Marine aerosol particles – tiny airborne particles over the sea – influence the Earth’s radiation balance both directly and indirectly by absorbing and reflecting incoming solar radiation. They are formed in various ways through interactions between the ocean and the atmosphere and are constantly changing under different environmental conditions.

A key formation process is known as ‘bubble bursting’: when air bubbles burst at the sea surface, components of the seawater are released directly into the atmosphere. In addition, volatile compounds from the ocean also contribute to the formation of aerosol particles. After their emission, these particles continue to change, for example through chemical or biogenic reactions in the atmosphere or through interactions with other particles and gases. These ageing processes alter their physicochemical properties and thus also their role in the climate system.

 

Fig. 1: Interaction between ocean and atmosphere leading to the formation of ma-rine aerosol. Source: TROPOS

To better understand the sources, transport and formation pathways of marine aerosol particles and to assess their significance for the global climate, it is crucial to investigate both their chemical composition and their microphysical and optical properties. In addition to sea salt, they contain a significant proportion of organic compounds that have a major influence on their properties.

An important source of these organic substances is seawater itself. Of particular relevance here is the sea surface microlayer (SML) – a layer just a few micrometres thick that forms the direct interface between the ocean and the atmosphere and is often heavily enriched with organic compounds.

Fig. 2: Sampling of the marine surface film using the glass plate technique (top left), collection of cloud water on Mount Verde in the Cape Verde Islands (bottom left) and sampling of marine aerosol particles during a ship-based expedition (right). Source: TROPOS

The glass plate technique is used to collect samples of this surface film: a glass plate is immersed vertically into the water and slowly withdrawn so that the film adheres to it. The film is then scraped off using a Teflon wiper. The samples obtained in this way are immediately frozen and transported to the TROPOS laboratories using refrigerated containers and dry ice, where they undergo detailed chemical analysis. Coupled chromatographic and mass spectrometric methods are used to identify and quantify climate-relevant organic compounds.

In addition to the ocean samples, marine clouds (or fog, i.e. clouds near the surface) are also sampled by collecting their water. The aim is to understand how certain components from the ocean eventually reach clouds via aerosol particles and influence cloud formation and the Earth’s radiation balance there.

 

The diverse interactions between the ocean and the atmosphere are being investigated in field expeditions and laboratory measurements within various current research projects:

 

  • BASS: Research group on the marine surface film (SML) and its role as a reactive biogeochemical boundary layer.
  • AC³ (Arctic Amplification: Climate Relevant Atmospheric and Surface Processes): Transregional project investigating Arctic amplification and the underlying processes.
  • Ocean-GATE: Investigation of marine proteins in Antarctica and their influence on aerosol particles and clouds.
  • TransArctic: Research into the transport and ageing of aerosol components at high altitudes in the Arctic troposphere.
  • AIRSPACE: Investigation of the influence of anthropogenic air pollution on marine aerosol particles and exchange processes at the ocean surface.
  • Biocat-Aerosol: Analysis of aerosol particles in the Bay of Bengal and their interactions between marine and anthropogenic sources.

 

Completed projects (selection):

 

  • ORIGAMY: Aliphatic amines and their role in the tropical atmosphere: measurements and modelling (2020–2023)
  • MarParCloud: Marine surface film, aerosol particles and clouds: their interactions in the tropical Atlantic (2017–2020, Cape Verde Islands)
  • PASCAL/SIPCA: Marine carbohydrates in the Arctic environment (2017, Central Arctic)
  • MOSAiC: Annual cycle of organic compounds on Arctic aerosol particles (2019–2020, Central Arctic)
  • PI-ICE: Marine carbohydrates in Antarctica (2019, West Antarctic Peninsula)

 

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