Refractory Carbon Research Articles

Spectroscopic characterization of oceanic dissolved organic matter isolated by reverse osmosis coupled with electrodialysis

Oceanic dissolved organic matter (DOM) is one of the largest pools of reduced carbon on Earth, yet DOM remains poorly chemically characterized. Studies to determine the chemical nature of oceanic DOM have been impeded by the lack of efficient and non-fractioning methods to recover oceanic DOM. Here, a DOM fraction (~40 to 86% recovery) was isolated using reverse osmosis/electrodialysis (RO/ED) and analyzed by solid-state 13C nuclear magnetic resonance (NMR) spectroscopy. Samples were obtained from biogeochemically distinct environments: photobleached surface gyre, productive coastal upwelling zone, oxygen minimum, North Atlantic Deep Water, and North Pacific Deep Water. A ubiquitous ‘background’ refractory carbon pool was apparent throughout the ocean and dominated in the deep Pacific Ocean. Advanced NMR spectral editing revealed that condensed aromatic and quaternary anomeric carbons contribute to this deep refractory DOC pool, the quaternary anomeric carbons being a newly identified and potentially important component of bio-refractory carbohydrate-like carbon. Additionally, our results support the multi-pool (e.g. 3-pool: labile, semi-labile, and refractory) conceptual model of marine DOM biogeochemistry. Surface samples, hypothesized to be enriched in labile and semi-labile DOM, were enriched in carbohydrate-like material consistent with prior studies. High carboxyl signals in the deep Pacific support the hypothesis that a major fraction of the refractory pool consists of carboxyl-rich alicyclic molecules (CRAM).

Probing the photochemical reactivity of deep ocean refractory carbon (DORC): Lessons from hydrogen peroxide and superoxide kinetics

Most marine DOC is thought to be biologically-recalcitrant, especially that in the deep ocean pool (>1000m). In particular, the deep waters of the North Pacific should contain the most recalcitrant DOC because they do not form locally, with deep DOC having survived long isolation from the surface during global-scale thermohaline circulation. One of the proposed removal pathways involves photochemical reactions when refractory DOC circulates through sunlit surface waters (Mopper et al., 1991). Here, we reevaluate the general photoreactivity of refractory DOC by investigating the photochemical production of two reactive oxygen species (ROS), hydrogen peroxide (H2O2) and superoxide (O2−), using controlled irradiations at sea and in the laboratory. The photoproduction of these two ROS were compared between deep and surface water samples collected in the Gulf of Alaska. For irradiated samples, initial superoxide steady-state concentrations ([O2−]ss) and first-order decay constants (kpseudo) were similar between surface and deep waters, ranging from ~1–4nM and 4–12×10−3s−1, respectively. Initial photoproduction rates were comparable between surface and deep waters, ranging from 22–173nMh−1 for O2− and from 1–8.3nMh−1 for H2O2, indicating that a large portion of photoproduced O2− does not lead to H2O2 formation. In fact, the photoproduction ratio of O2− to H2O2 averaged ~4:1 in paired experiments, instead of the 2:1 stoichiometry expected for O2− dismutation to form H2O2. Continued irradiation for up to 48h showed photoproduced H2O2 to be much lower in deep samples compared to surface samples with accumulation slowing or stopping in deep samples despite both measurable [O2−]ss and photon absorbance by colored dissolved organic matter (CDOM). These results are consistent with a loss of source material (i.e. CDOM) for O2− photoproduction and a shift to a predominantly oxidative pathway for O2− decay. Low photoproduction rates, loss of continued accumulation with extended radiation, and an apparent loss of O2− source material argues that the deep refractory DOC pool is less photochemically reactive than previously suggested.

Biogeochemical drivers of the fate of riverine mercury discharged to the global and Arctic oceans

AbstractRivers discharge 28 ± 13 Mmol yr−1 of mercury (Hg) to ocean margins, an amount comparable to atmospheric deposition to the global oceans. Most of the Hg discharged by rivers is sequestered by burial of benthic sediment in estuaries or the coastal zone, but some is evaded to the atmosphere and some is exported to the open ocean. We investigate the fate of riverine Hg by developing a new global 3‐D simulation for Hg in the Massachusetts Institute of Technology ocean general circulation model. The model includes plankton dynamics and carbon respiration (DARWIN project model) coupled to inorganic Hg chemistry. Results are consistent with observed spatial patterns and magnitudes of surface ocean Hg concentrations. We use observational constraints on seawater Hg concentrations and evasion to infer that most Hg from rivers is sorbed to refractory organic carbon and preferentially buried. Only 6% of Hg discharged by rivers (1.8 Mmol yr−1) is transported to the open ocean on a global basis. This fraction varies from a low of 2.6% in East Asia due to the barrier imposed by the Korean Peninsula and Japanese archipelago, up to 25% in eastern North America facilitated by the Gulf Stream. In the Arctic Ocean, low tributary particle loads and efficient degradation of particulate organic carbon by deltaic microbial communities favor a more labile riverine Hg pool. Evasion of Hg to the Arctic atmosphere is indirectly enhanced by heat transport during spring freshet that accelerates sea ice melt and ice rafting. Discharges of 0.23 Mmol Hg yr−1 from Arctic rivers can explain the observed summer maximum in the Arctic atmosphere, and this magnitude of releases is consistent with recent observations. Our work indicates that rivers are major contributors to Hg loads in the Arctic Ocean.

TOWARD THE FORMATION OF CARBONACEOUS REFRACTORY MATTER IN HIGH TEMPERATURE HYDROCARBON-RICH ATMOSPHERES OF EXOPLANETS UPON MICROMETEOROID IMPACT

We report on laboratory simulation experiments mimicking the chemical processing of model atmospheres of exoplanets containing C3 and C4 hydrocarbons at moderate temperatures of 400 K upon interaction of catalytic surfaces of micrometeoroids. By utilizing an ultrasonic levitator device and heating singly levitated particles under simulated microgravity conditions, Raman spectroscopy is utilized as a non-invasive tool to probe on line and in situ the conversion of C3 and C4 hydrocarbons to refractory carbonaceous matter on the surfaces of levitated particles. Secondary Ion Mass Spectrometry and electron microscopic imaging were also conducted to gain further insight into the elementary composition and structures of the refractories formed. Our results provide compelling evidence that in the presence of a catalytic surface, which can be supplied in the form of micrometeoroids and atmospheric dust particles, hydrocarbon gases present in the atmospheres of exoplanets can be converted to refractory, carbon-rich carbonaceous matter of mainly graphitic structure with a carbon content of at least 90% at elevated temperatures. This finding might explain the low methane to carbon monoxide (CH4–CO) ratio in the hot Neptune GJ 436b, where the abundant methane photochemically converts to higher order hydrocarbons and ultimately to refractory graphite-like carbon in the presence of a silicon surface.

Quantification of refractory organic material in Amazon mudbanks of the French Guiana Coast

Abstract Sub-oxic overturning mudbanks originating in the Amazon outlet and traveling northwestward along the coast of South America store 3.5 Tg organic carbon on the Amazon shelf, annually. The predominance of old soil carbon burial associated with the sediment has been supported by relatively old bulk radiocarbon ages (~ 2200–3200 14C y) reported, but this amount has yet to be quantified for this dynamic setting. Here, we employ ramped pyrolysis radiocarbon dating to mudbank sediments from three cores to further constrain the amount of refractory sedimentary organic carbon present. Using radiocarbon age as a proxy for reactivity, we find that at least 36% of this organic carbon is pre-aged refractory terrestrial organic carbon, likely sourced from terrestrial soils and averaging ages of 16,100 ± 300 14C y. This implies significant preservation of pre-aged terrestrial soil material in this marine environment despite the mobility and oxygen availability in the muds. Concurrently, an average of 77% of this organic material is aged over 1000 14C y, consistent with previous estimates that the majority of organic carbon buried along the shelf is refractory. Analyses of extracted lignin phenols and terrestrial humic acids also support this preservation of refractory terrestrial material. These data indicate that sediment discharged from the Amazon River may preserve refractory terrestrial carbon in marine sediments at a minimum of 3.1 Tg C/y, which is more efficient than originally thought.

Mass and isotopic concentrations of water-insoluble refractory carbon in total suspended particulates at Mt. Waliguan Observatory (China)

Mass concentration and isotopic values δ13C and 14C are presented for the water-insoluble refractory carbon (WIRC) component of total suspended particulates (TSP), collected weekly during 2003, as well as from October 2005 to May 2006 at the WMO-GAW Mt. Waliguan (WLG) site. The overall average WIRC mass concentration was (1183±120)ng/m3 (n=79), while seasonal averages were 2081±1707 (spring), 454±205 (summer), 650±411 (autumn), and 1019±703 (winter) ng/m3. Seasonal variations in WIRC mass concentrations were consistent with black carbon measurements from an aethalometer, although WIRC concentrations were typically higher, especially in winter and spring. The δ13C PDB value (−25.3±0.8)‰ determined for WIRC suggests that its sources are C3 biomass or fossil fuel combustion. No seasonal change in δ13C PDB was evident. The average percent Modern Carbon (pMC) for 14C in WIRC for winter and spring was (67.2±7.7)% (n=29). Lower pMC values were associated with air masses transported from the area east of WLG, while higher pMC values were associated with air masses from the Tibetan Plateau, southwest of WLG. Elevated pMC values with abnormally high mass concentrations of TSP and WIRC were measured during a dust storm event.

Sources of polycyclic aromatic hydrocarbons (PAHs) to northwestern Saskatchewan lakes east of the Athabasca oil sands

The past several decades have witnessed a significant expansion of mining activities in the Athabasca oil sands region, raising concerns about their impact on the surrounding boreal forest ecosystem. To better understand the extent to which distal sites are impacted by oil sands-derived airborne contaminants, we examine sources of polycyclic aromatic hydrocarbons (PAHs) in surface sediments and dated sediment cores from Saskatchewan lakes situated ∼100–220km east–northeast of the main area of bitumen mining activities. The concentrations and fluxes of both parent and alkylated PAHs are low and show considerable variability over the past 70–100years. Small yet discernible increases in PAH concentrations and fluxes occurred over the past 30years, a trend which coincides with the rapid growth in bitumen production. However, several lines of evidence point to wildfires as the principal source of PAHs to these lakes: (1) the significant co-variations in most cores between retene (1-methyl-7-isopropyl phenanthrene) and other groups of parent and alkylated PAHs, (2) the similarity in compound specific δ13C signatures of the parent PAHs phenanthrene and pyrene in recently deposited surficial sediments and those corresponding to time intervals considerably pre-dating the large scale development of the oil sands and (3) the discernible up-core increases in the proportion of refractory carbon (i.e., char) in Rock-Eval 6 data. The collective evidence points to softwood combustion from boreal forest fires as the principal source of retene in sediments and the general increase in forest fire activity in this region over the past several decades as the source of refractory carbon. Mining activities associated with the Athabasca oil sands are thus not considered a major source of PAHs to these lakes.

Chemical compositions of black carbon particle cores and coatings via soot particle aerosol mass spectrometry with photoionization and electron ionization.

Black carbon is an important constituent of atmospheric aerosol particle matter (PM) with significant effects on the global radiation budget and on human health. The soot particle aerosol mass spectrometer (SP-AMS) has been developed and deployed for real-time ambient measurements of refractory carbon particles. In the SP-AMS, black carbon or metallic particles are vaporized through absorption of 1064 nm light from a CW Nd:YAG laser. This scheme allows for continuous "soft" vaporization of both core and coating materials. The main focus of this work is to characterize the extent to which this vaporization scheme provides enhanced chemical composition information about aerosol particles. This information is difficult to extract from standard SP-AMS mass spectra because they are complicated by extensive fragmentation from the harsh 70 eV EI ionization scheme that is typically used in these instruments. Thus, in this work synchotron-generated vacuum ultraviolet (VUV) light in the 8-14 eV range is used to measure VUV-SP-AMS spectra with minimal fragmentation. VUV-SP-AMS spectra of commercially available carbon black, fullerene black, and laboratory generated flame soots were obtained. Small carbon cluster cations (C(+)-C5(+)) were found to dominate the VUV-SP-AMS spectra of all the samples, indicating that the corresponding neutral clusters are key products of the SP vaporization process. Intercomparisons of carbon cluster ratios observed in VUV-SP-AMS and SP-AMS spectra are used to confirm spectral features that could be used to distinguish between different types of refractory carbon particles. VUV-SP-AMS spectra of oxidized organic species adsorbed on absorbing cores are also examined and found to display less thermally induced decomposition and fragmentation than spectra obtained with thermal vaporization at 200 °C (the minimum temperature needed to quantitatively vaporize ambient oxidized organic aerosol with a continuously heated surface). The particle cores tested in these studies include black carbon, silver, gold, and platinum nanoparticles. These results demonstrate that SP vaporization is capable of providing enhanced organic chemical composition information for a wide range of organic coating materials and IR absorbing particle cores. The potential of using this technique to study organic species of interest in seeded laboratory chamber or flow reactor studies is discussed.

A kinetic study of the formation of organic solids from formaldehyde: Implications for the origin of extraterrestrial organic solids in primitive Solar System objects

Aqueous organic solid formation from formaldehyde via the formose reaction and subsequent reactions is a possible candidate for the origin of complex primitive chondritic insoluble organic matter (IOM) and refractory carbon in comets. The rate of formation of organic solids from formaldehyde was studied as a function of temperature and time, with and without ammonia, in order to derive kinetic expressions for polymer yield. The evolution in molecular structure as a function of time and temperature was studied using infrared spectroscopy. Using these kinetic expressions, the yield of organic solids is estimated for extended time and temperature ranges. For example, the half-life for organic solid formation is ∼5days at 373K, ∼200days at 323K, and ∼70years at 273K with ammonia, and ∼25days at 373K, ∼13years at 323K, and ∼2×104years at 273K without ammonia. These results indicate that organic solids could form during the aqueous alteration in meteorite parent bodies. If liquid water existed early in the interiors of Kuiper belt objects (KBOs), formaldehyde could convert into organic solids at temperatures close to 273K, and possibly even below 273K in the ammonia–water system.

Resource Recovery from Wastewater: A Research Agenda

Traditionally wastewater treatment involved the removal of pollutants from wastewater to allow it to be discharged to the environment. This initially concentrated on carbon removal, but as environmental requirements became more stringent it was expanded to cover nitrogen and phosphorus removal. With increasing energy costs, more stringent environmental discharge limits and greater implementation of water sensitive urban design the economic viability of recovering water, energy and resources from wastewater is being considered more seriously. There are many examples worldwide of wastewater reuse and the methodologies are well known for the recovery of water which represents the most valuable resource in wastewater. On the contrary, the widespread application of energy, nitrogen and phosphorus recovery is just beginning to gain traction. A range of technological options for recovery of resources from wastewater are discussed in this report and in order of recovered value they include: 1) energy from methane capture, 2) direct phosphorus recovery, and 3) biosolids with improved phosphorus bioavailability. At this stage it is considered that the recovery of nitrogen via ammonia requires a step-change in technology for energy-efficient capture. Anaerobic wastewater treatment and more efficient anaerobic digestion of sludge offers major opportunities to improve the energy efficiency of the wastewater sector and to decrease biosolids levels, especially if additional sources of carbon can be included in the digestion process. However this raises the issue of the biologically un-available (refractory) carbon and how it can be converted to make it biologically available. With regards to nitrogen recovery an industry survey indicated this to be a lower priority than carbon or phosphorus recovery. However, as carbon recovery becomes more commonplace viable nitrogen removal technologies will be needed as carbon will not be available for this process. Therefore as energy costs continue to increase and existing plants start to age and need replacement or upgrading, it is considered that low footprint/low energy nitrogen removal technologies such as Anammox and Aerated Granular Biomass will become the industry norms in the future, compared to traditional nitrification/denitrification treatment. Phosphorus removal and recovery technologies that form an integral component of these processes for dilute wastewaters would seem to be the obvious pathway for future development, as processes for the recovery of phosphorus from concentrated side-streams such as struvite are well advanced. The most obvious methods would appear to be based on biological (such as phosphorus accumulating organisms – PAOs) or physical adsorption processes. Whilst efficient resource recovery is deemed as feasible, wastewater treatment will still leave a smaller sludge stream. In parts of Europe incineration is the preferred disposal option and opportunities are seen here for the simultaneous production of biochar and biogas. However, for many countries land application is still preferred. With this option, knowledge is still needed to understand the nutrient availability from biosolids relative to inorganic fertilizers. It is recognised that whilst resource recovery may not be a major revenue stream for wastewater treatment plants (WWTPs), it will help in offsetting treatment costs required to meet environmental goals. In this respect the commercial, regulatory and customer service aspects of resource recovery adoption still need to be addressed. This title belongs to WERF Research Report Series . ISBN: 9781780406640 (eBook)

Tritium and 14C background levels in pristine aquatic systems and their potential sources of variability

Tritium and 14C are currently the two main radionuclides discharged by nuclear industry. Tritium integrates into and closely follows the water cycle and, as shown recently the carbon cycle, as does 14C (Eyrolle-Boyer et al., 2014a, b). As a result, these two elements persist in both terrestrial and aquatic environments according to the recycling rates of organic matter. Although on average the organically bound tritium (OBT) activity of sediments in pristine rivers does not significantly differ today (2007–2012) from the mean tritiated water (HTO) content on record for rainwater (2.4 ± 0.6 Bq/L and 1.6 ± 0.4 Bq/L, respectively), regional differences are expected depending on the biomass inventories affected by atmospheric global fallout from nuclear testing and the recycling rate of organic matter within watersheds. The results obtained between 2007 and 2012 for 14C show that the levels varied between 94.5 ± 1.5 and 234 ± 2.7 Bq/kg of C for the sediments in French rivers and across a slightly higher range of 199 ± 1.3 to 238 ± 3.1 Bq/kg of C for fish. This variation is most probably due to preferential uptake of some organic carbon compounds by fish restraining 14C dilution with refractory organic carbon and/or with old carbonates both depleted in 14C. Overall, most of these ranges of values are below the mean baseline value for the terrestrial environment (232.0 ± 1.8 Bq/kg of C in 2012, Roussel-Debet, 2014a) in relation to dilution by the carbonates and/or fossil organic carbon present in aquatic systems. This emphasises yet again the value of establishing regional baseline value ranges for these two radionuclides in order to account for palaeoclimatic and lithological variations. Besides, our results obtained from sedimentary archive investigation have confirmed the delayed contamination of aquatic sediments by tritium from the past nuclear tests atmospheric fallout, as recently demonstrated from data chronicles (Eyrolle-Boyer et al., 2014a,b). Thus Sedimentary archives can be successfully used to reconstruct past 14C and OBT levels. Additionally, sediment repositories potentially represent significant storages of OBT that may account for in case of further remobilisation. We finally show that floods can significantly affect the OBT and 14C levels within suspended particles or sediments depending on the origin of particles reinforcing the need to acquire baseline value range at a regional scale.

Phosphorus Speciation in the Coastal Sediments of Khawr Ash Shaibah Al- Masdudah: Coastal Lagoon in the Eastern Red Sea, Kingdom of Saudi Arabia

The total phosphorus concentrations and its speciation were studied in the surface sediment of Khawr ash Shaibah al Maftuhah. The distribution pattern of total phosphorus in the sediment showed east-west gradient indicating different depositional environment of the lagoon. The largest pool of the sedimentary phosphorus was apatitic phosphorus (57%) followed by refractory organic phosphorus (42%). The impact of loosely adsorbed and exchangeable phosphorus (0.9 % of total phosphorus) and Metal oxide Phosphorus (0.6 % of total phosphorus) on the budget of total phosphorus in the sediments was minor. The concentration of dissolved phosphorus in the upper water column is most probably buffered by apatitic phosphorus. The low concentration of metal oxide phosphorus is suggested to be influenced by the calcareous nature of the lagoon. Possible transformation between apatitic and refractory organic phosphorus is inferred from the correlation of both parameters. The correlation of refractory organic carbon with total phosphorus in the sediments suggests in situ production due to biological activities.

Role of primary substrate composition and concentration on attenuation of trace organic chemicals in managed aquifer recharge systems

This study was undertaken to investigate the role of primary substrate composition and concentration on the attenuation of biodegradable emerging trace organic chemicals (TOrCs) in simulated managed aquifer recharge (MAR) systems. Four sets of soil columns were established in the laboratory, each receiving synthetic feed solutions comprising different ratios and concentrations of peptone-yeast and humic acid as the primary substrate to investigate the effect on removal of six TOrCs (atenolol, caffeine, diclofenac, gemfibrozil, primidone, and trimethoprim). Based on abiotic control experiments, adsorption was not identified as a significant attenuation mechanism for primidone, gemfibrozil and diclofenac. Caffeine, atenolol and trimethoprim displayed initial adsorptive losses, however, adsorption coefficients derived from batch tests confirmed that adsorption was limited and in the long-term experiment, biodegradation was the dominant attenuation process. Within a travel time of 16 h, caffeine – an easily degradable compound exhibited removal exceeding 75% regardless of composition or concentration of the primary substrate. Primidone – a poorly degradable compound, showed no removal in any column regardless of the nature of the primary substrate. The composition and concentration of the primary substrate, however, had an effect on attenuation of moderately degradable TOrCs, such as atenolol, gemfibrozil and diclofenac, with the primary substrate composition seeming to have a larger impact on TOrC attenuation than its concentration. When the primary substrate consisted mainly of refractory substrate (humic acid), higher removal of the moderately degradable TOrCs was observed. The microbial communities in the columns receiving more refractory carbon, were noted to be more diverse and hence likely able to express a wider range of enzymes, which were more suitable for TOrC transformation. The effect of the primary substrate on microbial community composition, diversity and gene expression potential confirmed its influence on TOrC degradation.

The Full Immersion Test Research of Refractory Weathering Steel

The paper mainly studied the corrosion properties of refractory weathering steel under chloride ion erosion environment. The full immersion tests on refractory weathering steel and carbon steel Q235 were conducted; and then a comparative analysis from the perspective of the corrosion weightlessness, the macro and micro morphology of rust layers have been made. Results indicated that refractory weathering steel and carbon steel corrosion weightlessness is relatively close to the early stage of corrosion, but the trend is reversed in the mid to late; refractory weathering steel corrosion weightlessness gradually decline, but the carbon steel’s is first increase then decrease. The carbon steel is mainly pitting corrosion, while refractory weathering steel develops general corrosion under chloride ion erosion environment. Rust layers of carbon steel are loose, hollow, and uneven. As the corrosion time goes on, the thickness of refractory weathering steel’s rust layers continuously thickening and the rust layers’ integrity are gradually increasing. The corrosion depth of refractory weathering steel is less than carbon steel’s; so does the longitudinal corrosion. This is because the microstructure of carbon steel is coarse pearlite and ferrite while the refractory weathering steel is granular bainite; the grain boundaries of carbon steel have more inclusions, especially MnS that is easily dissolved in chloride ion erosion environment. It is found that alloying elements Cr, Cu are enriched in the rust layers of refractory weathering steel by means of energy dispersive X-ray spectroscopy (EDS). The enrichment of these alloy elements in the rust layers improves the rust layer density, so that the uniform, dense, smooth rust layers formed on the surface of refractory weathering steel play a significant protective film to improve the substrate resistance corrosion.

Microstructure and Thermal Expansion of Hybrid - Copper Alloy Composites Reinforced with both Tungsten and Carbon Fibres

Tungsten as refractory material and high thermal conductive carbon fibres are promising candidates for production of copper matrix composites for high temperature applications. Three types of rod-like samples were prepared by gas pressure infiltration of different carbon/tungsten fibre preforms with copper and/or copper alloy (Cu-0.5Cr) respectively. The fibres are aligned parallel to rod axis and were combined with the tungsten wire cloth. The microstructure of prepared hybrid composites was examined. The samples were thermally cycled 3 times up to 550 °C at a relatively high heating/cooling rate (10 K/min) to touch real condition in applications where high heat is formed during short time. The thermal expansion behaviour in radial direction was also analysed. Results show that a combination of both types of reinforcements in rod-shapes samples insures good protection against composite disintegration during high temperature thermal loading.

Catalytic steam reforming of butanol in a fluidized bed and comparison with other oxygenated compounds

Fluidized bed steam reforming of butanol was studied at 650°C, atmospheric pressure and a steam to carbon (S/C) molar ratio of 14.7. The influence of the space velocity (GC1HSV) was tested with different catalysts. The use of a Ni/Al catalyst with 28.5wt.% Ni content gave almost equilibrium conditions at a GC1HSV of around 11000h−1. At higher GC1HSV values, carbon conversion to gas and gas yields diverged from equilibrium values. The catalyst composition was also analysed using several Ni/Al research catalysts modified with Ca or Mg, studying their effect on the nickel reducibility and activity. A comparative study of steam reforming of oxygenated compounds (butanol, ethanol, acetol and acetic acid) was also carried out. The steam reforming of alcohols showed high stability over time in comparison to the other compounds. The characterization of used catalysts by FESEM and TPO showed a greater proportion of refractory carbon when using acetic acid and acetol in comparison to the alcohol steam reforming which, in addition, presented less carbon content on the catalyst surface.

Mass spectrometry of refractory black carbon particles from six sources: carbon-cluster and oxygenated ions

Abstract. We discuss the major mass spectral features of different types of refractory carbonaceous particles, ionized after laser vaporization with an Aerodyne high-resolution soot-particle aerosol mass spectrometer (SP-AMS). The SP-AMS was operated with a switchable 1064 nm laser and a 600 °C thermal vaporizer, yielding respective measurements of the refractory and non-refractory particle components. Six samples were investigated, all of which were composed primarily of refractory material: fuel-rich and fuel-lean propane/air diffusion-flame combustion particles; graphite-spark-generated particles; a commercial fullerene-enriched soot; Regal Black, a commercial carbon black; and nascent aircraft-turbine combustion particles. All samples exhibited a spectrum of carbon-cluster ions Cxn+ in their refractory mass spectrum. Smaller clusters (x < 6) were found to dominate the Cxn+ distribution. For fullerene soot, fuel-rich-flame particles and spark-generated particles, significant Cxn+ clusters at x ≫ 6 were present, with significant contributions from multiply charged ions (n > 1). In all six cases, the ions C1+ and C3+ contributed over 60% to the total C1 5 were present. When such signals were present, C1+ / C3+ was close to 1. When absent, C1+ / C3+ was < 0.8. This ratio may therefore serve as a proxy to distinguish between the two types of spectra in atmospheric SP-AMS measurements. Significant refractory oxygenated ions such as CO+ and CO2+ were also observed for all samples. We discuss these signals in detail for Regal Black, and describe their formation via decomposition of oxygenated moieties incorporated into the refractory carbon structure. These species may be of importance in atmospheric processes such as water uptake and heterogeneous chemistry. If atmospherically stable, these oxidized species may be useful for distinguishing between different combustion sources. If unstable, they may provide a means to estimate the atmospheric age of an rBC sample. Future studies should attempt to establish which of these scenarios is more realistic.

Ecogeochemical fate of coarse organic particles in sediments of the Rhône River prodelta

Coarse particulate organic matter (CPOM) represents a small portion of the inner shelf sediments but occurs across all river outlets. To consider the ecogeochemical fate of CPOM in such an environment, we examined both the infauna community and secondary evidence of geochemical reactions preserved in the surface sediments of the Rhône prodelta. ICP-AES, scanning electron microscopy and energy dispersive X-ray spectrometry of the CPOM showed that the fate of organic matter in this environment is driven by sulphate reduction and geochemical reactions resulting from the precipitation of sulfide due to the presence of large amounts of iron-bearing minerals. Leaf litter debris contained such high quantities of iron that after dry ashing the remaining material is easily attracted by a magnet. The observed geochemical trade-off was proposed as a mechanism that helps to maintain a bioturbating animal community that in turn contributes to the mineralization of organic matter within this suboxic environment. This study showed that the accumulation of refractory organic carbon in sediments was intimately associated with the sequestering of iron and sulphur by providing a nucleation point for mineral deposition and also that the extent of decomposition of the organic materials did not necessarily increase progressively from coarser to finer particles.

Climate change and Mediterranean seagrass meadows: a synopsis for environmental managers

This synopsis focuses on the effects of climate change on Mediterranean seagrasses, and associated communities, and on the contribution of the main species, Posidonia oceanica, to the mitigation of climate change effects through its role of sequestering carbon dioxide. Whilst the regression of seagrass meadows is well documented, generally linked to anthropogenic pressures, global warming could be a cause of new significant regressions, notably linked to the introduction of exotic species, the rise of Sea-Surface Temperature (SST), and relative sea level. Seagrass communities could also be affected by climate change through the replacement of seagrass species having high structural complexity by species of lower complexity and even by opportunistic introduced species. Although it is currently very difficult to predict the consequences of these alterations and their cascade effects, two main conflicting trends in the functioning of seagrass ecosystems that could occur are acceleration of the herbivore pathway or of the detritivore pathway. The mean net primary production of the dominant species, Posidonia oceanica, is relatively high and can be estimated to range between 92.5 to 144.7 g C m-2 a-1. Around 27% of the total carbon fixed by this species enters the sedimentary pathway leading to formation, over millennia, of highly organic deposits rich in refractory carbon. At the Mediterranean scale, the sequestration rate might reach 1.09 Tg C a-1. The amount of this stored carbon is estimated to range from 71 to 273 kg C m-2, which when considered at the Mediterranean scale would represent 11 to 42% of the CO2 emissions produced by Mediterranean countries since the beginning of the Industrial Revolution. The greatest value of the P. oceanica ecosystem, in the context of mitigation of global climate change, is linked to this vast long-term carbon stock accumulated over the millennia, and therefore, efforts should be focused on preserving the meadows to keep this reservoir intact.

ТЕРМОДИФФУЗИОННЫЕ ПРОЦЕССЫ НАСЫЩЕНИЯ ТУГОПЛАВКИМИ ЭЛЕМЕНТАМИ И УГЛЕРОДОМ ПОВЕРХНОСТИ ВНУТРЕННЕЙ ПОЛОСТИ ЛОПАТОК ТУРБИНЫ ВЫСОКОГО ДАВЛЕНИЯ ГТД ИЗ ПЕРСПЕКТИВНЫХ НИКЕЛЕВЫХ ЖАРОПРОЧНЫХ СПЛАВОВ

ТЕРМОДИФФУЗИОННЫЕ ПРОЦЕССЫ НАСЫЩЕНИЯ ТУГОПЛАВКИМИ ЭЛЕМЕНТАМИ И УГЛЕРОДОМ ПОВЕРХНОСТИ ВНУТРЕННЕЙ ПОЛОСТИ ЛОПАТОК ТУРБИНЫ ВЫСОКОГО ДАВЛЕНИЯ ГТД ИЗ ПЕРСПЕКТИВНЫХ НИКЕЛЕВЫХ ЖАРОПРОЧНЫХ СПЛАВОВ