Following the Hunga Tonga–Hunga Ha’apai (HTHH) eruption in January 2022, stratospheric ozone depletion was observed in the Southern Hemisphere mid-latitudes and Antarctica during the 2022 austral wintertime and springtime. This eruption injected sulfur dioxide and unprecedented amounts of water vapor into the stratosphere. This work examines and quantifies the chemistry contribution of the volcanic materials to the ozone depletion using chemistry-climate model simulations with nudged meteorology. Simulated 2022 ozone and nitrogen oxides (NOx) anomalies show a good agreement with satellite observations. We find that chemistry only contributes up to 6% and 20% ozone destruction at mid-latitudes wintertime and Antarctic springtime respectively. The majority of the ozone depletion is attributed to the internal variability and dynamical changes forced by the eruption. Both the simulation and observations show a significant NOx reduction associated with the HTHH aerosol plume, indicating the enhanced dinitrogen pentoxide hydrolysis on sulfate aerosol.

Chemistry transport models (CTMs) are essential tools for characterizing and predicting the role of atmospheric composition and chemistry in Earth’s climate system. This study demonstrates the use of airborne in situ observations to diagnose the representation of atmospheric composition by global CTMs. Process-based diagnostics are developed which minimize the spatial and temporal sampling differences between airborne in situ measurements and CTM grid points. The developed diagnostics make use of dynamical and chemical vertical coordinates as a means of highlighting areas where focused model improvement is needed. The chosen process is the chemical impact of the Asian summer monsoon (ASM), where deep convection serves a unique pathway for rapid transport of surface emissions and pollutants to the stratosphere. Two global CTM configurations are examined for their representation of the ASM upper troposphere and lower stratosphere (UTLS), using airborne observations collected over south Asia. Application of the developed diagnostics to the CTMs reveals the limitations of zonally-averaged surface boundary conditions for species with sufficiently short tropospheric lifetimes, and that species whose stratospheric loss rates are dominated by photolysis have excellent agreement compared to that observed. Overall, the diagnostics demonstrate the strength of airborne observations toward improving model predictions, and highlight the utility of highly-resolved CTMs to improve the understanding of reactive transport of anthropogenic pollutants to the stratosphere.

Following the Hunga Tonga–Hunga Ha’apai (HTHH) eruption in January 2022, a significant reduction in stratospheric hydrochloric acid (HCl) was observed in the Southern Hemisphere mid-latitudes during the latter half of 2022, suggesting potential chlorine activation. The objective of this study is to comprehensively understand the substantial loss of HCl in the aftermath of HTHH. Satellite measurements along with a global chemistry-climate model are employed for the analysis. We find strong agreement of 2022 anomalies between the modeled and the measured data. The observed tracer-tracer relations between N2O and HCl indicate a significant role of chemical processing in the observed HCl reduction, especially during the austral winter of 2022. Further examining the roles of chlorine gas-phase and heterogeneous chemistry, we find that heterogeneous chemistry emerges as the primary driver for the chemical loss of HCl, with the reaction between HOBr and HCl on sulfate aerosols identified as the dominant loss process.