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

Year: 2011

Authors: Weigel R., Borrmann S., Kazil J., Minikin A., Stohl A., Wilson J.C., Reeves J.M., Kunkel D., de Reus M., Frey W., Lovejoy E.R., Volk C.M., Viciani S., D’Amato F., Schiller C., Peter T., Schlager H., Cairo F., Law K.S., Shur G.N., Belyaev G.V., Curtius J.

Autors Affiliation: Institut für Physik der Atmosphäre, Johannes Gutenberg-Universität, Mainz, Germany; Abteilung Partikelchemie, Max-Planck-Institut für Chemie, Mainz, Germany; Cooperative Institute for Research in Environmental Sciences (CIRES), University of Colorado, Boulder, Colorado, USA; NOAA Earth System Research Laboratory, Boulder, Colorado, USA; Institut für Physik der Atmosphäre, Deutsches Zentrum für Luft- und Raumfahrt (DLR), Oberpfaffenhofen, Germany; Norwegian Institute for Air Research (NILU), Kjeller, Norway; Department of Engineering, University of Denver, Denver, Colorado, USA; Institut für Atmosphärenphysik, Bergische Universität Wuppertal, Germany; CNR-INO, Firenze, Italy; Institut für Energie- und Klimaforschung – Stratosphäre, Forschungszentrum Jülich, Germany; Institute for Atmospheric and Climate Science, Eidgenössische Technische Hochschule (ETH), Zürich, Switzerland; CNR-ISAC, Italy; UPMC Univ. Paris 06, France; Université Versailles St-Quentin Paris, France; CNRS/INSU, UMR 8190, LATMOS-IPSL, Paris, France; Central Aerological Observatory, Dolgoprudny, Moskow Region, Russia; MDB-Myasishchev Design Bureau, Zhukovsky-5, Moscow Region, Russia

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.


Volume: 11 (18)      Pages from: 9983  to: 10010

More Information: The TROCCINOX and SCOUT-O3 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.
KeyWords: aerosol formation; air mass; carbon monoxide; cloud; concentration (composition); condensation; convective system; nucleation; particulate matter; potential temperature; tropical environment; troposphere, Australia; Central America; South America; West Africa, Falconidae
DOI: 10.5194/acp-11-9983-2011

Citations: 54
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