Net CO2 Emissions Research Articles

Assessing the net carbon removal potential by a combination of direct air capture and recycled concrete aggregates carbonation

Removing and storing CO2 from the atmosphere has an important role in combating climate change. This study assessed the CO2 removal potential of combining direct air capture with carbonation of recycled concrete aggregates (RCAs). An industrial-scale RCA carbonation process model quantified key parameters' impacts on carbonation duration and energy consumption. Furthermore, a lifecycle analysis evaluated scenarios of two cases: (i) using pure CO2 with transportation between DAC and carbonation, and (ii) onsite production of low-purity CO2. For 90 % carbonation of 1 tonne of RCA, the performance of case-i scenarios ranged from ∼13 kg net CO2 removal to ∼14 kg net CO2 emission, influenced by DAC technology, transport option, and electricity carbon intensity. In case-ii scenarios, 1 % CO2 feed purity achieved 70 % greater CO2 removal than using pure CO2. This work provides an initial indication of the potential of this scheme while revealing key factors to investigate in future experimental exploration.

Exergo and enviro-economic analysis of thermal energy storage assisted finned solar still

The current investigation focuses on improving the performance of a single slope solar still integrated with Phase Change Material as energy storage media. The problem of low thermal conductivity of PCM which hinders the energy storage capability has been addressed by incorporating fins with different profiles into the energy storage unit. Initially, an experimental investigation was conducted and analyzed to assess the effective performance of a Conventional Single Slope Solar Still (CSS) using various water depth levels: 1–4 cm. The optimal basin water depth for testing solar still with energy storage material along with fins was identified as 2 cm. Subsequently, the CSS was subjected to performance enhancement investigation under three different conditions: Case 1 – Solar Still (SS) with PCM storage unit, Case 2 – SS with fins at the PCM storage unit, and Case 3 – SS with fins at the storage unit and a parallel plate attached to the other end of the fins. The experimental results demonstrated the production of fresh water and efficiency improvements are as follows 26.95%, 55.86%, 69.14% and 24.34%, 52.83%, 68.83% for cases I, II, and III, respectively. Further, it was observed that Case III exhibited a lower cost of water production and a shorter payback period compared to CSS. The enviro-economic analysis revealed that the net CO2 emissions (NCEM) and Carbon Credits Earned (CCE) for Case III were 15.60 tons and 312.07 USD respectively against 9.22 tons and 184.31 USD for CSS.

Perceptions of carbon dioxide emission reductions and future warming among climate experts

The Intergovernmental Panel on Climate Change (IPCC) employs emission scenarios to explore a range of future climate outcomes but refrains from assigning probabilities to individual scenarios. However, IPCC authors have their own views on the likelihood of different climate outcomes, which are valuable to understand because authors possess both expert insight and considerable influence. Here we report the results of a survey of 211 IPCC authors about the likelihood of four key climate outcomes. We found that most authors are skeptical that warming will be limited to the Paris targets of well below 2 °C, but are more optimistic that net zero CO2 emissions will be reached during the second half of this century. When asked about the beliefs of their peers, author responses showed strong correlations between personal and peer beliefs, suggesting that participants with extreme beliefs perceive their own estimates as closer to the community average than they actually are.

An analysis of the impact of CO2 emissions from deforestation and mining in Madre de Dios, Perú

The Madre de Dios Region of Peru faces significant deforestation largely due to a surge in artisanal-small scale gold mining (ASGM), propelled by rising gold prices. This study evaluates the full scope of ASGM activities on net CO2 emissions, accounting for both the deforestation that converts forests into mining territories and the emissions directly resulting from mining and transportation activities. By applying kriging to a comprehensive dataset, we determined the carbon content of the region and the annual loss of CO2 capture due to deforestation. Our analysis also incorporates emissions from the Interoceanic highway, which has contributed to the mining boom. The findings indicate a total net CO2 emission of 429.9 Gigagrams (Gg) per year, underscoring the critical environmental challenge these activities pose. Our study highlights the need for immediate and effective reclamation efforts, including reforestation with indigenous carbon-rich trees, as a counterbalance to the environmental damage inflicted. These efforts are essential to mitigate the adverse impacts and support the global movement towards net-zero emissions.

Reuse of straw in the form of hydrochar: Balancing the carbon budget and rice production under different irrigation management

Hydrochar is proposed as a climate-friendly organic fertilizer, but its potential impact on greenhouse gas (GHG) emissions in paddy cultivation is not fully understood. This two-year study compared the impact of exogenous organic carbon (EOC) application (rice straw and hydrochar) on GHG emissions, the net ecosystem carbon budget (NECB), net global warming potential (net GWP), and GHG emission intensity (GHGI) in a rice pot experiment using either flooding irrigation (FI) or controlled irrigation (CI). Compared with FI, CI increased ecosystem respiration by 23 – 44 % and N2O emissions by 85 – 137 % but decreased CH4 emissions by 30 – 58 % (p < 0.05). Since CH4 contributed more to net GWP than N2O, CI reduced net GWP by 16 – 220 %. EOC amendment increased crop yield by 5 – 9 % (p < 0.05). Compared with CK, hydrochar application increased initial GHG emission, net GWP and GHGI in the first year, while in the second year, there was no significant difference in net GWP and GHGI between CI–hydrochar and CK. Compared with straw addition, hydrochar amendment reduced net GWP and GHGI by 20 – 66 % and 21 – 66 %; and exhibited a lower net CO2 emission when considering the energy input during the hydrochar production. These findings suggest that integrated CI-hydrochar practices would be a sustainable and eco-friendly way for organic waste management in rice production as it holds potential to enhance the NECB and SOC sequestration of rice production, while also offsetting the extra carbon emissions from organic inputs.

A comparative techno-economic analysis for implementation of carbon dioxide to chemicals processes

CO2-based carbon-neutral organics production processes could potentially reshape the chemical industry. However, their feasibility and net carbon footprint rely strongly on the sources of H2. Herein, we present a comprehensive comparative techno-economic analysis of CO2-based methanol (CO2TM) and α-olefins (CO2TO) manufacturing using various feedstock supply modes: 1) the standalone mode, with external CO2 and H2 from on-site water electrolysis, 2) the integrated mode with CO2 and H2 recovered from coal-chemical plants, and 3) the integrated mode with recycled CO2 but H2 from on-site water electrolysis. The integration of CO2TM and CO2TO into coal-to-olefins (CTO) and coal-to-methanol (CTM) facilities is currently cost-effective and can reduce net CO2 emissions by 65.7% and 68.5%, resulting in a three-fold and two-fold increase in carbon efficiency, respectively. As carbon tax policies and electrolysis technologies continue to evolve, standalone CO2TM and CO2TO are projected to become more economically competitive than CTO and CTM by 2035–2045.

Impacts of Fire Frequency on Net CO2 Emissions in the Cerrado Savanna Vegetation

Impacts of Fire Frequency on Net CO2 Emissions in the Cerrado Savanna Vegetation

Investigation of modal integration for transit-access trips in motorcycle dependent cities—The case study of Hanoi, Vietnam

Micro-mobility has the potential to address first -mile challenges, improving transit accessibility and encouraging public transit usage. However, users’ acceptability of modal integration between various micro-mobility options and public transit remains largely unexplored in the literature. Our study investigates the user behavior for first-mile options, focusing on four alternatives: walking, bicycling, motorcycling, and bus, to access urban mass rapid transit (UMRT) in Hanoi, Vietnam. Based on data collected from 1380 individuals, a Nested Logit Model (NLM) was proposed to analyze the determinants of users’ acceptability under each access mode option as well as evaluate further impacts of shifts in access mode choice on vehicle-kilometer traveled and emissions. The analysis shows that the availability of access modes might increase UMRT use by 47.83%. While this increase further generates additional vehicle-kilometer traveled due to the increase in park-and-ride users, this is offset overall by the large number of motorcycle users shifting to UMRT. Under the most optimistic scenario, modal integration for transit-access trips leads to an average reduction of 17.7% in net vehicle-kilometer traveled or 14.5% in net CO2 emissions or 10.9% in NOx from private vehicles. Our findings also imply that the introduction of parking fees for bicycling- or motorcycling-access trips, while impactful, does not significantly change UMRT choice. Therefore, the pricing schemes should be a focus of parking planning surrounding stations. Finally, a number of policy suggestions for parking planning and first-mile vehicles are presented.

Deployment expectations of multi-gigatonne scale carbon removal could have adverse impacts on Asia’s energy-water-land nexus

Existing studies indicate that future global carbon dioxide (CO2) removal (CDR) efforts could largely be concentrated in Asia. However, there is limited understanding of how individual Asian countries and regions will respond to varying and uncertain scales of future CDR concerning their energy-land-water system. We address this gap by modeling various levels of CDR-reliant pathways under climate change ambitions in Asia. We find that high CDR reliance leads to residual fossil fuel and industry emissions of about 8 Gigatonnes CO2yr−1 (GtCO2yr−1) by 2050, compared to less than 1 GtCO2yr−1 under moderate-to-low CDR reliance. Moreover, expectations of multi-gigatonne CDR could delay the achievement of domestic net zero CO2 emissions for several Asian countries and regions, and lead to higher land allocation and fertilizer demand for bioenergy crop cultivation. Here, we show that Asian countries and regions should prioritize emission reduction strategies while capitalizing on the advantages of carbon removal when it is most viable.

Integrated CO2 capture and conversion into methanol units: Assessing techno-economic and environmental aspects compared to CO2 into SNG alternative

Using carbon dioxide (CO2) as a raw-material to produce value-added chemicals has a strategic role to play in the decarbonization of energy resources and the transition to a climate-neutral economy. E-methanol, Synthetic Natural Gas (SNG) and e-kerosene are one of the most promising pathways to convert CO2. In this context, the aim of this work is to propose an optimized and integrated CO2 to methanol process and then to compare it to the CO2 to SNG process from economic and environmental points of views. An optimized reactor configuration in the CO2 to methanol conversion unit has been successfully implemented in Aspen Plus® and leads to a thermal energy self-sufficiency of this unit. A heat integration with an advanced capture unit has been performed where 5 % of the heat requirement could be provided from the conversion unit while 95 % come from external steam source. Techno-economic assessment of the optimized process showed that methanol is more profitable when it is used as a raw material to synthetize other chemicals. As an energy carrier, SNG is more interesting. Compared to the reference scenario, a net CO2 emission reduction of 70 % in the CO2 to SNG route and of 60 % in the CO2 to methanol route were obtained. Concerning the fossil depletion impact, in both cases, a reduction of more than 60 % was noticed (ca. 75 % in CO2 to SNG route and 61 % in CO2 to methanol case).

Acceleration of chelator on mineralization reaction of cement paste at different CO2 pressures

In order to further improve the mechanical properties of CO2-cured cement paste, effects of chelator on the compressive strength of cement paste cured under different CO2 pressures were investigated, and the mechanism of chelator in accelerating the mineralization reaction was deduced from the analysis of the degree of mineralization reaction, microstructures, and phase compositions, with the contribution of chelator in reducing the net CO2 emissions of cement industry being evaluated. The results showed that the use of chelator could significantly enhance the compressive strength of cement paste cured at different CO2 pressures compared with other methods for improving the compressive strength of CO2-cured cement paste, and the compressive strength of cement paste cured for 48 h at 0.1 MPa and 0.4 MPa CO2 could be enhanced by 23.2 % and 9.4 %, respectively. Chelator could migrate Ca2+ from smaller pores and pore channels to larger pores, decreasing the Ca2+ content and degree of mineralization reaction in smaller pores and pore channels, avoiding the blockage of the stomata by generated CaCO3, and allowing more CO2 to penetrate and diffuse into the cement paste, thereby promoting mineralization reaction and significantly improving compressive strength of cement paste cured at atmospheric pressure. The use of chelator in mineralization curing cement-based materials could further reduce net CO2 emissions from cement production, making significant contribution to the advancement of mineralization curing technology and environmental sustainability.

Highly efficient hydrogenation of carbonate to methanol for boosting CO2 mitigation

The massive CO2 emissions from the energy-intensive industrial sectors can trace to the thermal decomposition of raw mineral carbonates during high-temperature manufactories. To mitigate CO2 emissions, we propose a novel strategy of carbonate-to-methanol through a highly efficient hydrogenation, where the carbon in mineral magnesite is used as a precious resource to unleash its tremendous value. More significantly, we break the trade-off between the excessive H2 for the complete magnesite conversion and the utilization efficiency of H2 by the recycle usage of H2 through the convenient gas–liquid separation of H2/CH3OH. Guided by the thermodynamic predictions, without any catalysts, the excessive H2 accelerates the direct hydrogenation of magnesite in a twin tower at a relatively low temperature of 550 °C, almost approaching thermodynamic limit of 67 % CO selectivity at a complete magnesite decomposition. The outlet syngas with an extremely high molar ratio of H2 to CO of 8 is further used for subsequent methanol production, achieving an outperformed 70 % CO conversion efficiency and over 99 % CH3OH selectivity. Comprehensive scale-up process simulations indicate that the proposed strategy could increase the H2 utilization efficiency by over 80 %, where the carbon footprint assessment illustrates when the green H2 from wind energy is supplied, the negative net CO2 emissions of −5.6 kgCO2/kgmethanol at a low energy consumption of 10 MJ/kgmethanol can be achieved, which highlights its promising industrialization prospects.

Assessment of Economic and Environmental Impacts of using Green Hydrogen Gas for Generating Electricity in the KSA

The energy sector in the Kingdom of Saudi Arabia (KSA) faces serious challenges regarding its current energy mix and energy policies. These challenges are even more complex in the sphere of electricity generation. Where on one side, these challenges are attributed to the fast-growing domestic demand for electricity. While on the other side, KSA depends extensively on traditional fossil fuels for generating electricity and hence facing high rates of carbon dioxide (CO2) emissions. To address these challenges, the Kingdom’s 2030 vision opted for economic diversification and decarbonization by encouraging the transition towards using green hydrogen gas for electricity generation as a clean energy source. This attempt has been associated with measures addressing rationalization of the demand side for electricity. The objective of this paper is to explore the economic and environmental viability of using green hydrogen gas for generating electricity in KSA. Working toward this objective, an economic assessment has been applied to five hypothetical cases or scenarios to identify the most cost-effective (least expensive) to run the turbine generator at net zero CO2 emission. In addition, an assessment of the environmental impact has been applied to the same five hypothetical cases or scenarios to identify the most environmentally friendly i.e., help effectively to reduce or minimize the CO2 emissions. The findings of this assessment reject the economic viability of the transition towards using green hydrogen gas for electricity generation in the KSA, where the calculations of the five cases registered an inverse relation between the NPV and the use of green hydrogen gas in electricity generation. These findings confirm the environmental variability of this transition, where the calculations of the five cases registered a positive relation between decarburization and the use of green hydrogen gas in electricity generation. Based on these findings, the economic ramifications and viability of this transition require a thorough investigation addressing economic and non-economic aspects.

Kinetic modeling of the oxidative dehydrogenation of propane with CO2 over a CrOx/SiO2 catalyst and assessment of CO2 utilization

Oxidative dehydrogenation of propane with carbon dioxide (ODPC) has gained attention as a sustainable process capable of simultaneously producing propylene and reducing carbon dioxide (CO2) emissions. In this study, we developed a kinetic model of the ODPC over a silica-supported chromium oxide catalyst based on the Mars–van Krevelen (MvK) mechanism using the experimental data obtained under controlled conditions. The constructed model estimated both reactant conversions and propylene yield within an absolute error of 3% of the experimental data, confirming the integrity of the kinetic model. The kinetic analysis provides insight into the activation of propane and CO2 via several reactions occurring under ODPC conditions, emphasizing that the ODPC cycle is limited by the high energy barrier for CO2 activation. In addition, it allows comparison of the contributions of non-oxidative and oxidative dehydrogenation reactions, the two main reactions producing propylene under ODPC conditions. The estimation results show a significant increase in the reaction rate of ODPC with increasing CO2 partial pressure, in contrast to a nearly constant reaction rate of non-oxidative dehydrogenation, highlighting the promoting effect of CO2 in enhancing the ODPC reaction. Furthermore, the potential of the ODPC process is assessed by considering propylene productivity, net CO2 emissions, including the energy consumption for the separation process, and the global warming index of the energy grid. A comprehensive investigation of the ODPC process through controlled experiments, kinetic modeling and evaluation of net CO2 utilization provides insight into future strategies for using the ODPC as an efficient and eco-friendly process.

The impacts of furnace and fuel types on the hazardous heavy metal contents and leaching behavior of woody biomass fly ash

In efforts to reduce net CO2 emissions, the use of woody biomass as a fuel for power generation has grown rapidly. However, this practice is expected to generate large amounts of combustion ash. To support the subsequent use and disposal of combustion ash, it is important to understand its hazardous heavy metal (HHM) contents and leaching behavior. Therefore, we investigated the impacts of furnace type and fuel on HHM contents and leaching behavior based on 60 types of woody biomass fly ash (WBFA). A safety assessment of WBFA as fertilizer based on HHM contents revealed that 20% of the WBFA samples exceeded the prescribed standards. Therefore, WBFA would require preprocessing before reuse as fertilizer. The leaching test results showed that 95% of the WBFA samples could be landfilled as industrial waste without special treatment. However, prior to reuse in construction materials or soil amendments, it would be necessary to remove or fix HHMs to prevent leaching. Overall, WBFA generated from the combustion of waste wood as fuel tended to have higher HHM contents and leachate concentrations than WBFA from other woody biomass-based fuel types.

Measuring the forest-based bioeconomy in Estonia, Latvia, Lithuania, and Finland

ABSTRACT This paper aims to present an input-output model of the forest-based bioeconomy, enabling insight into its contribution to total gross value added (GDP), employment, and CO2 emissions in Estonia, Latvia, Lithuania, and Finland. To quantify this contribution, the paper utilizes input-output tables of the four countries. The forest-based bioeconomy includes forestry, the processing of forestry products (forward linkages), and the direct and indirect use of inputs (backward linkages) from forestry and processing industries. Our analysis reveals that while forestry itself is a small industry, contributing minimally to GDP (ranging from 0.40% in Lithuania to 1.90% in Finland), and the forest-based bioeconomy is considerably larger. For instance, its contribution to GDP ranges from 3.59% in Lithuania to 7.22% in Estonia. Moreover, the forestry-based bioeconomy exhibits negative net CO2 emissions, primarily due to CO2 sequestration by forest lands and harvested wood products. Despite the substantial negative CO2 emissions associated with forestry activities, without sequestration, the forestry-based bioeconomy's share in total emissions ranges from 5.14% in Lithuania to 14.88% in Finland.

Energy Transition, fossil Fuels, and green Innovations: Paving the way to achieving sustainable development Goals in the United States

The United States, as the world's second-largest polluter, emitted a staggering 4.7 billion metric tonnes of carbon dioxide in 2020. During the Leaders’ Climate Summit, the US president articulated precise targets for combating climate change, notably a 50 to 52 percent reduction in net CO2 emissions from 2005 levels by 2030. Consequently, it becomes imperative to identify the pivotal factors that are driving this intensified dedication to achieving the Sustainable Development Goals (SDGs). Hence, it is vibrant to determine the basic causes propelling the intensified interest in meeting SDGs 7 and 13. From this perspective, this study explores the dynamic link between energy transition, fossil fuel energy, green innovation, and economic complexity index on CO2 emissions and ecological footprint in the United States from 1980 to 2020. The dynamic Autoregressive-Distributed Lag (ARDL) simulations and Frequency Domain Causality (FDC) techniques are applied for long-medium and short-run causal association among the variables. Our empirical evidence shows that energy transition, fossil fuel energy, and economic complexity increase CO2 emissions and ecological footprint. On the other hand, green innovation reduces CO2 emissions and ecological impact only in the long term. The pragmatic outcomes suggest that authorities should inhibit Fossil Fuel Energy, concentrate on energy transitions, and include more renewable sources in the US energy mix. The findings would assist the United States in meeting SDGs 7 and 13.

The connectedness and structural changes among green and conventional energy markets with CO2 emissions in the United States

As the world's biggest oil producer and second-biggest polluter, the United States has set a strict target to cut net CO2 emissions by 50–52 percent from 2005 levels by 2030 and a net zero emission by 2050 through various strategies, particularly clean energy initiatives. This research attempts to examine the effects of five specific renewable and conventional energy subsectors with carbon emission across five sectors, including power (POW), industry (IND), ground transportation (GT), domestic aviation (DA), and residential (RE). The data illustrate the decline and subsequent increase in CO2 emissions throughout the COVID-19 pandemic, the Russia-Ukrainian conflict, and the USA recession periods from January 1 2021 to September 30 2022. Employing the Vector Autoregressive (VAR) model and a novel quantile connectedness framework, it was found that risk transmission between different markets has been exceptionally high, exceeding 80% both in the COVID-19 outbreak and in the aftermath. The finding suggests that the COVID-19 pandemic shock and the Russian-Ukrainian conflict have intensified the connections between carbon emissions and clean and non-clean energy markets. Policymakers should adjust net zero targets to align with changing dynamics, prioritize wind and geothermal energy, and promote energy independence due to rising oil prices. Leverage lithium for electric vehicles and create specific policies for power, industry, transportation, aviation, and residential sectors to manage CO2 emissions effectively.

Design of a Charging Station for Electric Vehicles Based on a Photovoltaic-Biodiesel Hybrid Renewable Energy System Combined with Battery Storage

The rapid deployment of electric vehicles (EVs) in Jordan requires massive efforts to prepare the infrastructures that serve the transportation sector. The lack of EV charging stations is the major obstacle that faces EV drivers. Utilizing renewable energy in EV charging stations contributes to the spread of these stations. Renewable energy technologies are environmentally friendly as they mitigate greenhouse gases that cause the global warming phenomenon. In this paper, an EV charging station, based on a PV-biodiesel-battery hybrid system, is investigated. The importance of this article is to discuss the hybrid system of PV and waste vegetable oil (WVO) along with storage that applies the maximum reliability supply, having an environmentally friendly supply and achieving the lowest energy cost of charging. This station is designed based on renewable and WVO utilization. In fact, WVO, coming from restaurants, is exploited to produce electricity by a diesel generator through direct burning after converting it into biodiesel. The capacity of each station is 14 cars/day with a medium-speed charger of 7 kW. The system is simulated and optimized using iHOGA software where multiobjective optimization is applied to achieve the minimum net present cost (NPC) and CO2 emissions considering three cases, PV-diesel, PV-biodiesel, and PV-WVO, all with battery-hybrid system. These values for the EV charging station that uses the PV-biodiesel-battery hybrid system are 624408 € and 15.4 tons/year, respectively. The corresponding values are 781473 € and 15.14 tons/year and 615310 € and 18.84 tons/year for the systems that work with diesel and WVO, respectively, and energy cost is achieved in best solution to be 0.11 Euro/kWh. Simulation results show that the proposed technique led to enhanced operational efficiency in terms of both NPC and annual CO2 emissions.

Navigating sustainability in the US: A comprehensive analysis of green energy, eco-innovation, and economic policy uncertainty on sectoral CO2 emissions

The United States is the world's second-largest polluter, generating 4.7 billion metric tons of CO2 in 2020. To combat it, the US is targeting a precise goal of 50–52 percent decrease in net CO2 emissions from 2005 levels by 2030. Hence, it is vital to determine the critical factors contributing to Sustainable Development Goals (SDGs). With this motivation, this study examines dynamic link between green energy transition, eco-innovation, economic policy uncertainty, energy use, economic growth, and sectoral CO2 emissions (SCO2) in the United States from 1980 to 2020 by using novel Quantile-On-Quantile Regression (QQR) and Granger causality in quantile approaches. The results show that the quantiles of the green energy transition are positively related to all SCO2 quantiles. While eco-innovation and SCO2 are marginally favorable in the lower to higher quantiles, positive slope coefficients showcase the effect of economic policy uncertainty on SCO2 in the 0.2–0.95 quantiles. Similarly, SCO2 and the energy use showed positive and negative results across quantiles, whereas QQR slope coefficients between SCO2 and economic growth are positive and negative throughout the quantiles. Suggests that investment in green energy and eco-innovation also reduces economic policy uncertainty by delivering energy for all sectors is vital if SDG-7 is executed by 2030.