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. 

A network of photochemical reactions given here  https://doi.org/10.1073/pnas.1620870114 (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 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.

To charge negatively, the teflon tube that is standard on a tribo gun will have to be replaced by a tube made with an electron donor, or else corona charging used instead of tribocharging. I calculate that to rise in the atmospheric electric field, a particle needs a charge to mass ratio ("specific charge") greater than 50 millicoulomb/kilogram, which may be another factor requiring corona charging.

The figure of 50 mC/kg was derived by dividing g, the gravitational acceleration at the Earth's surface (about 10 m/s²), by 200 V/m, and multiplying by 1000 to get the units used in studies of powder-coating physics (and the units analysis checks out).

Extrapolating from data in Meng et al., 2008, http://dx.doi.org/10.1088/0022-3727/41/19/195207 , 2.3-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.

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.

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 in four to five days. 

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 without cloud formation.

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 5 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 0.23 microns (which uses up our margin for discharge) only gives 4.5 km, less than the minimum height 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

The weakening of the Earth’s gravity with height 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 ), 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.

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 according to the previous citation. 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 360 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). 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. The ozone byproduct generation (7 molecules per 100 eV of alpha-particle energy) should be manageable.

If the effect of this scavenging on air conductivity is uniform with height, there should be no effect on the profile of field intensity with height. If the conductivity change is concentrated at low altitudes, there will be. Injecting enough charge carriers to increase the air conductivity will, in this case, tend to flatten the profile of field strength with height, which could be advantageous and increase the height to which particles can be lifted. My circuit model for these conclusions was a multi-tapped voltage divider connected across a battery. 

Most of the resistance of the air column is concentrated at low altitudes, and this is where we can most easily reach it, so, it’s a break. Reducing this resistance should efficiently increase the current flowing in the air column, pulling it in at the top from the sides, thus concentrating it, thus concentrating the power available from this source. The enhanced current will enhance the vertical electric fields all the way up.

DISCUSSION:

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. 

Our task is not to build a cooling system, but a control system having enough power to overwhelm any heating or cooling positive feedbacks that may set in as the result of overshoots or undershoots in temperature control. Focusing narrowly on cooling will trigger a continental glaciation sooner or later.   

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 probably 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.

Can we relax some constraints here, given the anticipated economies of a coulombic hoist 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?

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. 

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.

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