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In situ observations of new particle formation in the tropical upper troposphere: the role of clouds and the nucleation mechanism

Weigel, Ralf and Borrmann, Stephan and Kazil, J. and Minikin, Andreas 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, C. and D'Amato, F. and Schiller, C. and Peter, T. and Schlager, Hans and Cairo, F. and Law, K. S. and Shur, G. N. and Belyaev, G. V. and Curtius, J. (2011) In situ observations of new particle formation in the tropical upper troposphere: the role of clouds and the nucleation mechanism. Atmospheric Chemistry and Physics, 11, pp. 9983-10010. European Geosciences Union. DOI: 10.5194/acp-11-9983-2011.

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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 (Januaryâ��March 2005), Australia (Novemberâ��December 2005), West Africa (August 2006) and Central America (2004â��2007). Particularly intense NPF was found at the bottom of the TTL. Measurements with a set of condensation particle counters (CPCs) with different dp50 (50% lower size detection efficiency diameter or "cut-off diameter") were conducted on board the M-55 Geophysica in the altitude range of 12.0â��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 NNM in the range of thousands of particles per cm3. 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 NNM > 1000 cmâ��3 were found to coexist with ice cloud particles (dp > 2 �¼m) as long as cloud particle concentrations remained below 2 cmâ��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. ~1â��4 km below the cold point tropopause). Analyses of the aerosol volatility (at 250 �°C) show that in the TTL on average 75â��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 NNM were observed. Recent lifting had influenced the probed air masses, and NNM reached up to 16 000 particles cmâ��3 (ambient concentration). A sensitivity study using an aerosol model, which includes neutral and ion induced nucleation processes, simulates NNM 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.

Document Type:Article
Title:In situ observations of new particle formation in the tropical upper troposphere: the role of clouds and the nucleation mechanism
AuthorsInstitution or Email of Authors
Weigel, RalfUniv. Mainz, Mainz
Borrmann, StephanMPI für Chemie, Mainz
Kazil, J.Univ of Colorado, Boulder, CO, USA
Minikin, AndreasDLR
Stohl, A.NILU, Kjeller, N
Wilson, J. C.Univ of Denver, Denver, CO, USA
Reeves, J. M.Univ of Denver, Denver, CO, USA
Kunkel, D.MPI für Chemie, Mainz
de Reus, M.Univ. Mainz, Mainz
Frey, W.MPI für Chemie, Mainz
Lovejoy, E. R.Univ of Colorado, Boulder, Colorado, USA
Volk, C. M.Univ. Wuppertal, Wuppertal
Viciani, C.Consiglio Nazionale delle Ricerche, Firenze, I
D'Amato, F.Consiglio Nazionale delle Ricerche, Firenze, I
Schiller, C.FZ, Jülich
Peter, T.ETH, Zürich, CH
Schlager, HansDLR
Cairo, F.ISAC-CNR, I
Law, K. S.CNRS/INSU, Paris, F
Shur, G. N.Central Aerological Observ, Dolgoprudny, Moskow Region, Russia
Belyaev, G. V.MDB, Moscow Region, R
Curtius, J.Univ. Mainz, Mainz
Date:29 September 2011
Journal or Publication Title:Atmospheric Chemistry and Physics
Refereed publication:Yes
In Open Access:Yes
In ISI Web of Science:Yes
Page Range:pp. 9983-10010
Publisher:European Geosciences Union
Keywords:new particle formation, aerosol, Falcon, Geophysica, upper troposphere, tropics, clouds, nucleation
HGF - Research field:Aeronautics, Space and Transport
HGF - Program:Space, Aeronautics, Transport
HGF - Program Themes:Earth Observation, ATM and Operation, Transport System
DLR - Research area:Raumfahrt, Aeronautics, Transport
DLR - Program:R EO - Erdbeobachtung, L AO - Air Traffic Management and Operation, V VS - Verkehrssystem
DLR - Research theme (Project):R - Vorhaben Atmosphären- und Klimaforschung, L - Climate, Weather and Environment, V - Verkehrsentwicklung und Umwelt (old)
Location: Oberpfaffenhofen
Institutes and Institutions:Institute of Atmospheric Physics > Atmospheric Trace Species
Deposited By: Dr.rer.nat. Andreas Minikin
Deposited On:07 Dec 2011 13:59
Last Modified:12 Dec 2013 21:27

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