Overview of the antarctic circumnavigation expedition: Study of preindustrial-like aerosols and their climate effects (ACE-SPACE)

Julia Schmale*, Andrea Baccarini, Iris Thurnherr, Silvia Henning, Avichay Efraim, Leighton Regayre, Conor Bolas, Markus Hartmann, André Welti, Katrianne Lehtipalo, Franziska Aemisegger, Christian Tatzelt, Sebastian Landwehr, Robin L. Modini, Fiona Tummon, Jill S. Johnson, Neil Harris, Martin Schnaiter, Alessandro Toffoli, Marzieh DerkaniNicolas Bukowiecki, Frank Stratmann, Josef Dommen, Urs Balten Sperger, Heini Wernli, Daniel Rosenfeld, Martin Gysel-Beer, Ken S. Carslaw

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

81 Scopus citations

Abstract

The first results from ACE-SPACE highlight that the Southern Ocean is a region with highly heterogeneous aerosol properties. The areas around the strong westerly wind belt are characterized by significant sea spray contributions to the total particle and CCN number concentrations in the MBL. Future work will link detailed wave and wind observations to sea spray production. In the Ross and Amundsen Sea polynyas (leg 2), biogenic emissions appear to play an important role for CCN abundance. There are a number of open questions associated with this observation. First, even though this particular region was probed during a phytoplankton bloom period, it was not the only region with microbial activity but showed the clearest link to high CCN concentrations. Hence, either DMS production from dimethylsulfoniopropionate in the water and/or DMS fluxes into the atmosphere were enhanced. Second, the major pathway of how MSA is added to the particle phase remains to be identified. There are two possibilities: It can condense from the gas into the particle phase, or it can be added during cloud processing. The latter process would be consistent with the reduced efficiency of wet removal because of droplet evaporation or snowflake sublimation in the cold and dry airmasses from Antarctica. Our results also indicate that the absence of MSA-related processes in the aerosol model could explain the underestimation of CCN concentration, particularly in high aerosol-MSA regions. Given that the number of CCN influence Nd, this is an important issue to solve, especially close to the coast of Antarctica where clouds could impact the surface snow mass balance by influencing both the surface energy budget and precipitation. Further studies are planned that more closely investigate the linkages between CCN number concentrations and model simulations that take DMS emissions fluxes and particle phase MSA into account. A comparison of satellite-retrieved Nd90 and ship-based measurements of CCN shows a clear underestimation of CCN from remote sensing, even for coupled cloud cases. This is a strong indication of the importance of surface sources as opposed to the free troposphere for particle origin. Further investigation is underway to understand the cause of the discrepancy between the remote sensing and in situ measurements. We did not find direct evidence for new particle formation as an important source of CCN. However, some nucleation events were observed and a nucleation mode was present in the clustered particle size distributions. A dedicated study will investigate the gases involved in these events and the fate of the nucleation mode in the atmosphere. Our ice nucleating particle findings suggest that concentrations are lower than in Northern Hemisphere marine airmasses and that concentrations decreased from summer toward fall with only small differences between open-ocean and coastal Antarctic samples. The ACE-SPACE INP concentrations are also consistent with findings of a recent study in the Southern Ocean (McCluskey et al. 2018a), but much lower than results from several decades ago (Bigg 1973). More detailed studies including information on potential island effects, long-range transport and fluorescent and microbial particles are underway. The ACE-SPACE project is motivated by the idea of constraining uncertainty in anthropogenic radiative forcing from aerosol-cloud interactions through measurement of preindustrial-like aerosol-cloud interactions. We have shown that the in situ data are suitable for constraining the aerosol model for preindustrial-like conditions. After a detailed model-measurement comparison, we will use the aerosol model to further constrain uncertainties of global radiative forcing from aerosol-cloud interactions.

Original languageEnglish
Pages (from-to)2260-2283
Number of pages24
JournalBulletin of the American Meteorological Society
Volume100
Issue number11
DOIs
StatePublished - 2019

Bibliographical note

Publisher Copyright:
© 2019 American Meteorological Society.

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