Aerosols scatter sun light and act as Cloud Condensation Nucleus (CCN), which cause the most uncertain man-made climate forcing. Sea spray aerosols (SSA) are the largest natural aerosol source. SSA emissions are driven by wind, water temperature, sea ice, salinity and marine micro-biology, all which are influenced by climate change, causing feed-back loops. We have got a fair grip on how physical factors influence the SSA sea salt part but are largely in the dark on the organic and biological fractions, and on the influence of salinity and biology. To quantify in situ emissions, we will use Eddy Covariance (EC ) fluxes. EC requires very fast sensors, which makes it impossible to characterise chemistry, microbiology and CCN-properties at the same time. Instead this will be done in a SSA simulation tank. We have previously successfully applied both methods separately. Applying both simultaneously, with water from the flux-foot-print in the tank, kept at in situ temperature, will give both characterisation and quantification. I smaller pilot project was published in 2021 (Nilsson et al., 2021), where the preliminary analysis had worked as “proof of concept” in the VR-proposal that financed this project.
In the original plans we intended to make a campaign at the ICOS-station of Östergarnsholm in the Baltic Sea, where we have unique multiple year EC -aerosol-fluxes, bringing the SSA simulation tank experiment to the island. The limited power available at the station has prevented that. We also intended to participate in one cruise in the Atlantic/Arctic/Pacific/Indian oceans, but currently the pandemic postponed most deep see expeditions. Limitations to travels and field work by Stockholm University or national authorities also postponed our work and forced us to reconsider our plans. We will therefore instead perform 3 shorter campaigns in the Baltic where smaller research ships are brought to Östergarnsholm, and the SSA simulation tank experiments are performed onboard the ships. These are:
–RV Oceania in May 2021.
–RV Electra in August 2021.
-RV Oceania in September-October 2021.
In combination, these three cruises will hopefully provide us with a large enough data set to meet the original objectives. The limitation is that we will only get data in brackish water, but that cannot currently be avoided.
Since such large part of the data set will be made in brackish water, and the effect of salinity on sea spray formation was not well understood, we have during 2020-21 carried through a number of laboratory experiments with salinities from 0 to 35 ppm and temperatures from 0 to 30 degrees Celcius. The analysis of these data assure that
we do not mistake an effect of salinity changes for an effect of for example changes in microbiological activity or organic surfactants. This study is currently in review (Zinker et al., in review).
The combination of EC aerosol fluxes and detailed physical, chemical and microbiological analysis of the sea spray produced in the sea spray simulation tank will enable us to derive source parameterizations for the organic SSA, and the effect of salinity, as well as enrichment factors for micro-organisms, suitable for climate
models or other large scale models. This is the main objective of the project.