Francesca Sprovieri

Intercomparison of methods for sampling and analysis of atmospheric mercury species

An intercomparison for sampling and analysis of atmospheric mercury species was held in Tuscany, June 1998. Methods for sampling and analysis of total gaseous mercury (TGM), reactive gaseous mercury (RGM) and total particulate mercury (TPM) were used in parallel sampling over a period of 4 days. The results show that the different methods employed for TGM compared well whereas RGM and TPM showed a somewhat higher variability. Measurement results of RGM and TPM improved over the time period indicating that activities at the sampling site during set-up and initial sampling affected the results. Especially the TPM measurement results were affected. Additional parallel sampling was performed for two of the TPM methods under more controlled conditions which yielded more comparable results.

Atmospheric mercury distribution in Northern Europe and in the Mediterranean region

Mercury species in air have been measured at five sites in Northwest Europe and at five coastal sites in the Mediterranean region during measurements at four seasons. Observed concentrations of total gaseous mercury (TGM), total particulate mercury (TPM) and reactive gaseous mercury (RGM) were generally slightly higher in the Mediterranean region than in Northwest Europe. Incoming clean Atlantic air seems to be enriched in TGM in comparison to air in Scandinavia. Trajectory analysis of events where high concentrations of TPM simultaneously were observed at sites in North Europe indicate source areas in Central Europe and provide evidence of transport of mercury on particles on a regional scale.

Dynamic processes of mercury over the Mediterranean region: results from the Mediterranean Atmospheric Mercury Cycle System (MAMCS) project

The Mediterranean Atmospheric Mercury Cycle System (MAMCS) project was performed between 1998 and 2000 and involved the collaboration of universities and research institutes from Europe, Israel and Turkey. The main goal of MAMCS was to investigate dynamic processes affecting the cycle of mercury in the Mediterranean atmosphere by combining ad hoc field measurements and modelling tasks. To study the fate of Hg in the Mediterranean Basin an updated emission inventory was compiled for Europe and the countries bordering the Mediterranean Sea. Models were developed to describe the individual atmospheric processes which influence the chemical and physical characteristics of atmospheric Hg, and these were coupled to meteorological models to examine the dispersion and deposition of Hg species in the Mediterranean Basin. One intercomparison and four two-week measurement campaigns were carried out over a three-year period. The work presented here describes the results in general terms but focuses on the areas where definite conclusions were unforthcoming and thus highlights those aspects where, in spite of advances made in the understanding of Hg cycling, further work is necessary in order to be able to predict confidently Hg and Hg compound concentration fields and deposition patterns.

Reactive gaseous mercury in the marine boundary layer: modelling and experimental evidence of its formation in the Mediterranean region

Reactive gaseous mercury (RGM) concentrations have been modelled using a photochemical box model of the marine boundary layer (MBL) and compared to measured data obtained during a research cruise. The model has been constrained by using measured concentrations of elemental Hg and ozone, as well as measured temperature and relative humidity. The results show good qualitative agreement both during the rough weather encountered on the first part of the voyage and the second, calmer period of the campaign. Quantitative agreement is obtained using a box height of 100 m during the first leg of the campaign. The modelled and measured results from the second leg agree as far as the nocturnal RGM concentration minima are concerned but underestimate the daytime maxima by a factor of two. The comparison of the modelled with measured results supports the hypothesis that there are daytime mercury oxidation reactions occurring which have not yet been identified.

Atmospheric mercury concentrations observed at ground-based monitoring sites globally distributed in the framework of the GMOS network

Long-term monitoring of data of ambient mercury (Hg) on a global scale to assess its emission, transport, atmospheric chemistry, and deposition processes is vital to understanding the impact of Hg pollution on the environment. The Global Mercury Observation System (GMOS) project was funded by the European Commission (http://www.gmos.eu) and started in November 2010 with the overall goal to develop a coordinated global observing system to monitor Hg on a global scale, including a large network of ground-based monitoring stations, ad hoc periodic oceanographic cruises and measurement flights in the lower and upper troposphere as well as in the lower stratosphere. To date, more than 40 ground-based monitoring sites constitute the global network covering many regions where little to no observational data were available before GMOS. This work presents atmospheric Hg concentrations recorded worldwide in the framework of the GMOS project (2010-2015), analyzing Hg measurement results in terms of temporal trends, seasonality and comparability within the network. Major findings highlighted in this paper include a clear gradient of Hg concentrations between the Northern and Southern hemispheres, confirming that the gradient observed is mostly driven by local and regional sources, which can be anthropogenic, natural or a combination of both.

Development and application of a regional-scale atmospheric mercury model based on WRF/Chem: a Mediterranean area investigation

The emission, transport, deposition and eventual fate of mercury (Hg) in the Mediterranean area has been studied using a modified version of the Weather Research and Forecasting model coupled with Chemistry (WRF/Chem). This model version has been developed specifically with the aim to simulate the atmospheric processes determining atmospheric Hg emissions, concentrations and deposition online at high spatial resolution. For this purpose, the gas phase chemistry of Hg and a parametrised representation of atmospheric Hg aqueous chemistry have been added to the regional acid deposition model version 2 chemical mechanism in WRF/Chem. Anthropogenic mercury emissions from the Arctic Monitoring and Assessment Programme included in the emissions preprocessor, mercury evasion from the sea surface and Hg released from biomass burning have also been included. Dry and wet deposition processes for Hg have been implemented. The model has been tested for the whole of 2009 using measurements of total gaseous mercury from the European Monitoring and Evaluation Programme monitoring network. Speciated measurement data of atmospheric elemental Hg, gaseous oxidised Hg and Hg associated with particulate matter, from a Mediterranean oceanographic campaign (June 2009), has permitted the model’s ability to simulate the atmospheric redox chemistry of Hg to be assessed. The model results highlight the importance of both the boundary conditions employed and the accuracy of the mercury speciation in the emission database. The model has permitted the reevaluation of the deposition to, and the emission from, the Mediterranean Sea. In light of the well-known high concentrations of methylmercury in a number of Mediterranean fish species, this information is important in establishing the mass balance of Hg for the Mediterranean Sea. The model results support the idea that the Mediterranean Sea is a net source of Hg to the atmosphere and suggest that the net flux is ≈30 Mg year−1 of elemental Hg.

The cycling and sea-air exchange of mercury in the waters of the Eastern Mediterranean during the 2010 MED-OCEANOR cruise campaign.

An oceanographic cruise campaign on-board the Italian research vessel Urania was carried out from the 26th of August to the 13th of September 2010 in the Eastern Mediterranean. The campaign sought to investigate the mercury cycle at coastal and offshore locations in different weather conditions. The experimental activity focused on measuring mercury speciation in both seawater and in air, and using meteorological parameters to estimate elemental mercury exchange at the sea-atmosphere interface. Dissolved gaseous mercury (DGM), unfiltered total mercury (UTHg) and filtered total mercury (FTHg) surface concentrations ranged from 16 to 114, 300 to 18,760, and 230 to 10,990pgL(-1), respectively. The highest DGM, UTHg and FTHg values were observed close to Augusta (Sicily), a highly industrialized area of the Mediterranean region, while the lowest values were recorded at offshore stations. DGM vertical profiles partially followed the distribution of sunlight, as a result of the photoinduced transformations of elemental mercury in the surface layers of the water column. However, at some stations, we observed higher DGM concentrations in samples taken from the bottom of the water column, suggesting biological mercury production processes or the presence of tectonic activity. Moreover, two days of continuous measurement at one location demonstrated that surface DGM concentration is affected by solar radiation and atmospheric turbulence intensity. Atmospheric measurements of gaseous elemental mercury (GEM) showed an average concentration (1.6ngm(-3)) close to the background level for the northern hemisphere. For the first time this study used a numerical scheme based on a two-thin film model with a specific parameterization for mercury to estimate elemental mercury flux. The calculated average mercury flux during the entire cruise was 2.2±1.5ngm(-2)h(-1). The analysis of flux data highlights the importance of the wind speed on the mercury evasion from sea surfaces.

Chasing quicksilver northward: mercury chemistry in the Arctic troposphere

Environmental Context. ‘Mercurial storms rage over the Arctic’ wrote Fred Pearce in New Scientist in June of 1997: he was referring to the recent discovery by Bill Schroeder and his colleagues (Nature, Vol. 394, 1998) of periods soon after Arctic dawn when the concentration of mercury in the atmosphere literally plummets to levels so low that they can be undetectable, even by the most sensitive of modern instruments. A decade and many measurement campaigns later, we think we understand how these so-called depletion events occur, if not all the mechanisms that go towards providing the conditions for them to happen. Nor do we really know what happens to the mercury removed from the atmosphere; the fear is that it is deposited and enters the Arctic ecosystem, where it is potentially extremely harmful. The present study questions whether that fear is grounded. Abstract. The tropospheric boundary layer chemistry of Hg has been simulated using a two-phase photochemical box model to see if our current (experimental and theoretical) understanding of Hg(g)0 reaction rates can account for the depletion events seen during Arctic spring, when the so-called ‘bromine explosion’ in the model is constrained by the measured ozone depletion rate. The simulations reveal that the observed rate of Hg(g)0 depletion can be accounted for; however, the measured concentrations of gas-phase oxidised Hg and HgP (Hg associated with particulate matter) cannot. Simulating the emission of Hg(g)0 from the snow pack to mimic the observed concentration recovery after a depletion event suggests the net Hg deposition from a depletion event is all but irrelevant.

Spatial coverage and temporal trends of land-based atmospheric mercury measurements in the Northern and Southern Hemispheres

This chapter presents a review of atmospheric mercury measurements (as total and as speciated mercury) conducted at terrestrial sites during the last decade. A large number of activities have been carried out in different regions of the world aiming to assess the level of mercury in ambient air and precipitation, and its variation over time and with changing meteorological conditions. Recent studies have highlighted that in fast developing countries (i.e., China, India) mercury emissions are increasing in a dramatic fashion due primarily to a sharp increase in energy production from the combustion of coal (Chapter-2 by Street et al.; Chapter-3 by Feng et al. in this report). The large increase in mercury emissions in China over the last decade are not currently reflected in the long-term measurement of total gaseous mercury at Mace Head, Ireland between 1996 to 2006, nor in the precipitation data of the North American Mercury Deposition Network (MDN). There are documented recent increases in the oxidation potential of the atmosphere which might account, at least in part, for the discrepancy between observed gaseous mercury concentrations (steady or decreasing) and global mercury emission inventories (increasing). This chapter provides a detailed overview of atmospheric measurements performed at industrial, remote and rural sites during the last decade with reference to the monitoring techniques and location of monitoring sites in most of the continents.

Mercury speciation in the Adriatic Sea

Mercury and its speciation were studied in surface and deep waters of the Adriatic Sea. Several mercury species (i.e. DGM – dissolved gaseous Hg, RHg – reactive Hg, THg – total Hg, MeHg – monomethyl Hg and DMeHg – dimethylmercury) together with other water parameters were measured in coastal and open sea deep water profiles. THg concentrations in the water column, as well as in sediments and pore waters, were the highest in the northern, most polluted part of the Adriatic Sea as the consequence of Hg mining in Idrija and the heavy industry of northern Italy. Certain profiles in the South Adriatic Pit exhibit an increase of DGM just over the bottom due to its diffusion from sediment as a consequence of microbial and/or tectonic activity. Furthermore, a Hg mass balance for the Adriatic Sea was calculated based on measurements and literature data.