Aerosol dynamic processes in the Hunga plume in January 2022: Does water vapor accelerate aerosol aging?

Abstract. The 2022 Hunga eruption injected an unprecedented amount of 150 Tg of water vapor into the stratosphere, accelerating SO₂ oxidation and sulfate aerosol formation. Despite releasing less ash than previous eruptions of similar magnitude, the role of ash in the early plume and its rapid removal remains unclear. We performed experiments with the ICOsahedral Nonhydrostatic model with Aerosols and Reactive Tracers (ICON-ART) to better understand the role of water vapor, SO₂ and ash emission, aerosol-radiation interaction, and aerosol dynamical processes (nucleation, condensation, coagulation) in the Hunga plume in the first week after the eruption. Furthermore, we compared our results to satellite observations to validate SO₂ oxidation and aerosol dynamical processes. Our results show that about 1.2 Tg SO₂ emission as well as water vapor emission is necessary to explain both the SO₂ column loadings and sulfate aerosol optical depth during the first week after the eruption. Although the model reproduces well the development of SO₂ and sulfate aerosols, the aerosol dynamics alone cannot explain the ash removal after the eruption, as was seen in satellite images. However, some of the ash might not be detected because of the exceptionally strong coating of the ash particles. Both, the strong coating and a doubling of the sulfate effective radii within one week, occur only when the water vapor emission is considered in the chemistry. Furthermore, aerosol-radiation interaction warms the plume and reduces or, depending on the experiments, even reverses the descent of the water vapor plume due to radiative cooling.