HR: 15:45h
AN: A23D-08    [Abstracts]
TI: Why Modelling on Different Scales is Necessary to Understand the Balance of Mercury in the Atmosphere
AU: * Pirrone, N
EM: n.pirrone@cs.iia.cnr.it
AU: Hedgecock, I M
EM: i.hedgecock@cs.iia.cnr.it
AU: Jung, G
EM: g.jung@cs.iia.cnr.it
AB: Two apparently conflicting facts concerning atmospheric mercury have prompted debate and an intensification of research activity over the last five years. The first is that global background atmospheric mercury concentrations are extremely uniform, with a slightly lower in the southern hemisphere compared to the northern hemisphere. This indicates that the atmospheric residence time pf mercury is long enough for it to be transported from its main emission source areas. The second is the by now well established presence of oxidised mercury compounds in the marine BL, far from anthropogenic sources. Oxidised mercury compounds make up a fairly small component of anthropogenic emissions, but are much more readily scavenged or deposited than elemental mercury and therefore not expected to be transported over any great distance. The presence of these compounds in the MBL therefore suggests that in-situ production occurs, which would also infer in-situ deposition thereby reducing the local concentration of mercury. However, as stated previously background concentrations are hemisperically extremely uniform. In order to investigate the atmospheric transport and transformation of mercury, modelling studies at different scales are required. Complex photochemical box models are used to study chemical processes in detail. Regional transport models with less complex chemistry but including anthropogenic and natural emission sources and a parameterised description of deposition processes are used to study source receptor relationships and estimate Hg exchange budgets between the atmosphere and terrestrial and marine receptors. Global transport models (with simplified chemistry) are used to investigate long-distance (intercontinental) transport pathways and the uniformity of hemispherical background concentrations. Results from the photochemical box model studies indicate that the atmospheric lifetime of mercury due to reactions with Br and OH may be shorter than previously thought, while the regional models indicate that emission and deposition processes may actually act to maintain the uniformity of the background concentration away from emission sources. The role of oceans and the reactions which occur in the atmospheric boundary layer and the surface layer of seas and oceans merit further investigation.
UR: http:www.cs.iia.cnr.it
DE: 0312 Air/sea constituent fluxes (3339, 4504)
DE: 0330 Geochemical cycles (1030)
DE: 0341 Middle atmosphere: constituent transport and chemistry (3334)
DE: 0345 Pollution: urban and regional (0305, 0478, 4251)
SC: Atmospheric Sciences [A]
MN: 2007 Joint Assembly