Lower N2O Emissions Research Articles

Nitrogen and Water Additions Affect N2O Dynamics in Temperate Steppe by Regulating Soil Matrix and Microbial Abundance

Elucidating the effects of nitrogen and water addition on N2O dynamics is critical, as N2O is a key driver of climate change (including nitrogen deposition and shifting precipitation patterns) and stratospheric ozone depletion. The temperate steppe is a notable natural source of this potent greenhouse gas. This study uses field observations and soil sampling to investigate the seasonal pattern of N2O emissions in the temperate steppe of Inner Mongolia and the mechanism by which nitrogen and water additions, as two different types of factors, alter this seasonal pattern. It explores the regulatory roles of environmental factors, soil physicochemical properties, microbial community structure, and abundance of functional genes in influencing N2O emissions. These results indicate that the effects of nitrogen and water addition on N2O emission mechanisms vary throughout the growing season. Nitrogen application consistently increase N2O emissions. In contrast, water addition suppresses N2O emissions during the early growing season but promotes emissions during the peak and late growing seasons. In the early growing season, nitrogen addition primarily increased the dissolved organic nitrogen (DON) levels, which provided a matrix for nitrification and promoted N2O emissions. Meanwhile, water addition increased soil moisture, enhancing the abundance of the nosZ (nitrous oxide reductase) gene while reducing nitrate nitrogen (NO3−-N) levels, as well as AOA (ammonia-oxidizing archaea) amoA and AOB (ammonia-oxidizing bacteria) amoA gene expression, thereby lowering N2O emissions. During the peak growing season, nitrogen’s role in adjusting pH and ammonium nitrogen (NH4+-N), along with amplifying AOB amoA, spiked N2O emissions. Water addition affects the balance between nitrification and denitrification by altering aerobic and anaerobic soil conditions, ultimately increasing N2O emissions by inhibiting nosZ. As the growing season waned and precipitation decreased, temperature also became a driver of N2O emissions. Structural equation modeling reveals that the impacts of nitrogen and water on N2O flux variations through nitrification and denitrification are more significant during the peak growing season. This research uncovers innovative insights into how nitrogen and water additions differently impact N2O dynamics across various stages of the growing season in the temperate steppe, providing a scientific basis for predicting and managing N2O emissions within these ecosystems.

Temperature has an enhanced role in sediment N2O and N2 fluxes in wider rivers.

Riverine N2O and N2 fluxes, key components of the global nitrogen budget, are known to be influenced by river size (often represented by average river width), yet the specific mechanisms behind these effects remain unclear. This study examined how environmental and microbial factors influenced sediment N2O and N2 fluxes across rivers with varying widths (2.8 to 2,000 m) in China. Sediment acted as sources of both N2O and N2 emissions, with both N2 (0.2 to 20.8 mmol m-2 d-1) and N2O fluxes (0.7-54.2 μmol m-2 d-1) decreasing significantly as river width increased. N2 fluxes were positively correlated with denitrifying bacterial abundance, whereas N2O fluxes, when normalized by the abundance of denitrifying bacteria, were negatively correlated with the abundance of N2O-reducing microbes. Water physicochemical factors, particularly temperature and nitrate, were more important drivers of these fluxes than sediment factors. Nitrate significantly increased denitrifying bacterial abundance, whereas higher temperatures enhanced cell-specific activity. Lower N2O and N2 emissions in wider rivers were attributed to decreased denitrifying microbial abundance and lower denitrification rates, in addition to the commonly assumed reduction in exogenous N2O and N2 inputs. Rolling regression analysis showed that nitrate concentration had a stronger effect on sediment N2O and N2 fluxes in narrower rivers, whereas temperature was more influential in wider rivers. This difference is attributed to more stable nitrate concentrations and decreased nitrogen removal efficiency in wider rivers, while temperature variation remained consistent across all river widths. Beyond sediments, temperature had a greater effect on excess N2O concentrations than nitrate in the overlying water of wider rivers (>165 m), highlighting its broader impact. This study provides new biogeochemical insights into how river width influences sediment N2O and N2 fluxes and highlights the importance of incorporating temperature into flux predictions, particularly for wider rivers.

Mechanisms of N2O Emission in Drip-Irrigated Saline Soils: Unraveling the Role of Soil Moisture Variation in Nitrification and Denitrification

Drip irrigation generates structural bodies in soil, forming layered structures with moisture content gradients. There are four typical soil moisture characteristic values in this concentric structure as saturation capacity (θs), field capacity (FC), 60% field capacity (60% FC), and 30% field capacity (30% FC). In this study, we simulated these four soil water characteristic values to conduct an indoor soil incubation experiment under three different incubation conditions: aerobic (O), aerobic with 10 pa acetylene (OC), and anaerobic (AO). The results indicate that in soil with saturated water content, denitrification under aerobic conditions leads to high N2O emissions; in soil at field holding capacity, nitrification under aerobic conditions dominates low N2O emissions, which is most conducive to N2O reduction and greenhouse gas emission mitigation; in soil with 60% of field holding capacity, denitrification under anaerobic conditions leads to high N2O emissions; and in soil with 30% of field holding capacity, microbial activity decreases, inhibiting nitrification, denitrification, and N2O emissions. Our research has found that when conducting aerobic drip irrigation in soil at field capacity (FC), denitrification was reduced by 99%, nitrification was increased by 70%, and microbial activity was enhanced by 5%. Therefore, during drip irrigation, the position and flow rate of the dripper should be controlled to reduce soil water saturation areas, maintain soil aeration, control soil moisture content below field holding capacity, promote the nitrification process, reduce N2O emissions, and improve soil nitrogen use efficiency. Our study elucidates the characteristics of nitrogen transformation and N2O emissions across various soil moisture contents within the soil water structure under drip irrigation conditions, providing a scientific basis for the formulation of precise irrigation management practices and strategies for efficient soil nitrogen utilization.

Enhancement of nitrogen transformation in media-based aquaponics systems using biochar and zerovalent iron

Aquaponics combines aquaculture and hydroponics, offering methods to produce fish and plants. However, optimization of its nitrogen transformation processes, which would lead to higher nitrogen utilization efficiency (NUE) and lower nitrous oxide (N2O) emission, is still a daunting challenge. This study investigated these issues by using biochar and zerovalent iron (ZVI) with low (LD) and high (HD) doses. Results showed that LD improved NUE by 15%, reaching 57%, along with a significant 36% reduction in N2O emissions. Conversely, denitrifying bacteria were disturbed in HD due to incomplete denitrification, resulting in higher N2O emissions. Microbial analysis showed that the abundance of denitrifying bacteria increased from 12% to 24% in LD, compared with the control, leading to lower N2O emissions and optimized nitrogen cycling. These findings suggested that using the appropriate proportion of biochar and ZVI would be a promising approach to enhance the sustainability and productivity of aquaponics systems.

Soil properties drive nitrous oxide accumulation patterns by shaping denitrifying bacteriomes

In agroecosystems, nitrous oxide (N₂O) emissions are influenced by both microbiome composition and soil properties, yet the relative importance of these factors in determining differential N₂O emissions remains unclear. This study investigates the impacts of these factors on N₂O emissions using two primary agricultural soils from northern China: fluvo-aquic soil (FS) from the North China Plain and black soil (BS) from Northeast China, which exhibit significant differences in physicochemical properties. In non-sterilized controls (NSC), we observed distinct denitrifying bacterial phenotypes between FS and BS, with BS exhibiting significantly higher N₂O emissions. Cross-inoculation experiments were conducted by introducing extracted microbiomes into sterile recipient soils of both types to disentangle the relative contributions of soil properties and microbiomes on N₂O emission potential. The results showed recipient-soil-dependent gas kinetics, with significantly higher N₂O/(N₂O + N₂) ratios in BS compared to FS, regardless of the inoculum type. Metagenomic analysis further revealed significant shifts in denitrification genes and microbial diversity of the inoculated bacteriomes influenced by the recipient soil. The higher ratios of nirS/nosZ in FS and nirK/nosZ in BS indicated that the recipient soil dictates the formation of different denitrifying guilds. Specifically, the BS environment fosters nirK-based denitrifiers like Rhodanobacter, contributing to higher N₂O accumulation, while FS supports a diverse array of denitrifiers, including Pseudomonas and Stutzerimonas, associated with complete denitrification and lower N₂O emissions. This study underscores the critical role of soil properties in shaping microbial community dynamics and greenhouse gas emissions. These findings highlight the importance of considering soil physicochemical properties in managing agricultural practices to mitigate N₂O emissions.

Impact of excess air factor on performance and NOx emissions of an industrial water tube boiler with hydrogen enrichment

This study investigates the impact of excess air factor (λ) on performance and NOx emissions of a 207-MW boiler furnace, used for steam generation in an industrial water tube boiler installed at Saudi Aramco, at fixed volumetric fuel composition of hydrogen/methane of 10%/90%. The numerical approach employed for this investigation utilized ANSYS-Fluent software. The findings of the study revealed robust correlations between λ, temperature, and NO emissions. An increase in λ led to a decrease in both the average furnace temperature and average NO emissions at the boiler exit. Specifically, increasing the value of λ from 1.05–1.45 consistently reduces the average NO emissions from 1541 ppm to 653 ppm. In other words, a 27% increase in λ resulted in approximately a 55% reduction in NOx emissions. As λ increases, the volumetric absorbed of radiation decreases owing to the reduced concentrations of CO2 and H2O. Notably, the maximum combustion efficiency, reaching 37.88%, is achieved at a λ value of 1.35, corresponding to the lowest average flue gas temperature. The results show that to achieve the best performance with high efficiency and low NO emissions, the boiler needs to be operated at an excess air factor of about 1.35.

Experimental and numerical investigations on NH3/H2 fueled combustion in the combustor with block for improved micro power generation

To advance the application of zero-carbon fuels in micro combustion, enhance energy conversion, and reduce NOx emissions in NH3/H2-fueled micro power generators, a micro-combustor with an inserted block is proposed and tested under various chamber configurations and operational conditions. Experimental and numerical tests are conducted in micro-combustors with varied block settings, burner dimensions, NH3 blended ratios (mN), and fuel flow rates (Vf). The results indicate that mN significantly impacts the generation and consumption of H, O, and OH radicals, as well as NO, affecting flame regime and heat transfer. Specifically, adding 5∼15 % NH3 improves the operating performance of the burner, with the highest mean temperature achieved in combustor #24C3-0.4 at mN = 15 %. Block insertion alters flame characteristics and enhances gas-wall heat transfer, and the combustor with thinner blocks at higher mN and thicker blocks at lower mN contributes to better thermal performance. Furthermore, combustors with thinner blocks exhibit lower NO emissions. The working performance of the micro-thermophotovoltaic system can be enhanced by selecting the appropriate burner length with block thickness W = 0.4 mm and position Lb = 7 mm based on Vf. The maximum electrical power of 3.7 W is achieved with a burner length of 28 mm for the system using InGaAsSb cells at Vf = 1200 mL/min.

Addressing Climate Change: The Role of Agriculture in Greenhouse Gas Mitigation

Agriculture is a cornerstone of global food security, which is significantly affected by climate change, primarily driven by human activities that increase greenhouse gas (GHG) emissions. Accounting for approximately 13% of global anthropogenic GHG emissions, agricultural practices-such as livestock rearing, rice cultivation and synthetic fertilizer use which contribute substantially to global warming. Emissions from nitrous oxide (N₂O), methane (CH₄) and carbon dioxide (CO₂) exacerbate this issue, with N₂O being particularly concerning due to its high global warming potential. Mitigation strategies within the agricultural sector are essential, including improved nutrient management, the use of nitrification inhibitors and innovative fertilizer application technologies. Organic farming demonstrates lower N₂O emissions compared to conventional practices, emphasizing the importance of sustainable agricultural methods. Additionally, conservation tillage and practices like zero-tillage help reduce CO₂ emissions by minimizing soil disturbance and enhancing carbon sequestration. Biochar application further supports soil health and GHG reduction by enhancing carbon storage. To mitigate methane emissions from rice fields, reduced tillage and the introduction of electron acceptors can effectively inhibit methanogenesis. As CO₂ constitutes about 72% of total GHG emissions, agricultural practices that increase soil organic carbon (SOC) are critical for effective carbon sequestration. Overall, the agricultural sector holds significant potential for GHG mitigation, with studies suggesting that 89% of the mitigation potential can be achieved through carbon sequestration. Therefore, adopting these strategies is crucial not only for reducing emissions but also for ensuring sustainable agricultural productivity in the face of climate change challenges.

Responses of N2O, CO2, and NH3 Emissions to Biochar and Nitrification Inhibitors Under a Delayed Nitrogen Application Regime

Greenhouse gas and NH3 emissions are exacerbated by the inappropriate timing and excessive application of nitrogen (N) fertilizers in wheat cultivation in China. In this study, the impacts on N2O, CO2, and NH3 emissions of a delayed and reduced N application regime on the Huang-Huai-Hai Plain were investigated. The treatments comprised the control (N0), conventional N at 270 kg N ha−1 (N270) and optimized N application of 180 kg N ha−1 (N180), N180 + biochar at 7.5 t ha−1 (N180B7.5), N180 + biochar at 15 t ha−1 (N180B15), N180 + DMPP (a nitrification inhibitor; N180D), N180D + biochar at 7.5 t ha−1 (N180DB7.5), and N180D + biochar at 15 t ha−1 (N180DB15). Reduced N application (N180) lowered N2O and NH3 emissions. Biochar application resulted in a 4–25% and 12–16% increase in N2O and NH3 emissions, respectively. Application of DMPP significantly decreased N2O emissions by 32% while concurrently inducing a 9% increase in NH3 emissions. Co-application of DMPP and biochar significantly reduced the activity of nitrification enzymes (HAD, NOO), resulting in a reduction of 37–38% in N2O emissions and 13–14% in NH3 emissions. No significant differences in CO2 emissions were observed among the various N treatments except the N0 treatment. Application of DMPP alone did not significantly affect grain yield. However, biochar, in combination with DMPP, effectively increases grain yield. The findings suggest that the N180DB15 treatment has the potential to reduce emissions of N2O and NH3 while concurrently enhancing soil fertility (pH, SOC) and wheat yield.

Understanding nitrogen removal and N2O emission mechanisms in an anaerobic-swing-anoxic-oxic (ASAO) continuous plug-flow system for low C/N municipal wastewater

This study aims to investigate effects of dissolved oxygen (DO) levels and aerated hydrodynamic retention time (HRT) on nitrogen removal and nitrous oxide (N2O) emissions in a novel anaerobic-swing-anoxic-oxic (ASAO) continuous plug-flow system for treating low carbon to nitrogen ratio municipal wastewater. The swing zones had varying DO levels and volumes, deciding the aerated HRT of the ASAO system. Results showed that low DO level (0.8–1.0 mg/L) and short aerated HRT led to high nitrogen removal performance (91.4 %–96.3 %) and low N2O emission factor (2.8 %). The simultaneous nitrification and denitrification (SND) in swing zones and endogenous denitrification in anoxic zones contributed to the nitrogen removal. Meanwhile, the SND and autotrophic denitrification processes were identified as the N2O sources. Low DO level enriched ammonia-oxidizing bacteria and enhanced the SND and autotrophic denitrification pathway. These findings suggest that the ASAO system is promising for reducing carbon emissions in municipal wastewater treatment.

Patterns and Drivers of Greenhouse Gas Emissions in a Tropical Rubber Plantation from Hainan, Danzhou

The intensification of global climate change has made the study of greenhouse gas (GHG) emissions increasingly important. To gain a deeper understanding of the emission characteristics and driving factors of nitrous oxide (N2O), carbon dioxide (CO2), and methane (CH4) from rubber plantation soils, this study conducted a 16-month continuous observation in a rubber plantation in Danzhou, Hainan, employing the static chamber method for the monthly sampling and measurement of GHG emissions while analyzing the soil’s physical and chemical properties. The results indicated that the N2O flux exhibited no significant diurnal variation between the dry and rainy seasons, with an average emission rate of 0.03 ± 0.002 mg·m−2·h−1. A clear seasonal trend was observed, with higher emissions in summer than in winter, resulting in an annual flux of 3 kg·hm−2·a−1 (equivalent to 1.9 kg N·hm−2·a−1). N2O emissions were significantly correlated with soil temperature and moisture, explaining 46% and 40% of the variations, respectively, while soil ammonium nitrogen content also significantly influenced N2O and CO2 emissions. The rubber plantation soil acted as a source of N2O and CO2 emissions and a sink for CH2, with lower emissions of N2O and CO2 during the daytime compared to nighttime, and higher CH4 uptake during the daytime. In the dry season, there was a significant positive correlation between N2O and CO2 emissions (R2 = 0.74, p < 0.001). This study reveals the diurnal and seasonal patterns of GHG emissions from rubber plantation soils in Hainan and their interrelationships, providing a scientific basis for the low-carbon management of rubber plantations and GHG mitigation strategies, thereby contributing to attempts to reduce the impact of rubber cultivation on climate change.

Biochar captures ammonium and nitrate in easily extractable and strongly retained form without stimulating greenhouse gas emissions during composting.

During composting of organic waste, nitrogen is lost through gaseous forms and ion leaching. Biochar has been shown to capture mineral nitrogen (Nmin: NH4 + and NO3 -) from compost, which we hypothesize reduces N2O formation. However, associating Nmin captured by biochar with the dynamics of N2O and other greenhouse gas (GHG) emissions during composting remains unstudied and was the aim of this work. We composted (outdoor for 148 days) together kitchen scraps (43.3% dw, where dw is dry weight), horse manure (40.9% dw), and wheat (Triticum aestivum L) straw (15.8% dw) without (Control) or with biochar (Bc, 15% compost dw). The biochar consisted of hardwood and softwood pieces pyrolyzed at 680°C and exhibited 60% of particles with 4-8mm. We monitored compost GHG (CO2, CH4, N2O) emissions, Nmin content in compost and biochar particles (sequential extractions), and biochar surface transformations (SEM-EDX and 13C-NMR spectroscopy) along composting. Biochar did not significantly reduce or increase GHG emissions and Nmin content (mg kg-1) in compost. However, the final NO3 - amount (g compost pile-1) in the Bc treatment was significantly higher (54%) compared to the Control, indicating lower NO3 - losses. Despite the high aromaticity and minimal contribution of carboxyl C to the biochar structure, biochar retained NH4 +, mainly in easily extractable form (55%), in the first 2 weeks of composting and mainly in strongly retained form (75%) in the final compost. The NO3 - content in biochar increased continuously during composting. In the final compost, the NO3 - content extracted from biochar was 164 (37%, easily extractable), 80 (19%, moderately extractable), and 194mg NO3 --N kg-1 (44%, strongly retained). Although Nmin retention in biochar was not accompanied by lower N2O emissions, contradicting our hypothesis, we demonstrated the efficacy of biochar to recover Nmin from organic waste without stimulating GHG emissions.

Greenhouse gas emissions during alfalfa cultivation: How do soil management and crop fertilisation of preceding maize impact emissions?

ContextThe use of alfalfa in rotation with intensive crops is common practice to mitigate the physical and chemical issues arising from intensive farming practices. However, there is a dearth of studies on this practice. Given the current concern regarding climate change and the significant impact agriculture has on greenhouse gas (GHG) emissions, understanding the emissions associated with this practice, as well as the most suitable soil and crop management techniques for their mitigation, is of paramount importance. ObjectiveThe present study aimed to (i) quantify emissions of N2O, CO2 and CH4 in an alfalfa crop following a maize cropping scenario; (ii) to determine which tillage system generates the lowest GHG emissions, and; (iii) to determine how N fertilisation from a preceding intensive maize crop affects GHG emissions during alfalfa cropping period. MethodsA three-year field experiment (2019, 2020 and 2021) was conducted to assess the emissions of N2O, CO2 and CH4 from alfalfa cultivation following a three-year period of irrigated maize. Two soil management practices (no-tillage and conventional tillage) were implemented during both the maize cropping period and the alfalfa establishment. Additionally, the nitrogen (N) fertilisation rates applied to the preceding maize crop were included as a treatment (0, 200, and 400 kg N ha⁻¹, corresponding to zero, medium, and high fertilisation levels, respectively) in a randomized block design with two factors. ResultsEmissions of N2O in alfalfa ranged from 0.05 to 0.32 mg N2O-N m⁻² day⁻¹, being significantly higher only during first month of sampling in the treatments that had received fertilisation. CO2 emissions ranged from 1158 to 4258 mg CO2-C m⁻² day⁻¹. Year-average CH4 fluxes were −0.27 g C ha⁻¹ day⁻¹. The average total dry matter produced by alfalfa was 17700 kg ha⁻¹ year⁻¹, being higher for the no-tillage treatment, though significantly so only during first month of sampling. ConclusionsUnder Mediterranean conditions, the tillage system and mineral N fertilizer rates have a relative effect on greenhouse gas emissions during the alfalfa cropping period. Plots without N fertilization initially produced lower N2O emissions and higher total dry matter, resulting in the lowest scaled emissions. For the tillage treatment, no significant differences were found in emission dynamics, which may be due to the fact that alfalfa does not involve soil disturbance, leading to a homogenization of the treatments. However, the NT treatment showed lower scaled emissions due to higher yields in the first year. Therefore, alfalfa cultivation is characterized by low GHG emissions, high yields, and a notable capacity to mitigate the negative effects of previous intensive crops. SignificanceThis study provides data on GHG emissions during alfalfa cropping in the typical Maize-alfalfa crop rotation under Mediterranean irrigated systems, which is useful for new agricultural policies aimed at reducing pollution in the agricultural sector. Additionally, it demonstrates the capability of this crop to mitigate adverse agronomic and environmental conditions caused by preceding intensive farming practices.

Greenhouse gas emission and denitrification kinetics of woodchip bioreactors treating onsite wastewater

The accurate evaluation of denitrification rate and greenhouse gas (GHG) emission in field-scale woodchip bioreactors for onsite wastewater treatment are problematic due to inevitably varied environmental conditions and underestimated GHG production with limited analysis of dissolved gas in field samples. To address these problems, batch incubation experiments were conducted with controlled conditions to precisely evaluate the denitrification kinetics and N2O and CH4 emission of both gaseous and dissolved phases in fresh (6 months) and aged (5 years) woodchip bioreactors treating onsite wastewater at high (1–3 mg L-1) and no (0 mg L-1) dissolved oxygen (DO) levels. NO3- removal rate decreased from 37.5–119.0 g NO3--N m-3d-1 at no DO to 8.8–16.6 g NO3--N m-3d-1 at high DO (1–3 mg L-1) due to the growth suppression of NO2- reducing microorganisms (37–55 % lower nirS+nirK abundance). However, the presence of high DO increased N2O emission level from 5.6–6.9 mg N2ON m-3 at no DO to 179.5–273.6 mg N2ON m-3) due to the enhanced growth of NO reducing microorganisms (1–7 times higher norB levels) and the decreased abundance of N2O reducing microorganisms (53–75 % lower nosZ abundance). On the other hand, increased DO level negatively correlated with CH4 production (1.0–3.9 g CH4-C m-3d-1) in fresh woodchips, while showed insignificant impact on CH4 production (0.1–1.4 g CH4-C m-3d-1) in aged woodchips. Woodchip age increase (5 years) negatively impacted the NO3- removal rate (75–85 % lower than fresh woodchips) and CH4 production rate (>3 times lower than fresh woodchips), probably due to the reduced biomass density of NO2- reducing microorganisms (52–58 % lower nirS+nirK abundance) and methanogens (95–98 % lower mcrA levels). The incubation results suggested that long hydraulic retention time (>2–5 days) and anaerobic/anoxic condition are preferred for the optimal NO3- removal and low N2O emission potential of woodchip bioreactors treating onsite wastewater.

Lower NO emission conditions of NH3–H2 mixtures under the oxygen-enriched premixed combustion mode

Compared with pure NH3 fuel, the lower NO emission conditions of NH3–H2 mixtures under the oxygen-enriched combustion mode have been identified quantitatively. Furthermore, the effects of the H2 addition on the NO productions of premixed oxygen-enriched NH3–H2 flames are studied numerically, while the major reactions responsible for the variation of total NO are identified. Results show that the H2 addition is eligible to reduce the NO emissions of the oxygen-enriched NH3 combustion if the laminar burning velocity is fixed to a larger value (>23 cm/s). The quantitative equations are obtained to determine the optimum oxygen-enriched conditions of the NH3–H2 mixture, aiming to achieve lower NO emission and similar or improved combustion stability compared to pure NH3 fuel by restricting the minimum and maximum O2 percentages for the NH3–H2 mixtures. Based on the rate of production (ROP) analysis, for the oxygen-enriched NH3–H2 combustion, R144 (HNO + H<=>H2+NO) is consistently the most significant NO production reaction, while R85 (NH + NO<=>N2O + H) and R91 (N + NO<=>O + N2) play significant roles in the NO consumption. When the laminar burning velocity (SL) is kept to a lower value, the increased total NO of the oxygen-enriched NH3 flames with the H2 addition is ascribed to more efficient suppressions on the NO consumption reactions of R85, R91 and R77 (NH2+NO<=>NNH + OH). In contrast, thanks to the extra impact of the higher O2 percentage on the H/O/OH radical pool at larger SL, the NO production reactions begin to suffer stronger suppressions of the H2 addition, resulting in the reduced total NO of NH3–H2 mixtures. Furthermore, R144 is identified as the key reaction influencing the variation trend of total NO at both lower and higher SL values.

Experimental and numerical studies on performance investigation of a diesel engine converted to run on LPG

With the growing environmental concerns and depletion of energy resources, considerable efforts are focused on developing ecofriendly and sustainable transportation systems. This includes the conversion of outdated diesel engines into ecofriendly liquefied petroleum gas (LPG) engines. In this study, a Euro-6 diesel engine mounted on a commercial vehicle (mega truck) was converted into a propane LPG engine. The combustion chamber was modified by changing the piston shapes (PSs), compression ratios (CRs), ignition system, throttle body, and injector design to enable operation using propane. The performance of the modified engines with two different PSs, PS1 and PS2, were experimentally investigated. In terms of the power, the engine designed using PS2 demonstrated better performance than PS1 under all operating speeds, except 2600 rpm. Particularly, PS2 outperformed PS1 by more than 10 Nm in the low-speed range of 1000–1600 rpm. Under full load, the PS2-equipped LPG engine achieved the maximum torque and power of 834 Nm at 1600 rpm and 170 kW at 2600 rpm, achieving 106 % and 86 % of the target torque and power, respectively. Additional exhaust gas emission tests were performed using the PS2-equipped LPG engine. The engine performance varied with the application of exhaust-gas recirculation. Moreover, the results of the world-harmonized stationary cycle mode tests confirmed the conformance of the modified LPG engine to all Euro-6 emission standards. Furthermore, simulation-based performance optimization was conducted considering two PSs and four CRs. Based on the simulations, PS1 achieved higher engine performance and lower CO2 and soot emissions, whereas PS2 had lower NO emissions. Additionally, increasing the CR improved the performance and reduced the CO2 and soot emissions for both PSs. These results indicate the possibility of developing LPG engines with performance comparable to diesel engines. In particular, the modified LPG engine proposed in this work may be installed on buses and trucks in the future and is anticipated to replace outdated medium-generator and marine engines.

Low N2O emissions induced by root-derived residues compared to aboveground residues of red clover or grass mixed into soil

The default The Intergovernmental Panel on Climate Change (IPCC) guidelines assume a constant N2O emission factor (EFN2O) for both belowground crop residues (BGR) and aboveground residues (AGR), and that ∼70 % of total N2O emissions following renewal of temporary grasslands come from BGR. However, empirical evidence is lacking, which motivated this study. BGR-free and BGR-rich clay loam collected in grass or red clover leys were incubated alone or mixed with AGR and different doses of nitrate over 107 days. The average EFN2O of BGR was around 18 % of that of AGR, and remained low even when soil nitrate concentration was very high, whereas EFN2O of AGR varied largely and rocketed even with a small increase in soil nitrate. The decomposition of the carbon present in crop residues was critical for N2O emissions. Lower EFN2O of BGR relative to AGR were related to slower C decomposition, which was not predicted by the biochemical characteristics. It is also likely that BGR were less conducive than AGR to develop into hotspots for N2O emission because of the roots’ finer distribution and closer contact with soil particles. Differences in EFN2O among AGR were mostly linked to the availability of N, either derived from residue mineralization or present in the soil. In conclusion, N2O accountings based on present IPCC default methodology likely overestimate the contribution by crops’ BGR.

Climate change and greenhouse gas emissions from soils under the winter wheat agroecosystem in Ukraine

The issue of global climate change is one of the most important challenges for modern environmental science. In this regard, assessment of greenhouse gas emissions from soils under agroecosystems is an extremely important task. The main purpose of the study was to assess the potential emissions of greenhouse gases (CO2 and N2O) from the soils under the winter wheat agroecosystem during its spring-summer growing season under the climate change in Ukraine. A comprehensive model of greenhouse gas emissions from agroecosystem soils was used as a theoretical basis. The study considered the main agroclimatic regions of Ukraine, such as Polissia, Forest-Steppe, Northern Steppe, and Southern Steppe. The modelling was performed for average long-term conditions of 1981–2020 and under scenario conditions (using the RCP4.5 climate scenario) for the decades of 2021–2030, 2031–2040, and 2041–2050. Estimates of CO2 emissions were obtained for the agroclimatic regions of Ukraine. According to the results, the largest CO2 emissions (0.886-0.940 t C-CO2/ha) will be expected when the average productive moisture supplies in the arable soil layer for the spring-summer period of winter wheat vegetation are 20–40 mm and the air temperature is 12–15 °C. Rise in the level of moisture reserves, averaged for the period, for more than 40 mm and the air temperature of 11–12 °C is accompanied by decrease in the level of CO2 emission (0.645–0.658 t C-CO2/ha). In arid conditions, with a decrease in the period-average moisture supplies in the arable soil layer to less than 20 mm and heightened average air temperatures (14.5–15.2 °C), a decrease in CO2 emissions is expected (0.755–0.770 t C-CO2/ha). The study showed that the highest N2O emission (1.087–1.703 kg N-N2O/ha) is expected at a high level of moistening (Md being equal to 0.474–0.713 relative units and air temperature – 11.3–13.0 °C) with a high intensity of nitrification and denitrification processes. Conditions characterizing the average level of N2O emission (0.657–0.890 kg N-N2O/ha) are formed under the moistening at a level of Md equaling 0.296–0.447 relative units and air temperature of 13.4–14.7 °C. There is a slowdown in denitrification processes and an increase in the share of emissions owing to nitrification. It has been found that the lowest N2O emission (0.508–0.537 kg N–N2O/ha) is expected under conditions of severe and very severe drought (according to the Md criterion), with a heightened temperature averaged at the level of 14.5–15.2 °C during the spring-summer period of winter wheat vegetation.

Unraveling the synergistic promotion mechanism of Fe0 coupling phragmites australis biomass for nitrogen removal in coastal wetland: From low to moderate salinities

The simulated coastal constructed wetlands supplemented with Fe0 and phragmites australis (P.A) biomass (CW-M) were constructed to improve nitrogen removal under different salinities (0–15‰). Results showed that the denitrification performance of CW-M were improved significantly, with the higher NO3−-N removal of 72–94% and lower N2O emission flux, when compared with mono-P.A biomass(CW-bio), mono-Fe0 system (CW-Fe) and control system. The nitrogen removal showed a trend of first increasing (0‰–7‰) and then decreasing (7‰–15‰) with the highest NO3−-N removal of 94% and enhanced removal efficiency of 41%in CW-M. Fe0 and P.A biomass coupling could reduce the stress of salinity on denitrification. Batch experiments have demonstrated that Fe0 and P.A biomass could mutually stimulate more total organic carbon and total iron (TFe) release as electron donors for denitrification. Meanwhile, appropriate salinity could also promote the release of TFe. The typical heterotrophic denitrifying genera Bacillus and iron autotrophic denitrifying genera Thermomonas have the highest proportion in CW-M, with 21.83% and 0.10%, respectively. Fe0 and P.A biomass adding simultaneously promoted the carbon and iron metabolism, further enhancing the nitrogen metabolism process. The joint enhancement of autotrophic and heterotrophic denitrification contributes to NO3−-N removal in CW-M for treating saline, low C/N wastewater in coastal wetlands.

Carbon-free power generation strategy in South Korea: CFD simulation for ammonia injection strategies through boiler burner configurations in tangentially fired boiler

To achieve carbon neutrality in power generation, incorporating ammonia-coal co-firing into coal-fired boilers effectively reduces CO2 emissions. Here, we aimed to optimize ammonia injection methods by investigating the feasibility of 20 % ammonia co-firing in a pulverized coal (PC) boiler through numerical simulations. These simulations aim to analyze the effects of different ammonia injection strategies and burner configurations on the combustion performance and NOx emission characteristics of a 500 MW tangentially fired PC boiler. Results showed that compared to using five burners, single-burner injection reduced outlet NO concentration by 22.72 ppm and unburned carbon content to 0.30 %, which is 0.80 % lower than multi-burner injection and even below the 0.45 % in coal-only combustion. The optimal case (burner A for ammonia injection) achieved a furnace outlet flue gas temperature of 1247.35 K, close to 1241.98 K in coal-only combustion, with the lowest NO emissions (193.89 ppm) among all ammonia co-firing cases. Positioning the single burner for ammonia injection revealed that utilizing the blending method with the ammonia injection burner, such as in the case of upper burner injection, increases both furnace temperature and high-temperature zone areas. However, employing in-boiler blending methods with lower-positioned burner ammonia injection distributes high-temperature zones more extensively. Comparing ammonia injection through coal and auxiliary oil burners, using only the lowest-level burner can significantly reduce NOx emissions while maintaining combustion and thermal efficiencies. This study is the first to simultaneously consider the number, position, method, and type of ammonia injection burners in large-scale commercial coal-fired boilers, providing a valuable reference for future research and practical boiler operations. This comprehensive analysis underscores how ammonia injection strategy and position can optimize ammonia-coal co-firing boiler performance.