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Volume 16, issue 4
Atmos. Chem. Phys., 16, 2185–2206, 2016
https://doi.org/10.5194/acp-16-2185-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.
Atmos. Chem. Phys., 16, 2185–2206, 2016
https://doi.org/10.5194/acp-16-2185-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 25 Feb 2016

Research article | 25 Feb 2016

Unexpectedly high ultrafine aerosol concentrations above East Antarctic sea ice

R. S. Humphries1,a, A. R. Klekociuk2,3, R. Schofield4,5, M. Keywood6, J. Ward6, and S. R. Wilson1 R. S. Humphries et al.
  • 1Centre for Atmospheric Chemistry, University of Wollongong, Wollongong, Australia
  • 2Australian Antarctic Division, Hobart, Australia
  • 3Antarctic Climate and Ecosystems Cooperative Research Centre, Hobart, Australia
  • 4School of Earth Sciences, University of Melbourne, Melbourne, Australia
  • 5ARC Centre of Excellence for Climate System Science, University of New South Wales, Sydney, Australia
  • 6CSIRO Oceans and Atmosphere Business Unit, Aspendale, Australia
  • anow at: CSIRO Oceans and Atmosphere Business Unit, Aspendale, Australia

Abstract. Better characterisation of aerosol processes in pristine, natural environments, such as Antarctica, have recently been shown to lead to the largest reduction in uncertainties in our understanding of radiative forcing. Our understanding of aerosols in the Antarctic region is currently based on measurements that are often limited to boundary layer air masses at spatially sparse coastal and continental research stations, with only a handful of studies in the vast sea-ice region. In this paper, the first observational study of sub-micron aerosols in the East Antarctic sea ice region is presented. Measurements were conducted aboard the icebreaker Aurora Australis in spring 2012 and found that boundary layer condensation nuclei (CN3) concentrations exhibited a five-fold increase moving across the polar front, with mean polar cell concentrations of 1130 cm−3 – higher than any observed elsewhere in the Antarctic and Southern Ocean region. The absence of evidence for aerosol growth suggested that nucleation was unlikely to be local. Air parcel trajectories indicated significant influence from the free troposphere above the Antarctic continent, implicating this as the likely nucleation region for surface aerosol, a similar conclusion to previous Antarctic aerosol studies. The highest aerosol concentrations were found to correlate with low-pressure systems, suggesting that the passage of cyclones provided an accelerated pathway, delivering air masses quickly from the free troposphere to the surface. After descent from the Antarctic free troposphere, trajectories suggest that sea-ice boundary layer air masses travelled equatorward into the low-albedo Southern Ocean region, transporting with them emissions and these aerosol nuclei which, after growth, may potentially impact on the region's radiative balance. The high aerosol concentrations and their transport pathways described here, could help reduce the discrepancy currently present between simulations and observations of cloud and aerosol over the Southern Ocean.

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This work represents the first observational study of atmospheric sub-micron aerosols in the East Antarctic pack ice region and found springtime aerosol concentrations were higher than any observed elsewhere in the Antarctic and Southern Ocean region. Further analysis suggested these aerosols formed in the Antarctic free troposphere. Their subsequent transport to the Southern Ocean, as suggest by trajectory analyses, could help to reduce the discrepancy in the radiative budget in the region.
This work represents the first observational study of atmospheric sub-micron aerosols in the...
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