Search

OVSICORI, IAMC-CNR We review the state of knowledge on global volcanogenic Hg emissions to the atmosphere and present new data from seven active volcanoes (Poás, Rincón de la Vieja, Turrialba, Aso, Mutnovsky, Gorely and Etna) and two geothermal fields (Las Pailas and Las Hornillas). The variability of Hg contents (c. 4-125 ng m-3) measured in gaseous emissions reflects the dynamic nature of volcanic plumes, where the abundances of volatiles are determined by the physical nature of degassing and variable air dilution. Based on our dataset and previous work, we propose that an average Hg/SO2 plume mass ratio of c. 7.8 × 10-6 (± 1.5 × 10-6; 1 SE, n = 13) is best representative of open-conduit quiescent degassing. Taking into account the uncertainty in global SO2 emissions, we infer a global volcanic Hg flux from persistent degassing of c. 76 ± 30 t a-1. Our data are derived from active volcanoes during non-eruptive periods and we do not have any direct constraint on the Hg flux during periods of elevated SO2 flux associated with large-scale effusive or explosive eruptions. This suggests that the time-averaged Hg flux from these volcanoes is even larger if the eruptive contribution is considered. Conversely, closed-conduit degassing and geothermal emissions contribute modest amounts of Hg. Revisamos el estado del conocimiento sobre las emisiones globales de Hg volcanogénico a la atmósfera y presentamos nuevos datos de siete volcanes activos (Poás, Rincón de la Vieja, Turrialba, Aso, Mutnovsky, Gorely y Etna) y dos campos geotérmicos (Las Pailas y Las Hornillas). ). La variabilidad del contenido de Hg (c. 4-125 ng m-3) medido en emisiones gaseosas refleja la naturaleza dinámica de las columnas volcánicas, donde la abundancia de volátiles está determinada por la naturaleza física de la desgasificación y la dilución variable del aire. Basándonos en nuestro conjunto de datos y trabajos previos, proponemos que una relación promedio de masa de pluma Hg / SO2 de c. 7.8 × 10-6 (± 1.5 × 10-6; 1 SE, n = 13) es el mejor representante de la desgasificación inactiva de conducto abierto. Teniendo en cuenta la incertidumbre en las emisiones globales de SO2, inferimos un flujo de Hg volcánico global a partir de la desgasificación persistente de c. 76 ± 30 t a-1. Nuestros datos se derivan de volcanes activos durante períodos no eruptivos y no tenemos ninguna restricción directa sobre el flujo de Hg durante períodos de flujo elevado de SO2 asociados con erupciones efusivas o explosivas a gran escala. Esto sugiere que el flujo de Hg promediado en el tiempo de estos volcanes es aún mayor si se considera la contribución eruptiva. Por el contrario, la desgasificación de conductos cerrados y las emisiones geotérmicas aportan cantidades modestas de Hg. Revisamos o estado do conhecimento sobre as emissões de Hg vulcanogênicas globais para a atmosfera e apresentamos novos dados de sete vulcões ativos (Poás, Rincón de la Vieja, Turrialba, Aso, Mutnovsky, Gorely e Etna) e dois campos geotérmicos (Las Pailas e Las Hornillas ) A variabilidade dos conteúdos de Hg (c. 4-125 ng m-3) medidos nas emissões gasosas reflete a natureza dinâmica das plumas vulcânicas, onde as abundâncias de voláteis são determinadas pela natureza física da desgaseificação e diluição variável do ar. Com base em nosso conjunto de dados e trabalho anterior, propomos que uma razão média da massa da pluma de Hg / SO2 de c. 7,8 × 10-6 (± 1,5 × 10-6; 1 SE, n = 13) é o melhor representante da desgaseificação quiescente de conduíte aberto. Levando em consideração a incerteza nas emissões globais de SO2, inferimos um fluxo de Hg vulcânico global a partir da desgaseificação persistente de c. 76 ± 30 t a-1. Nossos dados são derivados de vulcões ativos durante períodos não eruptivos e não temos qualquer restrição direta sobre o fluxo de Hg durante os períodos de fluxo elevado de SO2 associado a erupções explosivas ou efusivas em grande escala. Isso sugere que o fluxo médio de Hg desses vulcões é ainda maior se a contribuição eruptiva for considerada. Por outro lado, a desgaseificação por conduíte fechado e as emissões geotérmicas contribuem com quantidades modestas de Hg. University of Palermo, Italy Universidad Nacional, Costa Rica Observatorio Vulcanológico y Sismológico de Costa Rica

Il mercurio (Ilg) è uno dei principali inquinanti emessi in atmosfera. La sua complessità geochimica, unitamente alla tossicità c agli effetti persistenti della sua presenza nell’ecosistema terrestre, lo hanno inserito nella lista delle priorità di un numero sempre crescente di accordi internazionali rivolti alla tutela ambientale e della stiline umana (The Arctic- Monitoring and Assessment Program, AMAR, United Nations - Economie Commission for Europe: Ileavy Metals Protocol, UN- ECE, The Helsinki Commission, IIELCOM, la convenzione OSPAR). I progressi raggiunti neH’ullimo decennio sullo studio del Hg come ‘global poi Intani '(Pirrone et al.. 2001; Hedgecock et al, 2000: Paeyna et al, 2006; Bullock and Jacgle, 2000; Dastoor e Davignon, 2009; Eriedli et al., 2(X)!); .Jaegle et al, 2009; Jung et al. 2009; Seigneur et al, 2009; Travnikov and Ilyin, 2009) hanno contribuito a fornire una valutazione aggiornata delle emissioni di Hg a scala globale provenienti sia da fonti antropogeniche che naturali. A oggi, le sorgenti antropiche sono responsabili di circa il 30% delle emissioni annue di mercurio in atmosfera. Un altro 10% proviene da fonti geologiche naturali, mentre il restante 60% dalla “ri-emissione” di mercurio precedentemente depositatosi nell’ecosistema terrestre (Kocman et al., 2013). E’stato stimato che circa 5207 t di Hg vengono emesse annualmente da parte dei processi naturali (emissioni primarie di mercurio + ri-emissioni). Nel complesso, di queste 5207 t anno1, circa 2429 t anno1 di Ilg vengono emessi dalle superfici terrest ri (47% del totale delle emissioni naturali di Hg), mentre l’evasione oceanica contribuisce con un flusso di - 2778 anno1 (Pirrone et al. 2010). Per mitigare il rischio associato a tali emissioni è necessario conoscere a fondo le dinamiche che regolano lo scambio di Hg tra la sorgente e il recettore. In che misura è possibile quindi prevedere la futura evoluzione del Ilg rilasciato in atmosfera?

Le interazioni del Hg con l'ambiente costituiscono il ciclo geochimico di questo elemento che si esplica per mezzo di complessi processi fisico-chimici differenti per ciascun comparto geochimico. Si stima che circa i due terzi del mercurio presente in ambiente sia stato prodotto durante il ventesimo secolo, e che il carico di mercurio immesso attualmente sia aumentato di circa 3 volte rispetto agli inizi del 1900 (Mason et al.. 1994). Il comparto ambientale certamente più coinvolto dalle emissioni di mercurio è quello atmosferico, da cui poi l’elemento si diffonde anche negli altri comparti, suolo e sedimenti compresi (Filzgerald & Clarkson, 1991). L’Atmosfera costituisce un importante reservoir temporaneo di mercurio. Infatti, i processi chimici che avvengono in atmosfera trasformano il mercurio dallo stato elementare allo stato bivalente, influenzandone cosi le modalità di trasporto e la velocità di deposizione di questo metallo sulla superficie terrestre. Il mercurio è rilasciato in atmosfera da una varietà di sorgenti naturali (Siegei e Siegei, 1983; Filzgerald, 1986; Xiao et al., 1991; Mason et al.. 1994; Lindberg et al., 1995) ed antropogeniche (Lindqvist et al., 1991; Ferrara et al., 1992; Pirrone et al., 2010; Carpi e Lindberg, 1997; Lacerda, 1997). Le sorgenti naturali includono i vulcani, i suoli, le foreste, i laghi, gli oceani apert i per un i nput totale di circa 2000 lon/anno (Mason et al., 1994); le sorgenti antropogeniche sono principalmente legate alla produzione energetica mediante l’utilizzo di carboni fossili, la combustione e l'incenerimento dei rifiuti, e ad alcuni processi industriali- metallurgici, determinando un flusso totale di circa 4000 lon/anno (Forcella et al., 1997). Il trend delle emissioni di mercurio antropogenico su scala globale è in crescila, soprattutto a causa delle emissioni dai Paesi in forte via di sviluppo (es., Cina, India).

Measuring Hg/SO₂ ratios in volcanic emissions is essential for better apportioning the volcanic contribution to the global Hg atmospheric cycle. Here, we report the first real-time simultaneous measurement of Hg and SO₂ in a volcanic plume, based on Lumex and MultiGAS techniques, respectively. We demonstrate that the use of these novel techniques allows the measurements of Hg/SO₂ ratios with a far better time resolution than possible with more conventional methods. The Hg/SO₂ ratio in the plume of FO fumarole on La Fossa Crater, Vulcano Island spanned an order of magnitude over a 30 minute monitoring period, but was on average in qualitative agreement with the Hg/SO₂ ratio directly measured in the fumarole (mean plume and fumarole ratios being 1.09 x 10⁻⁶ and 2.9 x 10⁻⁶, respectively). The factor 2 difference between plume and fumerole compositions provides evidence for fast Hg chemical processing the plume.

We review the state of knowledge on global volcanogenic Hg emissions to the atmosphere and present new data from seven active volcanoes (Poás, Rincón de la Vieja, Turrialba, Aso, Mutnovsky, Gorely and Etna) and two geothermal fields (Las Pailas and Las Hornillas). The variability of Hg contents (c. 4–125 ng m−3) measured in gaseous emissions reflects the dynamic nature of volcanic plumes, where the abundances of volatiles are determined by the physical nature of degassing and variable air dilution. Based on our dataset and previous work, we propose that an average Hg/SO2 plume mass ratio of c. 7.8×10−6 (±1.5×10−6; 1 SE, n=13) is best representative of open-conduit quiescent degassing. Taking into account the uncertainty in global SO2 emissions, we infer a global volcanic Hg flux from persistent degassing of c. 76±30 t a−1. Our data are derived from active volcanoes during non-eruptive periods and we do not have any direct constraint on the Hg flux during periods of elevated SO2 flux associated with large-scale effusive or explosive eruptions. This suggests that the time-averaged Hg flux from these volcanoes is even larger if the eruptive contribution is considered. Conversely, closed-conduit degassing and geothermal emissions contribute modest amounts of Hg.

Mercury (Hg) is emitted in the atmosphere by anthropogenic and natural sources, these last accounting for one third of the total emissions. Since the pre-industrial age, the atmospheric deposition of mercury have increased notably, while ocean emissions have doubled owing to the re-emission of anthropogenic mercury. Exchange between the atmosphere and ocean plays an important role in cycling and transport of mercury. We present the preliminary results from a study on the distribution and evasion flux of mercury at the atmosphere/sea interface in the Augusta basin (SE Sicily, southern Italy), a semi-enclosed marine area affected by a high degree of contamination (heavy metals and PHA) due to the oil refineries placed inside its commercial harbor. It seems that the intense industrial activity of the past have lead to an high Hg pollution in the bottom sediments of the basin, whose concentrations are far from the background mercury value found in most of the Sicily Strait sediments. The release of mercury into the harbor seawater and its dispersion by diffusion from sediments to the surface, make the Augusta basin a potential supplier of mercury both to the Mediterranean Sea and the atmosphere. Based on these considerations, mercury concentration and flux at the air-sea interface of the Bay have been estimated using a real-time atomic adsorption spectrometer (LUMEX-RA 915+) and an home-made accumulation chamber, respectively. Estimated Total Atmospheric Mercury ($TGM$) concentrations during the cruise on the bay were in the range of 1 - 3 ng∙m-3, with a mean value of about 1.4 ng∙m-3. This data well fit with the background Hgatm concentration values detected on the land (1-2 ng∙m-3, this work), and, more in general, with the background atmospheric TGM levels found in the North Hemisphere (1.5 – 1.7 ng∙m-3 ) [a]. Besides, our measurements are in the range of those reported for other important polluted marine areas. The mercury evasion flux at the air-sea interface measured during the first cruise ranges from 110 to 1500 ng m-2 day-1. This range is 1-2 order of magnitude higher than most of marine environments (Pacific Ocean, Mediterranean Sea, Artic Ocean) and some important polluted marine areas, such as the Tokyo Bay (19–259 ng m-2 day-1)[b] and the Yellow Sea (156–722 ng m-2 day-1)[c]. Further estimates on Hg atmospheric deposition flux (wet and dry) and biomonitoring are required for finally assessing a mass balance of Hg in Augusta basin.

The Eyjafjallajökull 2010 eruption was an extraordinary event in that it led to widespread over Europe. Volcanic processes which lead to eruptions can be investigated by monitoring a variety of parameters, including the composition of ash leachates. Fine-grained tephra erupted from active vents, and transported through volcanic plumes, can adsorbs, and therefore rapidly scavenge, volatile elements such as S, halogens, and metal species in the form of soluble salts adhering to ash surfaces. Analysis of such water-soluble phases is a suitable complement for the remote sensing of volcanic gases at inaccessible volcanoes, like Eyjafjallajökull. The 2010 Eyjafjallajökull eruption developed in four main phases, whose difference in gas chemistry and products has been marked in ash-leachates data too. The recurrent ash fallout provided a unique opportunity to characterize the compositional features of ash leachates, and to identify their relation (if any) with the eruptive activity styles of the volcano. By these considerations, we report on the chemical composition of leachates of 20 volcanic ash samples deposited during the most explosive Eyjafjallajökull activities (from 14 April to 8 May) and during the lava fountaining event (on 26th March 2010). We found that ash-leachate solutions are dominated - among cations - by Na and Ca, while they display nearly equal S:Cl:F abundances (mean S/Cl and S/F molar ratios of 0.85 and 0.33, respectively), as characteristic of divergent-plate and within-plate volcanism. The strong correlations between leached Ca-F, Ca-SO4, and Na-Cl (r2=0.7-0.9), suggest that fluorite, anhydrite, and halite are the most likely soluble surface minerals formed in the plume (and therefore leached during our experiments), as also reported at many active volcanoes. Our data bring evidence for variations in S and halogens proportions, with samples from 5-8th May which show the highest S/Cl and lowest Cl/F ratios. By combining the concentration of leached SO4, F and Cl with the mass/area ratio of deposited ash (normalized to 30 min of 5-8 May 2010 volcanic phase), we estimated mean depositional elemental fluxes of about 1.0×10-5, 1.1×10-3 and 1.2×10-3 g m-2 s-1, for the water-soluble SO4, Cl and F, respectively. By integrating these data over the whole sampling area, we estimated a total depositional flux of about 864, 605 and 691 t∙day-1, for SO4, Cl and F, respectively. These data mean that ~15% of Sgas and 29% of Clgas discharged into the plume during the same eruptive phase, may have been scavenged by adsorption processes on ash surfaces within the eruption column.

Volcanic processes which lead to eruptions can be investigated by monitoring a variety of parameters, including the composition of ash leachates. Fine-grained tephra erupted from active vents, and transported through volcanic plumes, can adsorb, and therefore rapidly scavenge, volatile elements such as sulphur, halogens, and metal species in the form of soluble salts adhering to ash surfaces. Analysis of such water-soluble surface materials is a suitable complement for the remote sensing of volcanic gases at inaccessible volcanoes. The April 2010 Eyjafjallajökull eruption has been characterised by several distinct phases, with an initial effusion of alkali basalt on the volcano's northeast flank since March 20th, followed (since April 14th) by a complex summit, sustained, explosive to mixed activity, characterised by trachyandesitic magma The first phase of the summit eruption (14 to 18 April) was initially characterised by interaction between glacial meltwater from the icecap and erupting magma, and by three main pulses during which dark ash plumes were dispersed to the SE and S. Following a decrease in the intensity in explosive activity associated to the emission of a lava flow (from 19 April to 4 May), activity renewed in intensity on 5 May, when an ash-laden plume, up to 10 km in height, was continuously dispersed until May 18. Activity progressively declined and eruption closed on 9 June [1]. Here, we report on the chemical composition of leachates from volcanic ash samples deposited during the Eyjafjallajökull explosive phase (from 14 April to 8 May). Twenty-eight freshly fallen volcanic ash samples were collected at various distances from the eruptive vent, and their leached solutions were analyzed for major and trace elements. We show that ash leachate solutions from Eyjafjallajökull are dominated - among cations - by Na and Ca, while they display nearly equal S:Cl:F abundances (mean S/Cl and S/F molar ratios of 1.04 and 0.76 respectively), as characteristic of divergent-plate and within-plate volcanism. The good correlations between Ca and F (r2=0.8), Ca and SO4 (r2=0.7), and Na and Cl (r2=0.9) in ash leachates suggest that fluorite, anhydrite, and halite were the most likely soluble surface minerals formed in the plume (and therefore leached during our experiments). These correlations in the extracted solutions also indicate that either the sources of cations and anions in ash leachates were the same (e.g. direct condensation of NaCl(g) and CaSO4(g) from the plume) or, more probably, that the highest the condensation of plume acidic compounds (e.g., SO2(g), HCl(g), HF(g)) on ash, the largest the leaching of cations from silicate fragments. Indeed, our data bring evidence for that the extent of gas-ash reaction (likely, a proxy for ash residence time in the plume) was a key casual factor in determining ash leachate composition. Samples from the 4- 8th May eruptive period, showing the most acid pH values (4.5-5.5), consistently have the highest abundances for all elements, and especially Mg, S and F. Large variations in S and halogens proportions are observed in our dataset, with samples from the 4-8th May eruptive period showing the highest S/Cl and lowest Cl/F ratios. To interpret these variations, and particularly to verify whether they reflect changes in plume gas composition, in gas-ash reaction dynamics and rates,2]will require in-depth comparison with direct (FTIR) measurement of the Eyjafjallajökull gas plume[2] . [1] Hoskuldsson, A., et al., 2011. Geophysical Research Abstracts Vol. 13, EGU2011-14165, 2011; [2] Allard, P., et al., 2010. Abstract V53F-07 presented at Fall Meeting, AGU, San Francisco, Calif. 13-17 Dec.

Besides human activities, volcanoes also introduce significant quantities of potentially harmful chemical compounds into the environment, mainly in the forms of gases and particles. High-temperature emissions from persistently degassing volcanoes are a known source of trace metal emissions to the atmosphere which may have important environmental consequences. Among these metals, mercury (Hg) is of particular interest since it is a toxic volatile metal found at elevated concentrations in remote regions of the world. Many natural Hg pathways include a recycled component of anthropogenic material. The anthropogenic contribution to the global atmospheric Hg budget is now well constrained, with most recent estimates ranging from 1484 [AMAP/UNEP, 2008] to 1894 t yr-1 [2005/2006 inventory; Streets et al 2009]. Hg emissions from natural sources are, on the other hand, still poorly characterized, though being likely in the same range [estimates from 500 to 3000 t yr-1; Nriagu 1989] of those reported for anthropogenic release. The poorly constrained Hg speciation in volcanic emissions, and the limited number of studies so far, have hampered accurate estimation of the global Hg flux, with previous estimates ranging from as low as ~1 t yr-1 [Ferrara et al. 2000] to >800 t yr-1 [Varekamp and Buseck 1986]. Besides, historical archives such as ice-cores documented that large eruptions can release quantities of Hg similar to the present anthropogenic burden. The effects, or potential effects, of active volcanoes on the environment and on public health is an important issue, given the large number of communities and populated cities that exist and keep growing around and upon active and dormant volcanoes. Poisonous gases, and in the specific mercury, are also released continuously or semi-continuously into the environment by non-erupting volcanoes causing however regional environmental effects equally severe to the volcanic events of massive proportions. A major uncertainty regarding the impacts of volcanic Hg is the extent to which Hg emitted from a volcano is deposited locally or transported globally. Actually, volcanogenic mercury fluxes are poorly constrained and there is an almost complete absence of data on the factors (magma composition, eruptive temperature, or volcanic gas composition) that influence its degassing rates at different volcanoes. In order to better understand the role of volcanoes in the global mercury budget and to extend the currently limited dataset on volcanogenic Hg emissions, a number of field campaigns were carried out to evaluate Hg flux in volcanic gases by the simultaneously-determined Hg/SO2 ratios and SO2 flux. Measurements were made at the crater edge of a number of quiescently degassing volcanoes (Etna, Stromboli, Asama, Miyakejima, Montserrat, Ambrym, Yasur, Nyiragongo, Masaya). Emissions from open vents were investigated and concentrations of Hg elevated above usual background levels (rural areas far from emitting source, 1-2 ng m-3) were detected. We found that in volcanic plume mercury is mainly found as the relatively inert form of gaseous elemental mercury (GEM) with concentrations ranging from 18 to 373 ng Hg m-3. GEM has a long atmospheric lifetime estimated as 0.5-2 years due to its low solubility and gaseous nature, promoting long-range global transport [Nriagu 1989; Pyle and Mather, 2003]. High variability found in plume Hg concentrations depends on both volcanic (gas flux) and non-volcanic factors (extent of mixing and dilution in the vent; wind speed and direction), hence comparing the concentrations of Hg species between different volcanoes is not necessarily meaningful and it is more useful to compare Hg/SO2 ratios. Using our determined Hg/SO2 mass ratios in tandem with the simultaneously-determined SO2 emission rates, we estimated that the investigated volcanoes have Hg emission rates ranging from 0.2 to 18 t•yr-1 (corresponding to a total Hg flux of ~54 t•yr-1). Based on our dataset and previous works, we propose that a Hg/SO2 plume ratio ~10-5 is best-representative of gas emissions from quiescent degassing volcanoes. Using this ratio, we infer a global volcanic Hg flux from persistent degassing of ~95 t•yr-1. If representative of other volcanoes, these results suggest degassing of basaltic magma plays an important part of the global atmospheric Hg budget. According to both these data and recent observations [Bagnato et al., 2010], volcanism thus would contribute from as little as 12 to as much as 78% of the estimated global natural Hg budget. Volcanic Hg therefore has a greater potential for local and global environmental impact than Hg from the more prodigious but diffuse natural and anthropogenic sources. In particular, Hg released from Mt Etna degassing, the largest active volcano in Europe, represents approximately 5% of the total industrial Hg emissions in the Mediterranean area [~105 t•yr-1, Pirrone et al., 2009] and about 2% of the anthropogenic Hg supplies throughout Europe [~239 t•yr-1, EMEP 2002]. With these new estimates we critically revisit the idea that volcanic activity is a trivial contribution to the atmospheric Hg supply in the Mediterranean area. We shall re-examine the status of the global volcanic mercury emissions budget and its uncertainties, even when only considering quiescent phases of volcanic activity. Besides, large sectors of the planet (SW Pacific) are still un-explored, and thus our global Hg flux value estimated from passive degassing may constitutes a lower limit. However, Hg flux measurements in eruptive gases is a priority for future mercury research at volcanoes.