Record growth of stratospheric aerosols from 2019 Raikoke eruption with sulfate-coating of submicronic ash

The 2019 Raikoke stratospheric eruption is one of the strongest in the satellite era, yet its particle composition remains debated. The eruption generated a long-lived, compact, and vorticized volcanic plume (VVP), usually observed in biomass burning smoke plumes, but identified for the first time from volcanic emissions. A synergistic analysis of S5P/TROPOMI, MetOp/IASI, CALIPSO/CALIOP and AERONET data is conducted to retrieve particle size in the VVP and the dispersed plumes. In the VVP, fine particle peak radii increased to 0.8–1 μm within three months after the eruption. This is three times greater than that observed in the dispersed plumes. The growth coincides with the decrease in SO 2 concentration, suggesting sulfate aerosol growth. However, dynamical, optical and radiative signatures point to a more complex composition, where submicronic ash ( r < 0.2–0.3 μm) become coated by sulfates. This phenomenon is enhanced in the VVP where SO 2 concentration is initially fourteen times higher than in the dispersed plumes, meaning that local SO 2 concentration is the critical factor limiting sulfate aerosol growth, and not the eruption SO 2 emission budget. Finally, this unprecedented particle size observed in the VVP with persisting submicronic ash calls for a re-evaluation of the current approach for modeling impacts of stratospheric eruptions on climate.