Stratospheric ozone depletion inside the volcanic plume shortly after the 2022 Hunga Tonga eruption

Zhu, Yunqian ; Portmann, Robert W. ; Kinnison, Douglas ; Toon, Owen Brian ; Millán, Luis ; Zhang, Jun ; Vömel, Holger ; Tilmes, Simone ; Bardeen, Charles G. ; Wang, Xinyue ; Evan, Stephanie ; Randel, William J. ; Rosenlof, Karen H.

Année de publication
2023
Résumé
<p align=justify>Near-term in-plume ozone depletion was observed for about 10 d by the Aura Microwave Limb Sounder (MLS) right after the January 2022 Hunga Tonga-Hunga Ha'apai (HTHH) eruption. This work analyzes the dynamic and chemical causes of this ozone depletion. The results show that the large water injection (∼ 150 Tg) from the HTHH eruption, with ∼ 0.0013 Tg injection of ClO (or ∼ 0.0009 Tg of HCl), causes ozone loss due to strongly enhanced HOx and ClOx cycles and their interactions. Aside from the gas-phase chemistry, the heterogeneous reaction rate for HOCl + HCl → Cl2 + H2O increases to 104 cm−3 s−1 and is a major cause of chlorine activation, making this event unique compared with the springtime polar ozone depletion where HCl + ClONO2 is more important. The large water injection causes relative humidity over ice to increase to 70 %-100 %, decreases the H2SO4  H2O binary solution weight percent to 35 % compared with the 70 % ambient value, and decreases the plume temperature by 2-6 K. These changes lead to high heterogeneous reaction rates. Plume lofting of ozone-poor air is evident during the first 2 d after the eruption, but ozone concentrations quickly recover because its chemical lifetime is short at 20 hPa. With such a large seawater injection, we expect that ∼ 5 Tg Cl was lifted into the stratosphere by the HTHH eruption in the form of NaCl, but only ∼ 0.02 % of that remained as active chlorine in the stratosphere. Lightning NOx changes are probably not the reason for the HTHH initial in-plume O3 loss.</p>
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