•A five-dimensional potential surface for N2 -N 2 O involving the Q3 asymmetric-stretch normal-mode coordinate was built.•Each averaged potential exhibits two equivalent skew T-shaped global minima ...and two equivalent shallow local minima.•The determined band origin shift in the infrared spectra in the N2O ν3 regionagrees well with the experimental value.
We propose a new potential energy surface for the N2–N2O complex, which encompasses the Q3 normal mode for the ν3 antisymmetric stretching coordinate of N2O. The interaction potential energies were obtained at the explicitly correlated coupled cluster with single, double, and perturbative triple excitations CCSD(T)-F12a level with aug-cc-pVTZ basis set plus mid-bond functions. Four-dimensional vibrationally averaged potentials with N2O in the ground and ν3 excited states were generated through integration over the Q3 coordinate. Both potentials exhibit two equivalent skew T-shaped global minima. The rovibrational energies were calculated by employing the radial discrete variable representation/angular finite basis representation approach. The determined fundamental band origin shift of the infrared spectra in the N2O ν3 region, transition frequencies and rotational constants are all consistent with the experimental values.
Shock-tube study of the oxidation of ammonia by N2O Mathieu, Olivier; Grégoire, Claire M.; Petersen, Eric L.
Proceedings of the Combustion Institute,
2024, 2024-00-00, Letnik:
40, Številka:
1-4
Journal Article
Recenzirano
The oxidation of ammonia by N2O was studied by following the time history of ammonia in a shock tube with a spectroscopic laser diagnostic. Dilute (99.5 % Ar) mixtures were studied around atmospheric ...pressure for several equivalence ratios: 0.25, 0.85, 1.0, and 2.0. The time at which the ammonia concentration reaches 50 % of its original value (τ50%) was also measured. Results were compared to several detailed kinetics models from the literature. Based on past work from the authors and a literature mechanism, a tentative model was also assembled to better represent the experiments at the conditions investigated herein. The quantitative NH3 diagnostic shed light on the limitations associated with the passivation method to counterbalance ammonia adsorption on the reactor's surface and showed that an ammonia diagnostic is necessary and critical to know the initial conditions for dilute mixtures. Experimental results show a relatively large effect of the equivalence ratio on the mixture's reactivity. The main outcome of this study is that while τ50% can be accurately predicted by all models considered, large variations are observed when comparing with the full NH3 time-history profile. Key features of the experimental profiles were not captured by the models, and large variations were observed between the models. Overall, the most recent models and the tentative models from this study performed the best, but more work remains necessary to fully capture the oxidation of ammonia by N2O. The effect of the third-body collision coefficient on N2O (+M) ⇆ N2 + O (+M) was investigated for several species, but no effect was found under the conditions investigated. However, it is likely that studying N2O (+NH3) ⇆ N2 + O (+NH3) is necessary for real-world applications.
In the development of ammonia - hydrogen blends as potential substitutes for fossil fuels, the retrofitting of existing devices running at very lean condition is one of the promising solutions for ...decarbonisation of the power sector. However, little is known about the impact of these conditions on the production of NOX, particularly N2O that is a potent greenhouse gas. Therefore, the influence of varying thermal power and Reynolds numbers on the flame and emission characteristics, especially N2O, of ammonia-hydrogen-air swirling flames has been evaluated for the first time through the use of spatially resolved OH*, NH* and NH2* chemiluminescence, spectrometry analyses and advanced emissions characterisation at a fixed lean equivalence ratio, Φ = 0.65, representative of the Dry Low NOX (DLN) approach in traditional stationary gas turbines. NO and NO2 emissions were found to be decreasing (from ∼ 5000 ppmv to ∼ 1000 ppmv; NO and from ∼ 150 ppmv to ∼ 50 ppmv; NO2) with increasing ammonia content (from 50% to 90%) in the fuel while N2O followed reverse trends (from ∼ 50 ppmv to ∼ 200 ppmv). More than 80% ammonia content in the fuel blends exhibited high amounts of unreacted ammonia fractions (∼ 100 to ∼ 1200 ppmv), which can be potentially linked to flame instability and/or low temperatures. Furthermore, any increasing or decreasing trends in NOX with ammonia fraction were made more extreme by increasing thermal power or Reynolds number due to the differences in relevant radicals (NH, OH, NH2 etc.) formation in the flames. Experimental results suggest the unviability of these blends at the conventional lean conditions utilised at the DLN power applications due to excessive NOX emissions. Detailed sensitivity analyses of N2O concentration at the flame and post flame zone has been carried out utilising Ansys Chemkin-PRO to identify and investigate the reactions responsible for N2O formation/consumption in the experimental flames. Results have identified the reaction NH + NO ↔ N2O + H as the major source of N2O production in the flame, while the reactions N2O + H ↔ N2 + OH and N2O(+M) ↔ N2 + O(+M) are responsible for N2O consumption at the post flame zone, with higher reactivity for the latter reaction at longer residence time and relatively lower temperatures.
Straw application in combination with synthetic N fertilizer could increase crop yield and improve soil fertility, however, contradictory observations have been reported on the effects of straw ...addition on soil N2O emission. Straw application can affect both denitrification rate and its product stoichiometry (N2O/(N2O + N2) ratio), whereas the latter remains rather unclear since the ratio is strongly regulated by other soil parameters, e.g. nitrate and oxygen concentrations at denitrifying micro-sites. In this context, we conducted an incubation experiment with a robotized continuous flow incubation system using a He/O2 atmosphere and measured N2O and direct N2 fluxes over 22 days. Soil amended with and without rice straw (2.5 g kg−1 soil) in conjunction with nitrate fertilizer (10 mM KNO3) and non-amended control soil were incubated under 85% water-filled pore space. To simulate a short soil anoxic period, three different O2 partial pressures phases were set (20%, 5% and 10%). Additionally, N2O site preference signatures of soil-emitted N2O were analyzed to identify the processes contributing to N2O fluxes. Addition of nitrate increased cumulative N2O fluxes and decreased cumulative N2 fluxes compared with non-fertilized control, while rice straw amendment increased both N2O and N2 emissions drastically compared with the nitrate only treatment. The N2O SP values ranged from 0.4 to 2.7‰ among all treatments, indicating denitrification/nitrifier denitrification was the dominating source. The results suggest that straw amendment can trigger high denitrification rate, whereas the effect of straw amendment on the amount of emitted N2O and the N2O/(N2O + N2) product ratio strongly depends on soil NO3− concentration. As a conclusion, the present study suggests that straw amendment in conjunction with nitrate-N can increase soil N2O emissions under conditions favoring denitrification, even though it may decrease the overall N2O/(N2O + N2) product ratio.
•Combined effect of straw addition and soil NO3− was shown on direct N2 fluxes.•Decrease in soil NO3− caused a quick shift from N2O production to reduction.•Effect of straw addition on N2O and N2 fluxes depends on soil NO3− content.
As a potent atmospheric greenhouse gas and a major source of ozone depletion, nitrous oxide (N2O) emission has been given increasing attention in aquatic systems, particularly at the ...aquatic-terrestrial interfaces, such as riparian zones. However, the microbial mechanisms regulating N2O emission in riparian zones remain unknown. Here, we measured the contributions of denitrification and ammonium oxidation to N2O emission along with the abundance and community structure of nirK-, nirS-, nosZ I- and nosZ II-harbouring bacteria in both surface sediments (0–10 cm) and overlying water along a lake riparian zone (including nearshore sites and offshore sites). Overall, the nearshore sites of the riparian zones emitted less N2O than the offshore sites. Nearshore N2O emission was dominated by denitrification with a high N2O reduction rate, whereas offshore N2O emission was driven by ammonium oxidation. Furthermore, N2O derived from ammonium oxidation was influenced by the NH4+-N content, and denitrification N2O was modulated by denitrifier communities. The N2O-producing community was dominated by nirS-harbouring bacteria, while the N2O-reducing community was dominated by nosZ I-harbouring bacteria. The relative abundance of Hydrogenophilales from nirS-denitrifiers and Chloroflexi unclassified from nosZ II-type communities influenced the N2O produced by denitrification, according to high-throughput sequencing analysis. Additionally, we also found lower levels of N2O production per unit volume in overlying water, which were 3–4 orders of magnitude less than in the surface sediment. Overall, we propose that using riparian zones can be an effective management tool for N2O mitigation by enhancing the N2O reduction process of denitrification and decreasing ammonium oxidation.
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•Riparian zones were not hotspots for N2O emission.•Denitrification and nitrification separately dominated N2O production at nearshore and offshore sites.•Nearshore sites had higher potential of N2O reduction by denitrification.•NH4+-N content was the key factor impacting ammonium oxidation and N2O emission.•Surface sediment rather than water column was the main contributor to N2O in riparian zone.
Soil dinitrogen (N2) emissions are a key nitrogen loss pathway of terrestrial ecosystems. However, the quantification of field N2 emissions from terrestrial ecosystems remains challenging, as ...sensitive field methods for measuring N2 fluxes are lacking. Here, we report a new approach to quantify field N2 emissions by (i) parameterizing the molar ratio of nitrous oxide (N2O) to N2O plus N2 emissions (RN2O) in the laboratory and (ii) measuring field N2O emissions and soil factors. Soil samples were taken from a maize field and incubated in the laboratory under simulated field conditions. Soil N2 and N2O emissions were determined using the gas-flow-soil-core method. The measurements revealed that the RN2O values were significantly higher (0.06–0.67) following urea fertilization and soil rewetting compared to those periods with no fertilization (0.03–0.08) (P < 0.01). A multivariate, nonlinear parameterization of RN2O against four easily measured soil factors (ammonia and nitrate concentrations, temperature, and moisture) (n = 20, r2 = 0.92, P < 0.001) was developed. The seasonal N2 emissions at the field scale were calculated by combining the laboratory-measured RN2O with the field-measured N2O emissions and the soil factors. Based on this approach, the cumulative emissions of N2 and N2+N2O for the maize season were 7.2 ± 2.8 and 9.6 ± 2.1 (standard error) kg N ha−1, respectively. Using a fixed RN2O, i.e., disregarding the temporal and spatial variability of RN2O, resulted in approximately 50%–70% lower estimates. Our study shows that a combination of field N2O and soil factors measurements and laboratory parameterization of RN2O allows field N2 emissions from croplands to be constrained. With additional measurements, including other soil properties, the development of a generalized parameterization of RN2O may become feasible. This approach would allow for a better understanding of gaseous N losses from agricultural ecosystems.
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•A method was developed to quantify dynamical field N2 fluxes from upland soils.•This method combined N2O/(N2O + N2) ratios with field-measured N2O fluxes.•N2O/(N2O + N2) ratio was parameterized as a function of multiple soil factors.•The obtained multivariate function was validated by independent literature data.
Based on current climate scenarios, a higher frequency of summer drought periods followed by heavy rainfall events is predicted for Central Europe. It is expected that drying/rewetting events induce ...an increased matter cycling in soils and may contribute considerably to increased emissions of the greenhouse gas N₂O on annual scales. To investigate the influence of drying/rewetting events on N₂O emissions in a mature Norway spruce forest in the Fichtelgebirge area (NE Bavaria, Germany), a summer drought period of 46 days was induced by roof installations on triplicate plots, followed by a rewetting event of 66 mm experimental rainfall in 2 days. Three nonmanipulated plots served as controls. The experimentally induced soil drought was accompanied by a natural drought. During the drought period, the soil of both the throughfall exclusion and control plots served as an N₂O sink. This was accompanied by subambient N₂O concentrations in upper soil horizons. The sink strength of the throughfall exclusion plots was doubled compared with the control plots. We conclude that the soil water status together with the soil nitrate availability was an important driving factor for the N₂O sink strength. Rewetting quickly turned the soil into a source for atmospheric N₂O again, but it took almost 4 months to turn the cumulative soil N₂O fluxes from negative (sink) to positive (source) values. N₂O concentration and isotope analyses along soil profiles revealed that N₂O produced in the subsoil was subsequently consumed during upward diffusion along the soil profile throughout the entire experiment. Our results show that long drought periods can lead to drastic decreases of N₂O fluxes from soils to the atmosphere or may even turn forest soils temporarily to N₂O sinks. Accumulation of more field-scale data on soil N₂O uptake as well as a better understanding of underlying mechanisms would essentially advance our knowledge of the global N₂O budget.
Biochar application to croplands has been proposed as a potential strategy to decrease losses of soil‐reactive nitrogen (N) to the air and water. However, the extent and spatial variability of ...biochar function at the global level are still unclear. Using Random Forest regression modelling of machine learning based on data compiled from the literature, we mapped the impacts of different biochar types (derived from wood, straw, or manure), and their interactions with biochar application rates, soil properties, and environmental factors, on soil N losses (NH3 volatilization, N2O emissions, and N leaching) and crop productivity. The results show that a suitable distribution of biochar across global croplands (i.e., one application of <40 t ha−1 wood biochar for poorly buffered soils, such as those characterized by soil pH<5, organic carbon<1%, or clay>30%; and one application of <80 t ha−1 wood biochar, <40 t ha−1 straw biochar, or <10 t ha−1 manure biochar for other soils) could achieve an increase in global crop yields by 222–766 Tg yr−1 (4%–16% increase), a mitigation of cropland N2O emissions by 0.19–0.88 Tg N yr−1 (6%–30% decrease), a decline of cropland N leaching by 3.9–9.2 Tg N yr−1 (12%–29% decrease), but also a fluctuation of cropland NH3 volatilization by −1.9–4.7 Tg N yr−1 (−12%–31% change). The decreased sum of the three major reactive N losses amount to 1.7–9.4 Tg N yr−1, which corresponds to 3%–14% of the global cropland total N loss. Biochar generally has a larger potential for decreasing soil N losses but with less benefits to crop production in temperate regions than in tropical regions.
Biochar is expected as a potential strategy for cropland N conservation. Uncertainties exist, however, regarding the extent and spatial variability of biochar function at the global level. Using Random Forest regression modelling of machine learning, this study mapped the impacts of different biochar types, and their interactions with biochar application rates, soil properties and environmental factors, on soil N losses (NH3 volatilization, N2O emissions, and N leaching) and crop productivity. Results show that a suitable biochar management has the potential to achieve a decrease in 3%–14% in global cropland N losses, with an increase in 4%–16% in global crop production.
Denitrification usually takes place under anoxic conditions and over short periods of time, and depends on readily available nitrate and carbon sources. Variations in CO2 and N2O emissions associated ...with plant residues have mainly been explained by differences in their decomposability. A factor rarely considered so far is water-extractable organic matter (WEOM) released to the soil during residue decomposition. Here, we examined the potential effect of plant residues on denitrification with special emphasis on WEOM. A range of fresh and leached plant residues was characterized by elemental analyses, 13C-NMR spectroscopy, and extraction with ultrapure water. The obtained solutions were analyzed for the concentrations of organic carbon (OC) and organic nitrogen (ON), and by UV-VIS spectroscopy. To test the potential denitrification induced by plant residues or three different OM solutions, these carbon sources were added to soil suspensions and incubated for 24 h at 20 °C in the dark under anoxic conditions; KNO3 was added to ensure unlimited nitrate supply. Evolving N2O and CO2 were analyzed by gas chromatography, and acetylene inhibition was used to determine denitrification and its product ratio. The production of all gases, as well as the molar (N2O + N2)–N/CO2–C ratio, was directly related to the water-extractable OC (WEOC) content of the plant residues, and the WEOC increased with carboxylic/carbonyl C and decreasing OC/ON ratio of the plant residues. Incubation of OM solutions revealed that the molar (N2O + N2)–N/CO2–C ratio and share of N2O are influenced by the WEOM's chemical composition. In conclusion, our results emphasize the potential of WEOM in largely undecomposed plant residues to support short-term denitrification activity in a typical ˈhot spot–hot momentˈ situation.
•Potential denitrification is closely related to water-soluble OC in plant residues.•Amount of water-soluble OC depends on the residue's chemical composition.•Chemical composition of water-soluble OM controls the molar (N2O + N2)–N/CO2–C ratio.
Dinitrogen (N2) and nitrous oxide (N2O) produced via denitrification may represent major nitrogen (N) loss in terrestrial ecosystems. A global assessment of soil denitrification rate, N2O/(N2O+N2) ...ratio, and their driving factors and mitigation strategies is lacking. We conducted a global synthesis using 225 studies (3367 observations) to fill this knowledge gap. We found that daily N loss through soil denitrification varied with ecosystems and averaged 0.25 kg N ha−1. The average emission factor of denitrification (EFD) was 4.8%. The average N2O/(N2O+N2) ratio from soil denitrification was 0.33. Soil denitrification rate was positively related to soil water-filled pore space (WFPS) (p < 0.01), nitrate (NO3-) content (p < 0.05) and soil temperature (p < 0.01), and decreased with higher soil oxygen content (p < 0.01). N2 emissions increased with latitude (p < 0.05), WFPS (p < 0.01) and soil mineral N (p < 0.05) but decreased with soil oxygen content (p < 0.05). The N2O/(N2O+N2) ratio increased with soil oxygen content (p < 0.01) but decreased with organic carbon (C) (p < 0.05), C/N ratio (p < 0.01), soil pH (p < 0.05) and WFPS (p < 0.01). We also found that optimizing N application rates, using ammonium-based fertilizers compared to nitrate-based fertilizers, biochar amendment, and application of nitrification inhibitors could effectively reduce soil denitrification rate and associated N2 emissions. These findings highlight that N loss via soil denitrification and N2 emissions cannot be neglected, and that mitigation strategies should be adopted to reduce N loss and improve N use efficiency. Our study presents a comprehensive data synthesis for large-scale estimations of denitrification and the refinement of relevant parameters used in the submodels of denitrification in process-based models.
•We used 225 studies (3367 observations) to conduct a global assessment of soil denitrification rate, N2O/(N2O+N2), and their driving factors and mitigation strategies.•N loss via soil denitrification and N2 emissions cannot be neglected, and that mitigation strategies should be adopted to reduce N loss and improve N use efficiency.•Soil denitrification rate and N2O/(N2O+N2) were highly related to soil properties.•Optimizing N application rates, using ammonium-based fertilizers compared to nitrate-based fertilizers, biochar amendment and application of nitrification inhibitors could effectively reduce soil denitrification rate and associated N2 emissions.
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