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

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 30 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) 35 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 40 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 5 Stephan Houdier , Jean-Luc Jaffrezo , Muriel Joly, Martin Leremboure , Jean-Marc Metzger , Jean-Marc Pichon, Mickaël Ribeiro, Manon Rocco , Pierre Tulet , Anthony Vella, Maud Leriche and Laurent Deguillaume* https://doi.org/10.5194/acp-2021-518 Preprint. Discussion started: 27 July 2021 c © Author(s) 2021. CC BY 4.0 License.