Net Greenhouse Gas Emissions Research Articles

Preparing for net zero greenhouse gas emissions in 2050: lifecycle emissions of dairy products in Brazil

Dairy products play an important role in human nutrition and the world economy. Livestock farming, including cows rearing to produce milk and dairy products, is one of the world's major sources of greenhouse gas emissions. Progress towards net zero goals requires monitoring emissions from companies and products, and greenhouse gas inventories are essential. This work quantifies greenhouse gas emissions from milk production, considering the milk delivered at the farm gate and the milk delivered at the cooperative gate. Emissions accounting was based on greenhouse gas inventories for two units and lifecycle emissions for major farm inputs. Results have shown that milk production on the farm emits 0.57 kg CO2e / liter, with enteric fermentation accounting for more than 90% of emissions at the farm gate, and more than 50% at the milk processing unit gate. Dairy production adds 0.533 kg CO2e / liter to the emissions coming from raw milk, most of which comes from wastewater treatment. Thus, the footprint of dairy products is 1.103 kg CO2e / liter of processed milk. The producers' cooperative's greenhouse gas emissions are essentially indirect and amount to 0.626 kg CO2e/liter of milk delivered to customers, in which emissions from purchased milk account for more than 85% and emissions from transportation account for around 15%.

Production of Aviation Fuel-Range Hydrocarbons Through Catalytic Co-Pyrolysis of Polystyrene and Southern Pine

Sustainable aviation fuels (SAFs), produced from waste and renewable sources, are a promising means for reducing net greenhouse gas emissions from air travel while still maintaining the quality of air transportation expected. In this work, the catalytic co-pyrolysis of polystyrene and pine with red mud (bauxite residue) and ZSM-5 catalysts at temperatures of 450 °C, 500 °C, and 550 °C was investigated as a method for producing aromatic hydrocarbons with carbon numbers ranging from 7 to 17 for use as additives to blend with SAF produced through other methods to add the required quantity of aromatic molecules to these blends. The maximum yield of kerosene-range aromatic hydrocarbons was 620 mg per gram of feedstock (62% of feedstock was converted to kerosene-range hydrocarbons) obtained at 550 °C in the presence of ZSM-5. Additionally, it was noted that a positive synergy exists between pine and polystyrene feedstocks during co-pyrolysis that cracks solid and liquid products into gaseous products similarly to that of a catalyst. The co-pyrolysis of pine and polystyrene without a catalyst produced on average 17% or 36.3 mg more kerosene-range hydrocarbons than predicted, with a maximum yield of 266 mg of C7–C17 aromatic hydrocarbons per gram of feedstock (26.6% conversion of initial feedstock) obtained at 550 °C.

Application of GIS in Introducing Community-Based Biogas Plants from Dairy Farm Waste: Potential of Renewable Energy for Rural Areas in Bangladesh

Dairy production is one of the most important economic sectors in Bangladesh. However, the traditional management of dairy cow manure and other wastes results in air pollution, eutrophication of surface water, and soil contamination, highlighting the urgent need for more sustainable waste management solutions. To address the environmental problems of dairy waste management, this research explored the potential of community-based biogas production from dairy cow manure in Bangladesh. This study proposed introducing community-based biogas plants using a geographic information system (GIS). The study first applied a restriction analysis to identify sensitive areas, followed by a suitability analysis to determine feasible locations for biogas plants, considering geographical, social, economic, and environmental factors. The final suitable areas were identified by combining the restriction and suitability maps. The spatial distribution of dairy farms was analyzed through a cluster analysis, identifying significant clusters for potential biogas production. A baseline and proposed scenario were designed for five clusters based on the input and output capacities of the biogas plants, estimating the location and capacity for each cluster. The study also calculated electricity generation from the proposed scenario and the net greenhouse gas (GHG) emissions reduction potential of the biogas plants. The findings provide a land-use framework for implementing biogas plants that considers environmental and socio-economic criteria. Five biogas plants were found to be technically and spatially feasible for electricity generation. These plants can collectively produce 31 million m3 of biogas annually, generating approximately 200.60 GWh of energy with a total electricity capacity of 9.8 MW/year in Bangladesh. Implementing these biogas plants is expected to increase renewable energy production by at least 1.25%. Furthermore, the total GHG emission reduction potential is estimated at 104.26 Gg/year CO2eq through the annual treatment of 61.38 thousand tons of dairy manure.

Briefing: Stocktaking global warming: the outcomes of the 2023 Dubai Climate Summit (COP28)

This article reviews outcomes of the 28th United Nations Climate Change Conference of the Parties (COP28) held in Dubai, United Arab Emirates in late 2023. In particular, it considered the first Global Stocktake (GST) of actions taken by signatory nations to the 2015 Paris Agreement on Climate Change. The GST examined the potential impact of bottom-up national pledges on greenhouse gas (GHG) mitigation required to limit global warming to 1.5°C above pre-industrial levels by the end of the twenty-first century. The achievements at COP28 were mixed, and disappointed many from the climate-vulnerable states at high risk from extreme weather events and rising sea levels. There is a significant GHG emissions gap between that needed to ‘keep 1.5°C alive’ and climate actions identified in the GST. Nonetheless, the parties agreed to ‘transition away from fossil fuels in energy systems’ in order to reach net zero GHG emissions (i.e. carbon neutrality) by 2050, and to triple renewable energy capacity and double energy efficiency by 2030. This assessment sets out the background to what needs to be achieved at future annual COP summits, including the next GST at COP30 to be held in the Brazilian city of Belém later in 2025.

Additionality in Blue Carbon Ecosystems: Recommendations for a Universally Applicable Accounting Methodology.

Blue carbon ecosystems (BCEs) remove carbon dioxide from the atmosphere and store significant amounts of organic carbon (OC) in their soils. Consequently, the protection and restoration of BCEs may contribute to net greenhouse gas emissions abatement and help address the global challenges of both mitigating and adapting to climate change. An ongoing debate is whether OC sequestered out with the blue carbon (BC) project and transported to its present location (allochthonous) should be counted as 'additional'. There are inconsistencies in the treatment of allochthonous carbon between BCE methodologies, potentially undermining the credibility of global BC accounting initiatives. To explore these inconsistences, we compare the methodologies which we were able to find online, with particular focus on the VERRA, IPCC and BlueCAM methodologies, and review the science underlying any approach to account for allochthonous OC. Our findings indicate that there are currently no robust scientific approaches to define an appropriate apportioning of allochthonous OC for discounting in the calculation of additionality. We therefore advocate for the inclusion of allochthonous OC in BC crediting projects when an observational and experimental approach does not support the calculation (and discounting) of the refractory allochthonous carbon contribution.

Methodological study on carbon sequestration accounting for emission reductions from the whole-chain utilization of livestock and poultry manure

Effective livestock manure management is crucial for carbon neutrality. Scientific accounting methods and integrated management strategies can help guide reductions in carbon emissions and promote green development. To reduce greenhouse gas emissions by livestock manure, this study analyzed current accounting systems and focused on the complete chain of “collection-treatment-storage-use-returning” of manure based on the theoretical framework of greenhouse gas emissions accounting in the IPCC 2019 Guidelines. Combined with a life cycle assessment, the accounting list and boundaries were clarified, and the whole chain of livestock and poultry manure greenhouse gas accounting methodology system was proposed. Using swine breeding as a case study, this study evaluated the carbon emission reduction and sequestration effect of the whole manure chain using a typical technology model and a typical technological framework. It predicted the carbon reduction potential and sequestration benefits of utilizing swine manure in 2025 and 2030 in four scenarios. The findings indicated that the greenhouse gas emission factor of the whole chain of the six typical swine manure utilization modes in China was −48.82–40.54 kgCO2et−1. In 2022, the net greenhouse gas emissions from swine manure in China totaled approximately 2.0 × 107 tCO2e, with manure resource utilization reducing emissions by 3.2 × 107 tCO2e. Our projections suggest that emissions from swine manure in China may range from −1.8 × 107 to 1.3 × 107 tCO2e by 2025 and from −3.1 × 107 to 4.5 × 106 tCO2e by 2030. This can help guide optimal greenhouse gas emission reduction pathways for livestock and poultry farming and aid in the formulation of policies.

Impact of biochar application on nitrous oxide and methane emissions in rainfed cropping systems within a semiarid region

AbstractThis study investigated the impact of biochar on Zea mays L. yield and greenhouse gas (GHG) emissions in rainfed maize fields in Northwest China. Four treatments were compared: unmodified control (CK), conventional nitrogen (BC0), nitrogen + 20 t ha−1 biochar (BC20), and nitrogen + 50 t ha−1 biochar (BC50). Results showed significant increases in grain yields with BC20 (11.1%) and BC50 (8.6%) compared to BC0. Emissions of nitrous oxide (N2O) were reduced by 14.0%–19.5% in biochar treatments compared to CK. Methane (CH4) uptake by the fields, acting as CH4 sinks, was not significantly impacted by biochar treatments, clarifying that the biochar did not alter the farmland's inherent ability to uptake CH4. Over 2 years, the addition of nitrogen fertilizer and biochar did not markedly alter cumulative CH4 uptake. Both net greenhouse gas (NGHG) emissions and yield‐scaled GHG intensity (NGHGI) were lowered by 16.7%–23.5% and 24.2%–30.3%, respectively, with biochar application. The integration of biochar effectively mitigated the GHG emission enhancement due to nitrogen fertilizer, mainly by decreasing nitrogen oxide emissions and boosting maize yields. Thus, proper biochar application would be an economical and effective strategy for mitigating gas emissions from rainfed maize cropping system in semiarid regions.

Assessment of Waste Animal Fats (WAFS) Biodiesel Production Potential as an Alternative Fuel for Zambia: A Case Study of Southern Province

The volatility in global fuel prices and the desire to reduce energy dependency on fossil fuels has necessitated the speeding up of alternative energy supply sources. Coupled to this is the global urgent need to reduce the accumulation of CO2 and green house gas (GHG) emissions as a result of fossil fuels production and use. Further, the mandate by united nations to move towards sustainably produced energy for the transportation, and power generation demands that we seek energy solutions that meet reduced negative impact on the environment. It is in this regard that this study seeks alternatives in waste animal fats (WAFs) biodiesel as an option that could meet the ever increasing demand for fossil fuel in the transport sector and power generation. For the transport sector and power generation , the biodiesel maybe blended with the fossil diesel in the approved ratios as stipulated by the Energy Regulation Board and the Zambia Bureau of Standards to help mitigate the net GHG and CO2 emissions. The biodiesel production in this study was based on the modified two-step process. These two steps involved passing the feedstock through esterification using sulphuric acid as catalyst and there after base catalysed using sodium hydroxide in a process referred to as transesterification. The resulting products in the esterification process are the esters and water whilst in the transesterification are the biodiesel and glycerol. The feedstock used are those of waste animal fats (WAFs) of cattle, pig and chicken that has been discarded from meat processing and animal slaughter houses. The feedstocks have been carefully selected based on the animals raised in the country with a bigger slaughtered population as well as reared. The population of animals reared and slaughtered annually are obtained from the Zambia Ministry of Agriculture animal population census records. Based on these records, the preferred feedstock sources where obtained. The study further 1. explored the economic potential of the biodiesel production for the Zambian government and beyond. 2. compared some of the characteristics of WAF biodiesel to that of imported fossil diesel 3. affirmed that WAF biodiesel has a very good impact in reducing environmental pollution as WAF dumping to land fills and the cost of disposal is reduced. Also,WAF biodiesel is bio-degradable. Thus, moving closer to an effective sustainable development as required by the united nations sustainability goals if full scale production is implemented in Zambia.

CH4 and CO2 Reductions from Methanol Production Using Municipal Solid Waste Gasification with Hydrogen Enhancement

This study evaluates the greenhouse gas (GHG) impacts of converting municipal solid waste (MSW) into methanol, focusing on both landfill methane (CH4) emission avoidance and the provision of cleaner liquid fuels with lower carbon intensity. We conduct a life cycle assessment (LCA) to assess potential GHG reductions from MSW gasification to methanol, enhanced with hydrogen produced via natural gas pyrolysis or water electrolysis. Hydrogen enhancement effectively doubles the methanol yield from a given amount of MSW. Special attention is given to hydrogen production through natural gas pyrolysis due to its potential for lower-cost hydrogen and reduced reliance on renewable electricity compared to electrolytic hydrogen. Our analysis uses a case study of methanol production from an oxygen-fired entrained flow gasifier fed with refuse-derived fuel (RDF) simulated in Aspen HYSYS. The LCA incorporates the significant impact of landfill methane avoidance, particularly when considering the 20-year global warming potential (GWP). Based on the LCA, the process has illustrative net GHG emissions of 183 and 709 kgCO2e/t MeOH using renewable electricity for electrolytic hydrogen and pyrolytic hydrogen, respectively, for the 100-year GWP. The net GHG emissions using 20-year GWP are −1222 and −434 kgCO2e/t MeOH, respectively. Additionally, we analyze the sensitivity of net GHG emissions to varying levels of fugitive methane emissions.

Impact of net zero policy scenarios on air pollution inequalities in England and Wales

BackgroundThe UK is committed to achieve net zero greenhouse gas emissions by 2050. The suite of policies needed to reach net zero will lead to improvements in air quality and, consequently, could lessen air pollution inequalities. We assessed air pollution inequalities across different sociodemographic groups in England and Wales and explored how these might be differentially impacted by future air pollution projections in 2030 and 2040 under net zero policies. MethodsWe employed a geodemographic classification approach to categorise neighbourhoods into five distinct clusters based on 2021 UK Census sociodemographic variables. We modelled fine particulate matter (PM2.5) and nitrogen dioxide (NO2) concentrations for the year 2019, and predicted concentrations in 2030 and 2040. We compared a business-as-usual (BAU) scenario and two policy pathways to achieve net zero currently considered by the UK government. We aggregated air pollution concentrations to the neighbourhood level and assessed differential neighbourhood-level concentrations across the geodemographic groups using descriptive statistics and box plots. ResultsThe Urban Central Professionals group experienced 14 µg/m3 higher average NO2 concentrations compared with the Rural Elderly group in 2019. Despite substantial improvements to air quality in 2030 and 2040 of up to 6.3 µg/m3 for NO2 based on BAU, and further reductions of up to 2.4 µg/m3 NO2 under net zero policies, the overall pattern of inequality persists, but is predicted to be less pronounced. ConclusionsOur findings demonstrate the effectiveness of targeted policies and innovations in reducing both air quality and greenhouse gas emissions and in bridging the environmental inequality gap. Our findings are essential to develop targeted communication campaigns to secure acceptance and willingness across the sociodemographic spectrum to support the significant behavioural changes needed to achieve net zero, by highlighting the wider co-benefits to the environment and health of such policies.

New perspectives on temperate inland wetlands as natural climate solutions under different CO2-equivalent metrics

There is debate about the use of wetlands as natural climate solutions due to their ability to act as a “double-edged sword” with respect to climate impacts by both sequestering CO2 while emitting CH4. Here, we used a process-based greenhouse gas (GHG) perturbation model to simulate wetland radiative forcing and temperature change associated with wetland state conversion over 500 years based on empirical carbon flux measurements, and CO2-equivalent (CO2-e.q.) metrics to assess the net flux of GHGs from wetlands on a comparable basis. Three CO2-e.q. metrics were used to describe the relative radiative impact of CO2 and CH4—the conventional global warming potential (GWP) that looks at pulse GHG emissions over a fixed timeframe, the sustained-flux GWP (SGWP) that looks at sustained GHG emissions over a fixed timeframe, and GWP* that explicitly accounts for changes in the radiative forcing of CH4 over time (initially more potent but then diminishing after about a decade)—against model-derived mean temperature profiles. GWP* most closely estimated the mean temperature profiles associated with net wetland GHG emissions. Using the GWP*, intact wetlands serve as net CO2-e.q. carbon sinks and deliver net cooling effects on the climate. Prioritizing the conservation of intact wetlands is a cost-effective approach with immediate climate benefits that align with the Paris Agreement and the Intergovernmental Panel on Climate Change timeline of net-zero GHG emissions by 2050. Restoration of wetlands also has immediate climate benefits (reduced warming), but with the majority of climate benefits (cooling) occurring over longer timescales, making it an effective short and long-term natural climate solution with additional co-benefits.

Development of national post-fire restoration system to assess net GHG impacts and salvage biomass availability

In light of the recent unprecedented wildfires in Canada and the potential for increasing burned areas in the future, there is a need to explore post-fire salvage harvest and restoration and the implications for greenhouse gas (GHG) emissions. Salvage logging and replanting initiatives offer a potential solution by regrowing forests more quickly while meeting societal demands for wood and bioenergy.This study presents a comprehensive modeling framework to estimate post-fire salvage biomass and net GHG emissions relative to a ‘do-nothing’ baseline for all of Canada's harvest-eligible forests. Forest ecosystem carbon emissions and removals were modeled at 1-ha spatial resolution for Canadian forests using the Generic Carbon Budget Model (GCBM) from 1990 to 2070 using several forest inventory data sources with future harvest and wildfires.Building upon previous research, our work integrated the Canadian Forest Fire Danger Rating System fire intensity to estimate fire severity of future wildfires. For 2024 to 2070, we assessed the changes in ecosystem carbon, emissions from harvested wood products, and substitution benefits from avoided emissions-intensive materials, relative to a forward-looking baseline. Our prototype system provides a comprehensive framework, configuration files, links to datasets to quantify the net GHG of post-fire restoration, and sample results for validation.•Developed spatially explicit forest carbon modeling system for all of Canada's forests.•Assessed the net GHG reduction from post-fire restoration.•Used system approach to consider forests, wood products and substitution benefits.

Characterization of Humic Acid Salts and Their Use for CO2 Reduction

The European Union aims to be climate neutral by 2050. To achieve this ambitious goal, net greenhouse gas emissions must be reduced by at least 55% by 2030. Post-combustion CO2 capture methods are essential to reduce CO2 emissions from the chemical industry, power generation, and cement plants. To reduce CO2, it must be captured and then stored underground or converted into other valuable products. Apromising alternative for CO2 reduction is the use of humic acid salts (HASs). This work describes a process for the preparation of potassium (HmK) and ammonium (HmA) humic acid salts from oxidized lignite (leonardite). A detailed characterization of the obtained HASs was conducted, including elemental, granulometric, and thermogravimetric analyses, as well as 1H-NMR and IR spectroscopy. Moreover, the CO2 absorption capacity and absorption rate of HASs were experimentally investigated. The results showed that the absorption capacity of the HASs was up to 10.9 g CO2 per kg. The CO2 absorption rate of 30% HmA solution was found to be similar to that of 30% MEA. Additionally, HmA solution demonstrated better efficiency in CO2 absorption than HmK. One of the issues observed during the CO2 absorption was foaming of the solutions, which was more noticeable with HmK.

Greenhouse Gas Fluxes from Cranberry and Highbush Blueberry Plantations on Former Peat Extraction Fields Compared to Active Peat Extraction Fields and Pristine Peatlands in Latvia

Emissions of carbon dioxide (CO2), nitrous oxide (N2O), and methane (CH4), particularly those from organic soils, need to be reduced in the context of climate change mitigation (CCM). Here, we estimated the greenhouse gas (GHG) fluxes from nutrient-poor organic soils in cranberry (Vaccinium macrocarpon) and highbush blueberry (Vaccinium corymbosum) plantations established on former peat extraction fields compared to active peat extraction fields and pristine raised bogs in Latvia. A two-year study (2016–2018) was conducted using the manual closed chamber method. In berry plantations and active peat extraction fields, annual net CO2 fluxes contributed the most to total GHG emissions, accounting for over 67%, and temperature had the most significant impact on CO2 fluxes. Conversely, annual CH4 fluxes were the primary contributor to total net GHG emissions in the pristine raised bog, which simultaneously acted as a slight CO2 sink. N2O fluxes were relatively low among all studied land use types. This study provided quantitative insights into the variation in GHG fluxes and the environmental variables influencing them, and the obtained data are valuable to estimate the impact of the establishment of berry plantations on former peat extraction fields on CCM in the hemiboreal region of Europe.

The Territorial Space of Green Transition / Transitioning from One Territorial System to Another through Nature-based Solutions - The Case of Finiq Municipality

Climate change has been recognised by many, be it nations or international organizations, as an existential threat to the world. In this context, the EU has introduced the European Green Deal, with the aim of transforming the continent into a modern, climate- neutral, resource-efficient, and competitive economy. In this scenario, the goals set by the EU are: no net emissions of greenhouse gases by 2050; economic growth decoupled from resource use; no person and no place left behind. The new growth strategy of the EU was also recognized by the Western Balkan Countries (nonmembers of the EU) through the Sofia Declaration in November 2020, acknowledging the need for transformation of the region to turn sustainability and resilience challenges into opportunities and transpose elements of the European Green Deal in all interrelated priority sectors. Those sectors are represented by five main pillars: Climate, energy, mobility; Circular economy; Depollution; Sustainable agriculture and food production; and Biodiversity. Even though it is a multi-sectorial approach, it does not directly address the territorial aspect. The territory is rather seen as a common dominator of the five pillars. This resizes the question, what is the spatial domain of green transition in a given territory? In the Albanian context, after the territorial reform of 2014, the territory was consolidated into 61 municipalities. In the framework of the General Local Plans, each municipality cat- egorized its territory into five main territorial systems: Urban; Nature; Agriculture; Water; and Infrastructure. Through the case of Finiq Municipality, we will further analyze the complexity of territorial systems in a given territory. For the purpose of analysis, a buffer of 1 km was ap- plied to the territory of Finiq Municipality (Bistrica River Basin) where the predominance of a territorial system over another and the mixture of them was evaluated. After this evaluation, an operational framework was conceptualized using the most relevant documents related to climate change, from the international level to the local level, that are pertinent to the case of Finiq Municipality. Taking into account the evidenced framework of green transition for the selected area, it is easier to propose effective nature-based solutions to be implemented in the transitional space between territorial systems. This was done by analyzing the concept of nature-based solutions, at first, and by reviewing case studies that deal with similar societal challenges as the ones identified in Finiq Municipality. The main focus will be the area surrendering the Bistrica River, for the simple fact that it flows from the east, where we find a high predominance of the natural landscape, to the west where a predominance of human activity is more evident. Through the river, we will illustrate the unfolding of what was explained above.

Synergic treatment of domestic wastewater and food waste in an anaerobic membrane bioreactor demo plant: Process performance, energy consumption, and greenhouse gas emissions

Ambient operation and large-scale demonstration have limited the implementation and evaluation of anaerobic membrane bioreactors (AnMBRs) for low-strength wastewater treatment. Here, we studied these issues at an AnMBR demo plant that treats domestic wastewater and food waste together at ambient temperatures (7–28 °C). At varied hydraulic retention times (HRTs, 8–42 h), the AnMBR achieved a COD removal efficiency and biogas production of 80.4% ± 3.9% and 66.5 ± 9.4 NL/m3-Influent, respectively. Moreover, a stable high membrane flux of 14.4 L/m2/h was reached. The electric energy consumption for the AnMBR operation was 0.269–0.433 kW·h/m3, and 49.4%–91.3% could be compensated by the electric energy produced from methane production. At an HRT of 10 h, the AnMBR system demonstrated an impressively low net electric energy consumption of merely 0.05 kW·h/m3, resulting in a net greenhouse gas emission of 0.015 CO2-eq/m3, cutting 85% compared to the conventional activated sludge process. Achievements in this study provide key parameters for the ambient operation of AnMBR and demonstrate that AnMBR is an energy-saving and low-carbon solution for low-strength wastewater treatment.

The path to 2060: Saudi Arabia's long-term pathway for GHG emission reduction

Saudi Arabia, as part of its Saudi Green Initiative, has announced its goal to achieve net zero green-house gas emissions by 2060. This ambitious target underscores the nation's dedication to addressing climate change. However, there is a significant gap in comprehensive analysis regarding the long-term effects of Saudi Arabia's climate policies and their collective contribution towards the net-zero objective. This study endeavors to bridge this gap through a detailed examination using the GCAM-KSA, a specialized version of the Global Change Analysis Model tailored for Saudi Arabia, employing a multi-sectoral methodology that integrates economic, energy, and land use systems within a coherent framework to assess the impact of climate policies on GHG emissions. Our analysis reveals that reaching net-zero GHG emissions by 2060 is a complex challenge requiring concerted efforts across all sectors of the economy. While transitioning to low-carbon electricity and improving energy efficiency offer considerable emission reductions, fully decarbonizing the industrial and transportation sectors poses a significant hurdle. Our findings suggest that Saudi Arabia must triple its emission reduction commitments in its next Nationally Determined Contributions (NDCs) update to align with its 2060 net-zero goal. Early action and increased ambition could avoid the chances of getting locked into the high emission assets and give enough time to transform the energy system. Furthermore, the adoption and integration of Carbon Dioxide Removal (CDR) technologies are identified as crucial for offsetting residual emissions, especially in sectors that might continue to rely on fossil fuels.

Benchmarking Performance Indices of Electrochemical CO2 Reduction to Ethylene Based on Prospective Life Cycle Assessment for Negative Emissions.

To mitigate global warming to the most ambitious targets, it is necessary to remove CO2 from the atmosphere and reduce fossil fuels use. The electrochemical conversion of CO2 to ethylene (C2H4) as a basic chemical is a promising technology that meets both requirements; however, its life cycle CO2 emissions remain inconclusive because of varying assumptions in the performance indices. This study aimed to set benchmarks for the four most sensitive indices to achieve -0.5 t-CO2/t-C2H4 by calculating net greenhouse gas (GHG) emissions through a prospective life cycle assessment of a model system including CO2 capture, CO2 enrichment, electrochemical conversion, CO2 recycling, and cryogenic separation. As a result, the electrochemical conversion process was the hotspot of life cycle emissions, and representative benchmarks were determined as follows: cell voltage, 3.5 V; C2H4 Faraday efficiency, 70%; conversion rate, 20%; and electrochemical CO2 recycling energy, 2.2 GJ/t-CO2. The gaps between the benchmarks and current top data of cell voltage and Faraday efficiency were <10%, and suppressing the performance degradation for up to one year was found to be a critical requirement. These results can direct research towards the development of a year-round stable system, rather than further improving the performance indices.

An in situ 15N labeling experiment unveils distinct responses to N application approaches in a mountain beech forest.

Atmospheric nitrogen (N) deposition has notably increased since the industrial revolution, doubling N inputs to terrestrial ecosystems. This could mitigate N limitations in forests, potentially enhancing productivity and carbon sequestration. However, excessive N can lead to forest N saturation, causing issues like soil acidification, nutrient imbalances, biodiversity loss, increased tree mortality and a potential net greenhouse gas emission. Traditional experiments often overlook the canopy's role in N fate, focusing instead on direct N addition to the forest floor. In our study, we applied 20kgNha y-1 of labeled 15NH415NO3 solution (δ15N=30‰) both above and below the canopy, maintaining also control plots. We assessed ecosystem components before and after treatment, calculated N stocks, and used mass balance for fertilizer recovery analysis. Findings revealed that the above-canopy N addition intercepted up to 31±4% of added N in foliage, a significant contrast to the negligible recovery in leaves with below-canopy treatment. Overall plant recovery was higher in the above-canopy treatment (43±11%) compared with below (9±24%). Post-vegetative season, about 15±1% of above-canopy added N was transferred to soil via litterfall, indicating substantial N reabsorption or loss through volatilization, stemflow or throughfall. In contrast, the below-canopy approach resulted in just 4.0±0.6% recovery via litterfall. These results highlight a significant difference in N fate based on the application method. Nitrogen applied to the canopy showed distinct recovery in transient compartments like foliage. However, over a few months, there was no noticeable change in N recovery in long-lived tissues across treatments. This implies that N application strategy does not significantly alter the distribution of simulated wet N deposition in high Carbon/N tissues, underscoring the complex dynamics of forest N cycling.

Environmental Impacts of Transportation Network Company (TNC)/Ride-Hailing Services: Evaluating Net Vehicle Miles Traveled and Greenhouse Gas Emission Impacts within San Francisco, Los Angeles, and Washington, D.C. Using Survey and Activity Data

Transportation Network Companies (TNCs) play a prominent role in mobility within cities across the globe. However, their activity has impacts on vehicle miles traveled (VMT) and greenhouse gas (GHG) emissions. This study quantifies the change in personal vehicle ownership and total miles driven by TNC drivers in three metropolitan areas: San Francisco, CA; Los Angeles, CA; and Washington, D.C. The data sources for this analysis comprise two surveys, one for TNC passengers (N = 8630) and one for TNC drivers (N = 5034), in addition to data provided by the TNC operators Uber and Lyft. The passenger survey was deployed within the three metropolitan areas in July and August 2016, while the driver survey was deployed from October to November 2016. The TNC operator data corresponded with these time frames and informed the distance driven by vehicles, passenger frequency of use, and fleet level fuel economies. The data from these sources were analyzed to estimate the impact of TNCs on travel behavior, personal vehicle ownership and associated VMT changes, as well as the VMT of TNCs, including app-off driving. These impacts were scaled to the population level and collectively evaluated to determine the net impacts of TNCs on VMT and GHG emissions using fuel economy factors. The results showed that the presence of TNCs led to a net increase of 234 and 242 miles per passenger per year, respectively, in Los Angeles and San Francisco, while yielding a net decrease of 83 miles per passenger per year in Washington, D.C. A sensitivity analysis evaluating net VMT change resulting from vehicle activity and key behavioral impacts revealed the conditions under which TNCs can contribute to transportation sustainability goals.