Abstract
Abstract. A large number of activities have been carried out to characterise the levels of mercury (Hg) species in ambient air and precipitation, in order to understand how they vary over time and how they depend on meteorological conditions. Following the discovery of atmospheric Hg depletion events (AMDEs) in Polar Regions, a significant research effort was made to assess the chemical-physical mechanisms behind the rapid conversion of atmospheric gaseous Hg (Hg0) into reactive and water-soluble forms which are potentially bioavailable. The understanding of the way in which Hg is released into the atmosphere, transformed, deposited and eventually incorporated into biota is of crucial importance not only for the polar regions but also for the marine environment in general. The oceans and seas are both sources and sinks of Hg and play a major role in the Hg cycle. In this work, the available Hg concentration datasets from a number of terrestrial sites (industrial, rural and remote) in both the Northern and Southern Hemispheres as well as over oceans and seas have been investigated. The higher Hg species concentration and variability observed in the Northern Hemisphere suggest that the majority of emissions and re-emissions occur there. The inter-hemispherical gradient with higher total gaseous mercury (TGM) concentrations in the Northern Hemisphere has remained nearly constant over the years for which data are available. The analysis of Hg concentration patterns indicates the differences in regional source/sink characteristics, with increasing variability toward areas strongly influenced by anthropogenic sources. The large increase in Hg emissions in rapidly developing countries (i.e., China, India) over the last decade, due primarily to a sharp increase in energy production from coal combustion, are not currently reflected in the long-term measurements of TGM in ambient air and precipitation at continuous monitoring sites in either Northern Europe or North America. The discrepancy between observed gaseous Hg concentrations (steady or decreasing) and global Hg emission inventories (increasing) has not yet been explained, though the potential oxidation of the atmosphere during the last decade is increasing. Currently, however, a coordinated observational network for Hg does not exist.
Highlights
Mercury is emitted into the atmosphere from a variety of anthropogenic (Pirrone et al, 1996, 1998, 2001) and natural sources in different chemical and physical forms (Pacyna et al, 2001; Carpi, 1997)
A comparison of total gaseous mercury (TGM), Total Particulate Mercury (TPM) and HgII measurements obtained during four synchronized seasonal field campaigns from 1998 to 1999 at 10 coastal sites in the Mediterranean Region (5 sites) and in North Europe (5 sites) during the MOE and MAMCS project showed that TGM was slightly higher in the Mediterranean, and that TPM and HgII concentrations were significantly higher at Mediterranean sites compared to northern Europe, even though the density of industrial and urban centres is higher in northern compared to southern Europe (Pirrone et al, 2001, 2003; Sprovieri et al, 2003; Wangberg et al, 2001; Munthe et al, 2001)
The gradient and higher variability observed in the Northern Hemisphere suggests that the majority of emissions and re-emissions are located in the Northern Hemisphere
Summary
Mercury is emitted into the atmosphere from a variety of anthropogenic (i.e., power generation facilities, smelters, cement production, waste incineration and many others) (Pirrone et al, 1996, 1998, 2001) and natural sources (i.e., volcanoes, crustal degassing, oceans) in different chemical and physical forms (Pacyna et al, 2001; Carpi, 1997). The reason for this is not yet clear, it was hypothesized that atmospheric Hg cycling is possibly faster than previously thought. In order to retrieve a history of atmospheric Hg0 at middle and high northern latitudes, Hg0 was measured in the interstitial air of firn (perennial snowpack) in the Greenland icecap From this record, it has been shown that anthropogenic emissions caused a two-fold increase in boreal atmospheric Hg0 concentrations before the 1970s, which possibly contributed to higher deposition rates of mercury both in industrialized and remote areas (Faın et al, 2008, 2009). The amount of data analysed for each continent/region is enormous; major findings of key studies/programmes carried out in all regions have been highlighted
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