Increase In Atmospheric CO2 Concentration Research Articles

Investigation on Electrochemical Reaction for Anion Exchange Membrane Electrode Assembly-Based Electrolyzer

Although the use of fossil fuels is gradually decreasing every year, it still accounts for more than 80% of global energy consumption, and discriminatory use is causing a significant increase in atmospheric CO2 concentration and global warming. In order to control the indiscriminate use of fossil fuels that cause environmental problems, establishing an eco-friendly energy conversion system is essential. The water electrolysis using surplus power generated from renewable energy is recognized as a representative system that can produce high-purity hydrogen from water. On the other hand, CO2 electrolysis is also a promising energy conversion technology that can reduce atmospheric CO2 centration because it electrochemically converts CO2 into valuable carbon products. Both of the above systems are based on electrochemical reactions, which means they can operate under moderate conditions with zero pollutant emissions.In general, the composition of conventional energy conversion system includes an electrolyte layer, which has a large ohmic resistance and limitation of CO2 solubility, which reduces energy efficiency. To address the disadvantage of the conventional system, membrane electrode assembly (MEA)-based electrolyzer are receiving attention. The MEA consists of an electrode and a membrane with a polymer membrane capable of ion exchange between the anode and the cathode. These MEA-based electrolyzer has a zero-gap configuration, providing minimized ohmic resistance and improved energy efficiency. Among them, various studies are being actively conducted on applying an anion exchange membrane (AEM) to MEA-based electrolyzers. When using AEM, water electrolysis has the advantage of being able to use a non-noble metal catalyst, which can reduce costs, and CO2 electrolysis has the advantage of reducing the hydrogen evolution reaction (HER), which is a competing reaction.Herein, the electrode with a structure in which electrocatalyst is loaded on a porous transport layer (PTL) is fabricated by the facile electrodeposition method. The electrodeposition is possible to fabricate self-supported electrodes by modulating catalytic properties such as morphology, composition, and crystallinity by controlling various parameters. Additionally, ionomer and binder-free electrode structure prepared through electrodeposition contributes to improving catalytic performance by promoting electron transfer to the active site. Moreover, the as-prepared porous transfer electrodes (PTE) are used as cathode and anode in anion exchange MEA-based electrolyzer and exhibit reasonable single-cell performance, suggesting that PTEs prepared via electrodeposition are suitable for energy conversion systems such as water electrolysis and CO2 electrolysis.In the MEA configuration, three cathodes, anodes, and AEM were optimized. In the cathode part, the HER was optimized using catalysts such as NiMo, Pt, and PtRu, and the CO2 electrolysis was optimized using Au, Ag, Cu, and Pd. In the anode part, the oxygen evolution reaction (OER) was optimized using catalysts such as NiFe, IrO2. In the membrane part, optimization was performed by comparing the commercial membrane and the fabricated fluorine-containing poly(fluorene)-based AEM.

Carbon dioxide fertilization enhanced carbon sink offset by climate change and land use in Amazonia on a centennial scale

The Amazon, the Earth's largest tropical forest, plays a critical role in the global carbon cycle, acting as a significant carbon sink. Recent studies, however, indicate a decline in its carbon sequestration capacity due to climate variability, intensive deforestation, and fires. This study aims to examine the impacts of these factors on the carbon dynamics of the Amazon over a centennial scale based on dynamic global vegetation models (DGVMs) of Trendy-v11. It was found that the Amazon region exhibited significant spatiotemporal variations in net land carbon (C) fluxes, and was a net C sink (40.02 ± 242.64 Tg C yr−1) during 1901–2021. The Amazonian net biome productivity (NBP) showed a 6-decades-scale shift from a decreasing trend (−3.78 Tg C yr−2) during 1901–1959 to an increasing trend (2.39 Tg C yr−2) during 1960–2021. The Amazonian NBP was negatively related to air temperature while positively related to dry-season precipitation during 1901–2021. Furthermore, the increase of atmospheric CO2 concentration during 1901–2020 enhanced Amazonian NBP by 36.40 ± 8.39 Pg C, which was largely offset by land use change (−18.84 ± 12.02 Pg C) and climate change (−10.03 ± 5.00 Pg C). Our findings underscore the critical need for sustainable management practices in the Amazon to enhance its C sink and preserve its function in the global climate system.

CFD modeling investigation of oxy-fuel combustion application in an industrial-scale FCC regenerator

The increase in atmospheric CO2 concentration and its consequential impact on climate change have elicited increased public concern. The refinery units including fluid catalytic cracking (FCC) generate substantial quantities of CO2. To mitigate the emission from the FCC process, oxy-fuel combustion has emerged as a prospective carbon capture and storage technology. This study presents the first trial for the modeling investigation of a 70 kt/a industrial FCC regenerator under the scenario of retrofitting it with oxy-fuel combustion technology. Employing the Eulerian-Eulerian model, a CFD model integrating heat transfer and coke combustion reactions has been established. The detailed hydrodynamics, temperature, and species concentration distribution inside the regenerator are obtained under both air-firing and oxy-firing conditions, which are further compared to exploit the possibility of oxy-fuel combustion retrofitting. As has been found, decreases in gas temperature and carbon conversion rate were observed for 21 % O2/79 % CO2 atmosphere in comparison to the air reference case due to the differences in gas properties between N2 and CO2. This discrepancy resulted in a drop of 17 K in dilute phase temperature and 2 K in dense phase temperature. The bed density also exhibited a large with the oxy-firing conditions, with notable observations revealing a lower bed density below a height of 4.2 m, transitioning to a higher density above said height. Sensitivity analysis was also conducted for three principal operating parameters, including superficial gas velocity, oxygen partial pressure, and catalyst circulation rate. An increase of oxygen partial pressure to 27 % or a decrease of the catalyst circulation rate to 20.7 kg/s proved effective in achieving the same temperature profile and even a slightly better carbon conversion in comparison to air-firing regeneration.

Gradual and abrupt increase in atmospheric CO2 concentrations trigger divergent responses of microbial necromass accumulation in paddy soils

Microbial necromass C (MNC) plays a critical role in promoting soil organic C (SOC) formation and stabilization, particularly in the context of climate change. Most investigations on the impact of elevated CO2 concentrations (eCO2) on MNC have been performed by exposing ecosystems to an abrupt increase in CO2. However, the atmospheric CO2 increase is a gradual process, and knowledge about the response of necromass to gradual increase in CO2 is lacking. We tested the hypothesis that microbial necromass would show different responses to abrupt and gradual CO2 increases. Furthermore, it is still unknown whether eCO2 will trigger similar responses between surface and subsurface soil layers. Here, we determined the MNC concentrations and their proportions in SOC in surface and subsurface soil layers via open-top chambers. CO2 treatments included ambient control, abrupt CO2 increase by 200 ppm above control, and gradual CO2 increase by 40 ppm each year until reaching 200 ppm over five years. Overall, compared with the ambient control, abrupt eCO2 induced a significantly stronger decrease in necromass (20.3 %) when averaged across three soil layers, while gradual eCO2 led to insignificant variations in necromass (6.7 %). The necromass proportion in SOC decreased with depth under both eCO2 treatments with a significant decline occurring in abrupt eCO2 treatment. The observed greater magnitude of eCO2 effects on fungal necromass relative to bacterial necromass in subsurface layers illustrates a distinct microbial community response to climate change. Taken together, abrupt and gradual eCO2 approaches differed in their impact on MNC, and its response to eCO2 may be somewhat overestimated by abrupt eCO2 approach. Furthermore, MNC in subsurface soil witnessed a more sensitivity or vulnerability to eCO2 than that of topsoil. We suggest vigilant attention will need to be paid to the feedback of necromass C in deep soil poised by future climate change.

Fabrication of indium doped Bi/Bi2O3 catalyst for efficiently selective electroreduction of carbon dioxide to formate

Highly selective electrocatalytic reduction of CO2 to formate is considered a valid route for alleviating the continuing increase in atmospheric CO2 concentration. Herein, Indium-doped Bi/Bi2O3 (In-Bi/Bi2O3) electrocatalyst grown in situ on carbon paper (CP) was obtained via a relatively simple one-step solvothermal synthesis method and utilized in CO2 reduction reaction (CO2RR) for formate production. The In-Bi/Bi2O3/CP exhibits superior Faradaic Efficiency for formate, i.e., FEformate = 96.3 %, and a partial current density of 6.74 mA cm−2 at −1.6 V (vs Ag/AgCl) in the H-type cell. Furthermore, FEformate of the electrode remains consistently above 90 % within long-term stability testing (60 h). By density functional theory (DFT) calculations, it is found that incorporating In into Bi/Bi2O3 can generate more active sites and facilitate the preferential adsorption of *OOCH intermediates, alleviating competitive adsorption of *H during CO2 reduction reaction (CO2RR), thereby accelerating formate production.

Cuticular analysis of Late Pleistocene, Middle Holocene, and modern Nothofagus dombeyi leaves from Chile: Implications for understanding changes in plant function at different atmospheric CO2 concentrations

How will forests respond to increases in atmospheric CO2 concentrations over the next century? This question is the subject of intensive research, and is based mostly on the results of greenhouse experiments, landscape-level experiments and modeling. In this paper, we examined leaf morphological and physiological characteristics of Nothofagus dombeyi populations exposed to different atmospheric CO2 levels by analyzing leaf cuticle from a Late Pleistocene (∼15,500–13,200 cal yr BP) fossil site, a Middle Holocene (∼6700–4900 cal yr BP) fossil site, and a modern (2016) collection in mid-latitude Chile. Atmospheric CO2 concentrations were inferred as ∼230 ppm, ∼270 ppm and ∼ 400 ppm based on a comparison with icecore and instrumental records. Our findings show that as atmospheric CO2 concentrations increased by 74% during the transition from late glacial to modern conditions, stomatal density decreased by 24% and maximum stomatal conductance decreased by 42%. In contrast, we observed a 10% increase in stomatal size, a 195% increase in intrinsic water use efficiency, and an increase in leaf nitrogen content. Carbon discrimination decreased as CO2 levels increased contrary to our expectations underscoring that additional factors such as water availability and nutrients can affect carbon discrimination. We also tested the paleo-CO2 method of Franks that performed well under high CO2 conditions (∼400 ppm) but failed under low levels (∼230 ppm) of atmospheric CO2 indicating the need for a better understanding of photosynthesis during glacial times.

Investigation of performance of potential adsorbents for emissions mitigation in a diesel generator.

Globally, the release of greenhouse gases primarily carbon dioxide (CO2) emissions to our Earth's surface has climbed by about 45% to its present atmospheric concentration rate of 420 parts per million (ppm) during the industrial era. An unprecedented rise in atmospheric CO2 concentration has been claimed to lead to significant factors such as global warming potential (GWP) and climate change effects. An increase in atmospheric CO2 concentrations is a serious threat to the environment. Recent research efforts have focused on mitigating emissionsfrom anthropogenic point sources. Adsorption-based post-combustion CO2 capture using solid adsorbents is the most effective and efficient method for mitigating gas adsorption in the exhaust system. In the current study, activated carbons are obtained from three potential biomass, namely, (i) coconut shell, (ii) rice husk, and (iii) eucalyptus wood, through a - single-stageactivation method. The prepared activated carbon materials are analyzed using proximate and ultimate analyses. Further investigations are performed using different characterization techniques to ensure their adsorption efficiency. Adsorbents are packed one after the other in an in-house fabricated double adsorption chamber and coupled to the exhaust unit of a generator. Test experiments are conducted to examine adsorbents' capture efficiency in emissions mitigation. Adsorbents' adsorption parameters are evaluated in experimental investigations. At 2.5bar and 50°C, a maximum loading capacity of samples is achieved by 4.85mmol/g, 4.58mmol/g, and 5.96mmol/g for coconut shell, rice husk, and eucalyptus wood adsorbents, respectively. With a post-combustion carbon adsorption chamber, CO2 and NO are captured about40-64% and 38-58%, respectively, for all three adsorbents. The thermodynamic parameter of isosteric heat of adsorption value is below 40kJ/mol, ensuring physisorption for all adsorbents.

Impacts of Land-Use Change from Primary Forest to Farmland on the Storage of Soil Organic Carbon

Land-use change (LUC) is a significant contributor to the increase in atmospheric CO2 concentrations, with previous studies demonstrating its profound impact on soil organic carbon (SOC). The conversion of primary forests to farmland has been recognized as the most significant type of LUC inducing CO2 release from the soil. Therefore, it is critical to understand the impacts of forest LUC on SOC storage, with a particular focus on primary forest to farmland conversion. In this study, we conducted a meta-analysis of 411 observations from 41 published works and found that SOC storage decreased significantly following the conversion of primary forests to farmland. Factors such as soil depth and climate zone influenced the degree of SOC storage loss, with SOC loss being less severe in deeper soil following a conversion from primary forests to farmland. Moreover, the loss of SOC storage was more severe in temperate regions compared to tropical regions. The input and output of surface SOC, changes in soil structure, and increases in atmospheric CO2 concentrations were significant reasons for the loss of SOC following primary forest to farmland LUC. However, improving tillage methods and implementing sustainable agricultural management strategies can help reduce SOC loss. These findings highlight the importance of sustainable land-use practices in mitigating the negative impacts of forest LUC on SOC storage and the global carbon cycle.

Increasing impacts of ocean acidification on coral reefs under global warming

The rapid increase in atmospheric CO2 concentration in recent decades has influenced the marine system to a great extent with ocean acidification being one of the consequences. Ocean acidifications impact on calcifying marine organisms has long been the subject of scientific studies. To determine the effect of ocean acidification on hard coral reefs, we analyzed five ocean coastal regions, comparing the trend in regional surface hydrogen ion activity with the change in hard coral coverage. In each region, we included both historical measured data and predicted data using RCP models as an implication of the potential future. The outcome does not provide substantial evidence to confirm the hypothesis linking the two variables. Additionally, the direct association between these variables cannot be ascertained due to the influence of uncontrolled factors such as local pollution, ocean warming, and ocean currents.

An Improved Gross Primary Production Model Considering Atmospheric CO2 Fertilization: The Qinghai–Tibet Plateau as a Case Study

Involving the effect of atmospheric CO2 fertilization is effective for improving the accuracy of estimating gross primary production (GPP) using light use efficiency (LUE) models. However, the widely used LUE model, the remote sensing-driven Carnegie–Ames–Stanford Approach (CASA) model, scarcely considers the effects of atmospheric CO2 fertilization, which causes GPP estimation uncertainties. Therefore, this study proposed an improved method for estimating GPP by integrating the atmospheric CO2 concentration into the CASA model and generated a long time series GPP dataset with high precision for the Qinghai–Tibet Plateau. The CASA model was improved by considering the impact of atmospheric CO2 on vegetation productivity and discerning variations in CO2 gradients within the canopy and leaves. A 500 m monthly GPP dataset for the Qinghai–Tibet Plateau from 2003 to 2020 was generated. The results showed that the improved GPP estimation model achieved better performances on estimating GPP (R2 = 0.68, RMSE = 406 g C/m2/year) than the original model (R2 = 0.67, RMSE = 499.32 g C/m2/year) and MODIS GPP products (R2 = 0.49, RMSE = 522.56 g C/m2/year). The GPP on the Qinghai–Tibet Plateau increased significantly with the increase in atmospheric CO2 concentration and the gradual accumulation of dry matter. The improved method can also be used for other regions and the generated GPP dataset is valuable for further understanding the ecosystem carbon cycles on the Qinghai–Tibet Plateau.

Physiological and Proteomic Responses of the Tetraploid Robinia pseudoacacia L. to High CO2 Levels.

The increase in atmospheric CO2 concentration is a significant factor in triggering global warming. CO2 is essential for plant photosynthesis, but excessive CO2 can negatively impact photosynthesis and its associated physiological and biochemical processes. The tetraploid Robinia pseudoacacia L., a superior and improved variety, exhibits high tolerance to abiotic stress. In this study, we investigated the physiological and proteomic response mechanisms of the tetraploid R. pseudoacacia under high CO2 treatment. The results of our physiological and biochemical analyses revealed that a 5% high concentration of CO2 hindered the growth and development of the tetraploid R. pseudoacacia and caused severe damage to the leaves. Additionally, it significantly reduced photosynthetic parameters such as Pn, Gs, Tr, and Ci, as well as respiration. The levels of chlorophyll (Chl a and b) and the fluorescent parameters of chlorophyll (Fm, Fv/Fm, qP, and ETR) also significantly decreased. Conversely, the levels of ROS (H2O2 and O2·-) were significantly increased, while the activities of antioxidant enzymes (SOD, CAT, GR, and APX) were significantly decreased. Furthermore, high CO2 induced stomatal closure by promoting the accumulation of ROS and NO in guard cells. Through a proteomic analysis, we identified a total of 1652 DAPs after high CO2 treatment. GO functional annotation revealed that these DAPs were mainly associated with redox activity, catalytic activity, and ion binding. KEGG analysis showed an enrichment of DAPs in metabolic pathways, secondary metabolite biosynthesis, amino acid biosynthesis, and photosynthetic pathways. Overall, our study provides valuable insights into the adaptation mechanisms of the tetraploid R. pseudoacacia to high CO2.

Accounting of carbon sequestration and tradeoff under various climatic scenarios in alternative agricultural system: a comprehensive framework toward carbon neutrality

IntroductionThe increase in atmospheric CO2 concentration, which mainly is attributed to fossil-fuel combustion and deforestation, is often suggested as one of the prime causative factors toward accelerated global warming. This commends for sequestration of atmospheric carbon under terrestrial systems to partially offset fossil-fuel emissions. Concerning the same, agricultural sector presents an extensive opportunity, especially for countries such as India where over 55% of the population is engaged in the agriculture sector.MethodsSequestering atmospheric carbon in agriculture requires the adoption of climate-resilient alternative agriculture practices without compromising food security. The deliberated study highlights the options of alteration in current conventional farming practices and its economic evaluation for sequestrating carbon under two Climate Change (CC) scenarios, viz., RCP 4.5 and 8.5, over three temporal scales, i.e., 2020, 2030, and 2050. Considering the current land-use pattern and existing growth rate in land-use shifting, three land-use policies, namely, Business as Usual (BaU), Optimistic, and Pessimistic scenario, integrated with CC scenarios were contemplated. Six possible futuristic scenarios were generated for the assessment of carbon sequestration and its valuation following the Integrated Valuation of Ecosystem Services and Tradeoff (InVEST) model.ResultsThe results suggested that across the studied region adopting an optimistic policy over BaU and pessimistic scenario, carbon can sequestrate an additional 0.64 to 1.46 Mt. (2.35 to 5.36 million ton CO2e) having an economic value of 193.4 to 504.8 million USD.ResultsMoreover, the outcomes of the study are advocated for the policy of carbon credit in the agriculture sector, which shall contribute toward meeting various nationally determined contributions (NDCs) and sustainable development goals (SDGs) as well.

Terrestrial Ecosystem Model in R (TEMIR) version 1.0: simulating ecophysiological responses of vegetation to atmospheric chemical and meteorological changes

Abstract. The newly developed offline land ecosystem model Terrestrial Ecosystem Model in R (TEMIR) version 1.0 is described here. This version of the model simulates plant ecophysiological (e.g., photosynthetic and stomatal) responses to varying meteorological conditions and concentrations of CO2 and ground-level ozone (O3) based on prescribed meteorological and atmospheric chemical inputs from various sources. Driven by the same meteorological data used in the GEOS-Chem chemical transport model, this allows asynchronously coupled experiments with GEOS-Chem simulations with unique coherency for investigating biosphere–atmosphere chemical interactions. TEMIR agrees well with FLUXNET site-level gross primary productivity (GPP) in terms of both the diurnal and monthly cycles (correlation coefficients R2>0.85 and R2>0.8, respectively) for most plant functional types (PFTs). Grass and shrub PFTs have larger biases due to generic model representations. The model performs best when driven by local site-level meteorology rather than reanalyzed gridded meteorology. Simulation using gridded meteorology agrees well for annual GPP in seasonality and spatial distribution with a global average of 134 Pg C yr−1. Application of Monin–Obukhov similarity theory to infer canopy conditions from gridded meteorology does not improve model performance, predicting an increase of +7 % in global GPP. Present-day O3 concentrations simulated by GEOS-Chem and an O3 damage scheme at high sensitivity show a 2 % reduction in global GPP with prominent reductions of up to 15 % in eastern China and the eastern USA. Regional correlations are generally unchanged when O3 is present and biases are reduced, especially for regions with high O3 damage. An increase in atmospheric CO2 concentration of 20 ppmv from the level in 2000 to the level in 2010 modestly decreases O3 damage due to reduced stomatal uptake, consistent with ecophysiological understanding. Our work showcases the utility of this version of TEMIR for evaluating biogeophysical responses of vegetation to changes in atmospheric composition and meteorological conditions.

Carbon dioxide sequestration in cementitious materials: A review of techniques, material performance, and environmental impact

The release of carbon dioxide (CO2) into the earth's atmosphere is a substantial global environmental concern that arises from the processes of industrialization and urbanization. The increase in atmospheric CO2 concentrations has resulted in the phenomenon of global warming and subsequent alterations in climate patterns. Accelerated CO2 sequestration in cementitious materials is currently the subject of extensive research as a highly efficacious approach to mitigating the carbon footprint of the concrete industry. The sequestration procedure entails the transformation of gaseous CO2 into carbonate minerals. The review presented in this paper outlines the most recent carbonation (i.e., CO2 sequestration) techniques, such as mineral carbonation, accelerated CO2 curing (ACC), pre-carbonation, and carbonation mixing, that have been recently explored. The potential of mineral carbonation of industrial wastes and the advantages of their incorporation in the concrete matrix is investigated. Carbonation technologies and their effect on the performance of cementitious composites are reported. Information on life cycle assessment are also included to evaluate the environmental impact associated with the production of carbonated materials. Various commercialized CO2 utilization technologies in construction sector, such as CarbonCure, Solidia, Carbstone, Calera, and Carbon8 are reviewed. Moreover, this review offers a thorough insight into the carbonation technologies, evaluating their advantages, limitations, and the existing gaps in research.

Polymer Sorbent Design for the Direct Air Capture of CO2.

Anthropogenic activities have resulted in enormous increases in atmospheric CO2 concentrations particularly since the onset of the Industrial Revolution, which have potential links with increased global temperatures, rising sea levels, increased prevalence, and severity of natural disasters, among other consequences. To enable a carbon-neutral and sustainable society, various technologies have been developed for CO2 capture from industrial process streams as well as directly from air. Here, direct air capture (DAC) represents an essential need for reducing CO2 concentration in the atmosphere to mitigate the negative consequences of greenhouse effects, involving systems that can reversibly adsorb and release CO2, in which polymers have played an integral role. This work provides insights into the development of polymer sorbents for DAC of CO2, specifically from the perspective of material design principles. We discuss how physical properties and chemical identities of amine-containing polymers can impact their ability to uptake CO2, as well as be efficiently regenerated. Additionally, polymers which use ionic interactions to react with CO2 molecules, such as poly(ionic liquids), are also common DAC sorbent materials. Finally, a perspective is provided on the future research and technology opportunities of developing polymer-derived sorbents for DAC.

Assessing watershed-scale impacts of best management practices and elevated atmospheric carbon dioxide concentrations on water yield

Changes in water yield are influenced by many intersecting biophysical elements, including climate, on-land best management practices, and landcover. Large-scale reductions in water yield may present a significant threat to water supplies globally. Many of these intersecting factors are intercorrelated and confounded, making it challenging to separate the factors' individual contributions to shaping local streamflow dynamics. Comprehensive hydrological models constructed based on a well-established understanding of biophysical processes are often employed to address these matters. However, these models rarely incorporate all relevant factors influencing local hydrological processes, due to the reliance of these models on the latest, albeit limited, state-of-the-art research. For instance, complexities inherent in watershed hydrology, which involve multilayered interactions among potentially many biophysical factors, leave the direct analysis of subtle impacts on water yields measured in-situ largely intractable. Therefore, we propose an innovative approach to assess impacts of elevated atmospheric CO2 concentrations and flow diversion terraces (FDTs) on stream discharge rates at the watershed scale. Initially, we use a comprehensive hydrological model to account for the impacts of major climatic and landuse/landcover factors on changes in field-acquired measurements of water yield. Next, we employ conventional and advanced statistical methods to decompose the residuals of model predictions to facilitate the identification of subtle influences promoted by increases in atmospheric CO2 concentrations and the application of FDTs in an agriculture-dominated watershed. Through this innovative approach, we find that FDTs contributed to a watershed-wide, net water-yield reduction of 188.0 mm (or 28.9 %) from 1992 to 2014. Ongoing increases in ambient CO2 concentrations, which are responsible for an overall reduction in a watershed-level assessment of stomatal conductance, have led to a minor increase in stream discharge rates during the same 23-year period, i.e., 0.45 mm of water yield per year, or 1.6 % overall. Streamflow reductions explicitly caused by regional warming in the area alone, on account of increased evapotranspiration, may be overestimated due to the opposing, synergistic effects on water yield associated with CO2-enrichment of the lower atmosphere and the annual application of FDTs.

Evaluating the performance of carbon-based adsorbents fabricated from renewable biomass precursors for post-combustion CO2 capture

The significant increase in atmospheric CO2 concentration originated mainly from fossil fuels combustion has encouraged the development and improvement of CO2 separation operations to reduce emissions and control climate change and global warming. Therefore, this work is focused on the separation of CO2 from N2 in flue gas streams under post-combustion conditions by developing low-cost adsorbents. Six carbons were fabricated from biomass resources (olive stones and almond shells) to assess their influence on CO2 adsorption capacity: One carbonized and two KOH-activated carbons with carbon/KOH ratio of 1:2 and 1:4 (w/w) for each precursor. The carbons were characterized by field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), elemental analysis, nitrogen and carbon dioxide adsorption–desorption analysis, X-ray diffraction (XRD), Fourier transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS) and point of zero charge determination. In addition, the equilibrium adsorption data of pure components for all adsorbents were measured at 0, 25 and 50 °C between 0 and 760 mmHg and CO2/N2 selectivity was determined. Activated carbons were found to have higher CO2 adsorption capacity but with a reduction in apparent selectivity. Dynamic binary adsorption simulations performed in a fixed-bed column demonstrated that the activated carbon produced from olive stones with a carbon/KOH ratio of 1:4 (w/w) can separate a mixture of 14 % CO2 and 86 % N2 at 25 and 50 °C with the highest selectivity, CO2 adsorption capacity, CO2 purity and N2 recovery factor. Reducing flow rate, the breakthrough time increased. Moreover, the breakthrough time was reduced by increasing the temperature from 25 to 50 °C owing to the exothermic nature of adsorption process.

Diverse projected climate change scenarios affect the physiology of broccoli plants to different extents.

Climate change caused by global warming involves crucial plant growth factors such as atmospheric CO2 concentration, ambient temperature or water availability. These stressors usually co-occur, causing intricate alterations in plant physiology and development. This work focuses on how elevated atmospheric CO2 levels, together with the concomitant high temperature, would affect the physiology of a relevant crop, such as broccoli. Particular attention has been paid to those defence mechanisms that contribute to plant fitness under abiotic stress. Results show that both photosynthesis and leaf transpiration were reduced in plants grown under climate change environments compared to those grown under current climate conditions. Furthermore, an induction of carbohydrate catabolism pointed to a redistribution from primary to secondary metabolism. This result could be related to a reinforcement of cell walls, as well as to an increase in the pool of antioxidants in the leaves. Broccoli plants, a C3 crop, grown under an intermediate condition showed activation of those adaptive mechanisms, which would contribute to coping with abiotic stress, as confirmed by reduced levels of lipid peroxidation relative to current climate conditions. On the contrary, the most severe climate change scenario exceeded the adaptive capacity of broccoli plants, as shown by the inhibition of growth and reduced vigour of plants. In conclusion, only a moderate increase in atmospheric CO2 concentration and temperature would not have a negative impact on broccoli crop yields.

Diurnal, Seasonal, and Vertical Changes in Photosynthetic Rates in Cinamomum camphora Forests in Subtropical China

The increase in the global atmospheric CO2 concentration is expected to increase the productivity of forests, but the dynamic processes of such increased productivity in the forest canopy remain unclear. In this study, diurnal and seasonal variations and vertical changes in photosynthetic rates were investigated in Camphor tree (Cinnamomum camphora) forests in subtropical China. The effect of photosynthetically active radiation (PAR) and CO2 concentrations on photosynthetic rates were also examined in the studied forests. Results showed the diurnal patterns of photosynthesis exhibited two peaks on sunny days, but only one peak on cloudy days. The daily average photosynthetic rate on cloudy days was approximately 74% of that on sunny days. The photosynthetic rate decreased along the vertical forest canopy profile. If the photosynthetic rate in the upper canopy layer was 100%, the corresponding rates were 83% and 25% in the middle and lower canopy layers, respectively. The rates of dark respiration derived from the PAR response curve were 1.73, 1.25, and 1.0 µmol m−2 s−1 for the upper, middle, and lower canopy layers, respectively. The apparent quantum yield of photosynthesis was 0.0183, 0.0186, and 0.0327 µmol CO2 µmol−1 PAR for the upper, middle, and lower canopy, respectively. The initial slope of the photosynthetic response curve to CO2 was highest in the upper canopy and lowest in the lower canopy. The seasonal variation in photosynthetic rates exhibited a two-peaked pattern at all canopy positions, with the two peaks occurring in June and September. The stand biomass and biomass carbon storage were 144.7 t ha−1 and 71.6 t C ha−1 in the examined forests, respectively. The study provides a scientific reference for future research on accessing carbon sequestration and designing forest management practices, specifically in regulating canopy structure in subtropical regions.

Research Progress of Non-Noble Metal Catalysts for Carbon Dioxide Methanation.

The extensive utilization of fossil fuels has led to a rapid increase in atmospheric CO2 concentration, resulting in various environmental issues. To reduce reliance on fossil fuels and mitigate CO2 emissions, it is important to explore alternative methods of utilizing CO2 and H2 as raw materials to obtain high-value-added chemicals or fuels. One such method is CO2 methanation, which converts CO2 and H2 into methane (CH4), a valuable fuel and raw material for other chemicals. However, CO2 methanation faces challenges in terms of kinetics and thermodynamics. The reaction rate, CO2 conversion, and CH4 yield need to be improved to make the process more efficient. To overcome these challenges, the development of suitable catalysts is essential. Non-noble metal catalysts have gained significant attention due to their high catalytic activity and relatively low cost. In this paper, the thermodynamics and kinetics of the CO2 methanation reaction are discussed. The focus is primarily on reviewing Ni-based, Co-based, and other commonly used catalysts such as Fe-based. The effects of catalyst supports, preparation methods, and promoters on the catalytic performance of the methanation reaction are highlighted. Additionally, the paper summarizes the impact of reaction conditions such as temperature, pressure, space velocity, and H2/CO2 ratio on the catalyst performance. The mechanism of CO2 methanation is also summarized to provide a comprehensive understanding of the process. The objective of this paper is to deepen the understanding of non-noble metal catalysts in CO2 methanation reactions and provide insights for improving catalyst performance. By addressing the limitations of CO2 methanation and exploring the factors influencing catalyst effectiveness, researchers can develop more efficient and cost-effective catalysts for this reaction.