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Discussion papers
https://doi.org/10.5194/acp-2019-775
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2019-775
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 02 Sep 2019

Submitted as: research article | 02 Sep 2019

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This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Chemistry and Physics (ACP).

Influx of African biomass burning aerosol during the Amazonian dry season through layered transatlantic transport of black carbon-rich smoke

Bruna A. Holanda1,2, Mira L. Pöhlker1, Jorge Saturno2,a, Matthias Sörgel2,3, Jeannine Ditas4,1, Florian Ditas1,2,b, Qiaoqiao Wang2,c, Tobias Donth5, Paulo Artaxo6, Henrique M. J. Barbosa6, Ramon Braga1, Joel Brito6,d, Yafang Cheng1, Maximilian Dollner5,6, Marco Aurélio Franco6, Johannes Kaiser3,8, Thomas Klimach1, Christoph Knote7, Ovid O. Krüger1, Daniel Fütterer8, Jošt V. Lavrič9, Nan Ma4,1, Luiz A. T. Machado10, Jing Ming1,2, Fernando Morais5, Hauke Paulsen1, Daniel Sauer8, Hans Schlager8, Hang Su1, Bernadett Weinzierl8,11, Adrian Walser5,8, David Walter1,9, Manfred Wendisch5, Helmut Ziereis8, Martin Zöger8, Ulrich Pöschl1, Meinrat O. Andreae2,12, and Christopher Pöhlker1,2 Bruna A. Holanda et al.
  • 1Multiphase Chemistry Department, Max Planck Institute for Chemistry, 55128 Mainz, Germany
  • 2Biogeochemistry Department, Max Planck Institute for Chemistry, 55128 Mainz, Germany
  • 3Atmospheric Chemistry Department, Max Planck Institute for Chemistry, 55128 Mainz, Germany
  • 4Center for Air Pollution and Climate Change Research (APCC), Institute for Environmental and Climate Research (ECI), Jinan University, Guangzhou, 511443, China
  • 5Leipzig Institute for Meteorology, Leipzig University, Leipzig, Germany
  • 6Institute of Physics, University of São Paulo, São Paulo 05508-900, Brazil
  • 7Meteorological Institute, Ludwig Maximilians University, Munich, Germany
  • 8German Aerospace Center (DLR), Institute for Atmospheric Physics & Flight experiments, 82234 Oberpfaffenhofen, Germany
  • 9Max Planck Institute for Biogeochemistry, 07701 Jena, Germany
  • 10National Institute for Space Research (INPE), São José Dos Campos, Brazil
  • 11University of Vienna, Aerosol Physics and Environmental Physics, 1090 Wien, Austria
  • 12Scripps Institution of Oceanography, University of California San Diego, La Jolla, California 92093, USA
  • anow at: Physikalisch-Technische Bundesanstalt, 38116 Braunschweig, Germany
  • bnow at: Hessisches Landesamt für Naturschutz, Umwelt und Geologie, 65203 Wiesbaden, Germany
  • cnow at: Institute for Environmental and Climate Research, Jinan University, China
  • dnow at: IMT Lille Douai, Univ. Lille, SAGE, 59000 Lille, France

Abstract. Black carbon (BC) aerosols are influencing the Earth’s atmosphere and climate, but their microphysical properties, spatiotemporal distribution and long-range transport are not well constrained. This study analyzes the transatlantic transport of BC-rich African biomass burning (BB) pollution into the Amazon Basin, based on airborne observations of aerosol particles and trace gases in and off the Brazilian coast during the ACRIDICON-CHUVA campaign in September 2014, combining in-situ measurements on the research aircraft HALO with satellite remote-sensing and numerical model results.

During flight AC19 over land and ocean at the Brazilian coastline in the northeast of the Amazon Basin, we observed a BC-rich atmospheric layer at ~ 3.5 km altitude with a vertical extension of ~ 0.3 km. Backward trajectory analyses suggest that fires in African grasslands, savannas, and shrublands were the main source of this pollution layer, and that the observed BB smoke had undergone more than 10 days of atmospheric transport and aging. The BC mass concentrations in the layer ranged from 0.5 to 2 μg m−3, and the BC particle number fraction of ~ 40 % was about 8 times higher than observed in a fresh Amazonian BB plume, representing the highest value ever observed in the region. Upon entering the Amazon Basin, the layer started to broaden and to subside, due to convective mixing and entrainment of the BB aerosol into the boundary layer. Satellite observations show that the transatlantic transport of pollution layers is a frequently occurring process, seasonally peaking in August/September.

By analyzing the aircraft observations within the broader context of the long-term data from the Amazon Tall Tower Observatory (ATTO), we found that the transatlantic transport of African BB smoke layers has a strong impact on the north-central Amazonian aerosol population during the BB-influenced season (July to November). Specifically, the early BB season in this part of the Amazon appears to be dominated by African smoke, whereas the later BB season appears to be dominated by South American fires. This dichotomy is reflected in pronounced changes of aerosol optical properties such as the single scattering albedo (increasing from 0.85 in August to 0.90 in November) and the BC-to-CO enhancement ratio (decreasing from 7.4 to 4.4 ng m−3 ppb−1). Our results suggest that, despite the high amount of BC particles, the African BB aerosol act as efficient cloud condensation nuclei (CCN) with potentially important implications for aerosol-cloud interactions and the hydrological cycle in the Amazon Basin.

Bruna A. Holanda et al.
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Short summary
African biomass burning smoke from savanna and grassland fires is transported across the Atlantic Ocean in defined layers within the free troposphere. The combination of in-situ aircraft and satellite observations as well as modeling results showed that these layers of aged smoke are transported into the Amazon Basin during the early dry season months. This influx of long-range transported pollution has important implications for the Amazonian cycling of aerosols and cloud condensation nuclei.
African biomass burning smoke from savanna and grassland fires is transported across the...
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