Preprints
https://doi.org/10.5194/acp-2021-518
https://doi.org/10.5194/acp-2021-518

  27 Jul 2021

27 Jul 2021

Review status: a revised version of this preprint is currently under review for the journal ACP.

Insights into tropical cloud chemistry at Reunion Island (Indian Ocean): results from the BIO-MAÏDO campaign

Pamela A. Dominutti1, Pascal Renard1, Mickaël Vaïtilingom2, Angelica Bianco1, Jean-Luc Baray1,3, Agnès Borbon1, Thierry Bourianne4, Frédéric Burnet4, Aurélie Colomb1, Anne-Marie Delort5, Valentin Duflot6, Stephan Houdier7, Jean-Luc Jaffrezo7, Muriel Joly5, Martin Leremboure5, Jean-Marc Metzger8, Jean-Marc Pichon3, Mickaël Ribeiro1, Manon Rocco1, Pierre Tulet6,9, Anthony Vella7, Maud Leriche1,10, and Laurent Deguillaume1,3 Pamela A. Dominutti et al.
  • 1Laboratoire de Météorologie Physique, UMR 6016, CNRS, Université Clermont Auvergne, 63178 Aubière, France
  • 2Laboratoire de Recherche en Géosciences et Energies, EA 4539, Université des Antilles, 97110 Pointe-à-Pitre, France
  • 3Observatoire de Physique du Globe de Clermont-Ferrand, UAR 833, CNRS, Université Clermont Auvergne, 63178 Aubière, France
  • 4Centre National de Recherches Météorologiques (CNRM), Université de Toulouse, Météo-France, CNRS, Toulouse, France
  • 5Institut de Chimie de Clermont-Ferrand, CNRS, SIGMA Clermont, Université Clermont Auvergne, 63178 Aubière, France
  • 6Laboratoire de l’Atmosphère et des Cyclones (LACy), UMR 8105, Université de la Réunion-CNRS-Météo-France, Saint-Denis de La Réunion, France
  • 7Université Grenoble Alpes, CNRS, IRD, IGE (UMR 5001), 38000 Grenoble, France
  • 8Observatoire des Sciences de l’Univers de La Réunion (OSUR), UAR 3365, Saint-Denis de la Réunion, France
  • 9Laboratoire d'Aérologie, UMR 5560 (Université de Toulouse, CNRS, IRD), Toulouse, France
  • 10Centre pour l’étude et la simulation du climat à l’échelle régionale (ESCER), Département des sciences de la terre et de l’atmosphère, Université du Québec à Montréal, Montréal, Canada

Abstract. We present here the results obtained during an intensive field campaign conducted in the framework of the French “BIO-MAÏDO” (Bio-physico-chemistry of tropical clouds at Maïdo (Réunion Island): processes and impacts on secondary organic aerosols’ formation) project. This study integrates an exhaustive chemical and microphysical characterization of cloud water obtained in March–April 2019 at Reunion Island (Indian Ocean). Fourteen cloud samples have been collected along the slope of this mountainous island. A comprehensive chemical characterization of these samples is performed, including inorganic ions, metals, oxidants, and organic matter (organic acids, sugars, amino acids, carbonyls, and low-soluble volatile organic compounds (VOCs)). Cloud water presents high molecular complexity with elevated water-soluble organic matter content partly modulated by microphysical cloud properties.

As expected, our findings show the presence of compounds of marine origin in cloud water samples (e.g., chloride, sodium) demonstrating ocean–cloud exchanges. However, the non-sea salt fraction of sulphate varies between 38 and 91 %, indicating the presence of other sources. Also, the presence of amino acids and for the first time in cloud waters of sugars, clearly indicates that biological activities contribute to the cloud water chemical composition.

A significant variability between events is observed in the dissolved organic content (25.5 ± 18.4 mgC L−1), with levels reaching up to 62 mgC L−1. This variability was not similar for all the measured compounds, suggesting the presence of dissimilar emission sources or production mechanisms. For that, a statistical analysis is performed based on back-trajectory calculations using the CAT (Computing Atmospheric Trajectory Tool) model associated with land cover registry. These investigations reveal that air mass origins and microphysical variables do not fully explain the variability observed in cloud chemical composition, highlighting the complexity of emission sources, multiphasic transfer, and chemical processing in clouds.

Additionally, several VOCs (oxygenated and low-soluble VOCs) were analysed in both gas and aqueous phases. Significant levels of biogenic low-soluble VOCs were detected in the aqueous phase, indicating the cloud-terrestrial vegetation exchange. Cloud scavenging of VOCs is assessed and compared to Henry’s law equilibrium to evaluate potential super or sub saturation conditions. The evaluation reveals the supersaturation of low-soluble VOCs from both natural and anthropogenic sources. Our results depict even higher supersaturation of terpenoids, suggesting their importance in the aqueous phase chemistry in highly impacted tropical areas.

Pamela A. Dominutti et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2021-518', Anonymous Referee #1, 19 Aug 2021
  • RC2: 'Comment on acp-2021-518', Anonymous Referee #2, 30 Aug 2021

Pamela A. Dominutti et al.

Pamela A. Dominutti et al.

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Short summary
We present here the results obtained during an intensive field campaign conducted in March–April 2019 at Reunion Island. Our study integrates a comprehensive chemical and microphysical characterization of cloud water. Our investigations reveal that air mass history and cloud microphysical properties do not fully explain the variability observed in their chemical composition. This highlights the complexity of emission sources, multiphasic exchanges, and transformations in clouds.
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