Evidence of a transient ozone depletion event in the early Hunga plume above the Indian Ocean

Abstract. On 15 January 2022, the Hunga volcano (20.5° S, 175.4° E) erupted, releasing significant amounts of water vapor (H2O) and a moderate quantity of sulfur dioxide into the stratosphere. The resulting volcanic plume traveled westward with the southern hemispheric stratospheric circulation, reaching the Indian Ocean and Réunion (21.1° S, 55.5° E) within days. This study presents the first analysis of Infrared Atmospheric Sounding Interferometer (IASI) ozone data to investigate the impact of the Hunga eruption, and also incorporates Microwave Limb Sounder (MLS) and Ozone Mapping and Profiler Suite Limb Profiler (OMPS-LP) data, as well as ground-based measurements from Réunion. IASI observations revealed a transient ozone depletion event in the first week following the eruption. OMPS-LP aerosol extinction profiles, sun-photometer measurements, and lidar observations characterized the plume's vertical and latitudinal extent, showing its presence over Réunion at altitudes ranging from 26.8 to 29.7 km and its spread across more than 30° longitude and 20° latitude by 21 January. IASI ozone spatial distributions showed marked decreases in total and stratospheric ozone on that date, with the fifth percentile of the anomaly reaching −18.6 DU for total column ozone and −14.5 DU for stratospheric column ozone. A key finding, as shown by MLS profiles, is that the ozone reduction was confined to two separate layers (-0.7±(1σ) 0.6 ppmv in the 14.68–12.12 hPa range, and -0.6±(1σ) 0.5 ppmv in the 31.62–21.54 hPa range), each associated with a distinct aerosol cloud with excess H2O. This layered structure of ozone loss offers new insight into the chemical and radiative effects of the Hunga plume on stratospheric ozone.