Airborne mercury species at the Råö background monitoring site inSweden: distribution of mercury as an effect of long-range transport

摘要

Within the EU-funded project, Global Mercury Observation System (GMOS)airborne mercury has been monitored at the background Råö measurementsite on the western coast of Sweden from mid-May 2012 to the beginning ofJuly 2013 and from the beginning of February 2014 to the end of May 2015. Thefollowing mercury species/fractions were measured: gaseous elemental mercury(GEM), particulate bound mercury (PBM) and gaseous oxidised mercury (GOM)using the Tekran measurement system. The mercury concentrations measured atthe Råö site were found to be low in comparison to other, comparable,European measurement sites. A back-trajectory analysis to study the origin ofair masses reaching the Råö site was performed. Due to the remotelocation of the Råö measurement station it receives background airabout 60 % of the time. However, elevated mercury concentrations arrivingwith air masses coming from the south-east are noticeable. GEM and PBMconcentrations show a clear annual variation with the highest valuesoccurring during winter, whereas the highest concentrations of GOM wereobtained in spring and summer. An evaluation of the diurnal pattern of GOM,with peak concentrations at midday or in the early afternoon, which often isobserved at remote places, shows that it is likely to be driven by localmeteorology in a similar way to ozone. Evidence that a significant part ofthe GOM measured at the Råö site has been formed in free troposphericair is presented.