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@ARTICLE{Weigel:17010,
      author       = {Weigel, R. and Borrmann, S. and Kazil, J. and Minikin, A.
                      and Stohl, A. and Wilson, J.C. and Reeves, J.M. and Kunkel,
                      D. and de Reus, M. and Frey, W. and Lovejoy, E.R. and Volk,
                      C.M. and Viciani, S. and D'Amato, F. and Schiller, C. and
                      Schlager, H. and Cairo, F. and Law, K.S. and Shur, G.NN. and
                      Belyaev, G.V. and Curtius, J.},
      title        = {{I}n situ observations of new particle formation in the
                      tropical upper troposphere: {T}he role of clouds and the
                      nucleation mechanism},
      journal      = {Atmospheric chemistry and physics},
      volume       = {11},
      issn         = {1680-7316},
      address      = {Katlenburg-Lindau},
      publisher    = {EGU},
      reportid     = {PreJuSER-17010},
      pages        = {9983 - 10010},
      year         = {2011},
      note         = {The TROCCINOX and SCOUT-O<INF>3</INF> projects were funded
                      by the EC under Contracts No. EVK2-CT-2001-00122 and
                      505390-GOCE-CT-2004-505390. The M-55 Geophysica campaigns
                      also were supported by the EEIG-Geophysica Consortium,
                      CNRS-INSU, EC Integrated Projects AMMA-EU (Contract No.
                      004089-2), and by the DLR. Based on a French initiative,
                      AMMA was funded by several research agencies from France,
                      the United Kingdom, the United States, Africa, Germany, and
                      in particular from the European Community Sixth Framework
                      Program (AMMA-EU). For us significant support also was
                      provided from the Max-Planck-Society. Also we acknowledge
                      logistical support from the AMMA Operations Centre in
                      Niamey, Niger. The local authorities, scientists, and staff
                      in Aracatuba (Brazil), Darwin (Australia) and Ouagadougou
                      (Burkina Faso) were extraordinarily helpful for conducting
                      the campaigns. We thank T. Drabo (Ouagadougou), S. Balestri
                      and the entire Geophysica crew, especially the pilots and
                      engineers. Essential technical support for our instruments
                      was provided by T. Bottger, W. Schneider, C. von Glahn, and
                      M. Flanz, and is most gratefully acknowledged. H. Ruba, T.
                      Hamburger and B. Weinzierl are acknowledged for supporting
                      the CPC measurements aboard the DLR Falcon-20. We thank U.
                      Schumann (DLR) for the coordination and the flight planning
                      during TROCCINOX. J. Kazil is supported by the NOAA OAR
                      Climate Program Office grant NA08OAR4310566. The flight
                      missions of the NASA WB-57F aircraft (Pre-AVE, AVE 0506,
                      Cr-AVE and TC4) in the years 2004 to 2007 during which the
                      University of Denver NMASS-FCAS instrument participated have
                      been supported by the NASA Earth Science Division.},
      abstract     = {New particle formation (NPF), which generates nucleation
                      mode aerosol, was observed in the tropical Upper Troposphere
                      (UT) and Tropical Tropopause Layer (TTL) by in situ airborne
                      measurements over South America (January-March 2005),
                      Australia (November-December 2005), West Africa (August
                      2006) and Central America (2004-2007). Particularly intense
                      NPF was found at the bottom of the TTL. Measurements with a
                      set of condensation particle counters (CPCs) with different
                      d(p50) $(50\%$ lower size detection efficiency diameter or
                      "cut-off diameter") were conducted on board the M-55
                      Geophysica in the altitude range of 12.0-20.5 km and on
                      board the DLR Falcon-20 at up to 11.5 km altitude. On board
                      the NASA WB-57F size distributions were measured over
                      Central America in the 4 to 1000 nm diameter range with a
                      system of nucleation mode aerosol spectrometers. Nucleation
                      mode particle concentrations (NNM) were derived from these
                      measurements which allow for identifying many NPF events
                      with N-NM in the range of thousands of particles per cm(3).
                      Over Australia and West Africa, we identified NPF in the
                      outflow of tropical convection, in particular of a Mesoscale
                      Convective System (MCS). Newly formed particles with N-NM >
                      1000 cm(-3) were found to coexist with ice cloud particles
                      (d(p) > 2 mu m) as long as cloud particle concentrations
                      remained below 2 cm(-3). The occurrence of NPF within the
                      upper troposphere and the TTL was generally confined within
                      340 K to 380 K potential temperature, but NPF was of
                      particular strength between 350 K and 370 K (i.e. similar to
                      1-4 km below the cold point tropopause). Analyses of the
                      aerosol volatility (at 250 degrees C) show that in the TTL
                      on average $75-90\%$ of the particles were volatile,
                      compared to typically only $50\%$ in the extra-tropical UT,
                      indicative for the particles to mainly consist of H2SO4-H2O
                      and possibly organic compounds. Along two flight segments
                      over Central and South America (24 February 2005 and 7
                      August 2006, at 12.5 km altitude) in cloud free air, above
                      thin cirrus, particularly high N-NM were observed. Recent
                      lifting had influenced the probed air masses, and N-NM
                      reached up to 16 000 particles cm(-3) (ambient
                      concentration). A sensitivity study using an aerosol model,
                      which includes neutral and ion induced nucleation processes,
                      simulates N-NM in reasonable agreement with the in situ
                      observations of clear-air NPF. Based on new, stringent
                      multi-CPC criteria, our measurements corroborate the
                      hypothesis that the tropical UT and the TTL are regions
                      supplying freshly nucleated particles. Our findings narrow
                      the altitude of the main source region to the bottom TTL,
                      i.e. to the level of main tropical convection outflow, and,
                      by means of measurements of carbon monoxide, they indicate
                      the importance of anthropogenic emissions in NPF. After
                      growth and/or coalescence the nucleation mode particles may
                      act as cloud condensation nuclei in the tropical UT, or,
                      upon ascent into the stratosphere, contribute to maintain
                      the stratospheric background aerosol.},
      keywords     = {J (WoSType)},
      cin          = {IEK-7},
      ddc          = {550},
      cid          = {I:(DE-Juel1)IEK-7-20101013},
      pnm          = {Atmosphäre und Klima},
      pid          = {G:(DE-Juel1)FUEK491},
      shelfmark    = {Meteorology $\&$ Atmospheric Sciences},
      typ          = {PUB:(DE-HGF)16},
      UT           = {WOS:000295368700037},
      doi          = {10.5194/acp-11-9983-2011},
      url          = {https://juser.fz-juelich.de/record/17010},
}