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@ARTICLE{Mller:842031,
      author       = {Müller, Rolf and Grooss, Jens-Uwe and Zafar, Abdul Mannan
                      and Lehmann},
      title        = {{T}he maintenance of elevated active chlorine levels in the
                      {A}ntarctic lower straosphere through {HC}l null cycles},
      journal      = {Atmospheric chemistry and physics / Discussions},
      volume       = {17},
      issn         = {1680-7367},
      address      = {Katlenburg-Lindau},
      publisher    = {EGU},
      reportid     = {FZJ-2018-00315},
      pages        = {833},
      year         = {2017},
      abstract     = {The Antarctic ozone hole arises from ozone destruction
                      driven by elevated levels of ozone destroying ("active")
                      chlorine in Antarctic spring. These elevated levels of
                      active chlorine have to be formed first and then maintained
                      throughout the period of ozone destruction. It is a matter
                      of debate, how this maintenance of active chlorine is
                      brought about in Antarctic spring, when the rate of
                      formation of HCl (considered to be the main chlorine
                      deactivation mechanism in Antarctica) is extremely high.
                      Here we show that in the heart of the ozone hole
                      (16–18 km or 100–70 hPa, in the core of the vortex),
                      high levels of active chlorine are maintained by effective
                      chemical cycles (referred to as HCl null-cycles hereafter).
                      In these cycles, the formation of HCl is balanced by
                      immediate reactivation, i.e. by immediate reformation of
                      active chlorine. Under these conditions, polar stratospheric
                      clouds sequester HNO3 and thereby cause NO2 concentrations
                      to be low. These HCl null-cycles allow active chlorine
                      levels to be maintained in the Antarctic lower stratosphere
                      and thus rapid ozone destruction to occur. For the observed
                      almost complete activation of stratospheric chlorine in the
                      lower stratosphere, the heterogeneous reaction
                      HCl + HOCl, the production of HOCl via HO2 + ClO,
                      with the HO2 resulting from CH2O photolysis, is essential.
                      These results are important for assessing the impact of
                      changes of the future stratospheric composition on the
                      recovery of the ozone hole. Our simulations indicate that,
                      in the lower stratosphere, future increased methane
                      concentrations will not lead to enhanced chlorine
                      deactivation (through the reaction
                      CH4 + Cl → HCl + CH3) and that extreme ozone
                      destruction to levels below ≈ 0.1 ppm will occur until
                      mid-century.},
      cin          = {IEK-7},
      ddc          = {550},
      cid          = {I:(DE-Juel1)IEK-7-20101013},
      pnm          = {244 - Composition and dynamics of the upper troposphere and
                      middle atmosphere (POF3-244)},
      pid          = {G:(DE-HGF)POF3-244},
      typ          = {PUB:(DE-HGF)16},
      doi          = {10.5194/acp-2017-833},
      url          = {https://juser.fz-juelich.de/record/842031},
}