Atmospheric Chemistry and Physics | 2021
Summer aerosol measurements over the East Antarctic seasonal ice zone
Abstract
Abstract. Aerosol measurements over the Southern Ocean have been\nidentified as critical to an improved understanding of aerosol–radiation and\naerosol–cloud interactions, as there currently exists significant\ndiscrepancies between model results and measurements in this region. The\natmosphere above the Southern Ocean provides crucial insight into an aerosol\nregime relatively free from anthropogenic influence, yet its remoteness\nensures atmospheric measurements are relatively rare. Here we present\nobservations from the Polar Cell Aerosol Nucleation (PCAN) campaign, hosted aboard the RV Investigator during a summer\n(January–March) 2017 voyage from Hobart, Australia, to the East Antarctic\nseasonal sea ice zone. A median particle number concentration (condensation\nnuclei >\u20093\u2009nm; CN3) of 354 (95\u2009%\u2009CI 345–363)\u2009cm−3 was\nobserved from the voyage. Median cloud condensation nuclei (CCN)\nconcentrations were 167 (95\u2009%\u2009CI 158–176)\u2009cm−3. Measured particle size\ndistributions suggested that aerosol populations had undergone significant\ncloud processing. To understand the variability in aerosol observations,\nmeasurements were classified by meteorological variables. Wind direction and\nabsolute humidity were used to identify different air masses, and aerosol\nmeasurements were compared based on these identifications. CN3\nconcentrations measured during SE wind directions (median 594\u2009cm−3)\nwere higher than those measured during wind directions from the NW (median\n265\u2009cm−3). Increased frequency of measurements from these wind\ndirections suggests the influence of large-scale atmospheric transport\nmechanisms on the local aerosol population in the boundary layer of the East\nAntarctic seasonal ice zone. Modelled back trajectories imply different air\nmass histories for each measurement group, supporting this suggestion.\nCN3 and CCN concentrations were higher during periods where the\nabsolute humidity was less than 4.3\u2009gH2O/m3, indicative of free\ntropospheric or Antarctic continental air masses, compared to other periods\nof the voyage. Increased aerosol concentration in air masses originating\nclose to the Antarctic coastline have been observed in numerous other\nstudies. However, the smaller changes observed in the present analyses\nsuggest seasonal differences in atmospheric circulation, including lesser\nimpact of synoptic low-pressure systems in summer. Further measurements in\nthe region are required before a more comprehensive picture of atmospheric\ncirculation in this region can be captured and its influence on local\naerosol populations understood.\n