Investigating local and remote terrestrial influence on air masses at contrasting Antarctic sites using Radon-222 and back trajectories

We report on the first summer of high-sensitivity radon measurementsfrom a two-filter detector at 12Jang Bogo Station(Terra Nova Bay), and contrast them with simultaneousobservations at King 13Sejong Station (King George Island).King Sejong radon concentrations were characteristic of a 14marinebaseline station (0.02 –0.3 Bq m-3), whereas Jang Bogo values were highly variable (0.06 –155.2 Bq m-3), mainlydue toemissions from exposed coastal ground(estimated mean flux 0.09–0.1116atoms cm-2s-1)and shallow atmospheric mixing depths.For wind speeds of ≤3.5 m s-1the influence 17of local radon emissions became increasingly more prominent at both sites. A cluster analysis of 18back trajectories from King Sejong (62S) revealed a fairly even distribution between air masses that 19had passed recently over South America, the Southern Ocean and Antarctica, whereasat Jang Bogo 20(75S) 80% of events had recently passed over the Ross Ice Shelf and West Antarctica, 12% were 21synoptically forced over Cape Adare, and 8% were associated with subsidence over the Antarctic 22interior and katabatic flowto the station. When cross-checked againstradonconcentrations, only 23half of the back trajectories ending atJang Bogo that hadindicateddistant contact with non-polar 24southern hemisphere continents within the past 10 days showed actual signs of terrestrial influence.25A simple-to-implement technique based on high-pass filtered absolute humidity is developedto 26distinguish betweenpredominantly katabatic, oceanic and near-coastal airmasses for 27characterisation of trace gas and aerosol measurementsat coastal East Antarctic sites.