Gaseous mercury in the Mediterranean marine boundary layer

Atmospheric Chemistry and Physics Discussions This discussion paper is/has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP if available. Abstract Atmospheric mercury concentrations were measured during two oceanographic cruise campaigns covering the Adriatic Sea, the first during the autumn in 2004 and the second in the summer of 2005. The inclement weather during the autumn campaign meant that no clear in-situ production of oxidised gas phase mercury was seen, and that 5 events where high values of Hg II (g) and/or Hg associated with particulates (Hg P) were observed, were the result of plumes from anthropogenic emission sources. During the summer campaign however, the by now rather familiar diurnal variation of Hg II (g) concentration , with maxima around midday, was observed. Again there were events when high Hg II (g) and particulates (Hg P) concentrations were seen which did not fit with the 10 pattern of daily in-situ Hg II (g) production, which were traceable, with the help of back trajectory calculations, to anthropogenic emission sources. All the emission plumes encountered could be traced back to ports, not all of which are associated with major industrial installations. It therefore seems likely in theses cases that the emissions are either due to shipping or to port activities. Box modelling studies of the summer 2005 15 campaign show that although the in-situ production of Hg II (g) occurs in the MBL, the exact chemical mechanism responsible is difficult to determine. However given the high O 3 concentrations encountered during this campaign it seems clear that if Hg 0 does react with O 3 , it does not produce gas phase Hg II , and the reaction between Hg 0 and OH if it occurs, does not contribute appreciably to Hg II (g) production.