Coast of Eastern Antarctica as the source of atmospheric mercury during austral summer

Abstract

Observations of atmospheric mercury over the Southern Ocean and Antarctica are still limited. We performed a ship cruise from Cape Point, South Africa, to the Indian Bharati station, Prydz Bay, Antarctica (42.72°S 24.52°E to 69.41°S 76.19°E, 2015.01.18–27) and subsequently stationed the ship near the Bharati till 2015.02.19. We report relatively constant values of gaseous elemental mercury (GEM) concentration during the cruise (1.08 ± 0.08 ng/m3, n = 541) and highly variable values at the coast (0.96 ± 0.36 ng/m3, n = 1050). Meteorological parameters: relative humidity, temperature and solar radiation had almost negligible effect on GEM concentration (adjusted R2 = 0.09 in multiple linear regression model) during the ship cruise and a limited effect on GEM (adjusted R2 = 0.34) during the ship stay at Bharati. Analysis of NOAA-HYSPLIT 24-h back trajectories showed that all trajectories were extremely shallow during the ship cruise and therefore results likely were affected by the marine boundary layer rather than long-range transport. On the other hand, highly variable values of GEM near Bharati station were explained as a result of interplay of shallow and descending air masses coming from the Antarctic coast and from the terrain. These factors together with temperature dependency indicated that the coast of Antarctica acted as a temperature-driven source of GEM during the austral summer. Measurements were performed with a portable atomic absorption (CVAAS) mercury analyzer model Gardis-5. In our knowledge, this was the first time the CVAAS method was successfully applied for the background Antarctic observations.