The impact of the Hunga eruption on the 2023 Antarctic ozone hole: contrasting effects in the core and edge regions of the polar vortex

Abstract. The January 2022 Hunga eruption injected an exceptional 150 Tg of water vapour (H₂O) into the stratosphere causing an enhancement not observed previously within the satellite era, with extensive and ongoing effects. From global chemical transport model simulations, we further assess the high-latitude H₂O enhancement caused by the eruption, and how it influenced the 2023 Antarctic ozone depletion across two vortex regimes: the cold core and the less cold, and more insolated vortex edge region. Our simulations show the H₂O chemical impacts arose mainly from the H₂O enhancement promoting earlier formation of polar stratospheric clouds (PSCs), which in turn enhanced chlorine activation and subsequent ozone loss. We also show ice PSC dehydration in the vortex core limited Hunga’s chemical effects to occur for only the first 25 % of the vortex season; consequently, the edge region experienced the largest chemical impact to ozone depletion in 2023. Overall, the H₂O enhancement increased Antarctic ozone hole area by 7 % but remaining within the historical variability over the past two decades. Sensitivity simulations including the Hunga sulfate aerosol show H₂O-driven heterogeneous chlorine activation on additional PSCs, dominated the chemical impacts of Hunga on polar ozone, with only minor impact from activation on volcanic sulfate aerosol. Our results highlight that while water-rich large volcanic eruptions can worsen polar ozone depletion, the magnitude of the impact is strongly influenced by stratospheric temperatures through dehydration. This suggests that less cold vortex environments, e.g. the Arctic, may experience larger relative changes in chlorine activation under similar conditions.