A new source of Southern Ocean and Antarctic aerosol from tropospheric polar cell chemistry of sea ice emissions

Ruhi S Humphries1, Andrew R Klekociuk2, Robyn Schofield Prof3, Andrew D Robinson4, Neil Richard Peter Harris5, Melita D Keywood6, Jason Ward6, Ian Edward Galbally7, Suzie Molloy7, Alan Thomas8 and Stephen R Wilson9, (1)University of Wollongong, Wollongong, NSW, Australia, (2)Australian Antarctic Division, Kingston, TAS, Australia, (3)University of Melbourne, School of Earth Sciences and ARC Centre of Excellence for Climate Extremes, Parkville, VIC, Australia, (4)University of Cambridge, Cambridge, United Kingdom, (5)Cranfield University, Cranfield, United Kingdom, (6)Climate Science Centre, CSIRO Oceans & Atmosphere, Aspendale, Australia, (7)CSIRO Marine and Atmospheric Research, Aspendale, Australia, (8)NIWA National Institute of Water and Atmospheric Research, Wellington, New Zealand, (9)University of Wollongong, Centre for Atmospheric Chemistry, School of Earth, Atmospheric and Life Sciences, Wollongong, NSW, Australia
Abstract:
The Antarctic region is a pristine environment with minimal anthropogenic influence. Aerosol measurements in this environment allow the study of natural aerosols and polar atmospheric dynamics. Measurements in this region have been limited primarily to continental and coastal locations where permanent stations exist, with a handful of measurements in the sea ice region. The MAPS campaign (Measurements of Aerosols and Precursors during SIPEXII) occurred as part of SIPEX II (Sea Ice Physics and Ecosystems eXperiment II) voyage in Spring, 2012, and produced the first Antarctic pack-ice focused aerosol dataset aimed at characterizing new particle formation processes off the coast of East Antarctica (~65°S, 120°E). Numerous atmospheric parameters and species were measured, including the number of aerosol particles in the 3-10 nm size range, the range associated with nucleating particle formation. A latitudinal transect through the sea ice identified the Polar Front from sudden changes in nucleating particle concentrations, averaging 51cm-3 north of the front in the Ferrel cell, and 766 cm-3 south of the front, in the Polar cell region. The Polar Front location was also confirmed by meteorological and back-trajectory data. Background aerosol populations in the Polar cell fluctuated significantly but displayed no growth indicators, suggesting transport. Back-trajectories revealed that air parcels often descended from the free-troposphere within the previous 24-48 hrs. It is proposed that particle formation occurs in the free troposphere from precursors uplifted at the polar front region which, being a sea-ice/ocean region, is a significant precursor source. After tropospheric formation, populations descending at the poles are transported northward and reach the sea ice surface, missing continental stations. Current measurements of Antarctic aerosol suggest very low loading which may be explained by these circulation patterns and may underestimate total regional loading and the contribution of Antarctic aerosol production to global loading. As climate change intensifies and the ozone hole recovers, the Antarctic polar front may shift latitudes, potentially changing Antarctic and regional aerosol loading, resulting in changes to tropospheric and stratospheric chemistry and radiative budgets.
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