NICOLA PIRRONE

CNR-Institute for Atmospheric Pollution, c/o: UNICAL, 87036 Rende, Italy

In recent years several studies have been done to assess the processes governing the cycle of atmospheric mercury in the environment including emissions, transport, chemical and physical transformations and atmospheric deposition to water and terrestrial receptors. During the 1980s and 1990s mercury problems have been investigated in the United States and Canada, North Europe and South America, whereas little attention has been devoted to assess spatial distributions of atmospheric mercury in the Mediterranean Sea region where significant mercury concentrations have been measured in air and water samples as well as in several fishes and types of food web. However, in the last three years the EU Directorate General on Research (EU-DG Research) in the frame of the Environment and Climate Program funded two major research projects on mercury, namely the “Mediterranean Atmospheric Mercury Cycle System – MAMCS” and the “Mercury over Europe (MOE)”. MAMCS is addressed to improve our understanding of all those mechanisms influencing the dynamics of mercury in the Mediterranean Sea region including emissions from natural and anthropogenic sources, atmospheric transport and deposition to water and terrestrial receptors, and chemical and physical transformations of Hg⁰ and other Hg species in the atmosphere. The MOE project is addressed to similar topics but concentrating on the North European region. Several tasks carried out in MAMCS and MOE have been coordinated (i.e., measurements, emission inventory) in order to improve the potential of utilisation of the outcomes of both projects.

Mercury emissions (see Figure 1) from coal combustion for electric power generation, cement manufacturing and solid waste disposal through incineration facilities increased since 1983 and are projected to increase during the next two decades if no policy will be implemented to reduce or/and control emissions from major industrial plants (Pirrone et al., 2000).

Figure 1 – Annual emissions (t yr^-1) of mercury to the atmosphere in the Mediterranean Se region from coal combustion, cement manufacturing and municipal solid waste incineration from 1983 to 2025.

In order to assess the horizontal distribution of elemental mercury and other mercury species over the Mediterranean Sea and in North Europe, four intensive measurements campaigns have been carried in the frame of the MAMCS and MOE projects simultaneously at five sites in the Mediterranean region and at five sites in the North Europe (see Figure 2).

Figure 2 - The measurement sites. 1: Mallorca (39º40’30’’N, 2º41’36’’E), 2: Calabria (39^o25’N, 16^o00’E), 3: Sicily (36^o40’N, 15^o10’E), 4: Turkey (36^o28’12”N, 30^o20’24”E), 5: Israel (32^o40’N, 34^o56’E), 6: Germany (53^o08’34”N, 13^o02’00”E), 7: Germany (54^o26’14”N, 12^o43’30”E), 8: Sweden (57^o24’48”N, 11^o56’06”E), 9: Sweden (58^o48’00”N, 17^o22’54”E), 10: Ireland (53^o20’N, 9^o54’W).

The average TGM concentrations varied between 1.6 and 2.4 ng m^-3 with no significant seasonal variations. The relative uniform distribution found for TGM depends primarily on the relatively stable global/hemispheric background concentration which only occasionally shows higher values due to long-range transport from major anthropogenic source in Europe. Except for the first campaign, the observations indicates that TGM levels were higher in the Mediterranean area than in North Europe.

Particulate mercury (TPM) shows more pronounced differences between the Mediterranean region and North Europe. The RGM concentrations in the Mediterranean region are also higher than that observed in Northern Europe suggesting that a pronounced photochemical activity and chemical reactions (i.e., with halogen radicals) within the marine boundary layer (MBL) may be responsible for these regional gradients in RGM levels. However, RGM trends were similar to that observed for TPM and TGM suggesting that spry formation and bubble ejection that take place at high wind speeds coupled with exchange mechanisms at the air-water interface (i.e., driven by a concentration gradient) may help to explain this behaviour. However, trajectory analysis and source-receptor modeling coupled with regional scale transport-transformation modeling are under way and will help to interpret these regional patterns in the horizontal mercury distributions in the atmosphere.

A correct evaluation of spatial and temporal evolutions of mercury concentrations (and all its species) in different environmental compartment (i.e., air, water, soil) and areas (i.e., industrial, urban, remote) coupled with a detailed description of chemical and physical processes of elemental mercury and its species as they interact with other atmospheric contaminants (i.e., O₃, halogen radicals) during different steps involved in the emission, transport and removal processes is of fundamental importance in assessing the overall mercury cycle between atmospheric, aquatic and terrestrial compartments on regional and global scales. An important task carried out in the frame of the MAMCS project (and in the MOE project as well) is the development of a comprehensive integrated modeling system for assessing dynamic processes of atmospheric mercury in the Mediterranean region.

The MAMCS integrated modeling system is based on two major well known meteorological-dispersion atmospheric models, the Regional Atmospheric Modeling System (RAMS) and the SKIRON/ETA meteorological system. The system based on RAMS is used primarily for assessing specific processes as it provides a detailed description of microphysics which requires significant computer time, making it inconvenient for long-term simulations (i.e., 1-2 years). On the other hand, the system based on the SKIRON/ETA is designed for long-term simulations which are very important for assessing regional scale mercury budgets for periods of 1-2 years, because it requires only 50% of the RAMS computer time. A number of ad-hoc models have been developed and dynamically coupled to both RAMS and SKIRON systems in order to account for the following mechanisms/processes: (a) particle dry deposition, (b) wet scavenging, (c) gas-particle partitioning, (d) chemical transformations during over-water transport, (e) in-cloud chemistry, and (f) gaseous mercury exchange at the air-water interface (i.e., Pirrone et al., 1999; Forlano et al., 2000; Hedgecock et al., 2000; Pirrone et al., 2000).

Meanwhile, several other initiatives addressed to assess the level of mercury in remote European areas (i.e., Arctic) as well as the fluxes of mercury from natural sources (i.e., seawater, volcanoes) have been carried out in the frame of other research projects funded at national and European level (Ferrara et al., 2000; Sprovieri and Pirrone, 2000). The outcomes of these research activities on different aspects of the mercury cycling in the European ecosystems is of primary interest for the preparation of the new European legislation on air quality. Indeed, current initiatives of the EU Directorate General on Environment are addressed to prepare the Position Paper on atmospheric mercury that will be the basis of the New Framework Directive (FWD) on mercury.

The purposes of this paper is to present the outcomes of the European research on different aspects/mechanisms involved in the mercury cycling on local and regional scales in Europe and its role in supporting the development of the New Air Quality Legislation (FWDs) in Europe.

REFERENCES

Ferrara, R., Mazzolai, B., Lanzillotta, E., Nucaro, E., Pirrone, N. (2000) Atmospheric Mercury Evasion from Mediterranean Sea Water. Science of the Total Environment (In press).

Forlano, L., Hedgecock, I., Pirrone, N. (2000) Deposition and Speciation of Atmospheric Mercury as it Interacts with the Ambient Aerosol. Science of the Total Environment (In press).

Hedgecock, I., Forlano, L. Pirrone, N. (1999) The Role of Ambient Aerosol Characteristics in the Speciation of Atmospheric Mercury. Journal of Aerosol Science, 30, 463-464.

Pirrone, N. (1998) Modeling the Dynamics of Atmospheric Mercury over the Mediterranean Sea: The MAMCS Project. Journal of Aerosol Science, 29, 1155-1156.

Pirrone, N., Costa, P., Pacyna, J. (1999) Past, Current and Projected Emissions of Trace Elements in the Mediterranean Basin. Water Science and Technology, 39, 1-7.

Pirrone, N., Hedgecock, I., Forlano, L. (2000) The Role of the Ambient Aerosol in the Atmospheric Processing of Semi-Volatile Contaminants: A Parameterised Numerical Model (GASPAR). Journal of Geophysical Research 105, D8, 9773-9790.

Pirrone, N., Costa, P., Pacyna, J.M., Ferrara, R. (2000) Mercury Emissions from Anthropogenic Sources in the Mediterranean Atmosphere. Atmos. Environ. (submitted).

Sprovieri, F. and Pirrone, N. (2000) A Preliminary Assessment of Mercury Levels in the Antarctic and Arctic Troposphere. Journal of Aerosol Science (In press).