Atmospheric mercury speciation dynamics at the high-altitude Pic du Midi Observatory, southern France

摘要

Continuous measurements of atmospheric gaseous elemental mercury(GEM), particulate bound mercury (PBM) and gaseous oxidized mercury (GOM) atthe high-altitude Pic du Midi Observatory (PDM Observatory, 2877 m a.s.l.) insouthern France were made from November 2011 to November 2012. The mean GEM, PBM andGOM concentrations were 1.86 ng m, 14 pg m and 27 pg m,respectively and we observed 44 high PBM (peak PBM values of 33–98 pg m) and 61 high GOM (peak GOM values of 91–295 pg m) events.The high PBM events occurred mainly in cold seasons (winter and spring)whereas high GOM events were mainly observed in the warm seasons (summer andautumn). In cold seasons the maximum air mass residence times (ARTs)associated with high PBM events were observed in the upper troposphere overNorth America. The ratios of high PBM ARTs to total ARTs over North America,Europe, the Arctic region and Atlantic Ocean were all elevated in the coldseason compared to the warm season, indicating that the middle and upperfree troposphere of the Northern Hemisphere may be more enriched in PBM incold seasons. PBM concentrations and PBM ∕ GOM ratios during the high PBMevents were significantly anti-correlated with atmospheric aerosolconcentrations, air temperature and solar radiation, suggesting in situformation of PBM in the middle and upper troposphere. We identified twodistinct types of high GOM events with the GOM concentrations positively andnegatively correlated with atmospheric ozone concentrations, respectively.High GOM events positively correlated with ozone were mainly related to airmasses from the upper troposphere over the Arctic region and middletroposphere over the temperate North Atlantic Ocean, whereas high GOM eventsanti-correlated with ozone were mainly related to air masses from the lowerfree troposphere over the subtropical North Atlantic Ocean. The ARTsanalysis demonstrates that the lower and middle free troposphere over theNorth Atlantic Ocean was the largest source region of atmospheric GOM at thePDM Observatory. The ratios of high GOM ARTs to total ARTs over thesubtropical North Atlantic Ocean in summer were significantly higher thanthose over the temperate and sub-arctic North Atlantic Ocean as well as thatover the North Atlantic Ocean in other seasons, indicating abundant in situoxidation of GEM to GOM in the lower free troposphere over the subtropicalNorth Atlantic Ocean in summer.