Marine organic matter in the remote environment of the Cape Verde Islands – An introduction and overview to the MarParCloud campaign
Authors: van Pinxteren Manuela , Fomba Khanneh Wadinga , Triesch Nadja , Stolle Christian , Wurl Oliver , Bahlmann Enno , Gong Xianda , Voigtländer Jens , Wex Heike , Robinson Tiera-Brandy , Barthel Stefan , Zeppenfeld Sebastian , Hoffmann Erik H. , Roveretto Marie , Li Chunlin , Grosselin Benoit , Daële Veronique , Senf Fabian , van Pinxteren Dominik , Manzi Malena , Zabalegui Nicolás , Frka Sanja , Gašparović Blaženka , Pereira Ryan , Li Tao , Wen Liang , Li Jiarong , Zhu Chao , Chen Hui , Chen Jianmin , Fiedler Björn , von Tümpling Wolf , Read Katie A. , Punjabi Shalini , C. Lewis Alastair C. , Hopkins James R. , Carpenter Lucy J. , Peeken Ilka , Rixen Tim , Schulz-Bull Detlef , Monge María Eugenia , Mellouki Abdelwahid , George Christian , Stratmann Frank , Herrmann Hartmut 
Published: December 2019

Abstract. The project MarParCloud (Marine biological production, organic aerosol Particles and marine Clouds: a process chain) aims at improving our understanding of the genesis, modification and impact of marine organic matter (OM), from its biological production, via its export to marine aerosol particles and, finally, towards its ability to act as ice nucleating particles (INP) and cloud condensation nuclei (CCN). A field campaign at the Cape Verde Atmospheric Observatory (CVAO) in the tropics in September/October 2017 formed the core of this project that was jointly performed with the project (MARine atmospheric Science Unravelled). A suite of chemical, physical, biological and meteorological techniques was applied and comprehensive measurements of bulk water, the sea surface microlayer (SML), cloud water and ambient aerosol particles collected at a ground-based and a mountain station took place. Key variables comprised the chemical characterization of the atmospherically relevant OM components in the ocean and the atmosphere as well as measurements of INP and CCN. Moreover, bacterial cell counts, mercury species and trace gases were analysed. To interpret the results, the measurements were accompanied by various auxiliary parameters such as air mass back trajectory analysis, vertical atmospheric profile analysis, cloud observations and pigment measurements in seawater. Additional modelling studies supported the experimental analysis. During the campaign, the CVAO exhibited marine air masses with low and partly moderate dust influences. The marine boundary layer was well mixed as indicated by an almost uniform particle number size distribution within the boundary layer. Lipid biomarkers were present in the aerosol particles in typical concentrations of marine background conditions. Accumulation and coarse mode particles served as CCN and were efficiently transferred to the cloud water. The ascent of ocean-derived compounds, such as sea salt and sugar-like compounds, to the cloud level as derived from chemical analysis and atmospheric transfer modelling results denote an influence of marine emissions on cloud formation. However, INP measurements indicated also a significant contribution of other non-marine sources to the local INP concentration or strong enrichment processes during upward transport. Lipids, sugar-like compounds, UV absorbing humic-like substances and low molecular weight neutral components were important organic compounds in the seawater and highly surface-active lipids were enriched within the SML. The selective enrichment of specific organic compounds in the SML needs to be studied in further detail and implemented in an OM source function for emission modelling to better understand transfer patterns, mechanisms of marine OM transformation in the atmosphere and the role of additional sources. In summary, when looking at particulate mass, we do see oceanic compounds transferred to the atmospheric aerosol and to the cloud level, while from a perspective of particle number concentrations, marine contributions to both CCN and INP are rather limited.