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

The 2019 Raikoke eruption injected material directly into the stratosphere and had major impact on climate. The particle composition of the volcanic aerosols still remains debated today. The eruption generated usual hemispherically-dispersed plumes, but also a long-lived, compact and vorticized volcanic plume (VVP). While this type of plume is usually observed for biomass burning aerosol smoke plumes, it is identified for the first time after a volcanic eruption. A synergistic analysis of S5P/TROPOMI, MetOp/IASI, CALIPSO/CALIOP and AERONET data is conducted to retrieve particle size in the VVP and in the dispersed plumes. In the VVP, fine particle peak radii increased to a record size within three months after the eruption. It is three times greater than the particle radius retrieved in the dispersed plumes, and even greater than the one reached by the strongest eruption of the last decades, i.e., the 1993 Mt Pinatubo eruption. The growth coincides with the decrease in SO₂ concentration, suggesting the growth of sulfate aerosols. However, dynamical, optical and radiative signatures point to a more complex composition, where submicronic ash become coated by sulfates. This phenomenon is enhanced in the VVP where SO₂ concentration is initially one order of magnitude higher than in the dispersed plumes, because of its vorticized nature. It means that the local SO₂ concentration is the critical factor limiting sulfate aerosols growth, and not the total eruption SO₂ 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.