Articles | Volume 18, issue 2
Atmos. Chem. Phys., 18, 921–961, 2018

Special issue: The ACRIDICON-CHUVA campaign to study deep convective clouds...

Atmos. Chem. Phys., 18, 921–961, 2018
Research article
 | Highlight paper
25 Jan 2018
Research article  | Highlight paper | 25 Jan 2018

Aerosol characteristics and particle production in the upper troposphere over the Amazon Basin

Meinrat O. Andreae1,12, Armin Afchine2, Rachel Albrecht3, Bruna Amorim Holanda1, Paulo Artaxo4, Henrique M. J. Barbosa4, Stephan Borrmann1, Micael A. Cecchini5,3, Anja Costa2, Maximilian Dollner9,13, Daniel Fütterer6, Emma Järvinen10, Tina Jurkat6, Thomas Klimach1, Tobias Konemann1, Christoph Knote9, Martina Krämer2, Trismono Krisna8, Luiz A. T. Machado5, Stephan Mertes7, Andreas Minikin6,16, Christopher Pöhlker1, Mira L. Pöhlker1, Ulrich Pöschl1, Daniel Rosenfeld14, Daniel Sauer6, Hans Schlager6, Martin Schnaiter10, Johannes Schneider1, Christiane Schulz1, Antonio Spanu6,13, Vinicius B. Sperling5, Christiane Voigt6,15, Adrian Walser9,6, Jian Wang1,11, Bernadett Weinzierl6,13, Manfred Wendisch8, and Helmut Ziereis6 Meinrat O. Andreae et al.
  • 1Biogeochemistry, Multiphase Chemistry, and Particle Chemistry Departments, Max Planck Institute for Chemistry, Mainz, Germany
  • 2Forschungszentrum Jülich, Jülich, Germany
  • 3Instituto de Astronomia, Geofísica e Ciências Atmosféricas, Universidade de São Paulo, São Paulo, Brazil
  • 4Institute of Physics, University of São Paulo, São Paulo, Brazil
  • 5National Institute for Space Research (INPE), São José dos Campos, Brazil
  • 6German Aerospace Center (DLR), Institute of Atmospheric Physics (IPA), Weßling, Germany
  • 7Leibniz Institute for Tropospheric Research, Leipzig, Germany
  • 8Leipzig Institute for Meteorology, Leipzig University, Leipzig, Germany
  • 9Meteorological Institute, Ludwig Maximilian University, Munich, Germany
  • 10Institute for Meteorology and Climate Research, Karlsruhe Institute of Technology, Karlsruhe, Germany
  • 11Brookhaven National Laboratory, Upton, NY, USA
  • 12Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA, USA
  • 13University of Vienna, Aerosol Physics and Environmental Physics, Vienna, Austria
  • 14Institute of Earth Sciences, The Hebrew University of Jerusalem, Jerusalem, Israel
  • 15Institute of Atmospheric Physics (IPA), Johannes Gutenberg University, Mainz, Germany
  • 16German Aerospace Center (DLR), Flight Experiments, Oberpfaffenhofen, Germany

Abstract. Airborne observations over the Amazon Basin showed high aerosol particle concentrations in the upper troposphere (UT) between 8 and 15 km altitude, with number densities (normalized to standard temperature and pressure) often exceeding those in the planetary boundary layer (PBL) by 1 or 2 orders of magnitude. The measurements were made during the German–Brazilian cooperative aircraft campaign ACRIDICON–CHUVA, where ACRIDICON stands for Aerosol, Cloud, Precipitation, and Radiation Interactions and Dynamics of Convective Cloud Systems and CHUVA is the acronym for Cloud Processes of the Main Precipitation Systems in Brazil: A Contribution to Cloud Resolving Modeling and to the GPM (global precipitation measurement), on the German High Altitude and Long Range Research Aircraft (HALO). The campaign took place in September–October 2014, with the objective of studying tropical deep convective clouds over the Amazon rainforest and their interactions with atmospheric trace gases, aerosol particles, and atmospheric radiation.

Aerosol enhancements were observed consistently on all flights during which the UT was probed, using several aerosol metrics, including condensation nuclei (CN) and cloud condensation nuclei (CCN) number concentrations and chemical species mass concentrations. The UT particles differed sharply in their chemical composition and size distribution from those in the PBL, ruling out convective transport of combustion-derived particles from the boundary layer (BL) as a source. The air in the immediate outflow of deep convective clouds was depleted of aerosol particles, whereas strongly enhanced number concentrations of small particles (< 90 nm diameter) were found in UT regions that had experienced outflow from deep convection in the preceding 5–72 h. We also found elevated concentrations of larger (> 90 nm) particles in the UT, which consisted mostly of organic matter and nitrate and were very effective CCN.

Our findings suggest a conceptual model, where production of new aerosol particles takes place in the continental UT from biogenic volatile organic material brought up by deep convection and converted to condensable species in the UT. Subsequently, downward mixing and transport of upper tropospheric aerosol can be a source of particles to the PBL, where they increase in size by the condensation of biogenic volatile organic compound (BVOC) oxidation products. This may be an important source of aerosol particles for the Amazonian PBL, where aerosol nucleation and new particle formation have not been observed. We propose that this may have been the dominant process supplying secondary aerosol particles in the pristine atmosphere, making clouds the dominant control of both removal and production of atmospheric particles.

Short summary
We made airborne measurements of aerosol particle concentrations and properties over the Amazon Basin. We found extremely high concentrations of very small particles in the region between 8 and 14 km altitude all across the basin, which had been recently formed by gas-to-particle conversion at these altitudes. This makes the upper troposphere a very important source region of atmospheric particles with significant implications for the Earth's climate system.
Final-revised paper