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