van Pinxteren, Manuela; Fomba, Khanneh Wadinga; Triesch, Nadja; Frka, Sanja; Gašparović, Blaženka; Herrmann, Hartmut
(2019)
Marine organic matter in the remote environment of the Cape Verde Islands – An introduction and overview to the MarParCloud campaign.
Atmospheric Chemistry and Physics, 20
(11).
pp. 6921-6951.
ISSN 1680-7316
Abstract
The project MarParCloud (Marine biological production, organic aerosol Particles and marine 50 Clouds: a process chain) aims at improving our understanding of the genesis, modification and 51 impact of marine organic matter (OM), from its biological production, via its export to marine 52 aerosol particles and, finally, towards its ability to act as ice nucleating particles (INP) and 53 cloud condensation nuclei (CCN). A field campaign at the Cape Verde Atmospheric 54 Observatory (CVAO) in the tropics in September/October 2017 formed the core of this project 55 that was jointly performed with the project MARSU (MARine atmospheric Science 56 Unravelled). A suite of chemical, physical, biological and meteorological techniques was 57 applied and comprehensive measurements of bulk water, the sea surface microlayer (SML), 58 cloud water and ambient aerosol particles collected at a ground-based and a mountain station 59 took place. 60 Key variables comprised the chemical characterization of the atmospherically relevant OM 61 components in the ocean and the atmosphere as well as measurements of INP and CCN. 62 Moreover, bacterial cell counts, mercury species and trace gases were analysed. To interpret 63 the results, the measurements were accompanied by various auxiliary parameters such as air 64 mass back trajectory analysis, vertical atmospheric profile analysis, cloud observations and 65 pigment measurements in seawater. Additional modelling studies supported the experimental 66 analysis. 67 During the campaign, the CVAO exhibited marine air masses with low and partly moderate 68 dust influences. The marine boundary layer was well mixed as indicated by an almost uniform 69 particle number size distribution within the boundary layer. Lipid biomarkers were present in 70 the aerosol particles in typical concentrations of marine background conditions. Accumulation 71 and coarse mode particles served as CCN and were efficiently transferred to the cloud water. 72 The ascent of ocean-derived compounds, such as sea salt and sugar-like compounds, to the 73 cloud level as derived from chemical analysis and atmospheric transfer modelling results denote 74 an influence of marine emissions on cloud formation. However, INP measurements indicated 75 also a significant contribution of other non- marine sources to the local INP concentration or 76 strong enrichment processes during upward transport. In addition, the number of CCN at the 77 supersaturation of 0.30% was about 2.5 times higher during dust periods compared to marine 78 periods. Lipids, sugar-like compounds, UV absorbing humic-like substances and low molecular 79 weight neutral components were important organic compounds in the seawater and highly 80 surface-active lipids were enriched within the SML. The selective enrichment of specific 81 organic compounds in the SML needs to be studied in further detail and implemented in an OM 82 source function for emission modelling to better understand transfer patterns, mechanisms of 83 marine OM transformation in the atmosphere and the role of additional sources. 84 In summary, when looking at particulate mass, we do see oceanic compounds transferred to the 85 atmospheric aerosol and to the cloud level, while from a perspective of particle number 86 concentrations, marine contributions to both CCN and INP are rather limited
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