Chlorine partitioning near the polar vortex edge observed with ground-based FTIR and satellites at Syowa Station, Antarctica in 2007 and 2011

We retrieved lower stratospheric vertical profiles of O₃, HNO₃, and HCl from solar spectra taken with a ground-based Fourier-Transform infrared spectrometer (FTIR) installed at Syowa Station, Antarctica (69.0°S, 39.6°E) from March to December 2007 and September to November 2011.  This was the first continuous measurements of chlorine species throughout the ozone hole period from the ground in Antarctica.  We analyzed temporal variation of these species combined with ClO, HCl, and HNO₃ data taken with the Aura/MLS (Microwave Limb Sounder) satellite sensor, and ClONO₂ data taken with the Envisat/MIPAS (The Michelson Interferometer for Passive Atmospheric Sounding) satellite sensor at 18 and 22 km over Syowa Station.  HCl and ClONO₂ decrease occurred from the end of May at both 18 and 22 km, and eventually in early winter, both HCl and ClONO₂ were almost depleted.  When the sun returned to Antarctica in spring, enhancement of ClO and gradual O₃ destruction were observed.  During the ClO enhanced period, negative correlation between ClO and ClONO₂ was observed in the time-series of the data at Syowa Station.  This negative correlation was associated with the relative distance between Syowa Station and the edge of the polar vortex.  We used MIROC3.2 Chemistry-Climate Model (CCM) results to investigate the behavior of whole chlorine and related species inside the polar vortex and the boundary region in more detail.  From CCM model results, rapid conversion of chlorine reservoir species (HCl and ClONO₂) into Cl₂, gradual conversion of Cl₂ into Cl₂O₂, increase of HOCl in winter period, increase of ClO when sunlight became available, and conversion of ClO into HCl, was successfully reproduced.  HCl decrease in the winter polar vortex core continued to occur due to both transport of ClONO₂ from the subpolar region to higher latitudes, providing a flux of ClONO₂ from more sunlit latitudes into the polar vortex, and the heterogeneous reaction of HCl with HOCl.  Temporal variation of chlorine species over Syowa Station was affected by both heterogeneous chemistries related to Polar Stratospheric Cloud (PSC) occurrence inside the polar vortex, and transport of a NOx-rich airmass from the polar vortex boundary region which can produce additional ClONO₂ by reaction of ClO with NO₂.  The deactivation pathways from active chlorine into reservoir species (HCl and/or ClONO₂) were confirmed to be highly dependent on the availability of ambient O₃.  At 18 km where most ozone was depleted, most ClO was converted to HCl.  At 22km where some O₃ was available, additional increase of ClONO₂ from pre-winter value occurred, similar as in the Arctic.