The superstatistical nature and interoccurrence time of atmospheric mercury concentration fluctuations.

The probability density function (PDF) of the time intervals between subsequent extreme events in atmospheric Hg0 concentration data series from different latitudes has been investigated. The Hg0 dynamic possesses a long-term memory autocorrelation function. Above a fixed threshold Q in the data, the PDFs of the interoccurrence time of the Hg0 data are well described by a Tsallis q-Exponential function. This PDF behavior has been explained in the framework of superstatistics, where the competition between multiple mesoscopic processes affects the macroscopic dynamics. An extensive parameter µ, encompassing all possible fluctuations related to mesoscopic phenomena, has been identified. It follows a χ 2-distribution, indicative of the superstatistical nature of the overall process. Shuffling the data series destroys the long-term memory, the distributions become independent of Q, and the PDFs collapse on to the same exponential distribution. The possible central role of atmospheric turbulence on extreme events in the Hg0 data is highlighted.

The GMOS cyber(e)-infrastructure: advanced services for supporting science and policy.

The need for coordinated, systematized and catalogued databases on mercury in the environment is of paramount importance as improved information can help the assessment of the effectiveness of measures established to phase out and ban mercury. Long-term monitoring sites have been established in a number of regions and countries for the measurement of mercury in ambient air and wet deposition. Long term measurements of mercury concentration in biota also produced a huge amount of information, but such initiatives are far from being within a global, systematic and interoperable approach. To address these weaknesses the on-going Global Mercury Observation System (GMOS) project ( www.gmos.eu ) established a coordinated global observation system for mercury as well it retrieved historical data ( www.gmos.eu/sdi ). To manage such large amount of information a technological infrastructure was planned. This high-performance back-end resource associated with sophisticated client applications enables data storage, computing services, telecommunications networks and all services necessary to support the activity. This paper reports the architecture definition of the GMOS Cyber(e)-Infrastructure and the services developed to support science and policy, including the United Nation Environmental Program. It finally describes new possibilities in data analysis and data management through client applications.

Study on the reduction of atmospheric mercury emissions from mine waste enriched soils through native grass cover in the Mt. Amiata region of Italy.

Atmospheric mercury emissions from mine-waste enriched soils were measured in order to compare the mercury fluxes of bare soils with those from other soils covered by native grasses. Our research was conducted near Mt. Amiata in central Italy, an area that was one of the largest and most productive mining centers in Europe up into the 1980s. To determine in situ mercury emissions, we used a Plexiglas flux chamber connected to a portable mercury analyzer (Lumex RA-915+). This allowed us to detect, in real time, the mercury vapor in the air, and to correlate this with the meteorological parameters that we examined (solar radiation, soil temperature, and humidity). The highest mercury flux values (8000ngm(-2)h(-1)) were observed on bare soils during the hours of maximum insulation, while lower values (250ngm(-2)h(-1)) were observed on soils covered by native grasses. Our results indicate that two main environmental variables affect mercury emission: solar radiation intensity and soil temperature. The presence of native vegetation, which can shield soil surfaces from incident light, reduced mercury emissions, a result that we attribute to a drop in the efficiency of mercury photoreduction processes rather than to decreases in soil temperature. This finding is consistent with decreases in mercury flux values down to 3500ngm(-2)h(-1), which occurred under cloudy conditions despite high soil temperatures. Moreover, when the soil temperature was 28°C and the vegetation was removed from the experimental site, mercury emissions increased almost four-fold. This increase occurred almost immediately after the grasses were cut, and was approximately eight-fold after 20h. Thus, this study demonstrates that enhancing wild vegetation cover could be an inexpensive and effective approach in fostering a natural, self-renewing reduction of mercury emissions from mercury-contaminated soils.

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.

Chemical composition of aerosol size fractions at a coastal site in southwestern Italy: seasonal variability and transport influence.

The present study focuses on the elemental characterization of fine and coarse particles collected at a coastal site of southwestern Italy, in a suburban area of the Calabria region. A chemical tracer analysis was carried out to identify the major emission sources influencing on the atmospheric aerosol levels. Size-resolved particulate samples were collected during three 2-week seasonal sampling campaigns: autumn (19 October to 2 November 2003), winter (19 January to 2 February 2004) and spring (26 April to 10 May 2004). Ambient concentrations of selected elements (Fe, Mn, Mg, Ca, V, Cu, Cr, Ni, Zn, Pb, and Cd) associated to fine and coarse size fractions were determined using atomic absorption spectrometry (AAS). The enrichment factor method was applied, suggesting a prevailing anthropogenic component for all the detected elements, with Fe, Mg, Mn, and Ca as exceptions. Trajectory sector analysis was used in order to discriminate the influence of different air mass origins and paths. Long-range transport from both the continental Europe and the Saharan region proved to be the main influencing factors. African dust outbreaks, whose occurrence frequency was greater during the autumn and spring seasonal monitoring periods, gave rise to a total of eight exceedances of the European Commission (EC) PM10 daily limit value as well as an increase in values of the crustal-derived elements (Fe, Mg, and Ca). Long-range transport from the heavily industrialized area of Central/Eastern Europe contributed to the high levels of Zn, Cd, and Pb that were recorded during the winter sampling campaign. Seasonal trend and comparison with measurements previously performed across the Mediterranean basin were also presented and discussed.

Variability of atmospheric aerosol and ozone concentrations at marine, urban, and high-altitude monitoring stations in southern Italy during the 2007 summer Saharan dust outbreaks and wildfire episodes.

In order to evaluate the spatial variation of aerosol (particulate matter with aerodynamic diameter < or = 10 microm [PM10]) and ozone (03) concentrations and characterize the atmospheric conditions that lead to 03 and PM10-rich episodes in southern Italy during summer 2007, an intensive sampling campaign was simultaneously performed, from middle of July to the end of August, at three ground-based sites (marine, urban, and high-altitude monitoring stations) in Calabria region. A cluster analysis, based on the prevailing air mass backward trajectories, was performed, allowing to discriminate the contribution of different air masses origin and paths. Results showed that both PM10 and 03 levels reached similar high values when air masses originated from the industrialized continental Europe as well as under the influence of wildfire emissions. Among natural sources, dust intrusion and wildfire events seem to involve a marked impact on the recorded data. Typical fair weather of Mediterranean summer and persisting anticyclone system at synoptic scale were indeed favorable conditions to the arrival of heavily dust-loaded air masses over three periods of consecutive days and more than half of the observed PM10 daily exceedances have been attributed to Saharan dust events. During the identified dust outbreaks, a consistent increase in PM10 levels with a concurrent decrease in 03 values was also observed and discussed.

Standardisation of a European measurement method for the determination of total gaseous mercury: results of the field trial campaign and determination of a measurement uncertainty and working range.

Working Group 25 of the European Committee for Standardisation's (CEN) Technical Committee 264 'Air Quality' is currently finalising a standard method for the measurement of total gaseous mercury (TGM) in ambient air, in response to the requirements of the European Union's Fourth Air Quality Daughter Directive (4(th) DD). We report the results of a programme of field measurements and the statistical analysis performed to assess the uncertainty of the proposed standard method, define its working range and determine its compliance with the required data quality objectives of the Fourth Air Quality Daughter Directive. The statistical analysis has shown that the maximum relative expanded uncertainty of 50% allowed by the 4(th) DD is met down to a mercury mass concentration of approximately 0.75 ng m(-3), and that the dominant contribution to this uncertainty is systematic bias between instruments, mainly arising from the uncertainty in the calibration of the instruments.