Trade-Offs between Sulfuric Acid Aerosol Precursors for Stratospheric Aerosol Geoengineering

[Geoengineering News]

https://pubs.acs.org/doi/10.1021/acs.est.5c15172

Authors: James Franke, Wake Smith, Angela Slavens, Frank N. Keutsch, Fangqun Yu, David Keith

22 June 2026

https://doi.org/10.1021/acs.est.5c15172

Abstract 

Solar geoengineering with sulfuric acid aerosols in the lower stratosphere might be used to reduce the impacts of climate change. Almost all studies have assumed sulfur is transported aloft as sulfur dioxide; several other sulfur compounds are plausible. We evaluated elemental sulfur (S8), hydrogen sulfide (H2S), sulfur dioxide (SO2), carbon disulfide (CS2), sulfur trioxide (SO3), and sulfuric acid (H2SO4), examining the mechanisms of dispersal in liquid form, safety, and costs for materials supply and deployment with a 20 km altitude aircraft. Levelized, combined costs for material production and lofting at 100 ktonne/year scale range from $1140 to $5150/tonne-S. We find that the cost to loft H2S is about half that of SO2, but the production cost of H2S is more uncertain and could be high enough to change this conclusion. The additional oxidation step required for H2S adds <20% to the aerosol formation time scale, so H2S and SO2 should produce similar aerosol size distributions if new particle formation is negligible. H2S and SO2 have high and roughly equivalent toxicity. H2S presents a further flammability risk that SO2 does not. S8 would be much safer than H2S or SO2, but it requires airborne combustor technology that is not yet developed. CS2 is not preferred on any metric. SO3 and H2SO4 are ∼4 times more expensive than H2S to loft but offer additional control over the aerosol size distribution that will likely reduce some side effects of sulfuric acid aerosol geoengineering.

Source: ACS Publications