Preprints
https://doi.org/10.5194/acp-2021-845
https://doi.org/10.5194/acp-2021-845

  25 Nov 2021

25 Nov 2021

Review status: this preprint is currently under review for the journal ACP.

High number concentrations of transparent exopolymer particles (TEP) in ambient aerosol particles and cloud water – A case study at the tropical Atlantic Ocean

Manuela van Pinxteren1, Tiera-Brandy Robinson2, Sebastian Zeppenfeld1, Xianda Gong3,a, Enno Bahlmann4, Khanneh Wadinga Fomba1, Nadja Triesch1, Frank Stratmann3, Oliver Wurl2, Anja Engel5, Heike Wex3, and Hartmut Herrmann1 Manuela van Pinxteren et al.
  • 1Atmospheric Chemistry Department (ACD), Leibniz-Institute for Tropospheric Research (TROPOS), 04318 Leipzig, Germany
  • 2Institute for Chemistry and Biology of the Marine Environment, Carl-von-Ossietzky University Oldenburg, 26382 Wilhelmshaven, Germany
  • 3Dept. of Experimental Cloud and Microphysics, Leibniz-Institute for Tropospheric Research (TROPOS), 04318 Leipzig, Germany
  • 4Leibniz Centre for Tropical Marine Research (ZMT), 28359 Bremen, Germany
  • 5GEOMAR Helmholtz Centre for Ocean Research, Kiel 24105, Germany
  • anow at: Center for Aerosol Science and Engineering, Department of Energy, Environmental and Chemical Engineering, Washington University in St. Louis, 63130, MO, USA

Abstract. Transparent exopolymer particles (TEP) exhibit the properties of gels and are ubiquitously found in the world oceans. Possibly, TEP may enter the atmosphere as part of sea spray aerosol. Here, we report number concentrations of TEP (diameter > 4.5 µm) in ambient aerosol and cloud water samples from the tropical Atlantic Ocean as well as in generated aerosol particles using a plunging waterfall tank that was filled with the ambient sea water. The ambient TEP concentrations ranged between 7 × 102 and 3 × 104 #TEP m−3 in supermicron aerosol particles and correlations to sodium (Na+) and calcium (Ca2+) (R2 = 0.5) suggested some contribution via bubble bursting. Cloud water TEP concentrations were between 4 × 106 and 9 × 106 #TEP L−1 corresponding to equivalent air concentrations of 2–4 × 103 #TEP m−3. The TEP concentrations in the tank-generated aerosol particles, produced from the same waters and sampled with an equivalent system, were significantly lower (4 × 102–2 × 103 #TEP m−3) compared to the ambient concentrations.

Based on Na+ concentrations in seawater and in the atmosphere, the enrichment factor for TEP in the atmosphere was calculated. The tank-generated TEP were enriched by a factor of 50 compared to sea water and, therefore, in-line with published enrichment factors for supermicron organic matter in general and TEP specifically. TEP enrichment in the ambient atmosphere was on average 1 × 103 in cloud water and 9 × 103 in ambient aerosol particles and therefore about two orders of magnitude higher than the corresponding enrichment from the tank study. Such high enrichment of supermicron particulate organic constituents in the atmosphere is uncommon and we propose that atmospheric TEP concentrations resulted from a combination of enrichment during bubble bursting transfer from the ocean and TEP in-situ formation in atmospheric phases. Abiotic in-situ formation might have occurred from aqueous reactions of dissolved organic precursors that were present in particle and cloud water samples, while biotic formation involves bacteria, which were abundant in the cloud water samples.

The ambient TEP number concentrations were two orders of magnitude higher than recently reported ice nucleating particle (INP) concentrations measured at the same location. As TEP likely possess good properties to act as INP, in future experiments it is worth studying if a certain part of TEP contributes a fraction of the biogenic INP population.

Manuela van Pinxteren et al.

Status: open (until 06 Jan 2022)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse

Manuela van Pinxteren et al.

Manuela van Pinxteren et al.

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Short summary
A class of marine particles (Transparent exopolymer particles – TEP) that is ubiquitously found in the world oceans was measured for the first time in ambient marine aerosol particles and marine clouds in the tropical Atlantic Ocean. TEP are likely to have good properties to influence clouds. We show that TEP are transferred from the ocean to the marine atmosphere via sea spray formation and our results suggest that they can also form directly in the aerosol particles and in cloud water.
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