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@ARTICLE{Weigel:894410,
      author       = {Weigel, Ralf and Mahnke, Christoph and Baumgartner, Manuel
                      and Dragoneas, Antonis and Vogel, Bärbel and Ploeger, Felix
                      and Viciani, Silvia and D'Amato, Francesco and Bucci, Silvia
                      and Legras, Bernard and Luo, Beiping and Borrmann, Stephan},
      title        = {{I}n situ observation of new particle formation ({NPF}) in
                      the tropical tropopause layer of the 2017 {A}sian monsoon
                      anticyclone – {P}art 1: {S}ummary of {S}trato{C}lim
                      results},
      journal      = {Atmospheric chemistry and physics},
      volume       = {21},
      number       = {15},
      issn         = {1680-7324},
      address      = {Katlenburg-Lindau},
      publisher    = {EGU},
      reportid     = {FZJ-2021-03210},
      pages        = {11689 - 11722},
      year         = {2021},
      abstract     = {During the monsoon season of the year 2017 the airborne
                      StratoClim mission took place in Kathmandu, Nepal, with
                      eight mission flights of the M-55 Geophysica in the upper
                      troposphere–lower stratosphere (UTLS) of the Asian monsoon
                      anticyclone (AMA) over northern India, Nepal, and
                      Bangladesh. More than 100 events of new particle formation
                      (NPF) were observed. In total, more than 2 h of flight
                      time was spent under NPF conditions as indicated by the
                      abundant presence of nucleation-mode aerosols, i.e. with
                      particle diameters dp smaller than 15 nm, which were
                      detected in situ by means of condensation nuclei counting
                      techniques. Mixing ratios of nucleation-mode particles (nnm)
                      of up to ∼ 50 000 mg−1 were measured at heights of
                      15–16 km (θ ≈ 370 K). NPF was most frequently
                      observed at ∼ 12–16 km altitude
                      (θ ≈ 355–380 K) and mainly below the tropopause.
                      Resulting nnm remained elevated (∼ 300–2000 mg−1)
                      up to altitudes of ∼ 17.5 km (θ ≈ 400 K),
                      while under NPF conditions the fraction (f) of
                      sub-micrometre-sized non-volatile residues
                      (dp > 10 nm) remained below $50 \%.$ At
                      ∼ 12–14 km (θ ≈ 355–365 K) the minimum of
                      f $(< 15 \%)$ was found, and underneath, the median f
                      generally remains below $25 \%.$ The persistence of
                      particles at nucleation-mode sizes is limited to a few
                      hours, mainly due to coagulation, as demonstrated by a
                      numerical simulation. The frequency of NPF events observed
                      during StratoClim 2017 underlines the importance of the AMA
                      as a source region for UTLS aerosols and for the formation
                      and maintenance of the Asian tropopause aerosol layer
                      (ATAL). The observed abundance of NPF-produced
                      nucleation-mode particles within the AMA is not
                      unambiguously attributable to (a) specific source regions in
                      the boundary layer (according to backward trajectory
                      analyses), or (b) the direct supply with precursor material
                      by convective updraught (from correlations of NPF with
                      carbon monoxide), or (c) the recent release of NPF-capable
                      material from the convective outflow (according to air mass
                      transport times in the tropical tropopause layer, TTL).
                      Temperature anomalies with ΔT of 2 K (peak-to-peak
                      amplitude), as observed at a horizontal wavelength of
                      ∼ 70–100 km during a level flight of several hours,
                      match with NPF detections and represent an additional
                      mechanism for local increases in supersaturation of the NPF
                      precursors. Effective precursor supply and widely
                      distributed temperature anomalies within the AMA can explain
                      the higher frequency of intense NPF observed during
                      StratoClim 2017 than all previous NPF detections with COPAS
                      (COndensation PArticle counting System) at TTL levels over
                      Brazil, northern Australia, or West Africa.},
      cin          = {IEK-7},
      ddc          = {550},
      cid          = {I:(DE-Juel1)IEK-7-20101013},
      pnm          = {2112 - Climate Feedbacks (POF4-211) / 2111 - Air Quality
                      (POF4-211)},
      pid          = {G:(DE-HGF)POF4-2112 / G:(DE-HGF)POF4-2111},
      typ          = {PUB:(DE-HGF)16},
      UT           = {WOS:000683773600002},
      doi          = {10.5194/acp-21-11689-2021},
      url          = {https://juser.fz-juelich.de/record/894410},
}