Strong Evidence of Heterogeneous Processing on Stratospheric Sulfate Aerosol in the Extrapolar Southern Hemisphere Following the 2022 Hunga Tonga‐Hunga Ha'apai Eruption

Abstract

The January 2022 eruption of Hunga Tonga‐Hunga Ha'apai (HT‐HH) caused the largest enhancement in stratospheric aerosol loading in decades and produced an unprecedented enhancement in stratospheric water vapor, leading to strong stratospheric cooling that in turn induced changes in the large‐scale circulation. Here we use satellite measurements of gas‐phase constituents together with aerosol extinction to investigate the extent to which the thick aerosol, excess moisture, and strong cooling enabled heterogeneous chemical processing. In the southern tropics, unambiguous signatures of substantial chlorine and nitrogen repartitioning appear over a broad vertical domain almost immediately after the eruption, with depletion of N2O5, NOx, and HCl accompanied by enhancement of HNO3, ClO, and ClONO2. After initially rising steeply, HNO3 and ClO plateau, maintaining fairly constant abundances for several months. These patterns are consistent with the saturation of N2O5 hydrolysis, suggesting that this reaction is the primary mechanism for the observed composition changes. The southern midlatitudes and subtropics show similar but weaker enhancements in ClO and ClONO2. In those regions, however, effects of anomalous transport dominate the evolution of HNO3 and HCl, obscuring the signs of heterogeneous processing. Perturbations in chlorine species are considerably weaker than those measured in the southern midlatitude stratosphere in 2020 following the Australian New Year's fires. The moderate HT‐HH‐induced enhancements in reactive chlorine seen throughout the southern middle and low‐latitude stratosphere, far smaller than those in typical winter polar vortices, do not lead to appreciable chemical ozone loss; rather, extrapolar lower‐stratospheric ozone remains primarily controlled by dynamical processes.

Stratospheric Climate Anomalies and Ozone Loss Caused by the Hunga Tonga‐Hunga Ha'apai Volcanic Eruption

“…This aligns with the conclusion in Santee et al. (2023) that no appreciable chemical ozone loss occurred in SH midlatitude. We note that while ozone changes in the SO 2 + H 2 O WACCM simulations result from a combination of transport and chemistry effects, it is not simple to separate dynamical and chemical contributions in our coupled simulation.…”

“…The consistency on the timing of circulation changes and LS ozone losses, which both maximize during SH winter (e.g., temperature anomalies in Figure 4 and ozone losses in Figures 8 and 9), is a fingerprint of substantial contribution due to changes in transport. This aligns with the conclusion in Santee et al (2023) that no appreciable chemical ozone loss occurred in SH midlatitude. We note that while ozone changes in the SO 2 + H 2 O WACCM simulations result from a combination of transport and chemistry effects, it is not simple to separate dynamical and chemical contributions in our coupled simulation.…”

Stratospheric Temperature and Ozone Impacts of the Hunga Tonga‐Hunga Ha'apai Water Vapor Injection

“…This contrasts with most of the stratosphere outside of the polar regions which was generally within ±1 σ of the long‐term average in May 2022 (Figure 2b). We note that temperature anomalies derived from MLS version 5 data (not shown) are very similar to those shown in Figure 2 (see also Santee et al., 2023).…”

“…The January 2022 Hunga Tonga-Hunga Ha'apai volcanic eruption increased stratospheric water vapor by ∼10% (∼150 Tg) (Millán et al, 2022) which significantly altered the radiative balance, dynamics, and photochemistry of the stratosphere (Coy et al, 2022;Santee et al, 2023;Schoeberl et al, 2022Schoeberl et al, , 2023Sellitto et al, 2022;Vömel et al, 2022). In this study, we examine how this unique natural perturbation impacted stratospheric temperature and ozone in the first 1-2 years following the eruption and estimate possible future responses over the next decade.…”

“…Water vapor in the stratosphere is a greenhouse gas (Forster & Shine, 1999, 2002; Solomon et al., 2010), and is a source of the OH radical as well as polar stratospheric clouds (PSCs), both of which strongly affect stratospheric ozone (Cohen et al., 1994; Jucks et al., 1998; Solomon et al., 2015). Because of these impacts, the enhanced H 2 O from the HT eruption significantly altered the radiative balance, dynamics, and photochemistry of the stratosphere in the months following the eruption (Coy et al., 2022; Santee et al., 2023; Schoeberl et al., 2022, 2023; Sellitto et al., 2022; Vömel et al., 2022). Given the long lifetime of water vapor in the stratosphere, this perturbation is expected to have a multi‐year impact.…”