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Discussion papers | Copyright
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 09 Apr 2018

Research article | 09 Apr 2018

Review status
This discussion paper is a preprint. A revision of the manuscript is under review for the journal Atmospheric Chemistry and Physics (ACP).

Aircraft-based observations of isoprene epoxydiol-derived secondary organic aerosol (IEPOX-SOA) in the tropical upper troposphere over the Amazon region

Christiane Schulz1, Johannes Schneider1, Bruna Amorim Holanda1, Oliver Appel1, Anja Costa2, Suzane S. de Sá3, Volker Dreiling4, Daniel Fütterer5, Tina Jurkat-Witschas5, Thomas Klimach1, Martina Krämer2, Scot T. Martin3,7, Stephan Mertes8, Mira L. Pöhlker1, Daniel Sauer5, Christiane Voigt5,6, Bernadett Weinzierl5,a, Helmut Ziereis5, Martin Zöger4, Meinrat O. Andreae1,9, Paulo Artaxo10, Luiz A. T. Machado11, Ulrich Pöschl1, Manfred Wendisch12, and Stephan Borrmann1,6 Christiane Schulz et al.
  • 1Particle Chemistry, Biogeochemistry and Multiphase Chemistry Departments, Max Planck Institute for Chemistry, Mainz, Germany
  • 2Institut für Energie- und Klimaforschung (IEK7), Forschungszentrum Jülich GmbH, Jülich, Germany
  • 3School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, USA
  • 4Flight Experiments, German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt), Oberpfaffenhofen, Germany
  • 5Institute for Atmospheric Physics, German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt), Oberpfaffenhofen, Germany
  • 6Institute for Physics of the Atmosphere, Johannes Gutenberg University, Mainz, Germany
  • 7Department of Earth and Planetary Sciences, Harvard University, Cambridge, Massachusetts, USA
  • 8Leibniz Institute for Tropospheric Research, Leipzig, Germany
  • 9Scripps Institution of Oceanography, University of California San Diego, La Jolla, California, USA
  • 10Instituto de Física, Universidade de São Paulo, São Paulo, Brazil
  • 11Instituto Nacional de Pesquisas Espaciais (INPE), Centro de Previsão de Tempo e Estudos Climáticos, São José dos Campos, Brazil
  • 12Leipzig Institute for Meteorology, University of Leipzig, Leipzig, Germany
  • anow at: Faculty of Physics, University of Vienna, Vienna, Austria

Abstract. During the ACRIDICON-CHUVA field project (September–October 2014; based in Manaus, Brazil) aircraft-based in-situ measurements of aerosol chemical composition were conducted in the tropical troposphere over the Amazon using the High Altitude and Long Range Research Aircraft (HALO), covering altitudes from the boundary layer height up to 14.4km. The submicron non-refractory aerosol was characterized by flash-vaporization/electron impact-ionization aerosol particle mass spectrometry. The results show that significant secondary organic aerosol (SOA) formation by isoprene oxidation products occurs in the upper troposphere, leading to increased organic aerosol mass concentrations above 10km altitude. The median organic mass concentrations in the upper troposphere above 10km range between 1.0 and 2.1μgm−3 (referring to standard temperature and pressure; STP) with interquartile ranges of 0.6 to 3.0μgm−3 (STP), representing 70% of the total submicron non-refractory aerosol particle mass. The presence of isoprene epoxydiol-derived isoprene secondary organic aerosol (IEPOX-SOA) was confirmed by marker peaks in the mass spectra. We estimate the contribution of IEPOX-SOA to the total organic aerosol in the upper troposphere to be about 20%. After isoprene emission from vegetation, oxidation processes occur at low altitudes and/or during transport to higher altitudes, which may lead to the formation of IEPOX (one oxidation product of isoprene). Reactive uptake or condensation of IEPOX on pre-existing particles leads to IEPOX-SOA formation and subsequently increasing organic mass in the upper troposphere. This organic mass increase was accompanied by an increase of the nitrate mass concentrations, most likely due to NOx production by lightning. We further found that the ammonium contained in the aerosol particles is not sufficient to neutralize the particulate sulfate and nitrate. Analysis of the ion ratio of NO+ to NO2+ indicated that nitrate in the upper troposphere exists mainly in the form of organic nitrate. IEPOX-SOA and organic nitrates are coincident with each other, indicating that IEPOX-SOA forms in the upper troposphere either on acidic nitrate particles forming organic nitrates derived from IEPOX or on already neutralized organic nitrate aerosol particles.

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Christiane Schulz et al.
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Short summary
Aerosol chemical composition measurements in the tropical upper troposphere over the Amazon region show that 70 % of the aerosol in the upper troposphere consists of organic matter. Up to 20 % of the organic aerosol can be attributed to isoprene epoxydiol secondary organic aerosol (IEPOX-SOA). Furthermore, organic nitrates were identified, suggesting a connection to the IEPOX-SOA formation.
Aerosol chemical composition measurements in the tropical upper troposphere over the Amazon...