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The remoteness of the Antarctic continent has important implications for the microphysical properties of clouds: In particular, the rare abundance of ice-nucleating particles (INP) limits the primary nucleation of ice crystals. Yet, persistent mixed-phase clouds with ice crystal number concentrations of 0.1-1l-1 are still observed in the Arctic and Antarctic. However, the ability of regional climate models to reproduce these mixed-phase clouds remains limited, much like the knowledge about their climatological effects. Thus, we added a module to the regional climate model COSMO-CLM² aimed at improving the parametrisation of the aerosol-cycle, which allows us to prescribe different concentrations of INPs. We examined the model response to different concentrations by running it in an area around the Belgian Princess Elisabeth Station in Dronning Maud Land for one month and with four different concentration settings: The first, corresponding to the low end of INP concentrations we observed at the station, the second, corresponding to the high end of INP concentrations we observed at the station, and the third and fourth, to the low and high end of continental observations. The performance was evaluated by comparing the simulation results with radar and ceilometer observations taken at the station. Finally, we analysed the differences between the four simulations to determine the overall sensitivity of the model to variability in INP concentrations, which allows us to draw conclusions about the importance of accurately simulating processes related to ice nucleation, and about the climatological implications that a change in aerosol concentrations would have.

Antarctica is considered the most pristine environment on Earth. However, a detailed understanding of present-day atmospheric transport pathways of particles and volatile organic compounds (VOC) from source to deposition in Antarctica and the atmospheric reactions they undergo is essential to document biogeochemical cycles. Atmospheric composition plays an important role in present and near-future climate change. Airborne particles can serve as cloud condensation and ice nuclei and have therefore a strong influence on cloud formation and thus also on precipitation. This is of interest in Antarctica, since precipitation is the only source of mass gain to the Antarctic ice sheet which is expected to become the dominant contributor to global sea level rise in the 21st century. VOCs and their atmospheric oxidation products, secondary organic aerosols (SOA’s) can play an important role in this cloud formation process. However, current knowledge on VOCs and on the interaction between clouds, precipitation and aerosols in the Antarctic is still limited, both from direct observations and from regional climate models.VOCs are traditionally sampled using axial thermal desorption sampling tubes containing a sorbent such as Tenax TA in a passive or active (pumped) fashion. While with passive sampling it is possible to sample over longer periods of time, up to a year in clean air conditions, the temporal information is lost. Because of uncertainties on the sample rate, which is driven by diffusion, obtaining precise air concentrations with passive sampling can be difficult. To sample VOC’s and oxidations products unsupervised and in a remote environment such as Antarctica a new active sequential sorbent tube autosampler was developed and deployed at the atmospheric observatory of the Princess Elisabeth Antarctic research station (71.95° S, 23.35° E, 1390 m asl). The autosampler collected samples from December 2019 to October 2020 and from January 2021 to June 2021. The obtained data is also used to complement and interpret atmospheric aerosol in-situ measurements conducted at the same location. Furthermore, to identify potential source regions, backward trajectory and dispersion modelling using FLEXTRA and FLEXPART will be applied.

By serving as condensation and ice nuclei, aerosols play a vital role in the formation of clouds. This has significant implications for the radiation balance and precipitation amounts over the Antarctic Ice Sheet, where type and amount of aerosols differ significantly from other places because of its remote location. However, that is also the reason observations are sparse, and consequently, few studies exist examining this effect. Recently, a module was added to the COSMO-CLM² regional climate model to account for the aerosol-cycle. The model was integrated for the region around the Princess Elisabeth Antarctic research station (PEA) in Dronning Maud Land for a period of 10 days in January 2016, of which the first 3 days were discarded. Varying cloud condensation and ice nuclei were prescribed to the model, based on observations from PEA. The model output was compared to observations of cloud structure and precipitation amounts taken at PEA, as well as the unmodified COSMO-CLM² model. The model integrations indicate that the number of ice nuclei has a significant impact on the microphysical composition of clouds, with higher numbers being associated with a lower amount of liquid water content of clouds and higher precipitation amounts. Additional runs are performed to confirm and extend these findings for an entire year. Recent measurements of ice nuclei particle concentrations obtained during two austral summers are also considered. Moreover, we analysed how atmospheric dynamics affect the cloud-aerosol interaction by analysing the model sensitivity for different weather regimes.

Ice nucleating particles (INPs) are rare but important atmospheric particles as they induce the formation of primary ice in mixed phase clouds and also in some cirrus clouds. A plethora of substances which can be found in atmospheric particles can induce ice nucleation. The most important ice active particle types in the atmosphere are assumed to be mineral dust and biological particles, which can originate from a large number of sources. It is hence not surprising that INP concentrations vary over several orders of magnitude at any ice nucleation temperature, with concentrations being typically larger in continental than in marine environments. Although research concerning INP and their global occurrence has seen a steep rise in the past years, global INP concentrations are still not well known, and not all important INP sources are clear, neither are there good parameterizations for describing INP concentrations in models.To increase the knowledge of typical global INP concentrations and to draw conclusions about INP sources, we examined INP concentrations in the Antarctic region, namely at the German research Station Neumayer III, located at shelf ice in close proximity (only some 10 km) to the ice edge, at the Belgian research Station Princess Elisabeth, located roughly 200 km inland and at an altitude of 1390 m, and during a campaign including ship- and land-based data at the Antarctic peninsula. We used our well-established methods of filter collection and off-line analysis with cold-stages to derive INP concentrations in these locations.For Neumayer, two years of data are available. INP concentrations there were generally lower than values derived, e.g., for northern mid latitudes, and they were similar to values published for the Southern Ocean in literature. No pronounced annual cycle was observed. Around and on the Antarctic peninsula, INP concentrations were roughly similar to those observed at Neumayer. However, the Princess Elisabeth station, for which only data obtained during two austral summers are available, showed the lowest values detected in this study. Our results suggest that sources of INP in the Antarctic region are rare, and particularly so on Antarctica itself.

During the time period December 2019 – January 2020, a lot of biomass burning has been ongoing in the Southern Hemisphere. This led to a large amount of fine dust being emitted and transported into the atmosphere of the Southern Hemisphere. With the dispersion model FLEXPART, we will simulate these fires, using the CAMS Global Fire Assimilation System (GFAS) which assimilates fire radiative power (FRP) observations from satellite-based sensors in order to reproduce daily estimates of biomass burning emissions. Also information on the injection height is available.Aerosol fluxes and sources in Antarctica and its closely associated Southern Ocean are poorly constrained, in particular the particle chemistry. A detailed understanding of present-day atmospheric transport pathways of particles and of volatile organic compounds (VOC) from source to deposition in Antarctica remains essential to document biogeochemical cycles and the relative importance of natural and anthropogenic compounds. Within the CHASE project (chase.meteo.be), the Royal Meteorological Institute of Belgium, Ghent University and the Université Libre de Bruxelles are doing research at the Belgian research station Princess Elisabeth (71.9°S, 23.3°E; East Antarctica, Dronning Maud Land) on the physical-chemical composition of both atmospheric particles, particles in surface snow particles as well as of VOCs. Since 2018, samples are taken both near the Belgian research station Princess Elisabeth (active sampling with pumps) and on a transect to the coast (passive samplers and surface snow samples). In this contribution we will thoroughly investigate the atmospheric transport pathways of the recent biomass burning plumes, and in particular to what extent parts of these plumes have reached Antarctica. The measured chemical signatures of atmospheric particles and VOCs will help to constrain the simulations of the dispersion model.

Identifying the provenance of mineral dust depositions in Antarctica is crucial to reconstruct Southern Hemisphere (SH) atmospheric circulation, validate numerical models, evaluate their contribution as micronutrients in the Southern Ocean and assess their control on the climate changes. For the last few decades, it has been demonstrated Southern South America (SSA) is the main precursor of dust reaching Antarctica during both ice ages and interglacial periods (e.g. Gili et al., 2017, 2016). However, the origin of modern dust depositions on the Antarctic continent is still poorly constrained. Back in the nineties, together with SSA, Australia, New Zealand, and Southern Africa were firstly identified as dust contributors to East Antarctica (EA) (e.g. Delmonte et al., 2004a). Since then, only SSA and Australian dust sources benefited from detailed studies. While some works identified the Makgadikgadi and Etosha Pans as southern Africa's major mineral dust sources in the SH, it was not until recently the Namib Desert coastal areas were described as another important regional dust sources. Within the Namib Desert and along the coast, the Kuiseb (K), Omaruru (O) and Huab (H) dry riverbeds are the three main areas identified as the dustiest ones with the higher frequency of dust emission events (Von Holdt et al., 2017). Here we use Sr, Nd and Pb isotopes (measured on HR-MC-ICP-MS) to characterize and evaluate the influence of this region in Southern Africa as a dust source to EA. Samples collected in K, O and H desertic areas were analyzed together with snow samples collected along a ~250 km N-S transect (defined from the coast to inland) at seven different sampling sites in the surroundings of Dronning Maud Land, EA. In addition, using the bulk of the Huab region, dust aerosols were generated into an atmospheric simulation chamber (CESAM) to reproduce, mechanically the saltation and sandblasting processes responsible for the release of mineral dust in natural conditions. Our isotopic results show Namibia’s coast emerged as another possible source end-member, together with some regions in SSA, that supply dust to EA during warmer periods.References:Delmonte, B., Basile-Doelsch, I., Petit, J.R., Maggi, V., Revel-Rolland, M., Michard, A., Jagoutz, E., Grousset, F., 2004. Comparing the EPICA and Vostok dust records during the last 220,000 years: stratigraphical correlation and provenance in glacial periods. Earth-Sci. Rev. 66, 63–87.Gili, S., Gaiero, D.M., Goldstein, S.L., Chemale, F. Jr., Koester, E., Jweda, J., Vallelonga, P., Kaplan, M.R., 2016. Provenance of dust to Antarctica: a lead isotopic perspective. Geophys. Res. Lett. 43. http://dx.doi.org/10.1002/2016GL068244.Gili, S., D.M. Gaiero, S.L. Goldstein, F. Chemale, J. Jweda, M.R. Kaplan, R.A. Becchio, and E. Koester (2017). Glacial/interglacial changes of Southern Hemisphere wind circulation from the geochemistry of South American dust. Earth Planet. Sci. Lett., 469, 98-109, doi: 10.1016/j.epsl.2017.04.007.Von Holdt, JR., Eckardt FD., and Wiggs GFS., 2017. Landsat identifies aeolian dust emission dynamics at the landform scale. Remote Sensing of Environment 198., 229–243.