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The eruption of the Hunga Tonga‐Hunga Ha'apai volcano on 15 January 2022 was one of the most explosive eruptions of the last decades. The amount of water vapor injected into the stratosphere was unprecedented in the observational record, increasing the stratospheric water vapor burden by about 10%. Using model runs from the ATLAS chemistry and transport model and Microwave Limb Sounder (MLS) satellite observations, we show that while 20%–40% more water vapor than usual was entrained into the Antarctic polar vortex in 2023 as it formed, the direct chemical effect of the increased water vapor on Antarctic ozone depletion in June through October was minor (less than 4 DU). This is because low temperatures in the vortex, as occur every year in the Antarctic, limit water vapor to the saturation pressure and thus reset any anomalies through the process of dehydration before they can affect ozone loss. The eruption of the Hunga Tonga‐Hunga Ha'apai volcano on 15 January 2022 was one of the most explosive eruptions of the last decades. An amount of water vapor unprecedented in the observational record was injected into the stratosphere, increasing the total stratospheric water vapor mass by about 10%. Using model runs and satellite observations, we show that while the dispersion of the plume increased water vapor in the Antarctic in 2023 by 20%–40% at the beginning of the ozone hole season compared to earlier years, the effect of the increased water vapor on the Antarctic ozone hole was minor. This is because low temperatures in the vortex, as occur every year in the Antarctic, limit water vapor due to condensation and thus reset any anomalies before they can affect ozone loss. The Hunga Tonga‐Hunga Ha'apai eruption increased water vapor in the emerging Antarctic vortex in 2023 by 20%–40% compared to earlier yearsThe increased water vapor from Hunga Tonga had a minor effect on Antarctic ozone depletion through the end of October (less than 4 DU)This minor effect is due to low, but not unusual, vortex temperatures that reset water vapor anomalies before they could impact ozone loss The Hunga Tonga‐Hunga Ha'apai eruption increased water vapor in the emerging Antarctic vortex in 2023 by 20%–40% compared to earlier years The increased water vapor from Hunga Tonga had a minor effect on Antarctic ozone depletion through the end of October (less than 4 DU) This minor effect is due to low, but not unusual, vortex temperatures that reset water vapor anomalies before they could impact ozone loss

The rise of ammonia emissions in Asia is predicted to increase radiative cooling and air pollution by forming ammonium nitrate particles in the lower troposphere. There is, however, a severe lack of knowledge about ammonia and ammoniated aerosol particles in the upper troposphere and their possible effects on the formation of clouds. Here we employ satellite observations and high-altitude aircraft measurements, combined with atmospheric trajectory simulations and cloud-chamber experiments, to demonstrate the presence of ammonium nitrate particles and also track the source of the ammonia that forms into the particles. We found that during the Asian monsoon period, solid ammonium nitrate particles are surprisingly ubiquitous in the upper troposphere from the Eastern Mediterranean to the Western Pacific—even as early as in 1997. We show that this ammonium nitrate aerosol layer is fed by convection that transports large amounts of ammonia from surface sources into the upper troposphere. Impurities of ammonium sulfate allow the crystallization of ammonium nitrate even in the conditions, such as a high relative humidity, that prevail in the upper troposphere. Solid ammonium nitrate particles in the upper troposphere play a hitherto neglected role in ice cloud formation and aerosol indirect radiative forcing. Solid ammonium nitrate particles are formed in the upper troposphere during the Asian monsoons, which bring large amounts of ground ammonia to this altitude, according to integrated analyses of measurements on ammoniated aerosol, together with model simulations.