100-year Global Warming Potential Research Articles

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.

Atmospheric oxidation pathways of CF3CH2CFCl2 (HCFC-234fb) with OH-radicals and Cl-atoms: insights into the mechanism, thermodynamics, and kinetics.

The atmospheric oxidation of 1,1-dichloro-1,3,3,3-tetrafluoropropane, HCFC-234fb (DTP), leads to the formation of harmful radicals, contributing to stratospheric ozone depletion. Thus, a detailed study of the gas-phase oxidation of the first-generation chlorofluorocarbon alternative HCFC-234fb by a reaction with hydroxyl radicals and chlorine atoms is important to understand its harmful effects on the environment. In this work, we have performed quantum chemical calculations to investigate the thermodynamic and kinetic aspects of the titled reaction. The potential energy profile calculated at the CCSD(T)/aug-cc-pVTZ//MP2/cc-pVTZ level of theory shows that the major reaction pathway involves the abstraction of the H-atom from the central carbon atom, C2, giving rise to the product radical CF3C˙HCCl2F. The calculated rate-coefficients for the reaction with ˙OH and Cl-atoms are 3.89 × 10-15 and 2.54 × 10-17 cm3 molecule-1 s-1, respectively, at 298 K and are in accordance with the experimental rate coefficients. The results suggest that the rate-coefficient for the reaction of DTP with ˙OH is two orders of magnitude higher than that with Cl-atoms, indicating greater significance of the former reaction in the atmosphere. With the rate-coefficient values, the lifetime and the radiative efficiency were calculated to be 8.2 years and 0.246 W m-2 ppb-1, respectively. A 100-year global warming potential (GWP) of 712 was also estimated using the lifetime corrected radiative efficiency value.

Flexible and synergistic methanol production via biomass gasification and natural gas reforming

Sustainable liquid fuels are essential for decarbonization of various means of transportation which are challenging to address through electrification or hydrogen use. A possible method for producing low-carbon liquid fuel is through the thermochemical biomass to liquid (BTL) process. In this study, we conduct a technoeconomic-environmental analysis of two processes which take advantage of integration of natural gas reforming and biomass gasification, with the objective of improving the economics. By integrating H2-rich syngas (a mixture of H2/CO) obtained from natural gas reforming with carbon-rich syngas from biomass gasification, we harness synergistic effects. This combination allows us to achieve the optimal H2/CO ratio required for methanol synthesis, while also ensuring efficient carbon utilization. In the first design, natural gas is reformed in an autothermal reformer (ATR) to produce syngas. A Solid Oxide Electrolysis Cell (SOEC) is utilized to supply the O2 for both gasification and reforming processes. The H2 produced by the SOEC adjusts the H2 content in the syngas before the methanol synthesis reactor. In the second design, natural gas is reformed in a gas-heated-reformer (GHR) before an ATR, while an Air Separation Unit (ASU) produces the O2 for the process. As a benchmark, the economics and flexible operation of both processes are compared to a conventional BTL process. In addition, the techno-economic impact of operating in biomass-only or natural gas-only modes are investigated. For a 134 MWth plant with 50 % of entering carbon from biomass, the levelized cost of methanol (LCOMeOH) of ATR+SOEC case is 34 % higher than the BTL reference case, while that of ATR+GHR case is 24 % lower than the BTL reference case. A lifecycle analysis (LCA) is conducted for these designs. Utilizing renewable electricity and 50 % biogenic carbon, the ATR+SOEC case emits 908 kgCO2e /tonne MeOH for a 100-year Global Warming Potential (GWP), while the ATR+GHR case emits 721 kgCO2e /tonne MeOH. For a 20-year GWP, these emissions are 1055 and 915 kgCO2e /tonne MeOH, respectively. These emissions correspond to more than 50 % reduction in LCA emissions when compared to natural gas based LCA emissions.

Optimization of a Hybrid Renewable Energy System for Off-Grid Residential Communities Using Numerical Simulation, Response Surface Methodology, and Life Cycle Assessment

This paper presents an optimized hybrid renewable energy system tailored for off-grid residential communities, integrating wind, solar, and hydrogen technologies to meet electricity, cooling, heating, and water needs. The proposed optimization methodology combines numerical simulation, response surface methodology (RSM), and life cycle assessment (LCA), ensuring robust performance across diverse conditions. Key components include fuel cells, reverse osmosis systems, heat pumps, photovoltaic/thermal solar collectors, wind turbines, and hydrogen generation systems. The optimization process targets critical variables such as PVT panel area, the number of wind turbines, and fuel cell power. The optimal configuration was found to include 24 small-scale wind turbines, 159.46 m2 of PVT collectors, and 79.73 kW of fuel cell power. This configuration generated surplus electricity with net electricity usage (NEU) values of -123084.27 kWh/year in New York, -224245.29 kWh/year in Forks, and -215949.30 kWh/year in Santa Barbara. Additionally, the optimized systems achieved a significant reduction in life cycle cost (LCC), with Forks showing the lowest LCC at 304428.97 USD. The environmental impact was also minimized using the novel optimization approach, with the optimized systems achieving negative 100-year global warming potential (GWP100) values, indicating a net reduction in greenhouse gas emissions.

Measurements of infrared absorption cross-sections for n-C3F8, c-C4F8, n-C4F10, and n-C5F12 from 298 to 350 K

Perfluoro-n-propane, perfluorocyclobutane, perfluoro-n-butane, and perfluoro-n-pentane are non-ozone-depleting industrial alternatives to chlorofluorocarbons and hydrochlorofluorocarbons. However, these perfluoroalkanes have significant band strength in the atmospheric window from 800 to 1200 cm−1. Coupled with their millennial-scale atmospheric lifetimes, they can lead to significant long-term global warming. Infrared spectra are required to quantify the climate impacts. This work provides a set of high-temperature infrared absorption cross-sections in the range 298–350 K at 0.1 cm−1 resolution from 515 to 1500 cm−1 for each compound. Our cross-sections generally agree with literature measurements except for perfluoro-n-pentane. We use density functional theory to calculate the absorption cross-sections from 0 to 515 cm−1 using the B3LYP functional and several basis sets. The 6-31G(d,p) basis set provides the best results for linear perfluoroalkanes, while the def2-TZVP basis set provides the best results for cyclic perfluoroalkanes. Using experimental cross-sections, we calculate the radiative efficiency and global warming potential for each compound, utilizing the Pinnock curve from Shine and Myhre (2020) and atmospheric lifetimes from Hodnebrog et al. (2020). These quantities are found to be independent of temperature. The average 100-year global warming potential derived from all cross-sections is 9,610±1,260, 10,800±1,420, 10,100±1,330, and 9,380±1,230 for perfluoro-n-propane, perfluorocyclobutane, perfluoro-n-butane, and perfluoro-n-pentane, respectively. Combining the data in this work with our previous measurements reveals that the global warming potential for perfluoroalkanes with an increasing number of CF bonds depends on the ratio of radiative efficiency to molecular weight.

Methane emissions partially offset carbon sink function in global wetlands: An analysis based on global data.

Wetlands serve as atmospheric carbon dioxide (CO2) sinks, as well as atmospheric methane (CH4) source due to the anaerobic soil environment. Although some studies report that the CH4 emission from wetlands partially offset their net CO2 uptake, there is no global data analysis on the offset of net ecosystem exchange of CO2 (NEE) by CH4 emission in wetland ecosystems. In this study, we collected the data sets of NEE and CH4 flux which were simultaneously measured in the inland wetlands (peatland and non-peatland wetland) and coastal wetlands (seagrass beds, salt marshes and mangroves) around the world. The results showed that all types of wetlands were atmospheric CO2 sink, with the NEE values ranking as follows: mangrove (-2011.0 g CO2·m-2·a-1) < salt marsh (-1636.6 g CO2·m-2·a-1) < non-peatland wetland (-870.8 g CO2·m-2·a-1) < peatland (-510.7 g CO2·m-2·a-1) < seagrass bed (-61.6 g CO2·m-2·a-1). When CH4 flux being converted into CO2-equivalent flux (CO2-eq flux) based on the 100-year scale global warming potentials, we found that the CH4 emissions partially offset 19.4%, 14.0%, 36.1%, 64.9% and 60.1% of the net CO2 uptake in seagrass beds, salt marshes, mangroves, non-peatland wetland and peatland, respectively. Over the 20-year scale, CH4 emissions partially offset 57.3%, 41.4%, 107.0%, 192.0% and 177.3% of the net CO2 uptake, respectively. Some mangroves, peatlands, and non-peatland wetlands acted as net CO2 equivalent source. Over the 100-year scale, the net greenhouse gas balance of each wetland ecosystem was negative value, which indicated that even accounting CH4 emission, wetland ecosystem was still an atmospheric carbon sink. Our results indicated that clarifying the main regulation mechanism of CH4 emission from wetland ecosystems and proposing reasonable CH4 reduction measures are crucial to maintain the carbon sink function in wetland ecosystems, and to mitigate the trend of climate warming.

Atmospheric composition and climate impacts of a future hydrogen economy

Abstract. Hydrogen is expected to play a key role in the global energy transition to net zero emissions in many scenarios. However, fugitive emissions of hydrogen into the atmosphere during its production, storage, distribution and use could reduce the climate benefit and also have implications for air quality. Here, we explore the atmospheric composition and climate impacts of increases in atmospheric hydrogen abundance using the UK Earth System Model (UKESM1) chemistry–climate model. Increases in hydrogen result in increases in methane, tropospheric ozone and stratospheric water vapour, resulting in a positive radiative forcing. However, some of the impacts of hydrogen leakage are partially offset by potential reductions in emissions of methane, carbon monoxide, nitrogen oxides and volatile organic compounds from the consumption of fossil fuels. We derive a refined methodology for determining indirect global warming potentials (GWPs) from parameters derived from steady-state simulations, which is applicable to both shorter-lived species and those with intermediate and longer lifetimes, such as hydrogen. Using this methodology, we determine a 100-year global warming potential for hydrogen of 12 ± 6. Based on this GWP and hydrogen leakage rates of 1 % and 10 %, we find that hydrogen leakage offsets approximately 0.4 % and 4 % respectively of total equivalent CO2 emission reductions in our global hydrogen economy scenario. To maximise the benefit of hydrogen as an energy source, emissions associated with hydrogen leakage and emissions of the ozone precursor gases need to be minimised.

Measurements of perfluoro-n-hexane and perfluoro-2-methylpentane infrared absorption cross-sections from 298 to 350 K

Perfluoro-n-hexane and perfluoro-2-methylpentane are fully fluorinated alkanes used as non-ozone-depleting alternatives to chlorofluorocarbons and hydrochlorofluorocarbons. These compounds are long-lived and potent greenhouse gases due to their strong CF bonds and infrared absorption in the atmospheric window. Infrared absorption cross-sections are required to quantify the climate impact of these compounds via the radiative efficiency and global warming potential. To our knowledge, there are only two experimental measurements for perfluoro-n-hexane, and there are no experimental measurements for perfluoro-2-methylpentane in the infrared. In this work, we provide a set of absorption cross-sections in the range 515–1500 cm−1, at 0.1 cm−1 resolution from 298 to 350 K for each compound. We calculate the absorption cross-section between 0 and 515 cm−1 using density functional theory with various basis sets. The 6-31,G(d,p) basis set with the B3LYP functional is found to provide the best results. Using both measurements and calculations combined, we calculate the radiative efficiency and global warming potential for each compound. No significant temperature dependence was observed in these quantities. The average radiative efficiency derived from all cross-sections is 0.48 ± 0.06 W m−2 ppbv−1 for perfluoro-n-hexane and 0.46 ± 0.06 W m−2 ppbv−1 for perfluoro-2-methylpentane. The average 100-year global warming potential derived from all cross-sections is 9590 ± 1260 for perfluoro-n-hexane and 9220 ± 1210 for perfluoro-2-methylpentane.

Soil nitrous oxide and methane fluxes from a land-use change transition of primary forest to oil palm in an Indonesian peatland

Despite the documented increase in greenhouse gas (GHG) emissions from Southeast Asian peat swamp forest degradation and conversion to oil palm over recent decades, reliable estimates of emissions of nitrous oxide (N2O) and methane (CH4) are lacking. We measured soil fluxes of N2O and CH4 and their environmental controls along a peatland transition from primary forest (PF) to degraded drained forest (DF) to oil palm plantation (OP) over 18 months in Jambi, Sumatra, Indonesia. Sampling was conducted monthly at all sites and more intensively following two fertilization events in the OP. Mean annual emissions of N2O (kg N ha−1 yr−1) were 1.7 ± 0.2 for the PF, 2.3 ± 0.2 for the DF and for the OP 8.1 ± 0.8 without drainage canals (DC) and 7.7 ± 0.7 including DC. High N2O emissions in the OP were driven by peat decomposition, not by N fertilizer addition. Mean CH4 annual fluxes (kg C ha−1 yr−1) were 8.2 ± 1.9 for the PF, 1.9 ± 0.4 for the DF, and 1.6 ± 0.3 for the OP with DC and 1.1 ± 0.2 without. Considering their 20-year global warming potentials (GWP), the combined non-CO2 GHG emission (Mg CO2-equivalent ha−1 yr−1) was 3.3 ± 0.6 for the PF and 1.6 ± 0.2 for the DF. The emission in the OP (3.8 ± 0.3 with or without DC) was similar to the PF because reductions in CH4 emissions offset N2O increases. However, considering 100-year GWP, the combined non-CO2 GHG emission was larger in the OP (3.4 ± 0.3 with DC and 3.5 ± 0.3 without) compared to both the PF and the DF (1.5 ± 0.2 and 1.2 ± 0.1, respectively). The increase in peat N2O emissions associated with the land-use change transition from primary forest to oil palm plantation at our sites provides further evidence of the urgent need to protect tropical peat swamp forests from drainage and conversion.

Multi-scale observations of mangrove blue carbon ecosystem fluxes: The NASA Carbon Monitoring System BlueFlux field campaign

The BlueFlux field campaign, supported by NASA’s Carbon Monitoring System, will develop prototype blue carbon products to inform coastal carbon management. While blue carbon has been suggested as a nature-based climate solution (NBS) to remove carbon dioxide (CO2) from the atmosphere, these ecosystems also release additional greenhouse gases (GHGs) such as methane (CH4) and are sensitive to disturbances including hurricanes and sea-level rise. To understand blue carbon as an NBS, BlueFlux is conducting multi-scale measurements of CO2 and CH4 fluxes across coastal landscapes, combined with long-term carbon burial, in Southern Florida using chambers, flux towers, and aircraft combined with remote-sensing observations for regional upscaling. During the first deployment in April 2022, CO2 uptake and CH4 emissions across the Everglades National Park averaged −4.9 ± 4.7 μmol CO2 m−2 s−1 and 19.8 ± 41.1 nmol CH4 m−2 s−1, respectively. When scaled to the region, mangrove CH4 emissions offset the mangrove CO2 uptake by about 5% (assuming a 100 year CH4 global warming potential of 28), leading to total net uptake of 31.8 Tg CO2-eq y−1. Subsequent field campaigns will measure diurnal and seasonal changes in emissions and integrate measurements of long-term carbon burial to develop comprehensive annual and long-term GHG budgets to inform blue carbon as a climate solution.

A multi-model assessment of the Global Warming Potential of hydrogen

With increasing global interest in molecular hydrogen to replace fossil fuels, more attention is being paid to potential leakages of hydrogen into the atmosphere and its environmental consequences. Hydrogen is not directly a greenhouse gas, but its chemical reactions change the abundances of the greenhouse gases methane, ozone, and stratospheric water vapor, as well as aerosols. Here, we use a model ensemble of five global atmospheric chemistry models to estimate the 100-year time-horizon Global Warming Potential (GWP100) of hydrogen. We estimate a hydrogen GWP100 of 11.6 ± 2.8 (one standard deviation). The uncertainty range covers soil uptake, photochemical production of hydrogen, the lifetimes of hydrogen and methane, and the hydroxyl radical feedback on methane and hydrogen. The hydrogen-induced changes are robust across the different models. It will be important to keep hydrogen leakages at a minimum to accomplish the benefits of switching to a hydrogen economy.

Techno-Economic and life cycle assessment of standalone Single-Stream material recovery facilities in the United states

Material Recovery Facilities (MRFs) are crucial players in achieving a circular economy. MRFs receive complex waste streams and separate valuable recyclables from these mixtures. This study conducts techno-economic analysis (TEA) to estimate the net present value (NPV) and life cycle assessment (LCA) to estimate different environmental impacts of a commercial scale standalone, single-stream MRF to assess the economic feasibility and environmental impacts of recovering valuable recyclables from an MRF processing 120,000 tonnes per year (t/y). The TEA employs a discounted cash flow rate of return (DCFROR) analysis over a 20-year facility lifetime, along with a sensitivity analysis on the impact of different operating and economic parameters. Results show that the total fixed cost of building the MRF facility is $23 MM, and the operating cost is $45.48/tonne. The NPV of the MRF can vary from $3.57 MM to $60 MM, while 100-year global warming potential can range from 5.98 to 8.53 kg carbon dioxide equivalents (CO2-eq) per tonne of MSW. We have also found that MSW composition (arising from regional effects) significantly impacts costs, 100-year global warming potential, and other impact categories such as acidification potential, eutrophication potential, ecotoxicity, ozone depletion, photochemical oxidation, carcinogenic effects, and non-carcinogenic effects. Sensitivity and uncertainty analysis indicate that waste composition and market prices significantly impact the profitability of the MRF, and the waste composition mostly impacts global warming potential. Our analysis also indicates that facility capacity, fixed capital cost, and waste tipping fees are vital parameters that affect the economic viability of MRF operations.

Radiative efficiencies and global warming potentials of agricultural fumigants

A rounded assessment of the environmental impacts of fumigants used within the agricultural sector must consider the potential climate impacts of their release into the atmosphere. Within policy settings, the 100-year Global Warming Potential (GWP100) is the most commonly used metric. While GWP100 values are available for the widely used fumigant sulfuryl fluoride, no estimates are available for 4 alternative fumigants: ethyl formate, cyanogen, hydrogen cyanide and phosphine. Existing laboratory measurements of the infrared spectra and reaction rate coefficients of these gases are used to produce new estimates of their radiative efficiencies and atmospheric lifetimes, and the first estimates of their GWP100 and other climate emission metrics. Although uncertainties are considerable, their GWP100 values are estimated to be no more than 2% of the GWP100 value of sulfuryl fluoride. These new estimates will enable informed estimates of the climate impact of the use of these fumigants, which must account for the differing usage and release rates to achieve the same fumigant efficacy.

Slow steaming application for short-sea shipping to comply with the CII regulation

Slow steaming is an effective operational measure that reduces fuel consumption and thus emissions on board. With the Carbon Intensity Indicator (CII) regulation coming into force in 2023 from the International Maritime Organization (IMO), ships will have to reduce their CO2 emissions even more. The practice of slow steaming is an important measure to comply with this regulation. In this study, real voyage data of a general cargo ship was used. The changes in fuel consumption, CO2, CH4, N2O, and BC emissions, 20-year global warming potential (GWP20), and 100-year global warming potential (GWP100) of the ship were analysed under different scenarios (75%, 38%, 27%, and 19% main engine load), and the voyage expenses and cost-benefit ratio were calculated. At 38% main engine load, 31.5% less emissions were released than at 75% main engine load. At 27% and 19% main engine load, the emission reduction was 40.6% and 50.1%, respectively. The CO2 reduction target of 40% by 2030 and 50% by 2050 compared to 2008 levels in the IMO Initial GHG Strategy was achieved with slow steaming. As CO2 emissions decreased due to the application of slow steaming, this had a positive impact on the ship's CII rating and it remained at the A rating without further action. Nevertheless, it remains at the A rating with slow steaming, the amount of emissions varies depending on the rate of application of slow steaming in three different scenarios, and this shows that the environmental impact of each A rating is not the same. The results of the economic analysis show that operating costs increase and fuel costs decrease when the travel time is extended with slow steaming. As a result, the total voyage expenses decreased by up to 23.3%.

Orphan No More—Federal Funds Begin Flowing to State Coffers for Orphan Well Remediation

Billions of dollars in federal funding secured under the 2021 Bipartisan Infrastructure Investment and Jobs Law (BIL) has started flowing into US state coffers for the plugging and remediation of orphan oil and gas wells. Signed into law in November 2021, the BIL is a $1.2 trillion “once-in-a-generation investment” that includes $4.7 billion in funding to plug and remediate orphan wells across the nation. According to the US Department of the Interior (DOI), these legacy pollution sites are environmental hazards and jeopardize public health and safety by contaminating groundwater, emitting noxious gases and methane, littering the landscape with rusted and dangerous equipment, and harming wildlife. The US Environmental Protection Agency (EPA) estimated in a 2020 inventory of greenhouse gas emissions that, on average, each unplugged abandoned oil and gas well emits 0.13 tons of methane per year. When multiplied by an estimated 2.1 million unplugged, abandoned oil and gas wells, the EPA estimated methane emissions of 276,472 tons in 2019, equivalent to roughly 9.5 mtpa of carbon dioxide (CO2) assuming a 100-year global warming potential (GWP) of 34. This is roughly 2.6% of total US energy-related methane emissions or roughly 0.2% of total US energy-related greenhouse gas emissions in 2019, assuming a 100-year GWP for methane of 34, according to a report published in Environmental Science &amp; Technology. The Intergovernmental Panel on Climate Change defines GWP as the cumulative radiative forcing, both direct and indirect effects, over a specified time horizon resulting from the emission of a unit mass of gas related to some reference gas. While the EPA pegs the number of orphaned wells in the millions, there are variations in the count, depending on how each state or organization defines what is and is not an orphaned well. A survey, for example, by the Interstate Oil and Gas Compact Commission in 2018 put the range of orphaned and idle wells at around 560,000 to 1.1 million. According to the Railroad Commission of Texas (RRC), the regulatory body that oversees Texas oil and natural gas development, an orphan well is an inactive and unplugged well that has not produced oil or natural gas for a minimum of 12 months. But the Colorado Oil &amp; Gas Conservation Commission defines an orphan as a well which has no owner or operator that can be found, or where the owner or operator is unwilling or unable to plug and abandon such a well. This JPT article described the hunt for the potentially hundreds of thousands of unknown, undocumented orphans across the country. In October 2021, the Environmental Defense Fund (EDF) released a map showing the location of more than 81,000 documented orphan wells in 28 states that are eligible for funding under the BIL. In the spring of 2022, thanks in part to states documenting more than 40,000 additional orphan wells, EDF released an updated map showing more than 120,000 documented orphan wells in 30 states (Fig. 1).

Design of a High-Rate Wastewater Treatment Process for Energy and Water Recovery at Biorefineries

Industrial wastewaters rich in organic carbon have potential for value generation, but conventional, low-rate, anaerobic–aerobic wastewater treatment (WWT) processes often incur significant capital expenses and energy consumption. In this study, we leveraged experimental data for biorefinery-derived wastewaters to characterize the implications of transitioning from a conventional, low-rate process to a high-rate, multistage anaerobic process. We designed and simulated these WWT processes across seven first- and second-generation (1G/2G) biorefineries and evaluated the implications for biorefinery sustainability through techno-economic analysis (TEA) and life cycle assessment (LCA). Compared to the conventional design, the new process can substantially reduce capital costs and electricity usage. These improvements were particularly evident for 2G biorefineries, translating to 5%–13% lower minimum product selling prices (MPSPs) and 7%–135% lower 100-year global warming potentials (GWPs; the 135% reduction is due to the transition of one biorefinery from net emission [0.87 kg of CO2e·gal–1] to net sequestration [−0.31 kg of CO2e·gal–1]). Biorefineries could further reduce the MPSP through the renewable identification number (RIN) credits by upgrading and selling the biogas as renewable natural gas, but at the expense of increasing GWP. When normalized, the COD management cost ranged from $–56 to $465 per tonne of COD, indicating that wastewater could be a net source of revenue for some biorefineries.

Measurements of perfluoro-n-heptane and perfluoro-n-octane absorption cross-sections from 300 to 350 K

Perfluoroalkanes are fully fluorinated greenhouse gases. These compounds are chemically inert due to their C–F bonds and therefore have atmospheric lifetimes of thousands of years. Although regulated under the Kyoto Protocol, atmospheric concentrations of perfluoroalkanes have continued to increase since 1997. To quantify the climate impact of perfluoro-n-heptane and perfluoro-n-octane, spectral data are required to calculate climate metrics such as the radiative efficiency and global warming potential. Experimental measurements are scarce for these compounds and are only available at 296 and 297 K. In this work, a set of absorption cross-sections is provided in the range 515–1500 cm−1 at 0.1 cm−1 resolution for nine temperatures between 300 and 350 K. There is general agreement between literature values and the absorption cross-sections and climate metrics measured in this work. These quantities do not show significant temperature dependence. The temperature averaged radiative efficiency is 0.50 ± 0.06 and 0.54 ± 0.07 Wm−2ppbv−1 for n–C7F16 and n–C8F18, respectively. The temperature averaged 100-year global warming potential is 8738 ± 1149 for n–C7F16 and 8392 ± 1103 for n–C8F18.

Greenhouse Gas and Air Pollutant Emissions from Composting.

Composting can divert organic waste from landfills, reduce landfill methane emissions, and recycle nutrients back to soils. However, the composting process is also a source of greenhouse gas and air pollutant emissions. Researchers, regulators, and policy decision-makers all rely on emissions estimates to develop local emissions inventories and weigh competing waste diversion options, yet reported emission factors are difficult to interpret and highly variable. This review explores the impacts of waste characteristics, pretreatment processes, and composting conditions on CO2, CH4, N2O, NH3, and VOC emissions by critically reviewing and analyzing 388 emission factors from 46 studies. The values reported to date suggest that CH4 is the single largest contributor to 100-year global warming potential (GWP100) for yard waste composting, comprising approximately 80% of the total GWP100. For nitrogen-rich wastes including manure, mixed municipal organic waste, and wastewater treatment sludge, N2O is the largest contributor to GWP100, accounting for half to as much as 90% of the total GWP100. If waste is anaerobically digested prior to composting, N2O, NH3, and VOC emissions tend to decrease relative to composting the untreated waste. Effective pile management and aeration are key to minimizing CH4 emissions. However, forced aeration can increase NH3 emissions in some cases.

Climate benefit of a future hydrogen economy

Hydrogen is recognised as an important future energy vector for applications in many sectors. Hydrogen is an indirect climate gas which induces perturbations of methane, ozone, and stratospheric water vapour, three potent greenhouse gases. Using data from a state-of-the-art global numerical model, here we calculate the hydrogen climate metrics as a function of the considered time-horizon and derive a 100-year Global Warming Potential of 12.8 ± 5.2 and a 20-year Global Warming Potential of 40.1 ± 24.1. The considered scenarios for a future hydrogen transition show that a green hydrogen economy is beneficial in terms of mitigated carbon dioxide emissions for all policy-relevant time-horizons and leakage rates. In contrast, the carbon dioxide and methane emissions associated with blue hydrogen reduce the benefit of a hydrogen economy and lead to a climate penalty at high leakage rate or blue hydrogen share. The leakage rate and the hydrogen production pathways are key leverages to reach a clear climate benefit from a large-scale transition to a hydrogen economy.

Life Cycle GHG Perspective on U.S. Natural Gas Delivery Pathways.

Recent emission measurement campaigns have improved our understanding of the total greenhouse gas (GHG) emissions across the natural gas supply chain, the individual components that contribute to these emissions, and how these emissions vary geographically. However, our current understanding of natural gas supply chain emissions does not account for the linkages between specific production basins and consumers. This work provides a detailed life cycle perspective on how GHG emissions vary according to where natural gas is produced and where it is delivered. This is accomplished by disaggregating transmission and distribution infrastructure into six regions, balancing natural gas supply and demand locations to infer the likely pathways between production and delivery, and incorporating new data on distribution meters. The average transmission distance for U.S. natural gas is 815 km but ranges from 45 to 3000 km across estimated production-to-delivery pairings. In terms of 100-year global warming potentials, the delivery of one megajoule (MJ) of natural gas to the Pacific region has the highest mean life cycle GHG emissions (13.0 g CO2e/MJ) and the delivery of natural gas to the Northeast U.S. has the lowest mean life cycle GHG emissions (8.1 g CO2e/MJ). The cradle-to-delivery scenarios developed in this work show that a national average does not adequately represent the upstream GHG emission intensity for natural gas from a specific basin or delivered to a specific consumer.