15 April 2026 | ZEROGeoengineering.com | Due to potential harmful effects of sulfur (SO₂₎ aerosols such as depletion of the ozone layer and aerosol-induced heating of the stratosphere, authors of the study below propose injection of solid alumina and calcite particles as alternative aerosol materials. According to the report, alumina and calcite particles require higher mass injection rates compared to SO₂.

“Despite the larger scattering cross sections of alumina and calcite particles compared to sulfuric acid, they require higher mass injection rates to achieve the same RF (see the overview provided in Fig. 5). This is primarily due to the in-situ oxidation of SO₂, which results in the biggest part of sulfuric acid aerosol burden already being in the stratosphere. Under conditions for the year 2090 and assuming a high GHG emissions scenario, even larger alumina and calcite particle injections would be required to achieve the same cooling of −1 W m⁻² compared to 2020 conditions (see Fig. 5).”

Vattioni, S., Peter, T., Weber, R. et al. Injecting solid particles into the stratosphere could mitigate global warming but currently entails great uncertainties. Commun Earth Environ 6, 132 (2025). https://doi.org/10.1038/s43247-025-02038-1

Fig. 5: Schematic overview of globally averaged quantities linearly normalized from 5 Mt[metric tons] yr⁻¹ injections to −1 W m⁻² total all sky ToA RF.

Upper part shows results for 2020 and lower part for 2090 boundary conditions in respect to GHG, sea surface temperatures (SST), sea ice concentrations (SIC) and ODS concentrations when injecting gaseous SO₂ (left), alumina (middle) and calcite (right) particles at radius of 240 nm. Shown are required stratospheric aerosol burden in Mt, the injection rate in Mt yr⁻¹, the resulting global average stratospheric residence time of the particles in years, the resulting heating in the tropical stratosphere in K and the resulting ozone column in Dobson units (DU). For comparison the ozone column of the reference scenario, the historical minimum in the years 1992–1995 (modeled by SOCOL-AERv2) as well as the uncertainty ranges for the resulting ozone column (grey areas) are shown (see Section Stratospheric ozone chemistry for details on the uncertainty ranges). For 2090 conditions also the 2090 reference ozone column is shown.

Link To Injecting solid particles into the stratosphere could mitigate global warming but currently entails great uncertainties