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@ARTICLE{Lauther:906264,
      author       = {Lauther, Valentin and Vogel, Bärbel and Wintel, Johannes
                      and Rau, Andrea and Hoor, Peter and Bense, Vera and Müller,
                      Rolf and Volk, C. Michael},
      title        = {{I}n situ observations of {CH}2{C}l2 and {CHC}l3 show
                      efficient transport pathways for very short-lived species
                      into the lower stratosphere via the {A}sian and the {N}orth
                      {A}merican summer monsoon},
      journal      = {Atmospheric chemistry and physics},
      volume       = {22},
      number       = {3},
      issn         = {1680-7316},
      address      = {Katlenburg-Lindau},
      publisher    = {EGU},
      reportid     = {FZJ-2022-01330},
      pages        = {2049 - 2077},
      year         = {2022},
      abstract     = {Efficient transport pathways for ozone-depleting very
                      short-lived substances (VSLSs) from their source regions
                      into the stratosphere are a matter of current scientific
                      debate; however they have yet to be fully identified on an
                      observational basis. Understanding the increasing impact of
                      chlorine-containing VSLSs (Cl-VSLSs) on stratospheric ozone
                      depletion is important in order to validate and improve
                      model simulations and future predictions. We report on a
                      transport study using airborne in situ measurements of the
                      Cl-VSLSs dichloromethane (CH2Cl2) and trichloromethane
                      (chloroform, CHCl3) to derive a detailed description of two
                      transport pathways from (sub)tropical source regions into
                      the extratropical upper troposphere and lower stratosphere
                      (Ex-UTLS) in the Northern Hemisphere (NH) late summer. The
                      Cl-VSLS measurements were obtained in the upper troposphere
                      and lower stratosphere (UTLS) above western Europe and the
                      midlatitude Atlantic Ocean in the frame of the WISE
                      (Wave-driven ISentropic Exchange) aircraft campaign in
                      autumn 2017 and are combined with the results from a
                      three-dimensional simulation of a Lagrangian transport model
                      as well as back-trajectory calculations. Compared to
                      background measurements of similar age we find up to
                      $150 \%$ enhanced CH2Cl2 and up to $100 \%$ enhanced
                      CHCl3 mixing ratios in the extratropical lower stratosphere
                      (Ex-LS). We link the measurements of enhanced CH2Cl2 and
                      CHCl3 mixing ratios to emissions in the region of southern
                      and eastern Asia. Transport from this area to the Ex-LS at
                      potential temperatures in the range of 370–400 K takes
                      about 6–11 weeks via the Asian summer monsoon anticyclone
                      (ASMA). Our measurements suggest anthropogenic sources to be
                      the cause of these strongly elevated Cl-VSLS concentrations
                      observed at the top of the lowermost stratosphere (LMS). A
                      faster transport pathway into the Ex-LS is derived from
                      particularly low CH2Cl2 and CHCl3 mixing ratios in the UTLS.
                      These low mixing ratios reflect weak emissions and a local
                      seasonal minimum of both species in the boundary layer of
                      Central America and the tropical Atlantic. We show that air
                      masses uplifted by hurricanes, the North American monsoon,
                      and general convection above Central America into the
                      tropical tropopause layer to potential temperatures of about
                      360–370 K are transported isentropically within 5–9
                      weeks from the boundary layer into the Ex-LS. This transport
                      pathway linked to the North American monsoon mainly impacts
                      the middle and lower part of the LMS with particularly low
                      CH2Cl2 and CHCl3 mixing ratios. In a case study, we
                      specifically analyze air samples directly linked to the
                      uplift by the Category 5 Hurricane Maria that occurred
                      during October 2017 above the Atlantic Ocean. CH2Cl2 and
                      CHCl3 have similar atmospheric sinks and lifetimes, but the
                      fraction of biogenic emissions is clearly higher for CHCl3
                      than for the mainly anthropogenically emitted CH2Cl2;
                      consequently lower CHCl3 : CH2Cl2 ratios are expected in
                      air parcels showing a higher impact of anthropogenic
                      emissions. The observed CHCl3 : CH2Cl2 ratio suggests
                      clearly stronger anthropogenic emissions in the region of
                      southern and eastern Asia compared to those in the region of
                      Central America and the tropical Atlantic. Overall, the
                      transport of strongly enhanced CH2Cl2 and CHCl3 mixing
                      ratios from southern and eastern Asia via the ASMA is the
                      main factor in increasing the chlorine loading from the
                      analyzed VSLSs in the Ex-LS during the NH late summer. Thus,
                      further increases in Asian CH2Cl2 and CHCl3 emissions, as
                      frequently reported in recent years, will further increase
                      the impact of Cl-VSLSs on stratospheric ozone depletion.},
      cin          = {IEK-7},
      ddc          = {550},
      cid          = {I:(DE-Juel1)IEK-7-20101013},
      pnm          = {2112 - Climate Feedbacks (POF4-211)},
      pid          = {G:(DE-HGF)POF4-2112},
      typ          = {PUB:(DE-HGF)16},
      UT           = {WOS:000759289700001},
      doi          = {10.5194/acp-22-2049-2022},
      url          = {https://juser.fz-juelich.de/record/906264},
}