The impact of dehydration and extremely low HCl values in the Antarctic stratospheric vortex in mid-winter on ozone loss in spring

• Published in: Atmospheric Chemistry and Physics
• Main Authors: Y. Zhang-Liu, R. Müller, J.-U. Grooß, S. Robrecht, B. Vogel, A. M. Zafar, R. Lehmann
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications 2024
• Subjects: Physics; QC1-999; Chemistry; QD1-999; Antarctic; The Antarctic; Antarc*; Antarctica
• Online Access: https://doi.org/10.5194/acp-24-12557-2024; https://doaj.org/article/b0facf1f0b714a2c95b1b26a17bfe5d6

Simulations of Antarctic chlorine and ozone chemistry in previous work show that in the core of the Antarctic vortex (16–18 km, 85–55 hPa, 390–430 K) HCl null cycles (initiated by reactions of Cl with CH 4 and CH 2 O ) are effective. These HCl null cycles cause both HCl molar mixing ratios to remain very low throughout Antarctic winter and spring. They cause ozone-destroying chlorine ( ClO x ) to remain enhanced so that rapid ozone depletion proceeds. Here we investigate the impact of the observed dehydration in Antarctica, which strongly reduces ice formation and the uptake of HNO 3 from the gas phase; however the efficacy of HCl null cycles is not affected. Moreover, also when using the observed very low HCl molar mixing ratios in Antarctic winter as an initial value, HCl null cycles are efficient in maintaining low HCl (and high ClO x ) throughout winter and spring. Further, the reaction CH 3 O 2 +ClO is important for the efficacy of the HCl null cycle initiated by the reaction CH 4 +Cl . Using the current kinetic recommendations instead of earlier ones has very little impact on the simulations. All simulations presented here for the core of the Antarctic vortex show extremely low minimum ozone values (below 50 ppb) in late September to early October in agreement with observations.