A 2-year record of atmospheric mercury species at a background Southern Hemisphere station on Amsterdam Island

Although essential to fully understand the cycling of mercury at the global scale, mercury species records in the Southern Hemisphere are scarce. Under the framework of the Global Mercury Observation System (GMOS) project, a monitoring station has been set up on Amsterdam Island (37 degrees 48'S, 77 degrees 34'E) in the remote southern Indian Ocean. For the first time in the Southern Hemisphere, a 2-year record of gaseous elemental mercury (GEM), reactive gaseous mercury (RGM) and particle-bound mercury (PBM) is presented. GEM concentrations were remarkably steady (1.03 +/- 0.08 ng m(-3)) while RGM and PBM concentrations were very low and exhibited a strong variability (mean: 0.34 pg m(-3), range: < detection limit-4.07 pg m(-3); and mean: 0.67 pg m(-3), range: < detection limit-12.67 pg m(-3), respectively). Despite the remoteness of the island, wind sector analysis, air mass back trajectories and the observation of radonic storms highlighted a long-range contribution from the southern African continent to the GEM and PBM budgets from July to September during the biomass burning season. Low concentrations of GEM were associated with southerly polar and marine air masses from the remote southern Indian Ocean. This unique data set provides new baseline GEM concentrations in the Southern Hemisphere midlatitudes while mercury speciation along with upcoming wet deposition data will help to improve our understanding of the mercury cycle in the marine boundary layer.