Bubble ascent and rupture in mud volcanoes.

Large gas bubbles can reach the surface of pools of mud and lava where they burst, often through the formation and expansion of circular holes. Bursting bubbles release volatiles and generate spatter, and hence play a key role in volcanic degassing and volcanic edifice construction. Here, we study the ascent and rupture of bubbles using a combination of field observations at Pâclele Mici (Romania), laboratory experiments with mud from the Imperial Valley (California, USA), numerical simulations and theoretical models. Numerical simulations predict that bubbles ascend through the mud as elliptical caps that develop a dimple at the apex as they impinge on the free surface. We documented the rupture of bubbles in nature and under laboratory conditions using high-speed video. The bursting of mud bubbles starts with the nucleation of multiple holes, which form at a near-constant rate and in quick succession. The quasi-circular holes rapidly grow and coalesce, and the sheet evolves towards a filamentous structure that finally falls back into the mud pool, sometimes breaking up into droplets. The rate of expansion of holes in the sheet can be explained by a generalization of the Taylor-Culick theory, which is shown to hold independent of the fluid rheology.

Volcanic Eruption in the Nanoworld: Efficient Oxygen Exchange at the Si/SnO2 Interface.

Here, a phenomenon of efficient oxygen exchange between a silicon surface and a thin layer of tin dioxide during chemical vapor deposition is presented, which leads to a unique Sn:SiO2 layer. Under thermodynamic conditions in the temperature range of 725-735 °C, the formation of nanostructures with volcano-like shapes in "active" and "dormant" states are observed. Extensive characterization techniques, such as electron microscopy, X-ray diffraction, synchrotron radiation-based X-ray photoelectron, and X-ray absorption near-edge structure spectroscopy, are applied to study the formation. The mechanism is related to the oxygen retraction between tin(IV) oxide and silicon surface, leading to the thermodynamically unstable tin(II)oxide, which is immediately disproportionate to metallic Sn and SnO2 localized in the SiO2 matrix. The diffusion of metallic tin in the amorphous silicon oxide matrix leads to larger agglomerates of nanoparticles, which is similar to the formation of a magma chamber during the natural volcanic processes followed by magma eruption, which here is associated with the formation of depressions on the surface filled with metallic tin particles. This new effect contributes a new approach to the formation of functional composites but also inspires the development of unique Sn:SiO2 nanostructures for diverse application scenarios, such as thermal energy storage.

Optimizing the Intermediates Adsorption by Manipulating the Second Coordination Shell of Ir Single Atoms for Efficient Water Oxidation.

The precise regulation of single-atom catalysts (SACs) with the desired local chemical environment is vital to elucidate the relationship between the SACs structure and the catalytic performance. The debate on the effect of the local coordination environment is quite complicated even for the SACs with the same composition and chemical nature, calling for increased attention on the regulation of second coordination shell. For oxide-supported SACs, it remains a significant challenge to precisely manipulate the second coordination shell of single atoms supported on oxides due to the structural robustness of oxides. Here, Ir single atoms are anchored on NiO supports via different bonding strategies, resulting in the diverse Ir-O-Ni coordination numbers for Ir sites. Specifically, Ir1/NiO, Ir1-NiO, and Ir1@NiO SACs with increasing Ir-O-Ni coordination numbers of 3, 4, and 5 were synthesized, respectively. We found that the activity of the three samples towards oxygen evolution reaction (OER) exhibited a volcano-shaped relationship with the Ir-O-Ni coordination number, with Ir1-NiO showing the lowest overpotential of 225 mV at 10 mA cm-2. Mechanism investigations indicate that the moderate coordination number of Ir-O-Ni in Ir1-NiO creates the higher occupied Ir dz2 orbital, weakening the adsorption strength for *OOH intermediates and thereby enhancing the OER activity.

Diversity, Methane Oxidation Activity, and Metabolic Potential of Microbial Communities in Terrestrial Mud Volcanos of the Taman Peninsula.

Microbial communities of terrestrial mud volcanoes are involved in aerobic and anaerobic methane oxidation, but the biological mechanisms of these processes are still understudied. We have investigated the taxonomic composition, rates of methane oxidation, and metabolic potential of microbial communities in five mud volcanoes of the Taman Peninsula, Russia. Methane oxidation rates measured by the radiotracer technique varied from 2.0 to 460 nmol CH4 cm-3 day-1 in different mud samples. This is the first measurement of high activity of microbial methane oxidation in terrestrial mud volcanos. 16S rRNA gene amplicon sequencing has shown that Bacteria accounted for 65-99% of prokaryotic diversity in all samples. The most abundant phyla were Pseudomonadota, Desulfobacterota, and Halobacterota. A total of 32 prokaryotic genera, which include methanotrophs, sulfur or iron reducers, and facultative anaerobes with broad metabolic capabilities, were detected in relative abundance >5%. The most highly represented genus of aerobic methanotrophs was Methyloprofundus reaching 36%. The most numerous group of anaerobic methanotrophs was ANME-2a-b (Ca. Methanocomedenaceae), identified in 60% of the samples and attaining relative abundance of 54%. The analysis of the metagenome-assembled genomes of a community with high methane oxidation rate indicates the importance of CO2 fixation, Fe(III) and nitrate reduction, and sulfide oxidation. This study expands current knowledge on the occurrence, distribution, and activity of microorganisms associated with methane cycle in terrestrial mud volcanoes.

Strontium isotope signature of the PGI lemons Limone Costa d'Amalfi and Limone di Sorrento, and of the orchard soils from Sorrento peninsula.

The Limone Costa d'Amalfi and Limone di Sorrento lemons from the Sorrento Peninsula have Protected Geographical Indication (PGI) and are subject to origin fraud. The 87Sr/86Sr ratio (SrIR) signature of lemons and soils was investigated to verify its reliability to trace the PGI lemons and to highlight environmental factors responsible of the lemon SrIRs. The SrIR ranges of each PGI lemon were not discriminating as they overlapped with each other and some non-PGI lemon SrIRs fell within these ranges. The lemon SrIRs were generally not correlated with bulk and bioavailable soil SrIRs, rather, they were the result of plant Sr uptake with different SrIRs depending on interaction between water supplied to soil and soil with different chemical and physical characteristics. The study of lemon SrIRs and the causes of their origin and variability provides a reliable forecast reference for the other PGI agri-food products in the study area.

Metagenome-Assembled Genome of "Candidatus Aramenus sp. CH1" from the Chichon volcano, Mexico.

The Chichon volcano contains several thermal manifestations including an acidic crater lake. Here we report a metagenome-assembled genome of "Candidatus Aramenus sp. CH1," a Sulfolobales archaeon inhabiting the crater lake from the Chichon volcano. In this study, we generated a novel Aramenus genome sequence from a thermal area in Southern Mexico.

Comparing microbial populations from diverse hydrothermal features in Yellowstone National Park: hot springs and mud volcanoes.

Geothermal features, such as hot springs and mud volcanoes, host diverse microbial life, including many extremophile organisms. The physicochemical parameters of the geothermal feature, such as temperature, pH, and heavy metal concentration, can influence the alpha and beta diversity of microbial life in these environments, as can spatiotemporal differences between sites and sampling. In this study, water and sediment samples were collected and analyzed from eight geothermal sites at Yellowstone National Park, including six hot springs, a mud volcano, and an acidic lake within the same week in July 2019, and these geothermal sites varied greatly in their temperature, pH, and chemical composition. All samples were processed and analyzed with the same methodology and taxonomic profiles and alpha and beta diversity metrics determined with 16S rRNA sequencing. These microbial diversity results were then analyzed with respect to pH, temperature, and chemical composition of the geothermal features. Results indicated that predominant microbial species varied greatly depending on the physicochemical composition of the geothermal site, with decreases in pH and increases in dissolved heavy metals in the water corresponding to decreases in alpha diversity, especially in the sediment samples. Similarly, sites with acidic pH values had more similar microbial populations (beta diversity) to one another than to relatively neutral or alkaline pH geothermal sites. This study suggests that pH and/or heavy metal concentration is a more important driver for microbial diversity and population profile than the temperature for these sites and is also the first reported microbial diversity study for multiple geothermal sites in Yellowstone National Park, including the relatively new mud volcano Black Dragon's Caldron, which erupted in 1948.

Influence of Geothermal Fumaroles in Driving the Microbial Community Dynamics and Functions of Adjacent Ecosystems.

Growing evidence suggests that the hydrochemical properties of geothermal fumaroles may play a crucial role in shaping the diversity and functions of microbial communities in various environments. In the present study, the impact of geothermal furaneols on the microbial communities and their metabolic functions across the rock-soil-plant continuum was explored considering varying distances from the fumarole source. The results revealed that bacterial phylum Proteobacteria was predominant in all sample types, except in the 10 m rock sample, irrespective of the sampling distance. Archaeal phyla, such as Euryarchaeota and Crenarchaeota, were more prevalent in rock and soil samples, whereas bacterial phyla were more prevalent in plant samples. Thermoacidophilic archaeons, including Picrophilus, Ferroplasma, and Thermogymnomonas were dominant in rocks and soil samples of 1 and 5 m distances; acidophilic mesophiles, including Ferrimicrobium and Granulicella were abundant in the rhizoplane samples, whereas rhizosphere-associated microbes including Pseudomonas, Pedobacter, Rhizobium, and Novosphingobium were found dominant in the rhizosphere samples. The functional analysis highlighted the higher expression of sulfur oxidative pathways in the rock and soil samples; dark iron oxidation and nitrate/nitrogen respiratory functions in the rhizosphere samples. The findings underscore microbial adaptations across the rock-soil-plant continuum, emphasizing the intricate relationship between geothermal fumaroles and microbial communities in adjacent ecosystems. These insights offer a crucial understanding of the evolution of microbial life and highlight their pivotal roles in shaping ecosystem dynamics and functions.

Airfall volume of the 15 January 2022 eruption of Hunga volcano estimated from ocean color changes.

On 15 January 2022, Hunga volcano erupted, creating an extensive and high-reaching umbrella cloud over the open ocean, hindering traditional isopach mapping and fallout volume estimation. In MODIS satellite imagery, ocean surface water was discolored around Hunga following the eruption, which we attribute to ash fallout from the umbrella cloud. By relating intensity of ocean discoloration to fall deposit thicknesses in the Kingdom of Tonga, we develop a methodology for estimating airfall volume over the open ocean. Ash thickness measurements from 41 locations are used to fit a linear relationship between ash thickness and ocean reflectance. This produces a minimum airfall volume estimate of 1.8-0.4+0.3 km3. The whole eruption produced > 6.3 km3 of uncompacted pyroclastic material on the seafloor and a caldera volume change of 6 km3 DRE. Our fall estimates are consistent with the interpretation that most of the seafloor deposits were emplaced by gravity currents rather than fall deposits. Our proposed method does not account for the largest grain sizes, so is thus a minimum estimate. However, this new ocean-discoloration method provides an airfall volume estimate consistent with other independent measures of the plume and is thus effective for rapidly estimating fallout volumes in future volcanic eruptions over oceans. Supplementary Information: The online version contains supplementary material available at 10.1007/s00445-024-01744-6.

Complete Organelle Genome of the Desiccation-Tolerant (DT) Moss Tortula atrovirens and Comparative Analysis of the Pottiaceae Family.

Tortula atrovirens (Sm.) Lindb. is an important component of biological soil crusts and possesses an extraordinary tolerance against desiccation in dryland habitats. However, knowledge of the organelle genome of this desiccation-tolerant (DT) moss is still lacking. Here, we assembled the first reported Tortula organelle genome and conducted a comprehensive analysis within the Pottiaceae family. T. atrovirens exhibited the second largest chloroplast genome (129,646 bp) within the Pottiaceae, whereas its mitogenome (105,877 bp) and those of other mosses were smaller in size compared to other land plants. The chloroplast and mitochondrial genomes of T. atrovirens were characterized by the expansion of IR boundaries and the absence of homologous recombination-mediated by large repeats. A total of 57 RNA editing sites were detected through mapping RNA-seq data. Moreover, the gene content and order were highly conserved among the Pottiaceae organelle genomes. Phylogenetic analysis showed that bryophytes are paraphyletic, with their three lineages (hornworts, mosses, and liverworts) and vascular plants forming successive sister clades. Timmiella anomala is clearly separated from the monophyletic Pottiaceae, and T. atrovirens is closely related to Syntrichia filaris within the Pottioideae. In addition, we detected four hypervariable regions for candidate-molecular markers. Our findings provide valuable insights into the organelle genomes of T. atrovirens and the evolutionary relationships within the Pottiaceae family, facilitating future discovery of DT genetic resources from bryophytes.

Modulating Electron Transfer between Pt and MOF Support through Pd Doping Promotes Nanozyme Catalytic Efficiency.

Electron transfer is considered to be a typical parameter that affects the catalytic activity of nanozymes. However, there is still controversy regarding whether higher or lower electron transfer numbers are beneficial for improving the catalytic activity of nanozymes. To address this issue, we propose the introduction of Pd doping as an important electron regulation strategy to tune electron transfer between Pt and ZIF-8 carriers (PtxPd1@ZIF-8). We observe a volcano-shaped relationship between the electron transfer number and catalytic activity, reaching its peak at Pt4Pd1@ZIF-8. Mechanism studies indicate that as the electron transfer number from Pt to ZIF-8 carriers increases, the d-band center of the active site Pt increases, reducing the occupancy of antibonding states and enhancing the adsorption capacity of the key intermediate (*O). However, a further increase in the adsorption of *O energy makes it difficult to desorb and participate in the next reaction, thus exhibiting volcanic activity. The optimized Pt4Pd1@ZIF-8 nanozyme is applied to develop an immunoassay for the detection of zearalenone, achieving a detection limit of 0.01 µg/L, which is 6 times higher than that of the traditional enzyme-linked immunosorbent assay. This work not only reveals the potential regulatory mechanism of electron transfer on the catalytic activity of nanozymes but also improves the performance of nanozyme-based biosensors.

Fast Bacterial Succession Associated with the Decomposition of Larix gmelinii Litter in Wudalianchi Volcano.

In order to understand the role of microorganisms in litter decomposition and the nutrient cycle in volcanic forest ecosystems, the dominant forest species Larix gmelinii in the volcanic lava plateau of the Wudalianchi volcano was considered as the research object. We analyzed the response of bacterial community structure and diversity to litter decomposition for 1 year, with an in situ decomposition experimental design using litter bags and Illumina MiSeq high-throughput sequencing. The results showed that after 365 days, the litter quality residual rate of Larix gmelinii was 77.57%, and the litter N, P, C:N, C:P, and N:P showed significant differences during the decomposition period (p < 0.05). The phyla Cyanobacteria and the genus unclassified_o_Chloroplast were the most dominant groups in early decomposition (January and April). The phyla Proteobacteria, Actinobacteriota, and Acidobacteriota and the genera Massilia, Pseudomonas, and Sphingomona were higher in July and October. The microbial communities showed extremely significant differences during the decomposition period (p < 0.05), with PCoa, RDA, and litter QRR, C:P, and N as the main factors driving litter bacteria succession. Microbial functional prediction analysis showed that Chloroplasts were the major functional group in January and April. Achemoheterotrophy and aerobic chemoheterotrophy showed a significant decrease as litter decomposition progressed.

Tailoring hypervalent Nickel induced by oxygen vacancy toward enhanced oxygen evolution reaction performance in self-supporting NiFe-(oxy)hydroxides electrodes.

NiFe-(oxy)hydroxides are the most active transition metal oxide electrocatalysts for oxygen evolution reaction (OER) under the alkaline media. Herein, we controllably manipulated oxygen vacancy (VO)-tunable NiFe-(oxy) hydroxides that their OER performances possessed a volcano-type relationship with VO concentration, positively-correlated with Ni3+/Ni2+ ratio. Theoretical simulations further unearthed the enhanced activation and dissociation of H2O by the inserting of VO. As a result, the optimal sample featuring the Ni3+/Ni2+ ratio of 30.3 % and VO of 23.8 % exhibited the overpotential of 243 mV at the current density of 100 mA cm-2, simultaneously lasting 120 h durability without any attenuation, exceding the most reported NiFe-(oxy)hydroxides. This work offers an innovative view to understand the OER performance using hypervalent Ni ratio induced by VO defects.

Tracking magma pathways and surface faulting in the Southwest Rift Zone and the Koa'e fault system (Kilauea volcano, Hawai 'i) using photogrammetry and structural observations.

Volcanic islands are often subject to flank instability, resulting from a combination of magmatic intrusions along rift zones and gravitational spreading causing extensional faulting at the surface. Here, we study the Koa'e fault system (KFS), located south of the summit caldera of Kilauea volcano in Hawai'i, one of the most active volcanoes on Earth, prone to active faulting, episodic dike intrusions, and flank instability. Two rift zones and the KFS are major structures controlling volcanic flank instability and magma propagation. Although several magmatic intrusions occurred over the KFS, the link between these faults, two nearby rift zones and the flank instability, is still poorly studied. To better characterize the KFS and its structural linkage with the surrounding fault and rift zones, we performed a detailed structural analysis of the extensional fault system, coupled with a helicopter photogrammetric survey, covering part of the south flank of Kilauea. We generated a high-resolution DEM (~ 8 cm) and orthomosaic (~ 4 cm) to map the fracture field in detail. We also collected ~ 1000 ground structural measurements of extensional fractures during our three field missions (2019, 2022, and 2023). We observed many small, interconnected grabens, monoclines, rollover structures, and en-echelon fractures that were in part previously undocumented. We estimate the cumulative displacement rate across the KFS during the last 600 ~ 700 years and found a decrease toward the west of the horizontal component from 2 to 6 cm per year, consistent with GNSS data. Integrating morphology observations, fault mapping, and kinematic measurements, we propose a new kinematic model of the upper part of the Kilauea's south flank, suggesting a clockwise rotation and a translation of a triangular wedge. This wedge is bordered by the extensional structures (ERZ, SWRZ, and the KFS), largely influenced by gravitational spreading. These findings illustrate a structural linkage between the two rift zones and the KFS, the latter being episodically affected by dike intrusions. Supplementary Information: The online version contains supplementary material available at 10.1007/s00445-024-01735-7.

A High-Entropy Single-Atom Catalyst Toward Oxygen Reduction Reaction in Acidic and Alkaline Conditions.

The design of high-entropy single-atom catalysts (HESAC) with 5.2 times higher entropy compared to single-atom catalysts (SAC) is proposed, by using four different metals (FeCoNiRu-HESAC) for oxygen reduction reaction (ORR). Fe active sites with intermetallic distances of 6.1 Å exhibit a low ORR overpotential of 0.44 V, which originates from weakening the adsorption of OH intermediates. Based on density functional theory (DFT) findings, the FeCoNiRu-HESAC with a nitrogen-doped sample were synthesized. The atomic structures are confirmed with X-ray photoelectron spectroscopy (XPS), X-ray absorption (XAS), and scanning transmission electron microscopy (STEM). The predicted high catalytic activity is experimentally verified, finding that FeCoNiRu-HESAC has overpotentials of 0.41 and 0.37 V with Tafel slopes of 101 and 210 mVdec-1 at the current density of 1 mA cm-2 and the kinetic current densities of 8.2 and 5.3 mA cm-2, respectively, in acidic and alkaline electrolytes. These results are comparable with Pt/C. The FeCoNiRu-HESAC is used for Zinc-air battery applications with an open circuit potential of 1.39 V and power density of 0.16 W cm-2. Therefore, a strategy guided by DFT is provided for the rational design of HESAC which can be replaced with high-cost Pt catalysts toward ORR and beyond.

Effects of the 2021 La Palma volcanic eruption on groundwater hydrochemistry: Geochemical modelling of endogenous CO2 release to surface reservoirs, water-rock interaction and influence of thermal and seawater.

Volcanic islands face unique challenges in protecting and managing their water resources due to their small size, limited freshwater availability, and vulnerability to natural hazards. The recent 2021 eruption of the Tajogaite volcano on La Palma Island in the Canary Islands, Spain, raised concerns regarding the potential impact on groundwater hydrochemistry. This work aimed to characterize and model the processes that lead to the measured hydrochemical impacts in the groundwater of La Palma as a consequence of the volcanic eruption. The study involved conducting three groundwater sampling campaigns during the eruption, and six after the eruption ceased. A total of 15 monitored points, including piezometers, wells, water galleries, and the main gully collector of the island, all relatively close (2 to15 km) to the erupted volcano, were sampled for the analysis of major solutes and SiO2. Unpublished hydrochemical data previous to the eruption were provided by the local water management authorities of La Palma (CIALP) and the Geological Survey of Spain (IGME). Statistical analyses were performed to assess the differences in groundwater composition before, during, and after the eruption, and a Principal Component Analysis (PCA) mixing model was calculated. Three compositional extreme waters were defined as end members in the system: (1) a high SiO2 computed thermal end member; (2) a low salinity computed fresh groundwater; (3) and seawater. The results of the mixing model showed two main events of maximum mixing ratios in the fresh groundwater reservoirs of La Palma after the eruption; the first one of seawater in July 2022, and the next one of thermal fluids in December 2022. This water mixing during and after the eruption, together with a volcanic CO2 input to the reservoirs, led to significant increases in the concentrations of Na, Ca, SiO2 and SO4 in fresh groundwater, as well as a drop in pH. The significance of these findings relies in improving our understanding of the effects of volcanic eruptions on groundwater, emphasizing the necessity for frequent monitoring and evaluation, given the scarcity and vulnerability of groundwater resources in volcanic islands.

The last 1100 years of activity of La Fossa caldera, Vulcano Island (Italy): new insights into stratigraphy, chronology, and landscape evolution.

A detailed study of past eruptive activity is crucial to understanding volcanic systems and associated hazards. We present a meticulous stratigraphic analysis, a comprehensive chronological reconstruction, thorough tephra mapping, and a detailed analysis of the interplay between primary and secondary volcanic processes of the post-900 AD activity of La Fossa caldera, including the two main systems of La Fossa volcano and Vulcanello cones (Vulcano Island, Italy). Our analyses demonstrate how the recent volcanic activity of La Fossa caldera is primarily characterized by effusive and Strombolian activity and Vulcanian eruptions, combined with sporadic sub-Plinian events and both impulsive and long-lasting phreatic explosions, all of which have the capacity to severely impact the entire northern sector of Vulcano island. We document a total of 30 eruptions, 25 from the La Fossa volcano and 5 from Vulcanello cones, consisting of ash to lapilli deposits and fields of ballistic bombs and blocks. Volcanic activity alternated with significant erosional phases and volcaniclastic re-sedimentation. Large-scale secondary erosion processes occur in response to the widespread deposition of fine-grained ash blankets, both onto the active cone of La Fossa and the watersheds conveying their waters into the La Fossa caldera. The continuous increase in ground height above sea level, particularly in the western sector of the caldera depression where key infrastructure is situated, is primarily attributed to long-term alluvial processes. We demonstrate how a specific methodological approach is key to the characterization and hazard assessment of low-to-high intensity volcanic activity, where tephra is emitted over long time periods and is intercalated with phases of erosion and re-sedimentation.

Upper holocene tephro-chronostratigraphy of Irazú Volcano, Costa Rica.

Irazú is one of the largest and most active volcanoes in Costa Rica. We present the tephro-chronostratigraphy of the last 2.6 ka of the Irazú volcano based on detailed field work and C14 radiometric dating, as well as a revision of the geological and historical records. In the stratigraphic record we identified at least 30 tephra units. Eight of them corresponding to the historical period (i.e., after 1700 A.D.), separated by repose periods of different durations. The distribution of the deposits, the volcanic morphologies (craters and pyroclastic cones) and the radiometric ages indicate that most of this recent eruptive activity has occurred from the summit of Irazú along an E-W fissure (~ 4 km long). Toward the west of the summit, near the Sapper hill may be the source of the oldest eruptions at 200 A.D., while the La Laguna cone, located to the east of the summit, could have formed around 1540 A.D., and Main Crater to the west could have formed around sixteenth-seventeenth century. Since then, the historical eruptions (i.e., 1723-1724, 1917-1921, 1924, 1928, 1930, 1933, 1939-1940 and 1963-1965) have been sourced from this crater, but not all of them are registered in the stratigraphy. The eruption frequency of Irazú during this period ranges from 23 to 100 years, with a major event about every 80 years. Irazu's eruptions have been mainly phreatomagmatic and Strombolian, including some phreatic explosions. We present a detailed tephro-chronostratigraphy that will help to building temporal analysis for hazard assessment and risk management plans to face future eruptions at Irazú.

Lessons Learnt from Monitoring the Etna Volcano Using an IoT Sensor Network through a Period of Intense Eruptive Activity.

This paper describes the successes and failures after 4 years of continuous operation of a network of sensors, communicating nodes, and gateways deployed on the Etna Volcano in Sicily since 2019, including a period of Etna intense volcanic activity that occurred in 2021 and resulted in over 60 paroxysms. It documents how the installation of gateways at medium altitude allowed for data collection from sensors up to the summit craters. Most of the sensors left on the volcanic edifice during winters and during this period of intense volcanic activity were destroyed, but the whole gateway infrastructure remained fully operational, allowing for a very fruitful new field campaign two years later, in August 2023. Our experience has shown that the best strategy for IoT deployment on very active and/or high-altitude volcanoes like Etna is to permanently install gateways in areas where they are protected both from meteorological and volcanic hazards, that is mainly at the foot of the volcanic edifice, and to deploy temporary sensors and communicating nodes in the more exposed areas during field trips or in the summer season.

Electrochemical production of hydroxylamine from nitrate on metal electrodes: A comparative study of selectivity and efficiency.

Despite the great potential of electrochemical nitrate reduction as a hydroxylamine production method, this strategy has not been sufficiently examined, and the effects of electrode material type on the selectivity and efficiency of this reduction remain underexplored. To bridge this gap, the present study evaluated six metals (Ag, Cu, Ni, Sn, Ti, and Zn) as cathode materials for the electrochemical reduction of nitrate to hydroxylamine, showing that the selectivity of hydroxylamine production was maximal for Sn, while the corresponding faradaic and energy utilization efficiencies were maximal for Ti. Although all tested materials favored nitrate reduction over hydrogen evolution, the disparity in the onset potentials of these reactions did not adequately explain the variations in nitrate removal efficiency, which was found to be influenced by material resistance and charge-transfer properties. The rate constants of elementary nitrate reduction steps determined from the time-dependent concentrations of nitrate and its reduction products (nitrous acid, hydroxylamine, and ammonium) were used to calculate the selectivity and efficiency of hydroxylamine production for each electrode. In turn, these selectivities and efficiencies were correlated with the density functional theory-computed adsorption energies of a key hydroxylamine precursor on different electrodes to afford a volcano-type plot with Ti and Sn at its pinnacle. Thus, this study introduces valuable descriptors and methods for the further screening of electrocatalysts for hydroxylamine generation and the establishment of more environmentally friendly hydroxylamine production techniques utilizing sustainable electricity.