Characterizing Atmospheric Transport Pathways to Antarctica and the Remote Southern Ocean Using Radon-222

We discuss remote terrestrial influences on boundary layer air over the Southern Ocean and Antarctica, and the mechanisms by which they arise, using atmospheric radon observations as a proxy. Our primary motivation was to enhance the scientific community’s ability to understand and quantify the potential effects of pollution, nutrient or pollen transport from distant land masses to these remote, sparsely instrumented regions. Seasonal radon characteristics are discussed at 6 stations (Macquarie Island, King Sejong, Neumayer, Dumont d’Urville, Jang Bogo and Dome Concordia) using 1–4 years of continuous observations. Context is provided for differences observed between these sites by Southern Ocean radon transects between 45 and 67°S made by the Research Vessel Investigator. Synoptic transport of continental air within the marine boundary layer (MBL) dominated radon seasonal cycles in the mid-Southern Ocean site (Macquarie Island). MBL synoptic transport, tropospheric injection, and Antarctic outflow all contributed to the seasonal cycle at the sub-Antarctic site (King Sejong). Tropospheric subsidence and injection events delivered terrestrially influenced air to the Southern Ocean MBL in the vicinity of the circumpolar trough (or “Polar Front”). Katabatic outflow events from Antarctica were observed to modify trace gas and aerosol characteristics of the MBL 100–200 km off the coast. Radon seasonal cycles at coastal Antarctic sites were dominated by a combination of local radon sources in summer and subsidence of terrestrially influenced tropospheric air, whereas those on the Antarctic Plateau were primarily controlled by tropospheric subsidence. Separate characterization of long-term marine and katabatic flow air masses at Dumont d’Urville revealed monthly mean differences in summer of up to 5 ppbv in ozone and 0.3 ng m-3 in gaseous elemental mercury. These differences were largely attributed to chemical processes on the Antarctic Plateau. A comparison of our observations with some Antarctic radon simulations by global climate models over the past two decades indicated that: (i) some models overestimate synoptic transport to Antarctica in the MBL, (ii) the seasonality of the Antarctic ice sheet needs to be better represented in models, (iii) coastal Antarctic radon sources need to be taken into account, and (iv) the underestimation of radon in subsiding tropospheric air needs to be investigated

Characteristics of airborne particle number size distributions in a coastal-urban environment

Particle number size distributions are among the most important parameters in trying to understand the characteristics of particle population. Atmospheric particles were measured in an interaction of mixed environments in the Southeastern coastal city of Wollongong, Australia, during a comprehensive field campaign known as Measurements of Urban, Marine and Biogenic Air (MUMBA). MUMBA ran in summer season between 21 st December 2012 and 15 th February 2013. Particle number concentrations measured during this campaign were indicative of the interplay between marine environments and urban air which met the objective of this campaign. Particle number size distributions ranging from 14 nm to 660 nm in diameter, as measured by Scanning Mobility Particle Sizer (SMPS) in this study, were grouped using Principal Component Analysis. Based on strong component loadings (value ≥ 0.75), three different factors were identified (i) Small Factor (N S ): 15 nm \u3c Dp \u3c 50 nm, (ii) Medium Factor (N M ): 60 nm \u3c Dp \u3c 150 nm and (iii) Large Factor (N L ): 210 nm \u3c Dp \u3c 450 nm. The three factors describe 89% of the dataset cumulative variance. Particles in this region are dependent upon the interaction between the sources, and cannot be viewed as a simple mixture of biogenic and anthropogenic sources associated with various mechanical processes. The particles observed in the morning were found to be influenced by combustion emissions, presumably primarily from traffic, which is most obvious in N L . The particle population during the day was found to be influenced by a mixture of marine sources and secondary aerosols production initiated by photochemical oxidation. The local steel works and the urban environment were the major contributors of particles at night. Secondary organic aerosols were identified in this study by the mass ratio of organic carbon to elemental carbon (OC/EC). Biogenic sources influenced secondary organic aerosols formation as a moderate correlation (R 2 = 0.6) was observed between secondary organic aerosols mass and biogenic isoprene. The processes described in this paper are likely repeated at other coastal urban environments worldwide

Aerosol size distribution measurements at Cataract Scout Park, Australia, taken during the COALA-2020 campaign

Measurements of aerosol size distribution between 14 and 661 nm diameter were measured using a TSI Scanning Mobility Particle Sizer (consisting of 3080 DMA, 3772 CPC and x-ray aerosol neutraliser, TSI Incorporated, Shoreview, MN, USA). Measurements were taken at Cataract Scout Park, Appin, N.S.W. (34°14'42.29"S 150°49'24.97"E) from an inlet 5.13 m above ground level as part of the Characterising Organics and Aerosol Loading over Australia (COALA-2020) campaign. Zero and flow checks logged have been removed from the published measurements, presented at 1-minute temporal resolution. 1-minute data are spline interpolations of the 5-minute scan measurements output by the instrument. Measurements span from January 29 2020 until March 15 2020. Please note that the instrument was run with leaky impactor until February 18 2020. Measurements in this period should be treated with caution. Measurements made during February 18-20 were disrupted due to impactor testing and have been removed. Following February 20, measurements were made without an impactor. Measurements were not made between February 25 and February 29

Condensation nuclei >3 nm (CN3) measurements at Cataract Scout Park, Australia, taken during the COALA-2020 campaign

Measurements of condensation nuclei greater than 3 nm diameter (CN3) were collected using an ultrafine condensation particle counter (TSI Ultrafine Condensation Particle Counter 3776, TSI Incorporated, Shoreview, MN, USA). Measurements were taken at Cataract Scout Park, Appin, N.S.W. (34°14'42.29"S 150°49'24.97"E) from an inlet 5.13 m above ground level as part of the Characterizing Organics and Aerosol Loading over Australia (COALA-2020) campaign. The instrument was operated a using a sample flow rate of 300mL/min until 2020-02-18 23:30 UTC. Following this date, a sample flow rate of 1500mL/min was used to ensure consistency between comparable campaign measurements. No effect on measurements was evident. Logged zero and flow checks have been removed from the published measurements, presented are 1-minute temporal resolution means and standard deviations of native 1-second measurements output by the instrument