Powerful Greenhouse Gas Research Articles

Distinctive Patterns and Controls of Nitrous Oxide Concentrations and Fluxes from Urban Inland Waters.

Inland waters are significant sources of nitrous oxide (N2O), a powerful greenhouse gas. However, considerable uncertainty exists in the estimates of N2O efflux from global inland waters due to a lack of direct measurements in urban inland waters, which are generally characterized by high carbon and nitrogen concentrations and low carbon-to-nitrogen ratios. Herein, we present direct measurements of N2O concentrations and fluxes in lakes and rivers of Beijing, China, during 2018-2020. N2O concentrations and fluxes in the waters of Beijing exceeded previous estimates of global rivers due to the high carbon and nutrient concentrations and high aquatic productivity. In contrast, the N2O emission factor (N2O-N/DIN, median 0.0005) was lower than global medians and the N2O yield (ΔN2O/(ΔN2O + ΔN2), average 1.6%) was higher than those typically observed in rivers and streams. The positive relationship between N2O emissions and denitrifying bacteria as well as the Michaelis-Menten relationship between N2O emissions and NO3--N concentrations suggested that bacteria control the net production of N2O in waters of Beijing with N saturation, leading to a low N2O emission factor. However, low carbon-to-nitrogen ratios are beneficial for N2O accumulation during denitrification, resulting in high N2O yields. This study demonstrates the significant N2O emissions and their distinctive patterns and controls in urban inland waters and suggests that N2O emission estimates based on nitrogen loads and simple emission factor values are not appropriate for urban inland water systems.

Efficient Nitrification and Low-Level N2O Emission in a Weakly Acidic Bioreactor at Low Dissolved-Oxygen Levels Are Due to Comammox.

Nitrification is an essential process for nutrient removal from wastewater and an important emission source of nitrous oxide (N2O), which is a powerful greenhouse gas and a dominant ozone-depleting substance. In this study, nitrification and N2O emissions were tested in two weakly acidic (pH 6.3 to 6.8) reactors: one with dissolved oxygen (DO) at over 2.0 mg/liter and the other with DO at approximately 0.5 mg/liter. Efficient nitrification was achieved in both reactors. Compared to that in the high-DO reactor, N2O emission in the low-DO reactor decreased slightly, by 20%, and had insignificant correlation with the fluctuations of DO (P = 0.935) and nitrite (P = 0.713), indicating that N2O might not be produced mainly via nitrifier denitrification. Based on quantitative PCR (qPCR), quantitative fluorescent in situ hybridization (qFISH), and functional gene amplicon and metagenome sequencing, it was found that complete ammonia oxidizers (comammox), i.e., Nitrospira organisms, significantly outnumbered canonical ammonia-oxidizing bacteria (AOB) in both weakly acidic reactors, especially in the low-DO reactor with the comammox/AOB amoA gene ratio increasing from 6.6 to 17.1. Therefore, it was speculated that the enriched comammox was the primary cause for the slightly decreased N2O emission under long-term low DO in the weakly acidic reactor. This study demonstrated that the comammox Nitrospira can survive well under the weakly acidic and low-DO conditions, implying that achieving efficient nitrification with low N2O emission as well as low energy and alkalinity consumption is feasible for wastewater treatment.IMPORTANCE Nitrification in wastewater treatment is an important process for eutrophication control and an emission source for the greenhouse gas N2O. The nitrifying process is usually operated at a slightly alkaline pH and high DO (>2 mg/liter) to ensure efficient nitrification. However, it consumes a large amount of energy and chemicals, especially for wastewater without sufficient alkalinity. This paper demonstrates that comammox can adapt well to the weakly acidic and low-DO bioreactors, with a result of efficient nitrification and low N2O emission. These findings indicate that comammox organisms are significant for sustainable wastewater treatment, which provides an opportunity to achieve efficient nitrification with low N2O production as well as low energy and chemical consumption simultaneously.

Spatial Distribution of Dissolved Methane Over Extreme Oceanographic Gradients in the Subtropical Eastern South Pacific (17° to 37°S)

AbstractMethane (CH4) is one of the most powerful greenhouse gases with the capacity to influence the Earth's radiative budget as well as contribute to atmospheric chemistry. Natural oceanic production makes up to ∼4% of the overall global CH4 emissions, however, there is uncertainty around the accuracy of this value due to a lack of accurate measurements. Such is the case in the Subtropical Eastern South Pacific Ocean (SESP), a region with pronounced chlorophyll‐a and oxygen gradients, which in turn affect the microbial CH4 cycling. This study was conducted during spring‐summer (2014–2016) in the SESP. The region (∼17°–37°S/71°–110°W) is separated into (i) eutrophic, (ii) mesotrophic, and (iii) oligotrophic areas, according to oceanographic and biogeochemical criteria. The SESP presents high CH4 zonal variability with levels ranging from 0.63 to 33.4 nmol L−1, corresponding to 29% and 1,423% saturation, respectively. High CH4 concentrations (>1,000% saturation) are observed in the narrow eutrophic area subjected to coastal upwelling. These conditions clearly differ to those observed in the extended oligotrophic subtropical gyre (∼100% saturation). Furthermore, CH4 also tends to accumulate in the mesotrophic area (with upto 1,423% saturation), where oceanographic conditions as stratification, mesoscale eddies and island mass effect could trigger the presence of a microbial biomass that may be able to induce CH4 regeneration. The CH4 efflux is estimated to be between 0.13 and 19.1 µmol m−2 d−1 (mean ± SD = 4.72 ± 4.67) and the SESP has an emission rate of ∼87.9 Gg CH4 yr−1.

Fifteen Years of HFC‐134a Satellite Observations: Comparisons With SLIMCAT Calculations

AbstractThe phase out of anthropogenic ozone‐depleting substances such as chlorofluorocarbons under the terms of the Montreal Protocol led to the development and worldwide use of hydrofluorocarbons (HFCs) in refrigeration, air conditioning, and as blowing agents and propellants. Consequently, over recent years, the atmospheric abundances of HFCs have dramatically increased. HFCs are powerful greenhouse gases and are now controlled under the terms of the 2016 Kigali Amendment to the Montreal Protocol. HFC‐134a is currently the most abundant HFC in the atmosphere, breaking the 100 ppt barrier in 2018, and can be measured in the Earth's atmosphere by the satellite remote‐sensing instrument ACE‐FTS (Atmospheric Chemistry Experiment‐Fourier Transform Spectrometer), which has been measuring since 2004. This work uses the ACE‐FTS v4.0 data product to investigate global distributions and trends of HFC‐134a. These measurements are compared with a simulation of SLIMCAT, a state‐of‐the‐art three‐dimensional chemical transport model, which is constrained by global surface HFC‐134a measurements. The agreement between observation and model is good, although in the tropical troposphere ACE‐FTS measurements are biased low by up to 10–15 ppt. The overall ACE‐FTS global trend of HFC‐134a for the altitude range 5.5–24.5 km and 2004–2018 time period is approximately linear with a value of 4.49 ± 0.02 ppt/year, slightly lower than the corresponding SLIMCAT trend of 4.66 ppt/year. Using a simple box model, we also estimate the annual global emissions and burdens of HFC‐134a from the model data, indicating that emissions of HFC‐134a have increased almost linearly, reaching 236 Gg by 2018.

Attribution of production-stage methane emissions to assess spatial variability in the climate intensity of US natural gas consumption

Although natural gas is often viewed as a commodity fuel with limited variability due to standardization for pipeline transportation, life cycle impacts of natural gas vary substantially. Greenhouse gas (GHG) intensity is one of the most policy-relevant environmental characteristics of natural gas, particularly as decarbonization efforts proceed. Given that natural gas is mostly methane, a powerful GHG, methane emissions from the natural gas system contribute substantially to the GHG intensity of natural gas. Research has established that methane emissions from natural gas systems are climatically relevant and higher than long understood, in part due to variation in production-stage emissions by basin. This work combines recent estimates of basin-level US production-stage methane emissions, data on US natural gas production, consumption, and trade, and a spatial evaluation of pipeline connections between production basins and consumer states to generate first-order estimates of the production-stage methane emissions intensity of natural gas consumed in the United States. Although natural gas is a commodity product, the environmental footprint of a given unit of natural gas varies based on its origin and infrastructural needs. We find that production-stage methane emissions intensity of delivered natural gas by state varies from 0.9% to 3.6% (mass methane emitted from natural gas production sites per mass methane withdrawn). These production-stage emissions add 16%–65% (global warming potential (GWP)-100; 38%–157%, GWP-20) to combustion carbon dioxide emissions. Other sources of life cycle methane emissions downstream of production can be similar in magnitude. Natural gas consumed in Arizona, Kansas, and New Mexico has the highest estimated production-stage methane emissions intensity, largely due to reliance on high-emission basins. Limitations include emissions-related data gaps and sensitivity to allocation approaches, but results demonstrate decision-relevant variability in the GHG impact of natural gas.

Global importance of methane emissions from drainage ditches and canals

Globally, there are millions of kilometres of drainage ditches which have the potential to emit the powerful greenhouse gas methane (CH4), but these emissions are not reported in budgets of inland waters or drained lands. Here, we synthesise data to show that ditches spanning a global latitudinal gradient and across different land uses emit large quantities of CH4 to the atmosphere. Area-specific emissions are comparable to those from lakes, streams, reservoirs, and wetlands. While it is generally assumed that drainage negates terrestrial CH4 emissions, we find that CH4 emissions from ditches can, on average, offset ∼10% of this reduction. Using global areas of drained land we show that ditches contribute 3.5 Tg CH4 yr−1 (0.6–10.5 Tg CH4 yr−1); equivalent to 0.2%–3% of global anthropogenic CH4 emissions. A positive relationship between CH4 emissions and temperature was found, and emissions were highest from eutrophic ditches. We advocate the inclusion of ditch emissions in national GHG inventories, as neglecting them can lead to incorrect conclusions concerning the impact of drainage-based land management on CH4 budgets.

Exploring simultaneous nitrous oxide and methane sink in wetland sediments under anoxic conditions

Methane (CH4) and nitrous oxide (N2O) are the most powerful greenhouse gases globally; recent emissions exceed previous estimates. The potential link between N2O reduction and CH4 oxidation in anoxic wetland sediments would be a sink for both gases, which has attracted broad attention. To explore the simultaneous N2O and CH4 biotransformation, wetland sediments were used to inoculate an enrichment reactor, continuously fed with CH4 and N2O for 500 days. After enrichment, the CH4 oxidation rate reached 2.8 μmol·g-1dw·d-1, which was 800-fold higher than the rate of the wetland sediments used as inoculum. Moreover, stable isotopic tracing proved CH4 oxidation was driven by N2O consumption under anoxic conditions. Genomic sequencing showed that the microbial community was dominated by methanotrophs. Species of Methylocaldum genus, belonging to γ-Proteobacteria class, were significantly enriched, and became the predominant methanotrophs. Quantitative analysis indicated methane monooxygenase and nitrous oxide reductase increased by 38- and 8-fold compared to the inoculum. As to the potential mechanisms, we propose that N2O-driven CH4 oxidation was mediated by aerobic methanotrophs solely or along with denitrifying bacteria under hypoxia. Electrons and energy are generated and transferred in the oxidative phosphorylation pathway. Our findings expand the range of electron acceptors associated with CH4 oxidation as well as elucidate the significant role of methanotrophs relative to both carbon and nitrogen cycles.

Bacterial diversity changes in agricultural soils influenced by poultry litter fertilization.

Poultry litter is widely applied as agricultural fertilizer and can affect the soil microbiome through nutrient overload and antibiotic contamination. In this study, we assessed changes in soil bacterial diversity using high-throughput sequencing approaches. Four samples in triplicate were studied: soils with short- and long-term fertilization by poultry litter (S1 = 10 months and S2 = 30 years, respectively), a soil inside a poultry shed (S3), and a forest soil used as control (S0). Samples S0, S1, and S2 revealed a relatively high richness, with confirmed operational taxonomic units (OTUs) in the three replicates of each sample ranging from 1243 to 1279, while richness in S3 was about three times lower (466). The most abundant phyla were Proteobacteria, Bacteroidetes, and Actinobacteria. Acidobacteria, Planctomycetes, and Verrucomicrobia were also abundant but highly diminished in S3, while Firmicutes was less abundant in S0. Changes in bacterial communities were very evident at the genera level. The genera Gaiella, Rhodoplanes, Solirubacter, and Sphingomonas were predominant in S0 but strongly decreased in the other soils. Pedobacter and Devosia were the most abundant in S1 and were diminished in S2, while Herbiconiux, Brevundimonas, Proteiniphilum, and Petrimonas were abundant in S2. The most abundant genera in S3 were Deinococcus, Truepera, Rhodanobacter, and Castellaniella. A predictive analysis of the metabolic functions with Tax4Fun2 software suggested the potential presence of enzymes associated with antibiotic resistance as well as with denitrification pathways, indicating that the S3 soil is a potential source of nitrous oxide, a powerful greenhouse gas.

Enrichment of novel Verrucomicrobia, Bacteroidetes, and Krumholzibacteria in an oxygen-limited methane- and iron-fed bioreactor inoculated with Bothnian Sea sediments.

Microbial methane oxidation is a major biofilter preventing larger emissions of this powerful greenhouse gas from marine coastal areas into the atmosphere. In these zones, various electron acceptors such as sulfate, metal oxides, nitrate, or oxygen can be used. However, the key microbial players and mechanisms of methane oxidation are poorly understood. In this study, we inoculated a bioreactor with methane‐ and iron‐rich sediments from the Bothnian Sea to investigate microbial methane and iron cycling under low oxygen concentrations. Using metagenomics, we investigated shifts in microbial community composition after approximately 2.5 years of bioreactor operation. Marker genes for methane and iron cycling, as well as respiratory and fermentative metabolism, were identified and used to infer putative microbial metabolism. Metagenome‐assembled genomes representing novel Verrucomicrobia, Bacteroidetes, and Krumholzibacteria were recovered and revealed a potential for methane oxidation, organic matter degradation, and iron cycling, respectively. This work brings new hypotheses on the identity and metabolic versatility of microorganisms that may be members of such functional guilds in coastal marine sediments and highlights that microorganisms potentially composing the methane biofilter in these sediments may be more diverse than previously appreciated.

Causes and climatic influence of centennial-scale denitrification variability in the southeastern Arabian Sea since the last glacial period

AbstractDenitrification occurring in the oxygen minimum zone of the Arabian Sea produces nitrous oxide, a powerful greenhouse gas. Therefore, it is important to understand the mechanisms controlling denitrification's intensity and evaluate its influence on the global climate at various timescales. We studied multiple geochemical and isotopic proxies in a sediment core from the southeastern Arabian Sea (SEAS) at a high (centennial-scale) resolution. We find that since the last glacial period, both the ventilation and the productivity caused by the South Asian summer monsoon played a major role in controlling the denitrification variability in SEAS. During the Last Glacial Maximum (LGM) and since the Holocene, denitrification increased in SEAS despite reduced monsoon-induced productivity. During the LGM, weakened thermohaline circulation resulted in reduced ventilation of the intermediate waters of SEAS, causing increased denitrification. During the Holocene, the increase in denitrification is caused by an enhanced inflow of oxygen-depleted Red Sea and Persian Gulf waters into the intermediate depth of SEAS owing to a rising sea level that prohibited ventilation by the Antarctic Intermediate Water. We further find millennial-scale synchronicity between denitrification in SEAS, global monsoons, and the North Atlantic climate, implying systematic linkages via greenhouse gases abundance.

The importance of nutrients for microbial priming in a bog rhizosphere

Wetlands host anaerobic microbes which convert organic carbon into methane (CH4), a powerful greenhouse gas. Wetland plants can influence which carbon compounds are available for microbial processing by exuding freshly fixed carbon from their roots. Exudation of carbon from plant roots can trigger microbial priming: the process of new carbon stimulating the microbial community into processing more soil carbon than they otherwise would have. This study utilized high resolution Fourier transform ion cyclotron mass spectrometry (FT-ICR-MS) analysis to probe the composition of soil organic compounds from the rhizosphere of Carex aquatillis, a common wetland sedge, which is known to have stimulated microbial priming within peat soil. The goal was to identify what types of molecules were created or lost during microbial priming in the wetland rhizosphere and thus advance mechanistic understanding of the process. FT-ICR-MS analysis demonstrated that more microbial transformations of carbon occurred among water-soluble compounds than among hydrophobic compounds, but that some hydrophobic compounds were processed. Crucially for understanding microbial priming, the root exudates triggered increased processing of high molecular weight molecules regardless of nutrient content but processed low molecular weight compounds only if they contained nitrogen or sulfur, essential nutrients for plant growth. The importance of sulfur in determining molecular utilization is noteworthy because priming literature typically focuses on nitrogen-mining. The fact that some molecules were processed and others were not is evidence for a selective priming effect in which some carbon compounds with specific properties are used at an increased rate, while others are left unaltered.

Role of Cadmium Addition in Promoting the Direct N2O Decomposition of Co3O4 Spinel

Background: Increased environmental protection concerns urge more effort to develop new catalysts for the abetment of greenhouse gases. N2O is known as a powerful greenhouse gas. The literature review revealed that various catalysts have been developed for the direct decomposition of N2O. Special attention was given to the cobalt-based spinel oxides. However, there is a lack of information about the performance of the cadmium promoted spinels for N2O abetment. Objective: This paper addresses the nitrous oxide direct decomposition over a novel series of Cd- Co catalysts. Method: These catalysts, with Cd/(Cd + Co) ratios 0.00-0.333, were prepared with the aid of the co-precipitation route, which is followed by calcination at 500 °C. Characterization of these catalysts was performed employing TGA-DTA, XRD, FTIR, N2 adsorption/desorption, and atomic absorption spectrophotometry. Results: Phase analysis revealed the absence of a solid-state interaction between CdO and Co3O4. However, it was found that increasing the Cd/(Cd + Co) ratio is associated with continuous enhancement of the N2O decomposition activity. The activity was correlated with the presence of catalyst’s redox couples. Moreover, the role of the Cd presence in improving the activity was discussed. Finally, the activity performance change accompanying the calcination temperature raise was also investigated. Conclusions: Presence of cadmium has a positive effect on the N2O decomposition performance of Co3O4. Activity increased continuously with Cd/(Cd + Co) ratio increase over the examined range 0.083–0.333 structural, textural, and electronic roles of cadmium were proposed.

Emisní povolenky - Vykazování a budoucnost

Emission of the greenhouse gases has a significant impact on the environment of the whole planet. Innumerable international plenary sessions have agreed only on partial solutions. The signatory countries came up with the instrument which should improve the air quality- the emission allowances. The politicians and environmentalists involved in the Kyoto Protocol and subsequent Paris Agreement have negotiated emission reductions. Achievement of this goal is established for years 2005 - 2030. 43 % of current greenhouse gas emissions should be reduced. Each allowance represents the right to emit one tonne of carbon dioxide (CO2) or the equivalent amount of two more powerful greenhouse gases, nitrous oxide (N2O) and perfluorocarbons (PFCs). Allowances are distributed among individual countries, which allocate them free of charge to plants, factories and other fixed installations. These emission allowances can be the subject of trade between these operators. All these facts result in questions related to the accounting methods. How many allowances are needed? Should they be recognised as an asset? Is their price regulation necessary? Can emission allowances reduce greenhouse gases or are government subsidies and compensations - alternatively carbon taxes - more suitable for this purpose? Is the business environment more or less destroyed? The goal of this article is to contribute by critical discussion to easier, fair and true recognition of emission allowances.

Quantifying methane emissions from Queensland's coal seam gas producing Surat Basin using inventory data and a regional Bayesian inversion

Abstract. Methane (CH4) is a potent greenhouse gas and a key precursor of tropospheric ozone, itself a powerful greenhouse gas and air pollutant. Methane emissions across Queensland's Surat Basin, Australia, result from a mix of activities, including the production and processing of coal seam gas (CSG). We measured methane concentrations over 1.5 years from two monitoring stations established 80 km apart on either side of the main CSG belt located within a study area of 350 km × 350 km. Using an inverse modelling approach coupled with a bottom-up inventory, we quantify methane emissions from this area. The inventory suggests that the total emission is 173.2 × 106 kg CH4 yr−1, with grazing cattle contributing about half of that, cattle feedlots ∼ 25 %, and CSG processing ∼ 8 %. Using the inventory emissions in a forward regional transport model indicates that the above sources are significant contributors to methane at both monitors. However, the model underestimates approximately the highest 15 % of the observed methane concentrations, suggesting underestimated or missing emissions. An efficient regional Bayesian inverse model is developed, incorporating an hourly source–receptor relationship based on a backward-in-time configuration of the forward regional transport model, a posterior sampling scheme, and the hourly methane observations and a derived methane background. The inferred emissions obtained from one of the inverse model setups that uses a Gaussian prior whose averages are identical to the gridded bottom-up inventory emissions across the domain with an uncertainty of 3 % of the averages best describes the observed methane. Having only two stations is not adequate at sampling distant source areas of the study domain, and this necessitates a small prior uncertainty. This inverse setup yields a total emission of (165.8 ± 8.5) × 106 kg CH4 yr−1, slightly smaller than the inventory total. However, in a subdomain covering the CSG development areas, the inferred emissions are (63.6 ± 4.7) × 106 kg CH4 yr−1, 33 % larger than those from the inventory. We also infer seasonal variation of methane emissions and examine its correlation with climatological rainfall in the area.

Improved gap filling approach and uncertainty estimation for eddy covariance N2O fluxes

Agricultural nitrous oxide (N2O) emissions comprise a majority of the global source of this powerful greenhouse gas. Mitigation approaches for reducing emissions are difficult to evaluate at appropriate field scales because of the substantial effort and expense associated with relatively new technology allowing eddy covariance measurements of N2O fluxes (FN2O). Here we present a new approach for gap filling eddy covariance FN2O and estimating annual uncertainties for a temperate grazed grassland. We tested the potential of using one flux tower to evaluate emissions mitigation options in one paddock relative to an adjacent, unchanged paddock by partitioning data by source footprint contribution. Because of the complexity of spatiotemporal controls on FN2O, we generated a large set of environmental variables and features as input for machine learning algorithms. Inputs were transformed using partial least squares (PLS) decomposition, isolating features with the greatest influence on FN2O. PLS scores were fed to both a neural network (NN) and a locally-weighted k-nearest neighbours (kNN) regression. While the NN and kNN preformed similarly well, kNN regression accounted for the largest proportion of variance (52-72%) and resulted in the lowest bias for each of the three source footprint areas (full footprint and two separated adjacent paddocks, P53 and P54). Annual uncertainty estimates included random measurement uncertainty, accuracy and precision of the gap filling approach, and uncertainty associated with choice of threshold for atmospheric turbulence filtering and footprint contributions. Total N2O emissions for the full footprint, P53, and P54 were 7.4 ±0.35, 7.7 ±0.80, and 6.4 ±0.63 kg N2O-N ha−1, respectively in Year 1, and 6.9 ±0.33, 7.3 ±0.63, and 6.7 ±0.63 kg N2O-N ha−1, respectively in Year 2. These 95% confidence intervals on the annual FN2O suggest that we could detect differences of 10-15% between paddocks at this site when testing mitigation options.

1-Butyl-3-Methylimidazolium Tetrafluoroborate Ionic Liquid As an Electrolyte for Electrochemical Reduction of Nitrous Oxide.

Nitrous oxide (N2O), of which global warming potential is 310 times of CO2, is a powerful greenhouse gas [1]. The concentration of N2O has increased steadily from various agricultural and industrial activities such as cultivating crops in low-pH soil and manufacturing semiconductor devices [2,3]. Therefore, the importance of studying N2O reduction is emphasized. Thermal decomposition methods focusing on thermal catalyst have been reported, but there are limits such as process temperature and low efficiency [4,5]. Electrochemical reduction of N2O can be an attractive method since it is conducted at low temperatures and has low energy consumption. However, in aqueous solutions, the electrochemical reduction of N2O inevitably accompanies hydrogen evolution reaction (HER), which is the main side reaction. There were many trials to reduce HER through metal and metal oxide catalysts, but they also had limits in terms of efficiency and high cost of noble metal materials [6-9]. Ionic liquids are promising electrolytes in gas reduction field replacing water because they can avoid hydrogen evolution and enhance the solubility of gaseous reactants. Some imidazolium-based ionic liquids were adopted to electrochemical reduction of CO2 because of their favorable properties such as wide electrochemical potential window and high CO2 dissolution capacity [10,11]. Cations of ionic liquids are known to accept oxygen from CO2, and then return to initial state at counter electrode emitting oxygen [12]. According to the same principle, ionic liquids may also be suitable for the electrochemical reduction of N2O.In this study, an ionic liquid/organic solvent mixture was adopted as an electrolyte for the electrochemical reduction of N2O. The ionic liquid and organic solvent used for electrolyte were 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF4]) and propylene carbonate (PC), respectively. The use of [BMIM][BF4] in place of aqueous solutions could improve the solubility of N2O and also avoid the hydrogen evolution reaction, which is the main side reaction in an aqueous solution.Herein we observed the difference of LSV curves in aqueous solution and [BMIM][BF4]. Hydrogen evolution reaction was excluded, but the low current density was obtained in [BMIM][BF4]. The low electrical conductivity and high viscosity of [BMIM][BF4], the main disadvantages in the context of electrochemical reactions, were compensated on introducing PC. We measured the viscosity and electrical conductivity in various [BMIM][BF4]/PC composition, and the composition of the [BMIM][BF4]/PC was optimized considering both the electrical conductivity and N2O stability in the solution. The current and faradaic efficiency could be evaluated during chronoamperometry in aqueous solution and [BMIM][BF4]/PC. For the optimized [BMIM][BF4]/PC, high current efficiency and faradaic efficiency (>90%) were achieved for N2O reduction to N2.Figure captionsFigure 1. LSV curves for Cu electrode in (a) 0.3 M K2SO4 aqueous solution and (b) [BMIM][BF4]. The scan rate was 50 mV s-1.Figure 2. (a) Viscosity (black line) and conductivity (blue line) changes for [BMIM][BF4]/PC according to [BMIM][BF4] content (b) Current efficiency–time curves recorded at –1.3 V vs. SCE in 0.3 M K2SO4 aqueous solution (blue line) and at –2.27 V vs. Fc/Fc+ in 75 vol% [BMIM][BF4] (red line).

Can N2 O emissions offset the benefits from soil organic carbon storage?

To respect the Paris agreement targeting a limitation of global warming below 2°C by 2100, and possibly below 1.5°C, drastic reductions of greenhouse gas emissions are mandatory but not sufficient. Large-scale deployment of other climate mitigation strategies is also necessary. Among these, increasing soil organic carbon (SOC) stocks is an important lever because carbon in soils can be stored for long periods and land management options to achieve this already exist and have been widely tested. However, agricultural soils are also an important source of nitrous oxide (N2 O), a powerful greenhouse gas, and increasing SOC may influence N2 O emissions, likely causing an increase in many cases, thus tending to offset the climate change benefit from increased SOC storage. Here we review the main agricultural management options for increasing SOC stocks. We evaluate the amount of SOC that can be stored as well as resulting changes in N2 O emissions to better estimate the climate benefits of these management options. Based on quantitative data obtained from published meta-analyses and from our current level of understanding, we conclude that the climate mitigation induced by increased SOC storage is generally overestimated if associated N2 O emissions are not considered but, with the exception of reduced tillage, is never fully offset. Some options (e.g. biochar or non-pyrogenic C amendment application) may even decrease N2 O emissions.

Halocarbons: What Are They and Why Are They Important?

CFCs and other halocarbons have long been known for causing an ozone hole over the Antarctic, but many of them are also powerful greenhouse gases.

Comparison of GC-μECD and OA-ICOS Methods for High-Precision Measurements of Atmospheric Nitrous Oxide (N2O) at a Korean GAW Station

Nitrous oxide (N2O) is a powerful greenhouse gas and is the largest remaining anthropogenic source of stratospheric ozone-depleting substances as halocarbons return towards preindustrial levels. To verify the N2O emission inventory using inverse analysis, precise and reliable measurements are necessary. In this study, we compared the conventional gas chromatography with the microelectron capture detector method (GC-μECD, Agilent 7890A) with advanced off-axis integrated cavity output spectroscopy (OA-ICOS, Los Gatos, EP-30) for atmospheric N2O measurements at the Jeju Gosan Suwolbong Station (JGS, 126.16° E, 33.30° N, 71.47 m a.s.l) in South Korea. The measurement uncertainties from linearity, repeatability, and reproducibility derived from the two instruments were compared. The values derived from GC-μECD were 2.4 to 8.7 times greater than that of OA-ICOS in all factors at the station. Since these factors affect the measurement quality, the calibration strategy should be well-established to reduce the measurement uncertainty. These uncertainties resulted in biases from the measurement of atmospheric N2O. The parallel inter-comparison experiment was implemented at JGS for 22 months, and the difference in atmospheric N2O was 0.17 ± 0.9 ppb between the two instruments. The significant differences were observed in the nonlinear range of the GC-μECD. Finally, these differences resulted in the over/underestimation of N2O characteristics locally and seasonally. Overall, OA-ICOS has a more robust performance with a lower measurement uncertainty than GC-μECD. Based on this study, we also suggest a calibration strategy for both instruments to achieve precise N2O measurements.

Updated Global Warming Potentials and Radiative Efficiencies of Halocarbons and Other Weak Atmospheric Absorbers.

Human activity has led to increased atmospheric concentrations of many gases, including halocarbons, and may lead to emissions of many more gases. Many of these gases are, on a per molecule basis, powerful greenhouse gases, although at present‐day concentrations their climate effect is in the so‐called weak limit (i.e., their effect scales linearly with concentration). We published a comprehensive review of the radiative efficiencies (RE) and global warming potentials (GWP) for around 200 such compounds in 2013 (Hodnebrog et al., 2013, https://doi.org/10.1002/rog.20013). Here we present updated RE and GWP values for compounds where experimental infrared absorption spectra are available. Updated numbers are based on a revised “Pinnock curve”, which gives RE as a function of wave number, and now also accounts for stratospheric temperature adjustment (Shine & Myhre, 2020, https://doi.org/10.1029/2019MS001951). Further updates include the implementation of around 500 absorption spectra additional to those in the 2013 review and new atmospheric lifetimes from the literature (mainly from WMO (2019)). In total, values for 60 of the compounds previously assessed are based on additional absorption spectra, and 42 compounds have REs which differ by >10% from our previous assessment. New RE calculations are presented for more than 400 compounds in addition to the previously assessed compounds, and GWP calculations are presented for a total of around 250 compounds. Present‐day radiative forcing due to halocarbons and other weak absorbers is 0.38 [0.33–0.43] W m−2, compared to 0.36 [0.32–0.40] W m−2 in IPCC AR5 (Myhre et al., 2013, https://doi.org/10.1017/CBO9781107415324.018), which is about 18% of the current CO2 forcing.