Aerosols in the tropical and subtropical UT/LS: in-situ measurements of submicron particle abundance and volatility

Year: 2010

Authors: Borrmann S., Kunkel D., Weigel R., Minikin A., Deshler T., Wilson J. C., Curtius J., Volk C. M., Homan C. D., Ulanovsky A., Ravegnani F., Viciani S., Shur G. N., Belyaev G. V., Law K. S., Cairo F.

Autors Affiliation: Max-Planck-Institute for Chemistry, Particle Chemistry Department, Germany;
Institute for Atmospheric Physics, Johannes-Gutenberg-University, Mainz, Germany;
Institut fur Physik der Atmosphare, DLR, Oberpfaffenhofen, Germany;
Department of Atmospheric Science, University of Wyoming, Laramie, WY, USA;
Department of Mechanical Engineering, Denver University, Denver, CO, USA;
Institute for Atmospheric and Environmental Sciences, Goethe University of Frankfurt, Germany;
Department of Physics, Wuppertal University, Wuppertal, Germany;
Central Aerological Observatory, Dolgoprudny, Moscow Region, Russia;
Institute of Atmospheric Science and Climate, ISAC-CNR, Rome, Italy;
National Institute of Optics (INO), CNR, Florence, Italy;
MDB-Myasishchev Design Bureau, Zhukovsky-5, Moscow Region, Russia;
UPMC Univ. Paris 06, Universit´e Versailles St-Quentin CNRS/INSU, LATMOS-IPSL, Paris, France.

Abstract: 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, Î~, 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.


Volume: 10 (12)      Pages from: 5573  to: 5592

More Information: The SCOUT-O3 and TROCCINOX projects were funded by the European Commission through Contracts 505390-GOCE-CT-2004-505390 and EVK2-2001-00122. The M55 \”Geophysica\” campaign was supported by the EEIG-Geophysica Consortium, CNRS-INSU, EC Integrated Projects AMMA-EU (Contract Number 004089-2), SCOUT-O3, CNES, and EUFAR. The DLR Falcon-20 campaigns were funded through TROCCINOX, SCOUT-O3, AMMA-EU, and DLR. The balloon-borne experiments of the University of Wyoming received funding from the US National Science Foundation (ATM-0437406) and J.C. Wilson acknowledges the NASA Upper Atmosphere Research Program and Radiation Sciences Program for supporting the measurements and data analysis presented here.
KeyWords: aerosol; atmospheric chemistry; global climate; ozone; potential temperature; stratosphere; trace gas; troposphere; water vapor, Africa; Australia; Brazil; Costa Rica, Falconidae; Pinatubo
DOI: 10.5194/acp-10-5573-2010

Citations: 42
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