Sulfur Deposition Research Articles

Characterization of MSWI fly ashes along the flue gas cooling path and implications on heavy metal recovery through acid leaching

This study reports on detailed chemical and mineralogical characterization of the different municipal solid waste incineration ashes forming along the flue gas path of plants with separate dust removal and neutralization. In pursuit of optimizing heavy metal recovery through acid leaching, the metal extractability from empty pass ashes (EA), boiler ashes (BOA) and the electrostatic precipitator ashes (ESPA) was evaluated and compared. The focus was laid on matrix phases affecting leachability (e.g. alkalinity, oxidation–reduction potential), as well as on distribution and concentration of recoverable heavy metals and their binding forms. The data showed, that EA and BOA are geochemically similar and are essentially composed of two different materials: the heavy metal poor airborne ash particles and the Zn- and Pb-rich sulfate deposits that condensate on heat exchanger surfaces. Variation in relative amount and chemical composition of the deposits is responsible for fluctuations in bulk composition of EA and BOA. The ESPA shows different chemical and mineralogical characteristics than EA and BOA. The ESPA is enriched in the volatile heavy metals Zn, Pb, Cu, Cd and Sn, which are mainly incorporated in chlorides and sulfates. The high content of salt-bound and thus easily soluble heavy metals together with the lower alkalinity and lower oxidation–reduction potential indicates, that ESPA has a better leachability compared to EA and BOA. The EA and BOA, on the other hand, do not show any significant differences in leachability. The data may contribute to a basis for re-evaluating disposal routes of ash fractions with poor extraction properties.

Long-term variability in base cation, sulfur and nitrogen deposition and critical load exceedance of terrestrial ecosystems in China

The rapid development of China's industrial economy and implementation of air pollution controls have led to great changes in sulfur (S), nitrogen (N) and base cation (BC) deposition in the past three decades. We estimated China's anthropogenic BC emissions and simulated BC deposition from 1985 to 2015 with a five-year interval using a multilayer Eulerian model. Deposition of S and N from 2000 to 2015 with a five-year interval was simulated with the EMEP MSC-W model and the Multi-resolution Emission Inventory of China (MEIC). The critical load (CL) and its exceedance were then calculated to evaluate the potential long-term acidification risks. From 1985 to 2005, the BC deposition in China was estimated to have increased by 16 % and then decreased by 33 % till 2015. S deposition was simulated to increase by 49 % from 2000 to 2005 and then decrease by 44 % in 2015, while N deposition increased by 32 % from 2000 to 2010 with a limited reduction afterward. The maximum CL of S was found to increase in 67 % of mainland China areas from 1985 to 2005 and to decline in 55 % of the areas from 2005 to 2015, attributed largely to the changed BC deposition. Consistent with the progress of national controls on SO2 and NOX emissions, the CL exceedance of S increased from 2.9 to 4.6 Mt during 2000–2005 and then decreased to 2.5 Mt in 2015, while that of N increased from 0.4 in 2000 to 1.2 Mt in 2010 and then decreased to 1.1 Mt in 2015. The reduced BC deposition due to particle emission controls partially offset the benefit of SO2 control on acidification risk reduction in the past decade. It demonstrates the need for a comprehensive strategy for multi-pollutant control against soil acidification.

Thiolation behaviors of methanol catalyzed by bifunctional ZSM-5@t-ZrO2 catalyst

The catalytic properties of bifunctional ZSM-5@t-ZrO2 catalyst for methanol thiolation were revealed by using methanol and H2S as probe molecules. Taking the ZSM-5/t-ZrO2 physically-blended catalyst, pure ZSM-5 and t-ZrO2 as control catalysts, we investigated the characteristics of adsorption and transformation of different reaction molecules on or over different catalysts by combination of in-situ diffuse reflectance Fourier transform infrared spectroscopy (Drifts) and a variety of techniques including XRD, XPS, XRF, FT-IR, N2 adsorption-desorption, CO2/NH3-TPD, and DSC. The results showed that the synergistic effect of acid sites between ZSM-5 phase and t-ZrO2 phase in the bifunctional catalyst enhanced the adsorption and dissociation of methanol molecules, while the base sites in t-ZrO2 phase were mainly responsible for the adsorption and dissociation of H2S molecules. Due to the small specific surface area of pure t-ZrO2 catalyst, precursor species for sulfur deposition and carbon deposition were easily formed. Presulfurization could improve the initial activity of methanol thiolation and shorten the induction period. The dissociation of H2S at the base sites was the rate-determining step of the bimolecular reaction, and the appropriate increase of base sites in the bifunctional components could construct the matching formation rate of sulfhydryl and methoxy groups. At the same time, the special composite structure and meso-microporous system of ZSM-5@t-ZrO2 could effectively reduce the formation rate of carbon and sulfur deposits.

The response of streams in the Adirondack region of New York to projected changes in sulfur and nitrogen deposition under changing climate

Modeling studies project that in the future surface waters in the northeast US will continue to recover from acidification over decades following reductions in atmospheric sulfur dioxide and nitrogen oxides emissions. However, these studies generally assume stationary climatic conditions over the simulation period and ignore the linkages between soil and surface water recovery from acid deposition and changing climate, despite fundamental impacts to watershed processes and comparable time scales for both phenomena. In this study, the integrated biogeochemical model PnET-BGC was applied to two montane forest watersheds in the Adirondack region of New York, USA to evaluate the recovery of surface waters from historical acidification in response to possible future changes in climate and atmospheric sulfur and nitrogen deposition. Statistically downscaled climate scenarios on average project warmer temperatures and greater precipitation for the Adirondack by the end of the century. Model simulations suggest under constant climate, acid-sensitive Buck Creek would gain 12.8 μeq L−1 of acid neutralizing capacity (ANC) by 2100 from large reductions in deposition, whereas acid insensitive Archer Creek is projected to gain 7.9 μeq L−1 of ANC. However, climate change could limit those improvements in acid-base status. Under climate change, a negative offset relative to the ANC increases with no climate change are projected for both streams by 2100. In acid-insensitive Archer Creek the negative offset (−8.5 μeq L−1) was large enough that ANC is projected to decrease by −0.6 μeq L−1, whereas in acid-sensitive Buck Creek, the negative offset (−0.4 μeq L−1) resulted in a slight decline of the projected future ANC increase to 12.4 μeq L−1. Calculated target loads for 2150 for both sites decreased when future climate change was considered in model simulations, which suggests further reductions in acid deposition may be necessary to restore ecosystem structure and function under a changing climate.

Declining dry deposition of NO2 and SO2 with diverse spatiotemporal patterns in China from 2013 to 2018

The nitrogen and sulfur deposition results in damages on ecosystems, while the lack of direct observation on dry deposition limits our understanding of the total deposition. This study aimed to improve the methodology and estimates of NO2 and SO2 dry deposition in China and to explore the efficacy of China's recent emission control measures on dry deposition at the national and regional scales. We combined the random forest algorithm and the GEOS-Chem chemical transport model to predict the dry deposition fluxes of NO2 and SO2 and their inter-annual variabilities during 2013–2018 in mainland China. The annual NO2 dry deposition ranged between 2.1 and 3.1 kg N ha−1 yr−1, with an annual reduction rate of 0.21 kg N ha−1 yr−1 over this period. The areas with large deposition were located in the east, while the biggest reduction existed in the relatively clean Tibet Plateau region. The annual SO2 dry deposition ranged between 7.5 and 18.4 kg S ha−1 yr−1, with the annual reduction rate at 2.4 kg S ha−1 yr−1. Both the magnitude and relative reduction in the north were generally larger than the south. Regarding the four typical economically developed regions, the NO2 deposition declined slower than the national average, while SO2 generally declined faster than or equivalently to the national average, except for Pearl River Delta. The reduced emissions attributed to the national action on air pollution control were identified as an important reason for the declining deposition. However, the increased traffic and industrial capacity in the east weakened its benefit on NO2.

Experimental study coupled with thermodynamic assessment of the NiSO4–K2SO4 quasi binary system

Thermodynamic properties of the NiSO4–K2SO4 system play significant roles in various applications, e. g. in gas turbine components. In these components, Ni-base superalloys and coatings often suffer from the so-called hot corrosion induced by alkali sulphate deposits. In the present work, the phase equilibria in the system NiSO4–K2SO4 were experimentally determined for the first time using differential thermal analysis (DTA), dilatometry (DiL) and X-ray diffraction method (XRD). Two eutectic points and two stoichiometric compounds, K2Ni2(SO4)3 and K2Ni(SO4)2, were found in this system. The temperature and composition of the lower eutectic were determined to be 642 °C and 40 mol.% NiSO4, respectively. Another eutectic between NiSO4 and K2Ni2(SO4)3 was found at 819 °C, and the corresponding composition is around 75 mol.% NiSO4 and 25 mol. % K2SO4. Based on the obtained experimental data, the NiSO4–K2SO4 system was thermodynamically assessed using the CALPHAD methodology. The modified associate species model was used for the description of the liquid phase. Using the optimized dataset, the calculated phase diagram showed a good agreement with the experimental results. This dataset extends the previously developed general sulphate database including alkali- and alkaline-earth sulphates (CaSO4–MgSO4–Na2SO4–K2SO4) with the addition of NiSO4.

Modeling study of the impact of SO<sub>2</sub> volcanic passive emissions on the tropospheric sulfur budget

Abstract. Well constrained volcanic emissions inventories in chemistry transport models are necessary to study the impacts induced by these sources on the tropospheric sulfur composition and on sulfur species concentrations and depositions at the surface. In this paper, the changes induced by the update of the volcanic sulfur emissions inventory are studied using the global chemistry transport model MOCAGE (MOdèle de Chimie Atmosphérique à Grande Échelle). Unlike the previous inventory (Andres and Kasgnoc, 1998), the updated one (Carn et al., 2016, 2017) uses more accurate information and includes contributions from both passive degassing and eruptive emissions. Eruptions are provided as daily total amounts of sulfur dioxide (SO2) emitted by volcanoes in the Carn et al. (2016, 2017) inventories, and degassing emissions are provided as annual averages with the related mean annual uncertainties of those emissions by volcano. Information on plume altitudes is also available and has been used in the model. We chose to analyze the year 2013, for which only a negligible amount of eruptive volcanic SO2 emissions is reported, allowing us to focus the study on the impact of passive degassing emissions on the tropospheric sulfur budget. An evaluation against the Ozone Monitoring Instrument (OMI) SO2 total column and MODIS (Moderate-Resolution Imaging Spectroradiometer) aerosol optical depth (AOD) observations shows the improvements of the model results with the updated inventory. Because the global volcanic SO2 flux changes from 13 Tg yr−1 in Andres and Kasgnoc (1998) to 23.6 Tg yr−1 in Carn et al. (2016, 2017), significant differences appear in the global sulfur budget, mainly in the free troposphere and in the tropics. Even though volcanic SO2 emissions represent 15 % of the total annual sulfur emissions, the volcanic contribution to the tropospheric sulfate aerosol burden is 25 %, which is due to the higher altitude of emissions from volcanoes. Moreover, a sensitivity study on passive degassing emissions, using the annual uncertainties of emissions per volcano, also confirmed the nonlinear link between tropospheric sulfur species content with respect to volcanic SO2 emissions. This study highlights the need for accurate estimates of volcanic sources in chemistry transport models in order to properly simulate tropospheric sulfur species.

Trends of sulfur and nitrogen deposition from 2003 to 2017 in Japanese remote areas

Emissions of sulfur (S) and nitrogen (N) compounds in East Asia has drastically changed over the last two decades. To assess the influence of the drastic changes in air pollution on ecosystems in Japan, we investigated the trends of S and N deposition during 2003–2017 at remote sites of Acid Deposition Monitoring Network in East Asia (EANET). We measured wet deposition and inferentially estimated dry deposition of S and N using monitoring data from 2003 to 2017 at eight sites. We estimated dry deposition using the inferential method with an updated parameterization for gaseous surface resistance. The linear regression method and nonparametric Mann–Kendall test was used to analyze the temporal trends based on the monthly data sets. High S and N deposition amounts over 10 kg ha−1 year−1 were frequently found at most sites. There were significant increase trends in N deposition to S deposition (N/S) ratio at all sites throughout the 15-year period. Some trends were significantly found when the 15-year period was divided into three: 2003–2007, 2008–2012, and 2013–2017. S deposition had significantly decreased over a wide area in Japan, especially at Sado-seki, Happo, Oki, Hedo, and Ogasawara, in 2013–2017. Significant decreases in oxidized N deposition at Sado-seki and Oki were also found in 2013–2017. Because of almost flat N deposition mainly contributed by reduced N deposition, the N/S ratio clearly increased. These trends were associated with the recent reductions in SO2 and NOx emissions in China. The NOx emission reduction of China has not caught up with that of SO2, and NH3 emissions have not been reduced. This caused the significant increases in the N/S ratio not only in 2013–2017 but also in 2003–2017.

Post modification of Oxo-clusters in robust Zirconium-Based metal organic framework for durable SO2 capture from flue gas

The efficient capture of SO2 after the combustion of fossil fuels is of great challenge as the low SO2 concentration (<500 ppm) and coexisting with CO2, water, O2 in flue gas. Robust zirconium-based MOFs possessing accessible polar sites usually have high SO2 adsorption capacity but poor durably in adsorption desulfurization due to the acidic sulfate deposition on the Zr-O cluster. Herein, a Zr-O cluster post-modification method was introduced in a Zr-MOF (MOF-808) to form EDTA-MOF-808 (EDTA, ethylene diaminetetraacetic acid) for selective and durable removal of SO2. The introduction of EDTA not only improve their SO2 adsorption capacity, but also sharply increase their SO2/CO2 selectivity (57.2 vs 8.9) and SO2/N2 selectivity (1915.8 vs 292.7) at low SO2 partial pressure. Moreover, the synergistic effects of dipole and hydrogen bonding interaction between SO2 and EDTA in EDTA-MOF-808 make the capture of SO2 in a reversible manner, which can prevent the formation of S(VI) species in Zr-MOF. DFT calculation confirmed that SO2 was interacted with EDTA through moderate dipole–dipole interaction (S(SO2) with N(EDTA)) and hydrogen bonds (H(–COOH) with O(SO2)). Systematic investigations including thermodynamic SO2 adsorption, dynamic breakthrough experiments, stability tests and DFT-calculations in both MOF-808 and EDTA-MOF-808 confirmed the efficient performance of post modification of Zr-O clusters with EDTA in Zr-MOFs for durable SO2 capture.

Influence of Ni-Content on Crystallographic Parameters and Electrochemical Performance of the La0.25Sr0.25Ca0.4NixTi1 - xO3 - d SOC Fuel Electrode

The search for alternative fuel electrode materials to Ni-cermets is very active in the solid oxide cell (SOC) field due to several reasons. Metallic Ni is very sensitive to oxygen partial pressure (p O2) and reoxidizes to NiO if p O2 rises above the threshold level (temperature dependent). Ni-cermets are also prone to sulphur poisoning 1,2 and coking 3 if carbonaceous fuel without sufficient steam is used. Even if gases are carefully purified from sulphur, and correct steam to carbon ratio is used, metallic Ni centres still has a tendency to coarsen over time, which leads to performance losses 4,5.Full ceramic anodes are envisaged as redox stable materials when compared to metal-cermets – there is no immense expansion relating to metal oxidation reduction cycles and these materials are more resistant to coking and sulphur depositions 6–8. La0.2Sr0.7 - xCaxTiO3 - d (LSCTA-) has been demonstrated to be promising ceramic fuel electrode due to excellent electrical conductivity and stability if x ≤ 0.45 9.In this work, we investigated the influence of Ni concentration on the crystallographic properties of La0.25Sr0.25Ca0.4Ti1 - xNixO3 - d (LSCNT-x) (x = 0, 0.02, 0.05, 0.1, 0.2) using in situ X-ray diffraction. Sr mobility during the processing of electrodes with different Ni contents was demonstrated. The electrochemical performance of each synthesized electrodes was evaluated with electrochemical impedance spectroscopy (EIS) using a 3-electrode setup in LSCNT-x/GDC|GDC/ScCeSZ/GDC|LSC cell (LSC is La0.6Sr0.4CoO3 - d ). Two-electrode measurements were also conducted with the most stable and electrochemically active electrode in order to assess its performance in working systems. Additionally, steam electrolysis experiments were performed to establishx the best electrode’s performance in electrolysis mode.

Brine-driven destruction of clay minerals in Gale crater, Mars.

Mars' sedimentary rock record preserves information on geological (and potential astrobiological) processes that occurred on the planet billions of years ago. The Curiosity rover is exploring the lower reaches of Mount Sharp, in Gale crater on Mars. A traverse from Vera Rubin ridge to Glen Torridon has allowed Curiosity to examine a lateral transect of rock strata laid down in a martian lake ~3.5 billion years ago. We report spatial differences in the mineralogy of time-equivalent sedimentary rocks <400 meters apart. These differences indicate localized infiltration of silica-poor brines, generated during deposition of overlying magnesium sulfate-bearing strata. We propose that destabilization of silicate minerals driven by silica-poor brines (rarely observed on Earth) was widespread on ancient Mars, because sulfate deposits are globally distributed.

Modified clay minerals on Mars

Martian Geology Sedimentary rocks exposed in Gale crater on Mars contain extensive clay minerals. Bristow et al. analyzed drill samples collected by the Curiosity rover as it climbed up sedimentary layers in the crater. They found evidence of past reactions with liquid water and sulfate brines, which could have percolated through the clay from an overlying sulfate deposit. Similar sulfate deposits are widespread across the planet and represent some of the last sedimentary rocks to form before the planet lost its surface liquid water, so the results inform our understanding of the geologic processes that occurred as Mars dried out. Science, abg5449, this issue p. [198][1] [1]: /lookup/doi/10.1126/science.abg5449

Probing Sulfur Deposition onto Carbon Nanomaterials from Aqueous, Elemental Sulfur Sols for Lithium-Sulfur Batteries.

Sulfur cathodes for lithium-sulfur batteries often rely on integrating sulfur with high surface area carbonaceous materials. Nanoscale mixing is typically achieved by a lengthy, high-temperature melt imbibition approach that employs carbon nanomaterials in an aggregated solid form. In this work, we present a simple strategy to coat carbon nanomaterials with sulfur in a cost-effective, room-temperature process using inexpensive elemental sulfur. Our results are based on hydrophobic sulfur sols, which have rarely been examined for use in the preparation of sulfur cathodes. We study the deposition mechanism on different carbon materials and find that sulfur dissolves from the sol into the aqueous phase and coats the surface of reduced graphene oxide (rGO) by heterogeneous nucleation and growth, but that this mechanism is not favored for carbon materials such as Ketjen black (KB) and graphene oxide (GO), for which undesirable homogeneous nucleation of micron-sized, insulating sulfur crystals is observed. High loading (3-4 mgsulfur/cm2) rGO-based cathodes prepared using this approach achieve discharge capacities of 1300 mAh/gsulfur (∼4.8 mAh/cm2) at 0.1C and achieve capacities 7-fold higher than cells prepared via traditional melt imbibition approaches at higher rates of 0.8C and 1C. Cells prepared without the need for added binder or conductive additive achieve projected full cell energy densities of 468 Wh/kg at 0.1C when taking into account all inactive components and assuming no lithium metal degradation, indicating that the deposition of sulfur from hydrophobic sols onto carbon nanomaterials can serve as a simple, aqueous-based, one-step process to prepare high sulfur loading cathodes with high projected energy densities.

Temporal changes in the ground vegetation in spruce forests in the Erzgebirge (Ore Mountains) — bryophytes are better indicators of the impact of liming and of sulphur and nitrogen deposition than the herb layer

AbstractQuestionsHow have species composition and diversity in the herb and bryophyte layer of spruce forest communities developed on unlimed plots and on plots with varying liming intensity under the conditions of decreasing sulphur (S) deposition and unabated high nitrogen (N) deposition?LocationSpruce stands in the Erzgebirge, East Germany.MethodsWe repeated herb and bryophyte layer surveys on 36 quasi‐permanent plots after approx. 23 years (1989/1991 vs 2012/2014). Over this period, the study area experienced a sharp decline in S deposition and repeated liming of the spruce stands. Our plots represent a gradient of liming from zero to four applications. We analyse the change in species composition and species diversity depending on the liming intensity using Ellenberg indicator values (EIV), correspondence analysis, indicator species analysis and diversity parameters (alpha diversity, Lennon similarity).ResultsOn the unlimed plots, the species composition of the herb layer remained unchanged over the study period, despite the decrease in the coverage of Calamagrostis villosa and Deschampsia flexuosa and in the total coverage of the herb layer. In contrast, the bryophyte layer showed a significant increase in coverage and species richness with the decrease in S deposition. Liming led to a sharp increase in species richness in the herb layer, due to the appearance of disturbance indicators. The mean EIVs for acidity and nitrogen (EIV‐R and EIV‐N) also increased significantly. All observed effects increased with increasing liming intensity. We also noticed an increase in species richness over time in the bryophyte layer on the limed plots. However, this was less pronounced than on the unlimed plots, and decreased with increasing liming intensity. This was because the appearance of disturbance indicators or of typical species for the Calamagrostio villosae‐Piceetum was partially compensated for by the disappearance of acid indicators as a result of liming. The species turnover was thus much higher in the bryophyte layer than in the herb layer.ConclusionsIn contrast to the herb layer, the bryophyte layer proves to be a sensitive indicator of changes in air pollution. The effects of greatly reduced S deposition on the bryophyte layer outweigh those of continuous N deposition in the study area. Liming acts as a disturbance in both the herb layer and the bryophyte layer. This influence increases with increasing liming intensity. Our results do not support a general application of liming in large, contiguous forest areas. Rather, this measure should be applied in a differentiated manner.

Mechanistic study on H2S and subsequent O2 adsorption on iron oxides and hydroxides

Iron oxides are useful adsorbents for the alternating removal of H2S and O2 from natural gas and biogas. In this context, the present paper aims to elucidate the mechanisms behind the consecutive adsorption of both gases. Three different types of iron oxides/hydroxides were investigated using in-situ infrared and Raman spectroscopy as well as ex-situ X-ray diffraction.The spectroscopic studies confirm that H2S is adsorbed on all kinds of surface sites, particularly at Brønsted and Lewis acid sites. However, on the Brønsted acid sites, H2S undergoes dissociation, leading to the formation of SH−, S2− and H2O. This mechanism substantiates the high H2S uptake capacity of the OH-containing adsorbents. Prolonged H2S adsorption provokes an increasing consumption of the adsorbent, yielding amorphous FeS and elemental sulfur, with hydrogen sulfate and sulfate species also forming as by-products.Furthermore, the subsequent O2 adsorption on the sulfidized samples causes some re-formation of the initial adsorbent with the simultaneous production of elemental sulfur and sulfate entities. As a result of the mechanistic understanding gained in this study, it is concluded that the complete regeneration of the iron substrates is almost impossible due to their substantial degradation, associated with partial conversion into sulfates and the deposition of sulfur.

Exploring the Potential of Using Carbonyl Sulfide to Track the Urban Biosphere Signal

AbstractCities are implementing additional urban green as a means to capture CO2 and become more carbon neutral. However, cities are complex systems where anthropogenic and natural components of the CO2 budget interact with each other, and the ability to measure the efficacy of such measures is still not properly addressed. There is still a high degree of uncertainty in determining the contribution of the vegetation signal, which furthermore confounds the use of CO2 mole fraction measurements for inferring anthropogenic emissions of CO2. Carbonyl sulfide (OCS) is a tracer of photosynthesis which can aid in constraining the biosphere signal. This study explores the potential of using OCS to track the urban biosphere signal. We used the Sulfur Transport and dEposition Model (STEM) to simulate the OCS concentrations and the Carnegie Ames Stanford Approach ecosystem model to simulate global CO2 fluxes over the Bay Area of San Francisco during March 2015. Two observation towers provided measurements of OCS and CO2: The Sutro tower in San Francisco (upwind from the area of study providing background observations), and a tower located at Sandia National Laboratories in Livermore (downwind of the highly urbanized San Francisco region). Our results show that the STEM model works better under stable marine influence, and that the boundary layer height and entrainment are driving the diurnal changes in OCS and CO2 at the downwind Sandia site. However, the STEM model needs to better represent the transport and boundary layer variability, and improved estimates of gross primary productivity for characterizing the urban biosphere signal are needed.

Unknown Eruption Source Parameters Cause Large Uncertainty in Historical Volcanic Radiative Forcing Reconstructions

AbstractReconstructions of volcanic aerosol radiative forcing are required to understand past climate variability. Currently, reconstructions of pre‐20th century volcanic forcing are derived from sulfate concentrations measured in polar ice cores, mainly using a relationship between the average ice‐sheet sulfate deposition and stratospheric sulfate aerosol burden based on a single explosive eruption—the 1991 eruption of Mt. Pinatubo. Here we estimate volcanic radiative forcings and associated uncertainty ranges from ice‐core sulfate records of eight of the largest bipolar deposition signals in the last 2,500 years using statistical emulation of a perturbed parameter ensemble of aerosol‐climate model simulations of explosive eruptions. Extensive sampling of different combinations of eruption source parameters using the emulators reveals that a very wide range of eruptions in different seasons with different sulfur dioxide emissions, eruption latitudes, and emission altitudes produce ice‐sheet sulfate deposition consistent with ice‐core records. Consequently, we find a large range in the volcanic forcing that can be directly attributed to the unknown eruption source parameters. We estimate that the uncertainty in volcanic forcing caused by many plausible eruption realizations leads to uncertainties in the global mean surface cooling of around 1°C for the largest unidentified historical eruptions. Our emulators are available online (https://cemac.github.io/volcanic-forcing-deposition) where eruption realizations for given ice‐sheet sulfate depositions can be explored.

Concentrations of sulphur and trace elements in subarctic soils and mosses in relation to geothermal power plants at Hengill, Iceland – ecological implications

Amidst the globally accelerated plans to increase geothermal energy utilization, knowledge of ecological responses to power plant emissions is limited. The aim of this study is to investigate ecosystem accumulation of elements emitted from power plants in the Hengill geothermal field in Southwest Iceland, in relation to patterns of plant growth and health. The moss Racomitrium lanuginosum was used as a bio-indicator, a dominating plant in our study areas. Concentrations of sulphur, arsenic, boron, antimony, and mercury in soil and shoots of R. lanuginosum, were determined, and growth and other moss characteristics (moss damage, physiology and mat depth) assessed at different distances and directions from two geothermal power plants, Hellisheidi (303 MWe, operated since 2006) and Nesjavellir (120 MWe, operated since 1990). Higher concentrations of these elements were detected around Hellisheidi than Nesjavellir. Sulphur, antimony, and mercury concentrations in moss decreased with increasing distance from the power plant around Nesjavellir, while arsenic concentrations increased with increasing distance away and boron concentrations were relatively low, below detection. Similar trends for sulphur and antimony followed in soils. Arsenic concentrations in soil on the other hand, increased with increasing distance from the Nesjavellir power plant while boron concentrations were, below detection limit except at 250 m downwind and at 1000 m and 4000 m upwind. At Hellisheidi, sulphur and boron concentrations, in moss decreased with increasing distance away from the power plant and showed an opposite trend in soil. Arsenic, antimony and mercury concentrations in moss showed a general increase in concentrations with increasing distance away from the power plant; while in soil, trace element concentrations did not change significantly with distance, and there were no clear patterns related to the direction of prevailing winds. On average, moss growth and other moss trait values were higher at Hellisheidi than Nesjavellir. At Nesjavellir, moss mat depth and biomass moss response variables increased with increasing distance away and were greater upwind than downwind; while shoot turnover (%) and chlorophyll concentration decreased with increasing distance away from the power plant and did not vary with direction. Moss shoot length did not vary with distance but showed a decrease downwind. At Hellisheidi, trends were non-linear with distance, however biomass increase was the only response variable significantly higher downwind than upwind: other variables did not vary with direction. The frequency of moss damage was quite low around both power plants. We thus conclude that emitted sulphur from the geothermal power plants is deposited in the surrounding ecosystem and has so far no clear indications of harmful effects. In addition, the emerging patterns of arsenic, boron, antimony and mercury concentrations in the ecosystem were not clear to indicate deposition from the geothermal power plants and there were no related harmful effects. Nonetheless, further long-term monitoring of potential environmental impacts is advised. We recommend experimental studies to establish in detail if and how different levels of sulphur deposition may affect ecosystems for appropriate mitigation.

Surface-Modified Mxene Nanosheets to Enable Complete Utilization and Immobilization of Polysulfides in Lithium-Sulfur Batteries

Lithium-Sulfur batteries are of great interest owing to sulfur's high theoretical capacity, low-cost and environmental benignity. However, the practicality of these batteries has been impeded due to the infamous “polysulfide-shuttle” effect. Although several research articles in the past decade have focused to mitigate this effect, capacity fade and low coulombic efficiency still prevail. 2D MXenes are early transition metal carbides known for their high metallic conductivity with tunable surface functionalities. MXenes with formula Mn+1XnTx are usually derived from the parental MAX phases by selectively etching the A layer (where M represents a transition metal, A represents the group 13 or 14 elements in the periodic table and X represents carbon or nitrogen, Tx stands for the surface terminations). Thus, the obtained MXenes possess a unique layered structure. After etching, the surface of MXenes is terminated with various functional groups such as hydroxyl (-OH), oxygen (-O), chlorine (-Cl), and fluorine (-F).Rich surface polar sites in Ti3C2Tx enhance electrochemical performance via suppression of polysulfide shuttle. However, past synthesis procedures result in the development of hydrophilic MXene nanosheets unable to be coupled with hydrophobic sulfur. Herein, we propose a new design based on the functionalization of MXene nanosheets with an organic molecule for the effective deposition of sulfur nanoparticles on the surface. This strategy enables the dispersion of MXene sheets in sulfur dissolved solvents enabling the conformal deposition of sulfur on MXene sheets with negligible water in the composite. The metallic sheet-like conductivity (~103 S.cm-1) also aids in faster reaction kinetics during the conversion of polysulfides to Li2S, mitigating the shuttle effect. Consequently, the developed composite enables the efficient utilization of active surface sites to bind polysulfides and alleviate the shuttle effect. This novel cathode delivers a high initial reversible capacity of 1220 mAh·g-1 at 0.1 C and at 0.5C, these cathodes stabilize at 880mAh·g-1 after the first 5 cycles, 85% of which is retained post 500 cycles. Additionally, we developed cathodes with high sulfur loading of ~10.7 mg·cm-2 that delivers a stable areal capacity of ~7 mAh·cm-2 for 150 cycles. Moreover, these cathodes in a pouch cell configuration retained ~770 mAh·g-1 after ~200 cycles at 0.2C (85.5% retention). Ex-situ studies elucidated the nature of the LiPs–MXene interaction and the effect of surface functionalization towards improved performance +RP and VN have equal contribution

Reductions in the deposition of sulfur and selenium to agricultural soils pose risk of future nutrient deficiencies

Atmospheric deposition is a major source of the nutrients sulfur and selenium to agricultural soils. Air pollution control and cleaner energy production have reduced anthropogenic emissions of sulfur and selenium, which has led to lower atmospheric deposition fluxes of these elements. Here, we use a global aerosol-chemistry-climate model to map recent (2005–2009) sulfur and selenium deposition, and project future (2095–2099) changes under two socioeconomic scenarios. Across the Northern Hemisphere, we find substantially decreased deposition to agricultural soils, by 70 to 90% for sulfur and by 55 to 80% for selenium. Recent trends in sulfur and selenium concentrations in USA streams suggest that catchment mass balances of these elements are already changing due to the declining atmospheric supply. Sustainable fertilizer management strategies will need to be developed to offset the decrease in atmospheric nutrient supply and ensure future food security and nutrition, while avoiding consequences for downstream aquatic ecosystems.