Do you have a cost estimate for CO2 removal?
We estimate less than $1 per tonne of CO2 equivalent removal.
This is based on 150,000 tonnes of iron in the form of Iron Salt Aerosol, removing 12Gt CO2 equivalent per year. That 12Gt comprises 6Gt of CO2 and 6Gt equivalent other GHGs/cooling effects.
Given that Ferrocene costs around $35,000 per tonne of iron contained, removal of 12 billion tonnes of CO2e yields an estimated annual material cost of $5.3 billion. This translates to 44c per tonne. The dollar per tonne figure above allows for an error of over 50% and 10% operating costs.
However, this is a first order estimate. Combustion of Ferrocene is by no means the cheapest method of ISA precursor delivery when scaled up. But the ISA generation method will determine the particle diameter. ISA particle diameter is important in that it determines, for instance:
- sink speed of the ISA particles in the ISA plume
- reactivity of the ISA plume, determined by its surface area
- ISA particle life-time in the atmosphere
- ISA particle plume topography and/or plume volume (ISA iso-concentration areas)
- ISA plume topography and/or plume area in the upper ocean layer (ISA iso-concentration lines)
- specific methane depletion per mass of ISA iron
Another consideration is the ISA mass flux (rate of mass flow per unit area), which determines cooling efficiency. The ISA mass flux inside the ISA plume depends on the plume emission height. Higher emission heights will allow for larger mass fluxes than low elevation sources.
Efficiency also depends on particle life-time. Airborne ISA depletion of methane and other warming agents occurs by photo-catalytic reaction, in a closed cycle without limitation. When the ISA particles settle in the ocean they activate atmospheric CO2 depletion, via photosynthetic absorption of dissolved hydrogen carbonate. Once in the ocean, the iron from ISA particles can be used only once or twice by the phytoplankton that absorb it. After that their predators and downstream food web take the majority of it to the deep, along with the absorbed carbon.
We expect to quantify the efficiency of ISA much more accurately in both the atmosphere and ocean from the results of field trials.