Quantification of the depletion of ozone in the plume of Mount Etna

Volcanoes are an important source of inorganic halogen species into the atmosphere. Chemical processing of these species generates oxidised, highly reactive, halogen species which catalyse considerable O₃ destruction within volcanic plumes. A campaign of ground-based in situ O₃, SO₂ and meteorology measurements was undertaken at the summit of Mount Etna volcano in July/August 2012. At the same time, spectroscopic measurements were made of BrO and SO₂ columns in the plume downwind. <br><br> Depletions of ozone were seen at all in-plume measurement locations, with average O₃ depletions ranging from 11–35 nmol mol⁻¹ (15–45%). Atmospheric processing times of the plume were estimated to be between 1 and 4 min. A 1-D numerical model of early plume evolution was also used. It was found that in the early plume O₃ was destroyed at an approximately constant rate relative to an inert plume tracer. This is ascribed to reactive halogen chemistry, and the data suggests the majority of the reactive halogen that destroys O₃ in the early plume is generated within the crater, including a substantial proportion generated in a high-temperature "effective source region" immediately after emission. The model could approximately reproduce the main measured features of the ozone chemistry. Model results show a strong dependence of the near-vent bromine chemistry on the presence or absence of volcanic NO_x emissions and suggest that near-vent ozone measurements can be used as a qualitative indicator of NO_x emission

AGU Centennial Grand Challenge: Volcanoes and Deep Carbon Global CO2 Emissions From Subaerial Volcanism—Recent Progress and Future Challenges

Quantifying the global volcanic CO2 output from subaerial volcanism is key for a better understanding of rates and mechanisms of carbon cycling in and out of our planet and their consequences for the long-term evolution of Earth's climate over geological timescales. Although having been the focus of intense research since the early 1990s, and in spite of recent progress, the global volcanic CO2 output remains inaccurately known. Here we review past developments and recent progress and examine limits and caveats of our current understanding and challenges for future research. We show that CO2 flux measurements are today only available for ~100 volcanoes (cumulative measured flux, 44 Tg CO2/year), implying that extrapolation is required to account for the emissions of the several hundred degassing volcanoes worldwide. Recent extrapolation attempts converge to indicate that persistent degassing through active crater fumaroles and plumes releases ~53–88 Tg CO2/year, about half of which is released from the 125 most actively degassing subaerial volcanoes (36.4 ± 2.4 Tg CO2/year from strong volcanic gas emitters, Svge). The global CO2 output sustained by diffuse degassing via soils, volcanic lakes, and volcanic aquifers is even less well characterized but could be as high as 83 to 93 Tg CO2/year, rivaling that from the far more manifest crater emissions. Extrapolating these current fluxes to the past geological history of the planet is challenging and will require a new generation of models linking subduction parameters to magma and volatile (CO2) fluxes

First in-situ sensing of volcanic gas plume composition at Boiling Lake (Dominica, West Indies)

Dominica, a small Caribbean island between Martinique (to the South) and Guadeloupe (to the North), is, because of the high number of potentially active volcanic centres,one of the most susceptible sites to volcanic risk in the Lesser Antilles arc. Seven major volcanic centres, active during the last 10ka, are considered likely to erupt again, and one of these is the Valley of Desolation volcanic complex. This is an area of 0.5 km2, located in on SW Dominica, where a number of small explosion craters, hot springs,bubbling pools and fumaroles testify for vigorous and persistent hydrothermal activity. Two main phreatic explosions have been documented in historical time (1880 and 1997), and the most likely centre of future activity is the Boiling Lake, a nearby high-T volcanic crater lake produced by an undated phreatic/phreatomagmatic explosion. Hot (80 to 90\ub0C) and acidic (4-6) waters normally characterize the steady-state activity of the lake, whereby which vigorous gas upwelling in the lake\u2019s centre feeds a persistent steaming plume. Stability of the Boiling Lake has occasionally been interrupted in the past (since 1876) by crises, the most recent in 2004, involving rapid draining of the lake and changes in water temperature and pH, likely as a result of drastic decrease of hydrothermal fluid input into the lake. While the chemical and isotopic composition of the lake waters is well characterised, there are no compositional data available for the gas plume leaving the lake, due to inherent difficulties in direct gas sampling. Here, we present the results of the first direct measurements of the Boiling Lake\u2019s plume, performed by using the MultiGAS technique in February 2012. We acquired 0.5 Hz time-series of H2O, CO2, H2S and SO2 plume concentrations,which were seen to peak (with maximum background-corrected concentrations of 3680, 101 and 25 ppm for respectively H2O, CO2 and H2S) during phases of visible increase in lake outgassing. SO2 was virtually absent in the plume. From the concentration data, the characteristic CO2/H2S (5.2\ub10.4) and H2O/CO2 (31.4\ub16) volatile ratios in the Boiling lake\u2019s atmospheric plume were derived. This reveals similar C to S signature for Boiling lake and Valley of Desolation (for which we also obtained data using the same technique), likely indicative of common source reservoir. The Boiling lake\u2019s plume is far more H2O-rich than the Valley of Desolation gas, suggesting that a significant fraction of in-plume H2O in the former originates from re-evaporation of the lake water itself. Our data here provide a first compositional baseline for quiescent volcanic gas emissions at Boiling Lake, and may form the basis to stimulate emerging geochemical monitoring programs in the area

Mount Etna the major point source of metals in the Mediterranean basin: impact on atmospheric precipitation

Mount Etna is a huge volcano in the Mediterranean basin and is located in the eastern part of Sicily. It is considered to be, on the long-term average, the major atmospheric point source of many environmental harmful compounds. Their emission occurs either through continuous passive degassing from open-conduit activity or through sporadic paroxysmal eruptive activity, in the form of gases, aerosols or particulate. Volcanic volatiles and aerosol emitted into the atmosphere fall on the Earth’s surface as wet or dry deposition, and can influence the environment both at local and regional scale. To estimate the environmental impact of magma-derived trace metals and their depositions processes, bulk deposition samples have been collected approximately fortnightly, using a network of 5 rain gauges located at various altitudes on the upper flanks close to the summit craters, from April 2006 to December 2007. Samples were analyzed for the main chemicalphysical parameters (electric conductivity and pH) and for major and trace elements concentrations. The data obtained clearly show that the volcanic contribution is always prevailing in the sampling site closest to the summit craters (∼1.5 km). In the distal sites (5.5-10 km from the summit) and downwind of the summit craters, the volcanic contribution is also detectable but often overwhelmed by anthropogenic or other natural (seawater spray, geogenic dust) contributions. Volcanogenic contribution may derive from both dry and wet deposition of gases and aerosols from the volcanic plume, but sometimes also from leaching of freshly emitted volcanic ashes. In fact, in our background site (7.5 km in the upwind direction), after an ash deposition event high concentration of lithophiles elements (Si, Al, Fe, Ti) have been measured. Sulphur, Chlorine and Fluorine, represent the main constituents that characterize the volcanic contribution in the bulk deposition on Mt. Etna, although high concentrations of many trace elements (Si, Al, Fe, Ti, Cu, As, Rb, Pb, Tl, Cd, Cr, U and Ag) display, in the site most exposed to the volcanic emissions, average concentrations of about two orders of magnitude higher than those measured in the background site (Mount Intraleo)

The tropospheric processing of acidic gases and hydrogen sulphide in volcanic gas plumes as inferred from field and model investigations

Improving the constraints on the atmospheric fate and depletion rates of acidic compounds persistently emitted by non-erupting (quiescent) volcanoes is important for quantitatively predicting the environmental impact of volcanic gas plumes. Here, we present new experimental data coupled with modelling studies to investigate the chemical processing of acidic volcanogenic species during tropospheric dispersion. Diffusive tube samplers were deployed at Mount Etna, a very active open-conduit basaltic volcano in eastern Sicily, and Vulcano Island, a closed-conduit quiescent volcano in the Aeolian Islands (northern Sicily). Sulphur dioxide (SO₂), hydrogen sulphide (H₂S), hydrogen chloride (HCl) and hydrogen fluoride (HF) concentrations in the volcanic plumes (typically several minutes to a few hours old) were repeatedly determined at distances from the summit vents ranging from 0.1 to ~10 km, and under different environmental conditions. At both volcanoes, acidic gas concentrations were found to decrease exponentially with distance from the summit vents (e.g., SO₂ decreases from ~10 000 &mu;g/m³at 0.1 km from Etna&apos;s vents down to ~7 &mu;g/m³ at ~10 km distance), reflecting the atmospheric dilution of the plume within the acid gas-free background troposphere. Conversely, SO₂/HCl, SO₂/HF, and SO₂/H₂S ratios in the plume showed no systematic changes with plume aging, and fit source compositions within analytical error. Assuming that SO₂ losses by reaction are small during short-range atmospheric transport within quiescent (ash-free) volcanic plumes, our observations suggest that, for these short transport distances, atmospheric reactions for H₂S and halogens are also negligible. The one-dimensional model MISTRA was used to simulate quantitatively the evolution of halogen and sulphur compounds in the plume of Mt. Etna. Model predictions support the hypothesis of minor HCl chemical processing during plume transport, at least in cloud-free conditions. Larger variations in the modelled SO₂/HCl ratios were predicted under cloudy conditions, due to heterogeneous chlorine cycling in the aerosol phase. The modelled evolution of the SO₂/H₂S ratios is found to be substantially dependent on whether or not the interactions of H₂S with halogens are included in the model. In the former case, H₂S is assumed to be oxidized in the atmosphere mainly by OH, which results in minor chemical loss for H₂S during plume aging and produces a fair match between modelled and measured SO₂/H₂S ratios. In the latter case, fast oxidation of H₂S by Cl leads to H₂S chemical lifetimes in the early plume of a few seconds, and thus SO₂ to H₂S ratios that increase sharply during plume transport. This disagreement between modelled and observed plume compositions suggests that more in-detail kinetic investigations are required for a proper evaluation of H₂S chemical processing in volcanic plumes

Atmospheric impact of volcanic volatiles: trace elements in snow and bulk deposition samples at Mount Etna (Italy)

Volcanoes represent an important natural source of several trace elements to the atmosphere. For some species (e.g., As, Cd, Pb and Se) they may be the main natural source and thereby strongly influencing geochemical cycles from the local to the global scale. Mount Etna is one of the most actively degassing volcanoes in the world, and it is considered to be, on the long-term average, the major atmospheric point source of many environmental harmful compounds. Their emission occurs either through continuous passive degassing from open-conduit activity or through sporadic paroxysmal eruptive activity, in the form of gases, aerosols or particulate. To estimate the environmental impact of magma-derived trace metals and their depositions processes, rainwater and snow samples were collected at Mount Etna area. Five bulk collectors have been deployed at various altitudes on the upper flanks around the summit craters of the volcano; samples were collected every two week for a period of one year and analyzed for the main chemical-physical parameters (electric conductivity and pH) and for major and trace elements concentrations. Chemical analysis of rainwater clearly shows that the volcanic contribution is always prevailing in the sampling site closest to the summit crater (about 1.5 km). In the distal sites (5.5-10 km from the summit) and downwind of the summit craters, the volcanic contribution is also detectable but often overwhelmed by anthropogenic or other natural (seawater spray, geogenic dust) contributions. Volcanic contribution may derive from both dry and wet deposition of gases and aerosols from the volcanic plume, but sometimes also from leaching of freshly emitted volcanic ashes. In fact, in our background site (7.5 km in the upwind direction) volcanic contribution has been detected only following an ash deposition event. About 30 samples of fresh snow were collected in the upper part of the volcano, during the winters 2006 and 2007 to estimate deposition processes at high altitude during cold periods. Some of the samples were collected immediately after a major explosive event from the summit craters to understand the interaction between snow and fresh erupted ash. Sulphur, Chlorine and Fluorine, are the major elements that prevailingly characterize the volcanic contribution in atmospheric precipitation on Mount Etna, but high concentrations of many trace elements are also detected in the studied samples. In particular, bulk deposition samples display high concentration of Al, Fe, Ti, Cu, As, Rb, Pb, Tl, Cd, Cr, U and Ag, in the site most exposed to the volcanic emissions: median concentration values are about two orders of magnitude higher than those measured in our background site. Also in the snow samples the volcanic signature is clearly detectable and decreases with distance from the summit craters. Some of the analysed elements display very high enrichment values with respect to the average crust and, in the closest site to the summit craters, also deposition values higher than those measured in polluted urban or industrial sites

First-time lidar measurement of water vapor flux in a volcanic plume

The CO2 laser-based lidar ATLAS has been used to study the Stromboli volcano plume. ATLAS measured water vapor concentration in cross-sections of the plume and wind speed at the crater. Water vapor concentration and wind speed were retrieved by differential absorption lidar and correlation technique, respectively. Lidar returns were obtained up to a range of 3 km. The spatial resolution was 15 mand the temporal resolution was 20 s. By combining these measurements, the water vapor flux in the Stromboli volcano plume was found. To our knowledge, it is the first time that lidar retrieves water vapor concentrations in a volcanic plume.Published1295–12981.10. TTC - TelerilevamentoJCR Journalreserve

Vulcamera: a program for measuring volcanic SO2 using UV cameras

We report here on Vulcamera, a stand-alone program for the determination of volcanic SO2 fluxes using ultraviolet cameras. The code enables field image acquisition and all the required post-processing operations

Recent advances in ground-based ultraviolet remote sensing of volcanic SO2 fluxes

Measurements of volcanic SO2 emission rates have been the mainstay of remote-sensing volcanic gas geochemistry for almost four decades, and they have contributed significantly to our understanding of volcanic systems and their impact upon the atmosphere. The last ten years have brought stepchange improvements in the instrumentation applied to these observations, which began with the application of miniature ultraviolet spectrometers that were deployed in scanning and traverse configurations, with differential optical absorption spectroscopy evaluation routines. This study catalogs the more recent empirical developments, including: ultraviolet cameras; wideangle field-of-view differential optical absorption spectroscopy systems; advances in scanning operations, including tomography; and improved understanding of errors, in particular concerning radiative transfer. Furthermore, the outcomes of field deployments of sensors during the last decade are documented, with respect to improving our understanding of volcanic dynamics and degassing into the atmosphere

Leachate Analyses of volcanic ashes from the 2010 Eyjafjallaj\uf6kull eruption

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 Eyjafjallaj\uf6kull 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 Eyjafjallaj\uf6kull 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 Eyjafjallaj\uf6kull 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 Eyjafjallaj\uf6kull 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.