Abstract
<p>We retrieved lower stratospheric vertical profiles of O<sub>3</sub>, HNO<sub>3</sub>, 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 HNO<sub>3</sub> data taken with the Aura/MLS (Microwave Limb Sounder) satellite sensor, and ClONO<sub>2</sub> 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 ClONO<sub>2</sub> decrease occurred from the end of May at both 18 and 22 km, and eventually in early winter, both HCl and ClONO<sub>2</sub> were almost depleted.  When the sun returned to Antarctica in spring, enhancement of ClO and gradual O<sub>3</sub> destruction were observed.  During the ClO enhanced period, negative correlation between ClO and ClONO<sub>2</sub> 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 ClONO<sub>2</sub>) into Cl<sub>2</sub>, gradual conversion of Cl<sub>2</sub> into Cl<sub>2</sub>O<sub>2</sub>, 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 ClONO<sub>2</sub> from the subpolar region to higher latitudes, providing a flux of ClONO<sub>2</sub> 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 ClONO<sub>2</sub> by reaction of ClO with NO<sub>2</sub>.  The deactivation pathways from active chlorine into reservoir species (HCl and/or ClONO<sub>2</sub>) were confirmed to be highly dependent on the availability of ambient O<sub>3</sub>.  At 18 km where most ozone was depleted, most ClO was converted to HCl.  At 22km where some O<sub>3</sub> was available, additional increase of ClONO<sub>2</sub> from pre-winter value occurred, similar as in the Arctic.</p>
Highlights
Discussion of the detection of the recovery of the Antarctic ozone hole as the result of chlorofluorocarbon (CFC) regulations has been attracting attention
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 satellite sensor at 18 and 22 km over Syowa Station
During the ClO-enhanced period, a negative correlation between ClO and ClONO2 was observed in the time series of the data at Syowa Station
Summary
Discussion of the detection of the recovery of the Antarctic ozone hole as the result of chlorofluorocarbon (CFC) regulations has been attracting attention. Et al, 1999; Santee et al, 2003), which results in an additional increase in ClONO2 than the prewinter value at the time of chlorine deactivation in spring (von Clarmann et al, 1993; Müller et al, 1994; Oelhaf et al, 1994) In this way, the partitioning of the chlorine reservoir in springtime is related to temperature, PSC amounts, ozone, and NO2 concentrations (Santee et al, 2008; Solomon et al, 2015). The ozone and related atmospheric trace gas species have been intensively monitored by several measurement techniques since the discovery of the ozone hole These measurements consist of direct observations by high-altitude aircraft (e.g., Anderson et al, 1989; Ko et al, 1989; Tuck et al, 1995; Jaeglé et al, 1997; Bonne et al, 2000), remote-sensing observations by satellites (e.g., Müller et al, 1996; Michelsen et al, 1999; Höpfner et al, 2004; Dufour et al, 2006; Hayashida et al, 2007), remote-sensing observations of OClO using a UV–visible spectrometer from the ground (Solomon et al, 1987; Kreher et al, 1996), and remote-sensing observations of ClO by a microwave spectrometer from the ground (de Zafra et al, 1989).
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