and thus diameter. My extrapolation was to smaller diameters to achieve 75.5 mC/kg. Calculation: 5.5 x 35/75.5 = 2.6)

The diameter of the sulfur particle injected into the stratosphere is unrelated to the diameter of the eventual sulfuric acid droplets it produces upon oxidation in the stratosphere, because one reaction intermediate, sulfur dioxide, is gaseous.

Another possible payload particle in the Coulombic hoist (CH) would be one sulfur dioxide molecule with one electron charge on it. The specific charge works out to 1.51 × 10⁹ mC/kg, which is enormous. This only means that gravity can safely be neglected in the electromobility calculations. Air anions are known to move at 1.6 cm/s at a field strength of one volt per centimetre [4]. The “SO₂ anion” (probably a hydrated bisulfite anion) would therefore rise at 2.1 cm/s at near ground level, similar to my eyeball estimate for visible electrified particles.

Physical Issues 

At this time, my best guess as to how fast the particles would rise is 3 cm/s (because I believe I have seen it), which will take them up to the stratosphere (11 km high on average) in four to five days. This velocity will be the Stokes terminal velocity, which is a function of the net force acting on the particle, the particle radius, and the dynamic viscosity of air. The latter is 1.8 x 10-⁵ Ns/m² at ground level and 1.4 x 10-⁵ Ns/m² at the top of the troposphere (not much difference).

Ideal release conditions are low barometric pressure (i.e., rising airmass) but no clouds. This need not be a contradiction in terms if the rising air is dry to begin with. For example, dry polar air warmed by contact with arid ground should rise with little cloud formation.

Altitude Issues

However, thus far, my calculations have not addressed the fact that the sky electric field weakens with height. At an altitude of 12 km, it is only 4 V/m, versus 100--200 V/m at sea level. The altitude effect will cause the particles to stop ascending and start concentrating at a particular altitude  (a possibly useful effect) where gravitational and Coulombic forces are in equilibrium, but is it stratospheric? Unfortunately, no. Even reducing particle diameter 10-fold to 0.26 microns (which uses up our margin for discharge) only gives about 6 km, less than the minimum altitude of the stratosphere, 8 km. So, we don't get there, unless we stand on a mountain top in Greenland, but we get interestingly close with what is only the first scheme contemplated. My source for the dependence of electric field on height is figure 20-7a in https://www.ngdc.noaa.gov/stp/space-weather/online-publications/miscellaneous/afrl_publications/handbook_1985/Chptr20.pdf [4]

The weakening of the Earth’s gravity with increasing altitude is no help, because if you go up to 12 km, the difference is only one-half of one percent.

The problem of particles discharging en route is far from trivial, but charged dust particles suspended in air at ground level lose charge with a half-life of about 4 days ( https://doi.org/10.1093/pnasnexus/pgac220 [5]), independent of composition, which is not too discouraging, but the loss will be faster at altitude, where air ionization by cosmic rays is more intense.

Engineering Solutions

We could use electrons as an ion scavenging agent, to be released under the aerosols as a way to continuously guard the ascending aerosols from cation recruitment, which is the main mechanism of neutralization of negatively charged airborne particles [5]. Electrons (as hydrated hydroxide anions) could be injected into the air by smoke-detector-type Americium discs sitting on top of three-meter-high grounding stakes driven into the ground.  The ground is 275 kV negative relative to an imaginary capacitor plate in the ionosphere. Alpha particles, the main form of radiation from Americium, only travel 4.5 cm in air, if you are worried about safety. In that distance, they make many air cations (+)  and anions (-) through molecular collisions, giving a current of a few nanoamperes per disc (a thousand times greater than the natural current descending into one square meter, 2 nA [6] [7] vs 2 pA [4]). The local fair-weather electric field will be concentrated at the top of the pole and will pull down all the cations while repelling the anions upward.  An array of these "radioelectrodes," possibly extending over many square kilometers, will be needed because a fairly strong electric field will be pulling cations in from the sides. Inside the area covered by electrodes (the “ion farm”), there may be less electric-field concentration effect at the pole tops, however, but there will be some vertical field, at least about 1.3 V/cm, and this could be artificially enhanced (see below). The ozone byproduct generation (7 molecules per 100 eV of alpha-particle energy) should be manageable. Connecting all radioelectrodes to a central station by buried wires would allow grounding independent of soil moisture and, with suitably insulated poles, would also allow non-ground DC potentials to be applied to the radioelectrodes. The latter feature would be an elegant way to control the amount of current flowing from the radioelectrodes into the lower atmosphere. Voltages far less than those needed for corona discharge would suffice; the work of molecule busting would be done directly with atomic energy (from the Americium), not electrical. 

On second thought, the grounding wires should probably be elevated on standard electric utility poles, and the ion-release devices could be affixed to the wires at 30-meter intervals, let’s say one on each pole to keep it simple. Drones could be used to replace the Americium when needed. Tubes to distribute the payload particles could be slung from the same poles. This would be convenient if the payload particles were molecules of sulfur dioxide gas, but in that case, pollution issues might be prohibitive.

Early Simulation Results

Injecting enough charge carriers to increase the air conductivity will tend to modify the profile of field strength with altitude, which could be advantageous and increase the height to which particles can be lifted. In numerical simulations in Excel, I was able to make a particle go from 6 km up to 9 km by this method. My circuit model for these conclusions was a multi-tapped voltage divider connected across a battery. The air conductivity increment due to current injection was assumed to decay with altitude z as EXP(-0.305*z) in imitation of that due to natural ground radioactivity (square root of ionization rate from [4]) and start at 4x the natural ground-level total conductivity from equation 20.4 [4]. EXP is base e. The total resistance was taken as that of the bottom 50 km of the atmosphere and the applied voltage as 275 kV [4]. The specific charge or field strength needed for lift-off was taken as a free variable. The unmodified, comparison curve of field strength versus altitude was calculated from equation 20.4 in [4]. Conductivities were converted to conductances by assuming a cube of air one kilometre on a side and the system was modelled as a stack of 50 such cubes. Resistance is the inverse of conductance. 

Replacing the exponential decay of the added conductivity with an inverse squared law with addition of one to the argument to prevent division by zero was not as beneficial. This models a single radioelectrode but I think that the exponential decay models an ion farm.

DISCUSSION

Alternative Approaches 

Other climate manipulations can be imagined, such as increasing the winter snowpack in Canada and Russia by seeding supercooled clouds with ice-nucleating proteins isolated from Pseudomonas syringae and a few other species of bacteria.

Another possibility is carbon sequestration in fertilized wetlands, but the strong greenhouse gas methane will be produced as a byproduct. Combining direct physical temperature control with carbon sequestration, however, would unlock access to a simple wetlands strategy for regaining carbon balance. Carbon sequestration in wetlands is how the non-marine fossil carbon got into the ground in the first place, and it will be readily available to us as peat fuel if we need it again some day, for example, to reverse a temperature undershoot by burning some fossil fuel again. 

The Big Picture 

Our task is not to build a cooling system, but a well-engineered control system that can either heat or cool at need. Focusing narrowly on cooling will trigger a continental glaciation sooner or later.  Suggested key words for further reading are: proportional-derivative controller, controlled system response time, industrial process control.

Every crisis is an opportunity, and the opportunity in this one is to build a system of global climate control that in the future will protect us not only from climate disasters of our own making, but also from natural climate-impacting ones like volcanic explosions, long statistical pauses in volcanic explosions, and changes in solar radiance. For the first time in history, humans are now collectively powerful enough to control the global climate. This is in large part due to our presently great numbers, so population increase isn’t all bad; people not only consume resources, but they can also do work, and there is now less than one cubic kilometre of air per person (average tropopause altitude of 11 km x 0.51 Giga-square kilometres / 8.2 Giga-persons @y2025 / 0.75 fraction of air mass in the troposphere = 0.91). Consider this your environment stewardship air allotment. In terms of weight of air per person, the same weight as water would fill a cube standing 86 meters tall, slightly less than the height of the Peace Tower (92 m) or the Statue of Liberty (93 m).

Big Engineering 

Can we relax some constraints here, given the anticipated economies of a CH system? Does injection have to be stratospheric, or will high tropospheric do? Will the high-tropospheric UV flux and spectrum be adequate to convert sulfur aerosols into sulfuric acid before they settle out? Do the light-scattering particles have to be sulfuric acid or can they be electrified mineral dust, pollen, or sea salt? A dominant consideration of particle injection into the high troposphere will be avoidance of cirrus cloud formation, as these clouds have a net greenhouse effect. Ice-nucleating particles ameliorate the cirrus cloud problem. Such particles can consist of bismuth tri-iodide or natural isoprenoid organics of 0.1 microns or less. Moreover, cirrus clouds originate in precisely the dry updraft areas I previously identified as the best release sites for the CH, which is  sixty degrees north, the northernmost boundary of the prairie provinces, so the CH lends itself to raising particles into the high troposphere for purposes of cirrus cloud thinning. A net warming effect due to overseeding is thought to be a possibility, however. 

High-tropospheric injections will be more reversible, if mistakes are made (and they will be), than will stratospheric injections, because the climate effects of a pulsed injection at this altitude last only 1 to 3 months. Geographically, the effects will also be less than global, allowing a more pluralistic and thus acceptable governance model, as well as offering the enticing possibility of regional climate tweaking. Artificial heating and cooling effects at any altitude will have to be balanced between northern and southern hemispheres to avoid shifting the latitude of the monsoon rains; any such shift would cause hardship to millions of farmers and food insecurity for many more. If a CH must be built at about sixty degrees north for it to work, the balancing CH in the southern hemisphere would have to be built on Cape Horn (56 degrees south), because there is no land exactly on sixty degrees south.

As to the pollution aspects, nobody lives in the high troposphere, and acid rain from the amount of sulfuric acid needed for climate control will be diluted over large areas and need not be net-harmful. You can be poisoned by too much vitamin D, but that does not mean that nobody should have any vitamin D. This type of situation is called "hormesis," and it is quite common.

A search should be undertaken for natural Coulombic hoists or aeolian hoists already in existence that could be modified for climate control. Electric levitation is already implicated in greatly extending how far Saharan dust travels before settling out [5].

Additional References

[6] Wotiz R (2011) Ionization Detectors. Circuit Cellar Nov 2011 #256: 60-65.

[7] Litton CD (1979) Optimizing Ionization-type Smoke Detectors. Fire Technology 15 (1) 25-42. https://doi.org/10.1007/BF02101921 [not seen due to paywall].

I have a BSc in Engineering Chemistry [environmental emphasis], 1977, from Queen’s University, Ontario.