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| Titel |
The role of clouds and of neutral as well as ion induced pathway for the new particle formation in the tropical upper troposphere: In-situ measurements from continental South America and West Africa |
| VerfasserIn |
Stephan Borrmann, Ralf Weigel, Jan Kazil, Andreas Minikin, Andreas Stohl, James C. Wilson, Daniel Kunkel, Marian de Reus, Wiebke Frey, Edward R. Lovejoy |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250050979
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| Zusammenfassung |
| New particle formation which generates ultrafine aerosol was observed in the continental
tropical Upper Troposphere/Lower Stratosphere region (UT/LS), particularly within the
Tropical Tropopause Layer (TTL), by in-situ aircraft-borne measurements over South
America (January-March, 2005) and West Africa (August, 2006). Measurements with a set of
condensation particle counters with different dp50 (50Â % detection particle diameter) were
conducted in the altitude range of 12.0-20.5Â km on board the high altitude research
aircraft M-55 “Geophysica” and at up to 11.5Â km altitude on board the research
aircraft DLR Falcon-20. Concentrations of ultrafine particles in the size range of
about 6 to 15Â nm were derived from these measurements and several recent events
of new particle formation (NPF) can be identified. For two flight segments (24
February 2005 and 07 August 2006, at 12.5Â km altitude) when recent lifting had
influenced the probed air mass, concentrations of ultrafine particle reached up to 7700
particles cm-3 (ambient concentration). For clear, cloud free air the measurements are
in reasonable agreement with concentrations of ultrafine particle calculated with
an aerosol model which includes neutral and ion induced nucleation processes.
NPF over South America was observed above thin cirrus clouds while over West
Africa, in the outflow of a Mesoscale Convective System (MCS), newly formed
particles in the range of several hundred per cm3 were found to coexist with ice cloud
particles as long as the concentration of cloud particles (dp > 2 μm) remained below
2Â cm-3. The occurrence of NPF within the upper troposphere and the TTL was
generally confined within an altitude band extending from 340Â K to 380Â K potential
temperature. By means of a heated aerosol inlet line (at 250Ë C) measurements of particle
volatility were performed, which show that within the TTL over South America and
West Africa, on average 10-25Â % of the particles contained non-volatile cores. In
background UT/LS conditions the fractions of non-volatile particles typically range up to
50Â %. Our measurements provide further evidence for the hypothesis according
to which the tropical upper troposphere and the TTL are a major source region
for the stratospheric background aerosol by providing freshly nucleated particles. |
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