Atmospheric reactive mercury concentrations in coastal Australia and the Southern Ocean

Mercury (Hg), especially reactive Hg (RM), data from the Southern Hemisphere (SH) are limited. In this study, long-term measurements of both gaseous elemental Hg (GEM) and RM were made at two ground-based monitoring locations in Australia, the Cape Grim Baseline Air Pollution Station (CGBAPS) in Tasmania, and the Macquarie University Automatic Weather Station (MQAWS) in Sydney, New South Wales. Measurements were also made on board the Australian RV Investigator (RVI) during an ocean research voyage to the East Antarctic coast. GEM was measured using the standard Tekran® 2537 series analytical platform, and RM was measured using cation exchange membranes (CEM) in a filter-based sampling method. Overall mean RM concentrations at CGBAPS and MQAWS were 15.9 ± 6.7 pg m^-3 and 17.8 ± 6.6 pg m^-3, respectively. For the 10-week austral summer period on RVI, mean RM was 23.5 ± 6.7 pg m^-3. RM concentrations at CGBAPS were seasonally invariable, while those at MQAWS were significantly different between summer and winter due to seasonal changes in synoptic wind patterns. During the RVI voyage, RM concentrations were relatively enhanced along the Antarctic coast (up to 30 pg m^-3) and GEM concentrations were variable (0.2 to 0.9 ng m^-3), suggesting periods of enrichment and depletion. Both RM and GEM concentrations were relatively lower while transiting the Southern Ocean farther north of Antarctica. RM concentrations measured in this study were higher in comparison to most other reported measurements of RM in the global marine boundary layer (MBL), especially for remote SH locations. As observations of GEM and RM concentrations inform global ocean-atmosphere model simulations of the atmospheric Hg budget, our results have important implications for understanding of total atmospheric Hg (TAM).