Mercury speciation in the marine boundary layer along a 6000 km cruise path around the Mediterranean Sea

In the framework of the Med-Oceanor project simultaneous measurements of two atmospheric mercury species elemental mercury (Hg0) and reactive gaseous mercury (RGM) over the Mediterranean Sea were performed in order to investigate the dynamic patterns of mercury in the Marine Boundary Layer. Measurements of atmospheric mercury were performed on board the Italian Research Vessel (URANIA) along a 6000 km cruise path in the western and eastern sector of the Mediterranean Sea from 14 July to 9 August 2000. Hg0 ranged between 0.4 and 11.2 ng m−3 with an average of 1.9±1.02 ng m−3 over the entire period. Higher concentrations were observed in the Gulf of Naples due primarily to air masses transported from the mainland reflecting the contribution from anthropogenic sources. RGM levels were measured using KCl-coated annular denuders coupled to an automated gas phase mercury analyser (Tekran 2537A). RGM concentrations varied from 0.2 to 30.1 pg m−3 with an average of 7.9 pg m−3. A diurnal cycle of the RGM concentration was observed during the entire sampling period with the maximum around midday and the minimum during the night; the oxidation by daytime oxidants, i.e., OH, may have determined the observed diurnal cycle of RGM concentration in the MBL.