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| Titel |
Aerosols in the tropical and subtropical UT/LS: in-situ measurements of submicron particle abundance and volatility |
| VerfasserIn |
S. Borrmann, D. Kunkel, R. Weigel, A. Minikin, T. Deshler, J. C. Wilson, J. Curtius, C. M. Volk, C. D. Homan, A. Ulanovsky, F. Ravegnani, S. Viciani, G. N. Shur, G. V. Belyaev, K. S. Law, F. Cairo |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 10, no. 12 ; Nr. 10, no. 12 (2010-06-23), S.5573-5592 |
| Datensatznummer |
250008571
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| Publikation (Nr.) |
 copernicus.org/acp-10-5573-2010.pdf |
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| Zusammenfassung |
| Processes occurring in the tropical upper troposphere (UT), the Tropical
Transition Layer (TTL), and the lower stratosphere (LS) are of importance
for the global climate, for stratospheric dynamics and air chemistry, and
for their influence on the global distribution of water vapour, trace gases
and aerosols. In this contribution we present aerosol and trace gas
(in-situ) measurements from the tropical UT/LS over Southern Brazil,
Northern Australia, and West Africa. The instruments were operated on board
of the Russian high altitude research aircraft M-55 "Geophysica" and the
DLR Falcon-20 during the campaigns TROCCINOX (Araçatuba, Brazil,
February 2005), SCOUT-O3 (Darwin, Australia, December 2005), and SCOUT-AMMA
(Ouagadougou, Burkina Faso, August 2006). The data cover submicron particle
number densities and volatility from the COndensation PArticle counting
System (COPAS), as well as relevant trace gases like N2O, ozone, and
CO. We use these trace gas measurements to place the aerosol data into a
broader atmospheric context. Also a juxtaposition of the submicron particle
data with previous measurements over Costa Rica and other tropical locations
between 1999 and 2007 (NASA DC-8 and NASA WB-57F) is provided. The submicron
particle number densities, as a function of altitude, were found to be
remarkably constant in the tropical UT/LS altitude band for the two decades
after 1987. Thus, a parameterisation suitable for models can be extracted
from these measurements. Compared to the average levels in the period
between 1987 and 2007 a slight increase of particle abundances was found for
2005/2006 at altitudes with potential temperatures, Θ, above 430 K.
The origins of this increase are unknown except for increases measured
during SCOUT-AMMA. Here the eruption of the Soufrière Hills volcano in
the Caribbean caused elevated particle mixing ratios. The vertical profiles
from Northern hemispheric mid-latitudes between 1999 and 2006 also are
compact enough to derive a parameterisation. The tropical profiles all show
a broad maximum of particle mixing ratios (between Θ≈340 K and 390 K)
which extends from below the TTL to above the thermal
tropopause. Thus these particles are a "reservoir" for vertical transport
into the stratosphere. The ratio of non-volatile particle number density to
total particle number density was also measured by COPAS. The vertical
profiles of this ratio have a maximum of 50% above 370 K over Australia
and West Africa and a pronounced minimum directly below. Without detailed
chemical composition measurements a reason for the increase of non-volatile
particle fractions cannot yet be given. However, half of the particles from
the tropical "reservoir" contain compounds other than sulphuric acid
and water. Correlations of the measured aerosol mixing ratios with N2O
and ozone exhibit compact relationships for the tropical data from
SCOUT-AMMA, TROCCINOX, and SCOUT-O3. Correlations with CO are more scattered
probably because of the connection to different pollution source regions. We
provide additional data from the long distance transfer flights to the
campaign sites in Brazil, Australia, and West-Africa. These were executed
during a time window of 17 months within a period of relative volcanic
quiescence. Thus the data represent a "snapshot picture" documenting the
status of a significant part of the global UT/LS fine aerosol at low
concentration levels 15 years after the last major (i.e., the 1991 Mount
Pinatubo) eruption. The corresponding latitudinal distributions of the
measured particle number densities are presented in this paper to provide
data of the UT/LS background aerosol for modelling purposes. |
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