Search Results (22)

Recent studies have emphasized the diel nature of dissolved CO₂ (pCO₂) in lake systems; however, around the world, field measurements have been conducted at different times, and it is not clear how, and to what extent, this variable sampling time affects CO₂ emission (FCO₂). This research aimed to investigate whether 10:00 am. was an effective time for lake field sampling to capture 24 h mean pCO₂ and FCO₂ from subtropical eutrophic shallow lake systems. To accomplish this goal, our study compiled long-term data from three individual studies on a shallow lake system in southeast Louisiana, USA. The data comprised samples collected across three-hour intervals, seasonally, over five years. This study highlights that a lake system can function as a carbon sink during peak daylight hours and can shift to a source overnight to early morning. The findings from the longer-term data confirmed 9:00 am to 11:00 am as the time range when pCO₂ deviation from the daily mean is at its lowest (111% of the daily mean). Sampling outside of this time range resulted in an increase in FCO₂ (32.09 mmol m⁻² h⁻¹) of up to 271% (87.03 mmol m⁻² h⁻¹) in overnight samples, with daytime measurements of FCO₂ flipping the lake from source to sink sequestering −20.17 mmol m⁻² h⁻¹. Based on our findings, we strongly recommend that future studies in similar aquatic systems utilize the 9:00–11:00 am timeframe for field sampling to increase the accuracy and compatibility of shared data in carbon emission estimation. Full article

The equatorial Pacific serves as the world’s largest oceanic source of CO₂. The contrasting ocean environment in the eastern (i.e., upwelling) and western (i.e., warm pool) regions makes it difficult to fully characterize its CO₂ dynamics with limited in situ observations. In this study, we addressed this challenge using monthly surface partial pressure of CO₂ (pCO₂sw) and air-sea CO₂ fluxes (FCO₂) data products reconstructed from satellite and reanalysis data at a spatial resolution of 1° × 1° in the period of 1982–2021. We found that during the very strong El Niño events (1997/1998, 2015/2016), both pCO₂sw and FCO₂ showed a significant decrease of 41–58 μatm and 0.5–0.8 mol·m⁻²·yr⁻¹ in the eastern equatorial Pacific, yet they remained at normal levels in the western equatorial Pacific. In contrast, during the very strong La Niña events (1999/2000, 2007/2008, and 2010/2011), both pCO₂sw and FCO₂ showed a strong increase of 40–48 μatm and 1.0–1.4 mol·m⁻²·yr⁻¹ in the western equatorial Pacific, yet with little change in the eastern equatorial Pacific. In the past 40 years, pCO₂sw in the eastern equatorial Pacific was increasing at a higher rate (2.32–2.51 μatm·yr⁻¹) than that in the western equatorial Pacific (1.75 μatm·yr⁻¹), resulting in an accelerating CO₂ outgassing (at a rate of 0.03 mol·m⁻²·yr⁻²) in the eastern equatorial Pacific. We comprehensively analyzed the potential effects of different factors, such as sea surface temperature, sea surface wind speed, and ΔpCO₂ in driving CO₂ fluxes in the equatorial Pacific, and found that ΔpCO₂ had the highest correlation (R ≥ 0.80, at p ≤ 0.05), highlighting the importance of accurate estimates of pCO₂sw from satellites. Further studies are needed to constrain the retrieval accuracy of pCO₂sw in the equatorial Pacific from satellite remote sensing. Full article

The development and characterization of synthesis techniques for oxide materials based on ceria is a subject of extensive study with the objective of their wide-ranging applications in pursuit of sustainable development. The present study demonstrates the feasibility of controlled synthesis of Ce_1−xM_xO_2−δ (M = Fe, Ni, Co, Mn, Cu, Ag, Sm, Cs, x = 0.0–0.3) in combustion reactions from precursors comprising glycine, polyvinyl alcohol, polyvinylpyrrolidone, polyethylene glycol, and cellulose as organic components. Controlled synthesis is achieved by varying the composition of the precursor, the type of organic component, and the amount of organic component, which allows for the influence of the generation of high-density electrical charges and outgassing during synthesis. The intensity of charge generation is quantified by measuring the value of the precursor–ground potential difference. It has been demonstrated that an increase in the intensity of charge generation results in a more developed morphology, which is essential for the practical implementation of ceria as a catalyst to enhance contact with gases and solid particles. The maximum value of the potential difference, equal to 68 V, is obtained during the synthesis of Ce_0.7Ni_0.3O_2−δ with polyvinyl alcohol in stoichiometric relations, which corresponds to a specific surface area of 21.7 m² g⁻¹. A correlation is established between the intensity of gas release for systems with different organic components, the intensity of charge generation, morphology, and the value of the specific surface area of the samples. Full article

Carbon fiber reinforced polymer (CFRP) composites are renowned for their exceptional mechanical properties, with applications in industries such as automotive, aerospace, medical, civil, and beyond. Despite these merits, a significant challenge in CFRPs lies in their repairability and maintenance. This study, for the first time, delves into the processing and self-healing capability of aromatic thermosetting co-polyester vitrimer-based carbon fiber composites through mechanical testing. Vitrimers are an emerging class of thermosetting polymers, which, owing to their exchangeable covalent bonds, enable the re-formation of bonds across cracks. The specific vitrimer chosen for this study is an aromatic thermosetting co-polyester (ATSP). The mechanical properties of samples were analyzed initially through three-point bending (3PB) testing at room temperature before and after healing (by curing samples for 2 h at 280 °C). Samples were also 3PB tested at 100 °C to analyze their mechanical properties at an elevated temperature for comparison to the samples tested at room temperature. To investigate the fracture properties, optical microscopy images of samples were taken after 3PB tests, which were analyzed to observe crack initiation and crack growth behavior. Through load–displacement curves from double cantilever beam (DCB) mechanical testing, the Mode I crack initiation fracture toughness values of self-healed composites and control composites were calculated to evaluate healing efficiency in ATSP CFRP composites cured at 280 °C for 2 h. Scanning electron microscopy (SEM) showed a similar surface morphology of cracks before and after self-healing. Micro-computed tomography (CT) X-ray imaging confirmed that the healed samples closely resembled the as-fabricated ones, with the exception of some manufacturing voids, caused by outgassing in the initial healing cycle. This research demonstrated the ability for the in situ repair of ATSP CFRPs by restoring the fracture toughness to values comparable to the pristine composite (~289 J/m²). Full article

Aquatic CO₂ emission is typically estimated (i.e., not measured) through a gas exchange balance. Several factors can affect the estimation, primarily flow velocity and wind speed, which can influence a key parameter, the gas exchange coefficient K_T in the balancing approach. However, our knowledge of the uncertainty of predictions using these factors is rather limited. In this study, we conducted a numeric assessment on the impact of river flow velocity and wind speed on K_T and the consequent CO₂ emission rate. As a case study, we utilized 3-year (2019–2021) measurements on the partial pressure of dissolved carbon dioxide (pCO₂) in one of the world’s largest alluvial rivers, the lower Mississippi River, to determine the difference in CO₂ emission rate estimated through three approaches: velocity-based K_T, wind-based K_T, and a constant K_T (i.e., K_T = 4.3 m/day) that has been used for large rivers. Over the 3-year study period, river flow velocity varied from 0.75 ms⁻¹ to 1.8 ms⁻¹, and wind speed above the water surface fluctuated from 0 ms⁻¹ to nearly 5 ms⁻¹. Correspondingly, we obtained a velocity-based K_T value of 7.80–22.11 m/day and a wind-speed-based K_T of 0.77–8.40 m/day. Because of the wide variation in K_T values, the estimation of CO₂ emission using different approaches resulted in a substantially large difference. The velocity-based K_T method yielded an average CO₂ emission rate (FCO₂) of 44.36 mmol m⁻² h⁻¹ for the lower Mississippi River over the 3-year study period, varying from 6.8 to 280 mmol m⁻² h⁻¹. In contrast, the wind-based K_T method rendered an average FCO₂ of 10.05 mmol m⁻² h⁻¹ with a small range of fluctuation (1.32–53.40 mmol m⁻² h⁻¹,), and the commonly used constant K_T method produced an average FCO₂ of 11.64 mmol m⁻² h⁻¹, also in a small range of fluctuation (2.42–56.87 mmol m⁻² h⁻¹). Based on the findings, we conclude that the effect of river channel geometry and flow velocity on CO₂ outgassing is still largely underestimated, and the current estimation of global river CO₂ emission may bear large uncertainty due to limited spatial coverage of flow conditions and the associated gas exchange variation. Full article

The significance of CO₂ emissions at the water–air interface from inland water bodies in the global carbon cycle has been recognized and is being studied more and more. Although it is important to accurately assess CO₂ emission flux in a catchment, little research has been carried out to investigate the spatio-temporal variations in CO₂ emissions in view of a water continuum. Here, we systematically compared the differences and control factors of CO₂ degassing across the water–air interface of a spring–river–lake continuum in the discharge area of Baotuquan Spring in July 2017, which is a typical temperate karst spring area in Jinan city, northern China, using hydrogeochemical parameters, stable carbon isotope values, and CO₂ degassing flux. Affected by the pCO₂ concentration gradient between the water and ambient air, the spring water showed a high CO₂ degassing flux (166.19 ± 91.91 mmol/(m² d)). After the spring outlet, the CO₂ degassing flux in the spring-fed river showed a slight increase (181.05 ± 155.61 mmol/(m² d)) due to river flow rate disturbance. The river flow rate was significantly reduced by the “blockage” of the lake, which promoted the survival and reproduction of phytoplankton and provided favorable conditions for aquatic plant photosynthesis, increasing the plankton biomass in the lake to 3383.79 × 10⁴/L. In addition, the significant decrease in the dissolved inorganic carbon (DIC) concentration and the increase in the δ¹³C_DIC values in the lake also indicated that the photosynthesis of the lake’s aquatic plants resulted in a significant decrease in the pCO₂ concentration, thus limiting the amount of CO₂ off-gassing (90.56 ± 55.03 mmol/(m² d)). Full article

The volatiles released by the volcanic structures of the world contribute to natural environmental pollution both during the passive and active degassing stages. The Island of Vulcano is characterized by solfataric degassing mainly localized in the summit part (Fossa crater) and in the peripheral part in the Levante Bay. The normal solfataric degassing (high-temperature fumarolic area of the summit and boiling fluids emitted in the Levante Bay area), established after the last explosive eruption of 1888–90, is periodically interrupted by geochemical crises characterized by anomalous degassing that are attributable to increased volcanic inputs, which determine a sharp increase in the degassing rate. In this work, we have used the data acquired from the INGV (Istituto Nazionale di Geofisica e Vulcanologia) geochemical monitoring networks to identify, evaluate, and monitor the geochemical variations of the extensive parameters, such as the SO₂ flux from the volcanic plume (solfataric cloud) and the CO₂ flux from the soil in the summit area outside the fumaroles areas. The increase in the flux of volatiles started in June–July 2021 and reached its maximum in November of the same year. In particular, the mean monthly flux of SO₂ plume of 22 tons day⁻¹ (t d⁻¹) and of CO₂ from the soil of 1570 grams per square meter per day (g m² d⁻¹) increased during this event up to 89 t d⁻¹ and 11,596 g m² d⁻¹, respectively, in November 2021. The average annual baseline value of SO₂ output was estimated at 7700 t d⁻¹ during normal solfataric activity. Instead, this outgassing increased to 18,000 and 24,000 t d⁻¹ in 2021 and 2022, respectively, indicating that the system is still in an anomalous phase of outgassing and shows no signs of returning to the pre-crisis baseline values. In fact, in the first quarter of 2023, the SO₂ output shows average values comparable to those emitted in 2022. Finally, the dispersion maps of SO₂ on the island of Vulcano have been produced and have indicated that the areas close to the fumarolic source are characterized by concentrations of SO₂ in the atmosphere higher than those permitted by European legislation (40 μg m⁻³ for 24 h of exposition) on human health. Full article

The Mississippi River (MR) discharges on average 474 km³ of water annually into the Northern Gulf of Mexico (NGOM) with a large quantity of carbon, playing a vital role in the ecosystem’s food chain and water quality. In this study, we analyzed exports of dissolved inorganic (DIC) and organic carbon (DOC) from January 2021 to December 2021, during which the contiguous United States experienced one of the coldest winters as well as the hottest summer on record. Bi-weekly in situ river measurements and water sampling were conducted in the lower MR at Baton Rouge in Louisiana, USA, approximately 368 km from the river’s mouth. We found that the MR transported 12.61 Tg C of DIC and 4.54 Tg C of DOC into the NGOM during the study period. Much of the DOC mass export occurred during the winter (~38%), while much of the DIC mass export took place in the spring months (~35%). The seasonality of DOC and DIC exports was affected by their concentrations, water temperature, and discharge. DIC concentrations were significantly higher in the fall (32.0 mg L⁻¹) than those during the winter (20.4 mg L⁻¹), while DOC concentrations were highest during the winter months (11.3 mg L⁻¹) and varied seasonally, however, not significantly. Partial pressure of dissolved carbon dioxide (pCO₂) in the MR averaged 1703 ± 646 µatm peaking in the summer at 2594 µatm and reaching a low in the winter at 836 µatm. Outgassing of CO₂ (FCO₂) peaked in the spring averaging 3.43 g C m² d⁻¹ and was lowest in the winter at 1.62 g C m² y⁻¹. Our findings validate our initial hypotheses that seasonal variability and weather extremes strongly affect terrestrial-aquatic carbon transfer, and that climate change will likely intensify carbon export from the Mississippi River Basin. Full article

Direct current (DC) and radio frequency (RF) magnetron sputtering methods were selected for conducting the deposition of structural materials, namely ceramic and metallic co-depositions. A total of six configurations were deposited: single thin layers of oxides (Cr₂O₃, SiO₂) and co-deposition configurations (50:50 wt.%) as structural materials (W, Be)—(Cr₂O₃, SiO₂), all deposited on 304L stainless steel (SS). A comprehensive evaluation such as surface topology, thermal desorption outgassing, and structural/chemical state was performed. Moreover, mechanical characterization evaluating properties such as adherence, nano indentation hardness, indentation modulus, and deformation relative to yielding, was performed. Experimental results show that, contrary to SiO₂ matrix, the composite layers of Cr₂O₃ with Be and W exhibit surface smoothing with mitigation of artifacts, thus presenting a uniform and compact state with the best microstructure. These results are relevant in order to develop future dense coatings to be used in the fusion domain. Full article

The existence of adsorbed oxygen and oxides on the surface of initial powders has serious effects on the microstructure and mechanical properties of the powder metallurgy alloys. However, the powder surface is inevitably oxidized immediately after the powder preparation. In this work, the oxidation characteristics for the argon atomized powders of a Ni-based superalloy containing Cr, Co, W, Mo, Nb, Ti and Al after exposure at ambient condition for various time were investigated in detail. It is found that various gases can be absorbed on the powder surface, but most of them can be removed by low temperature (<151.5 °C) outgassing procedure. The thermodynamic calculation shows that the oxidation reaction occurs firstly with the alloying elements rather than Ni matrix, whether at room temperature or elevated temperature. The kinetic measurement indicates that the oxygen content on the powder surface approaches a saturation value after 24 h exposure and remains almost stable after 720 h. The oxygen content increases with the decrease of particle size after exposure. X-ray photoelectron spectroscopy characterized that, except the formed oxides, adsorbed oxygen also exists on the powder surface of the as-atomized initial fine powders with particle size <30 μm and the powders with size >18.7 μm after exposure, which may be caused by the internal stress and surface energy of the initial atomized powder. All alloying elements except Ti can form stable oxides directly on the powder surface. For the element of Ti, the metastable TiO forms on the initial powder surface after preparation and it transforms into stable TiO₂ or Ti₂O₃ during exposure. The results provide a deep understanding of absorbed gases and oxide on the surface of powders under treatment and possible desorption approach. Full article

As an important part of the global carbon cycle, dissolved inorganic carbon (DIC) concentration and its stable carbon isotopic composition (δ¹³C_DIC) have been used to constrain the sources of DIC in rivers. In this study, we systematically investigated the water chemistry, DIC contents, and δ¹³C_DIC values in a tropical agricultural river in northeast Thailand. The water temperature ranged from 20.3 to 31.3 °C, and water pH values ranged from 6.4 to 8.4, with seasonal variations. Based on the major ion compositions, the hydro-chemical type of the Mun River water was a unique Na–Ca–Cl–HCO₃ type, controlled by evaporite and silicate weathering. Seasonal variation of DIC concentrations and its carbon isotopic composition was obvious; DIC and δ¹³C_DIC were significantly lower in the wet season (135 to 3146 μmol/L and −31.0‰ to −7.0‰) compared to the dry season (185 to 5897 μmol/L and −19.6‰ to −2.7‰). A high level of ¹²C-enriched DIC/CO₂ from soil respiration and organic matter oxidation may cause the low pH values, δ¹³C_DIC values, and high partial pressure of CO₂ (pCO₂) in the middle and lower reaches during the wet/rainy season compared to the dry season. This may be responsible for the seasonal and spatial variations of DIC concentrations and δ¹³C_DIC values in the Mun River. According to the relationship between pCO₂ and δ¹³C_DIC values, CO₂ outgassing may be more significant in the dry season, due to the greater influx of groundwater with higher pCO₂ levels; and the rapid CO₂ diffusion into the atmosphere will continuously increase the δ¹³C_DIC values and decrease pCO₂ levels. These results show that riverine biologic effects and CO₂ outgassing play important roles in the DIC and δ¹³C_DIC evolution of this typical agriculturally-dominated watershed. Full article

Geogenic and anthropogenic sources of atmospheric particulate and CO₂ can lead to threats to human health in volcanic areas. Although the volcanic CO₂ hazard is a topic frequently debated in the related scientific literature, space and time distribution of PM_2.5 are poorly known. The results of combined CO₂/PM_2.5 surveys, carried out at Salina, Stromboli, and Vulcano islands (Aeolian archipelago, Italy) in the years 2020–2021, and integrated with investigations on bioaccumulation of metallic particulate matter by the mean of data on the magnetic properties of oleander leaves, are presented in this work. The retrieved results indicate that no significant anthropogenic sources for both CO₂ and PM_2.5 are active in these islands, at the net of a minor contribution due to vehicular traffic. Conversely, increments in volcanic activity, as the unrest experienced by Vulcano island since the second half of 2021, pose serious threats to human health, due to the near-ground accumulation of CO₂, and the presence of suspended micro-droplets of condensed hydrothermal vapor, fostering the diffusion of atmophile viruses, such as the COVID-19. Gas hazard conditions can be generated, not only by volcanic vents or fumarolic fields, but also by unconventional sources, such as the outgassing from shallow hydrothermal aquifers through drilled or hand-carved wells. Full article

In a volcanic area, the composition of air is influenced by the interaction between fluids generated from many different environments (magmatic, hydrothermal, meteoric, and marine). Any physical and chemical variation in one of these subsystems is able to modify the outgassing dynamic. The increase of natural gas hazard, related to the presence of unhealthy components in air, may depend on temporary changes both in the pressure and chemical gradients that generate transient fluxes of gases and can have many different causes. Sometimes, the content of unhealthy gases approaches unexpected limits, without clear warning. In this case, an altered composition of the air can be only revealed after accurate sampling procedures and laboratory analysis. The investigations presented here are a starting point to response to the demand for a new monitoring program in the touristic area of Baia di Levante at Vulcano Island (Aeolian archipelago, Italy). Three multiparametric geochemical surveys were carried in the touristic area of Baia di Levante at Vulcano Island (Aeolian archipelago, Italy) in 2011, 2014, and 2015. Carbon dioxide (CO₂) and hydrogen sulfide (H₂S) are the main undesired components, usually present at the local scale. Anomalous CO₂ and H₂S outputs from soil and submarine bubbling vents were identified; the thermal anomaly of the ground was mapped; atmospheric concentrations of CO₂ and H₂S were measured in the air 30 cm above the ground surface. Atmospheric concentrations above the suggested limits for the wellbeing of human health were retrieved in open areas where tourists stay and where CO₂ can accumulate under absence of wind. Full article

The reduction in CO₂ emissions is a major task for the coming decades. Accelerated weathering of limestone (AWL) can be used to capture CO₂ from effluent gas streams and store it as bicarbonate in marine environments. We give an overview of the fundamental aspects of AWL, including associated CO₂ emissions during the operation of AWL, characteristics of the accumulating bicarbonate-rich product water, and factors influencing the outgassing of CO₂ from the ocean back into the atmosphere. Based on these aspects, we identify locations where AWL could be carried out favorably. The energy demand for AWL reduces the theoretical CO₂ sequestration potential, for example, by only 5% in the case of a 100 km transport of limestone on roads. AWL-derived product water is characterized by high alkalinity but low pH values and, once in contact with the atmosphere, passive outgassing of CO₂ from AWL-derived water occurs. This process is mainly driven by the difference between the fCO₂ in the atmosphere and the oceanic surface layer, as well as the sea surface temperature at the discharge site. Promising sites for AWL may be in Florida or around the Mediterranean Sea, where outgassing could be prevented by injections into deep water layers. Full article

The Visible Infrared Imaging Radiometer Suite (VIIRS) on board the National Oceanic and Atmospheric Administration-20 (NOAA-20) and the Suomi National Polar-orbiting Partnership Program (S-NPP) satellites were launched in late 2017 and 2011, respectively. This paper presents a recent update in the VIIRS thermal emissive bands (TEB) on-orbit calibration algorithm and inter-compares long-term instrument and TEB sensor data records (SDR) performances of the two VIIRS, to support user communities. The VIIRS TEB calibration algorithm was improved to mitigate calibration biases during the blackbody warm-up/cool-down (WUCD) events. Four WUCD bias correction methods were implemented in the NOAA operational processing in 2019: (1) the Nominal-F method, (2) the WUCD-C method, (3) the Ltrace method, and (4) the Ltrace-2 method. Our evaluation results indicate that the on-orbit performances of the two VIIRS instruments have been generally stable and comparable with each other, except that NOAA-20 VIIRS blackbody and instrument temperatures are lower than those of the S-NPP VIIRS. The degradations in the S-NPP TEB detector responsivities remain small after 9 years on-orbit. NOAA-20 detector responsivities have been generally stable after the longwave infrared degradation during its early mission was resolved by the mid-mission outgassing. NOAA-20 and S-NPP VIIRS TEB SDRs agree with co-located Cross-track Infrared Sounder observations, with daily averaged biases within 0.1 K at nadir. After the implementation of operational WUCD bias correction, residual TEB WUCD biases are similar for NOAA-20 and S-NPP, with daily averaged biases ~0.01 K in all bands. Full article