Comparison of inorganic chlorine in the Antarctic and Arctic lowermost stratosphere by separate late winter aircraft measurements

• Published in: Atmospheric Chemistry and Physics
• Main Authors: M. Jesswein, H. Bozem, H.-C. Lachnitt, P. Hoor, T. Wagenhäuser, T. Keber, T. Schuck, A. Engel
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications 2021
• Subjects: Physics; QC1-999; Chemistry; QD1-999; Antarctic; Arctic; Austral; The Antarctic; Antarc*
• Online Access: https://doi.org/10.5194/acp-21-17225-2021; https://doaj.org/article/a11b4302f5b24cd5badf62662409f446

Stratospheric inorganic chlorine (Cl y ) is predominantly released from long-lived chlorinated source gases and, to a small extent, very short-lived chlorinated substances. Cl y includes the reservoir species (HCl and ClONO 2 ) and active chlorine species (i.e., ClO x ). The active chlorine species drive catalytic cycles that deplete ozone in the polar winter stratosphere. This work presents calculations of inorganic chlorine (Cl y ) derived from chlorinated source gas measurements on board the High Altitude and Long Range Research Aircraft (HALO) during the Southern Hemisphere Transport, Dynamic and Chemistry (SouthTRAC) campaign in austral late winter and early spring 2019. Results are compared to Cl y in the Northern Hemisphere derived from measurements of the POLSTRACC-GW-LCYCLE-SALSA (PGS) campaign in the Arctic winter of 2015/2016. A scaled correlation was used for PGS data, since not all source gases were measured. Using the SouthTRAC data, Cl y from a scaled correlation was compared to directly determined Cl y and agreed well. An air mass classification based on in situ N 2 O measurements allocates the measurements to the vortex, the vortex boundary region, and midlatitudes. Although the Antarctic vortex was weakened in 2019 compared to previous years, Cl y reached 1687±19 ppt at 385 K; therefore, up to around 50 % of total chlorine was found in inorganic form inside the Antarctic vortex, whereas only 15 % of total chlorine was found in inorganic form in the southern midlatitudes. In contrast, only 40 % of total chlorine was found in inorganic form in the Arctic vortex during PGS, and roughly 20 % was found in inorganic form in the northern midlatitudes. Differences inside the two vortices reach as much as 540 ppt, with more Cl y in the Antarctic vortex in 2019 than in the Arctic vortex in 2016 (at comparable distance to the local tropopause). To our knowledge, this is the first comparison of inorganic chlorine within the Antarctic and Arctic polar vortices. Based on the results of these two campaigns, ...