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

The January 2022 eruption of Hunga Tonga-Hunga Ha’apai (HT-HH) caused the largestenhancement in stratospheric aerosol loading in decades and produced an unprecedentedenhancement in stratospheric water vapor, leading to strong stratospheric cooling thatin turn induced changes in the large-scale circulation. Here we use satellite measurementsof gas-phase constituents together with aerosol extinction to investigate the extent towhich the thick aerosol, excess moisture, and strong cooling enabled heterogeneous chem-ical processing. In the southern tropics, unambiguous signatures of substantial chlorineand nitrogen repartitioning appear over a broad vertical domain almost immediately af-ter the eruption, with depletion of N2O5, NOx, and HCl accompanied by enhancementof HNO3, ClO, and ClONO2. After initially rising steeply, HNO3 and ClO plateau, main-taining fairly constant abundances for several months. These patterns are consistent withthe saturation of N2O5 hydrolysis, suggesting that this reaction is the primary mecha-nism for the observed composition changes. The southern midlatitudes and subtropicsshow similar but weaker enhancements in ClO and ClONO2. In those regions, however,effects of anomalous transport dominate the evolution of HNO3 and HCl, obscuring thesigns of heterogeneous processing. Perturbations in chlorine species are considerably weakerthan those measured in the southern midlatitude stratosphere in 2020 following the Aus-tralian New Year’s fires. The moderate HT-HH-induced enhancements in reactive chlo-rine seen throughout the southern middle and low-latitude stratosphere, far smaller thanthose in typical winter polar vortices, do not lead to appreciable chemical ozone loss; rather,extrapolar lower-stratospheric ozone remains primarily controlled by dynamical processes

2022年1月洪加汤加-洪加哈派（Hunga Tonga-Hunga Ha’apai，HT-HH）火山爆发导致了数十年来平流层气溶胶载荷（stratospheric aerosol loading）的最大增幅，并造成平流层水汽（stratospheric water vapor）的空前增加，进而引发强烈的平流层冷却，而冷却又诱导了大尺度环流（large-scale circulation）的变化。本文利用气相成分（gas-phase constituents）的卫星观测数据及气溶胶消光（aerosol extinction）数据，研究厚气溶胶、过量水汽和强烈冷却在多大程度上促成了非均相化学过程（heterogeneous chemical processing）。在南热带（southern tropics）地区，火山爆发后几乎立即在广阔的垂直范围内出现了氯和氮大量重新分配（chlorine and nitrogen repartitioning）的明确信号——N₂O₅、NOₓ和HCl消耗，同时HNO₃、ClO和ClONO₂增加。HNO₃和ClO在初期急剧上升后趋于平稳，其丰度在数月内保持相对稳定。这些模式与N₂O₅水解饱和现象一致，表明该反应是观测到的成分变化的主要机制。南中纬度和副热带（southern midlatitudes and subtropics）地区的ClO和ClONO₂也出现了类似但较弱的增加。然而，在这些区域，异常输送的影响主导了HNO₃和HCl的演变，掩盖了非均相化学过程的信号。氯物种的扰动明显弱于2020年澳大利亚新年火灾后在南中纬度平流层观测到的扰动。HT-HH火山在整个南中纬度和低纬度平流层引发的活性氯（reactive chlorine）中度增加，远小于典型冬季极涡（winter polar vortices）中的增幅，并未导致显著的化学臭氧损耗（chemical ozone loss）；相反，极外平流层下部的臭氧仍主要受动力过程（dynamical processes）控制。