NH3 Emissions Research Articles

Comparison analysis of microbial agent and different compost material on microbial community and nitrogen transformation genes dynamic changes during pig manure compost

This study aimed to assess the impact of microbial agent and different compost material, on physicochemical parameters dynamic change, nitrogen-transfer gene/bacterial community interaction network during the pig manure composting. Incorporating a microbial agent into rice straw-mushroom compost reduced the NH3 and total ammonia emissions by 25.52 % and 14.41 %, respectively. Notably, rice straw-mushroom with a microbial agent reduced the total ammonia emissions by 37.67 %. NH4+-N and pH emerged as primary factors of phylum-level and genus-level microorganisms. Microbial agent increased the expression of narG, nirK, and nosZ genes. Rice straw-mushroom elevated the content of amoA, nirK, nirS, and nosZ genes. Alcanivorax, Luteimonas, Pusillimonas, Lactobacillus, Aequorivita, Clostridium, Moheibacter and Truepera were identified as eight core microbial genera during the nitrogen conversion process. This study provides a strategy for reducing ammonia emissions and analyzes the potential mechanisms underlying compost processes.

Influence of Different Agro-Food Waste on Ammonia and Greenhouse Gas Emissions during Composting

Composting is one of the best organic waste management techniques, with zero waste; however, it generates environmental impacts. The objective of this study was to evaluate the emission of NH3, N2O, CO2, and CH4 from the composting of olive, elderberry, and grape agro-food waste. The experiment was carried out using reactors receiving straw as control and three treatments receiving mixtures of straw and olive, elderberry, or grape wastes. The gas emissions were measured for 150 days, and the composition of the mixtures and composts was determined. The results showed NH3 and CH4 emissions were reduced by 48% and 29% by the Olive and Elderberry treatments, while only NH3 loss was reduced by 24% by the Grape treatment. Nitrous oxide, CO2, and GWP emissions were reduced by 46%, 32%, and 34% by the Olive treatment, while these losses were not reduced by the Elderberry or Grape treatments. It can be concluded olive waste can effectively reduce NH3 and GWP, while elderberry and grape wastes are also effective in reducing NH3, but not GWP. Thus, the addition of agro-food waste appears to be a promising mitigation strategy to reduce gaseous losses from the composting process.

Physiology or Psychology: What Drives Human Emissions of Carbon Dioxide and Ammonia?

Humans are the primary sources of CO2 and NH3 indoors. Their emission rates may be influenced by human physiological and psychological status. This study investigated the impact of physiological and psychological engagements on the human emissions of CO2 and NH3. In a climate chamber, we measured CO2 and NH3 emissions from participants performing physical activities (walking and running at metabolic rates of 2.5 and 5 met, respectively) and psychological stimuli (meditation and cognitive tasks). Participants' physiological responses were recorded, including the skin temperature, electrodermal activity (EDA), and heart rate, and then analyzed for their relationship with CO2 and NH3 emissions. The results showed that physiological engagement considerably elevated per-person CO2 emission rates from 19.6 (seated) to 46.9 (2.5 met) and 115.4 L/h (5 met) and NH3 emission rates from 2.7 to 5.1 and 8.3 mg/h, respectively. CO2 emissions reduced when participants stopped running, whereas NH3 emissions continued to increase owing to their distinct emission mechanisms. Psychological engagement did not significantly alter participants' emissions of CO2 and NH3. Regression analysis revealed that CO2 emissions were predominantly correlated with heart rate, whereas NH3 emissions were mainly associated with skin temperature and EDA. These findings contribute to a deeper understanding of human metabolic emissions of CO2 and NH3.

Global meta-analysis and three-year field experiment shows that deep placement of fertilizer can enhance crop productivity and decrease gaseous nitrogen losses

Context or problemThere is an urgent need to address the contradiction between food security and climate change, and achieve the highest crop productivity at the lowest environmental cost. Scientific fertilization is the key to solving this problem. Objective or research questionDeep placement of fertilizer (DPF) is an effective fertilization strategy for improving crop productivity and reducing gaseous N losses, but its effectiveness varies among agricultural systems and appropriate fertilization depths have not yet been determined. MethodsIn this study, we synthesized 99 global studies (120 locations) and conducted a three-year field experiment to evaluate the effects of DPF on the crop yield, nitrogen use efficiency (NUE), and nitrous oxide (N2O), and ammonia (NH3) emissions, and explored their responses to different climates, field management practices, and environmental factors. ResultsDPF could increase the grain yield by 13.5%, and NUE by 33.8%, and reduce N2O emission by 16.2%, and NH3 emissions by 86.6%, respectively. Random forest analysis showed that the fertilization depth and nitrogen application rate were the most important factors that determined the impacts of DPF on the crop yield, NUE, and N2O and NH3 emissions, but their effects also depended on the climate conditions, field management practices, and soil environmental factors. Meta-regression modeling showed that the effects of DPF on the crop yield and NUE increased but then decreased as the fertilizer application depth and nitrogen application rate increased, and the effects on N2O and NH3 emissions tended to increase gradually. The meta-analysis also demonstrated that under DPF, the emission factors for N2O and NH3 decreased by 35.8% and 84.5%, respectively. According to the meta-analysis, the global N2O and NH3 emissions under DPF can be reduced by 0.23 and 5.46 Tg N·year–1 respectively. ConclusionsThe results obtained based on global meta-analysis and a three-year experiment demonstrated that DPF obtained higher grain production with lower environmental costs, and the most suitable fertilization depth was identified as 15–25 cm. Implications or significanceThe results obtained in this study provide valuable insights into food security and environmental costs under effective fertilization management.

Application of biochar to anaerobic digestion versus digestate: Effects on N emissions and C stability

Research attention is growing for biochar as amendment for anaerobic digestion (AD), as it may improve both the AD process and digestate properties. In this study, two biochars (from insect frass or the woody fraction of green waste, both pyrolyzed at 450 °C) were added (5 % w/w) during semi-continuous AD of organic kitchen waste and chicken manure. Biochar was mixed either during the AD process or to the digestate post-treatment. The impact of biochar addition on the AD process, NH3 and greenhouse gas emissions, as well as C and N mineralization following soil application, was examined. Biochar did not affect the biogas yield, but did lead to a reduction in NH3 levels in the biogas and NH4+-N sorption onto the biochars, reducing the risk of AD inhibition. N sorbed as NH4+-N onto the biochar was more available for mineralization than N sorbed as NH3. N sorption on biochar-amended digestates did not result in trade-offs when these digestates were applied to soil: the sorbed N was not released as NH3 or N2O after soil application and was not released as mineral N in either the short or medium term. The C-rich biochars increased the OC content of the digestate, which enhanced its value as soil improver. Additionally, mixing biochar with digestate decreased the soil CO2 emissions up to 33 % when it was added after AD; no priming effects were observed. These findings highlight the potential benefits of incorporating biochar into AD systems and the subsequent application of biochar-amended digestate in agricultural practices.

Impacts of Liquid Fractions from Two Solid–Liquid Separation Technologies on the Soil Porosity, Ammonia, and Greenhouse Gas Emissions

Application of organic manure on farmland is one of the most important tasks in agricultural recycling. However, few studies have investigated the potential impact of different solid–liquid separation (SLS) technologies on soil porosity and greenhouse gas (GHG) emissions as a result of the application of liquid fractions (LFs). A microcosm experiment was conducted to track the emissions of ammonia (NH3), nitrous oxide (N2O), carbon dioxide (CO2), and methane (CH4) from soils (1) without liquid manure application (CK), (2) with a raw dairy slurry (RM), (3) with the liquid fractions of mechanical solid–liquid separation (MS) technologies, and (4) with the LF of an enhanced solid–liquid separation technology including a flocculant (tannic acid, Ta) (MS + Ta). Soil porosities of different treatments were measured using computed tomography (CT). The saturated water conductivities of the RM and MS treatments were 53.38% and 78.63%, respectively, lower than that of the CK. The application of raw slurry and LFs reduced the gas diffusion due to the strong decrease in pore sizes >500 μm and increased gas emissions compared to the CK. Compared with RM, MS had greater N2O and lower CH4 emissions, whereas MS + Ta had lower NH3 and N2O emissions. MS had the greatest CO2-e emissions, mainly owing to high N2O emissions, followed by RM and MS + Ta. The implementation of a simple SLS led to an increase in nitrogen (N) loss and GHG emissions when the resultant LFs were applied to farmlands, whereas high emissions were reduced when a simple SLS was combined with a flocculant, such as Ta. Further research is required to elucidate the reduction mechanism and its effectiveness under field conditions.

The relationship between oxidative degradation and ammonia emission of carbon capture amines based on their chemical structures

Abstract This work investigates the effect of chemical structural positioning of different functional groups in 29 amines covering primary, secondary and tertiary alkanolamines as well as multi-alkylamines and cyclic amines on both amine degradation and ammonia (NH3) emissions during post-combustion amine-based carbon dioxide capture. The results helped to elucidate possible relationships between degradation and emissions as related to the chemical structure of the amine. The results showed that longer alkyl chain lengths in multi-alkylamines caused a more drastic decrease in both degradation and NH3 emissions followed by secondary alkanolamines. The decrease in those activities for primary and tertiary alkanolamines as well as cyclic amines was low and more so for NH3 emissions. In contrast, the increase in hydroxyl groups in secondary alkanolamines caused a drastic increase in degradation and NH3 emissions. On the other hand, having more hydroxyl groups in sterically hindered primary and tertiary alkanolamines caused a more drastic decrease in degradation and a smaller decrease in NH3 emissions due to the steric hindrance within their structure. An increase in the number of amino groups in an amine caused an increase in both degradation and NH3 emission rates because these provided the reactive sites for the formation of free radicals. This effect was not as large in alkyl-cyclic amines as in multi-alkylamines due to the ability of the former to resist oxidative degradation. Furthermore, branched alkyl groups between amino and hydroxyl groups more drastically increased both the degradation and NH3 emission activities than branched alkyl groups located at the nitrogen atom.

Nitrous oxide emissions are driven by environmental conditions rather than nitrogen application methods in a perennial hayfield.

Agricultural best management practices (BMPs) intended to solve one environmental challenge may have unintended climate impacts. For example, manure injection is often promoted for its potential to reduce runoff and nitrogen (N) loss as NH3 , but the practice has been shown to increase N2 O, a powerful greenhouse gas, compared to surface application. Urease inhibitor application with N fertilizer is another BMP that can enhance N retention by reducing NH3 emissions, but its impact on N2 O emissions is mixed. Thus, we measured N2 O, CO2 , soil mineral N availability, soil moisture, soil temperature, and yield in a 2-year perennial hayfield trial with four fertilization treatments (manure injection, manure broadcast, synthetic urea, and control) applied with or without a urease inhibitor in Alburgh, VT. We used linear models to examine treatment effects on daily and cumulative N2 O emissions and a boosted regression tree (BRT) model to identify the most important drivers of daily N2 O fluxes in our trial. While fertilization type had a significant impact on N2 O fluxes (p<0.05), our treatments explained an unexpectedly small amount of the variation in emissions (R2 =0.042), and urease inhibitor had no effect. Instead, soil moisture was the most important predictor of daily N2 O fluxes (39.7% relative influence in BRT model), followed by CO2 fluxes, soil inorganic N, and soil temperature. Soil moisture and temperature interacted to produce the largest daily N2 O fluxes when both were relatively high, suggesting that injecting manure during dry periods or during wet but cool periods could reduce its climate impacts.

Fe/BC co-conditioners with environmental and economic benefits on composting: reduced NH3 emissions and improved fertilizer quality

The significant volatilization of NH3 during aerobic composting causes nitrogen (N) losses and environmental risks. Both iron (Fe) and biochar (BC) can influence the N conversion process in composting. Fe application can delay the maturation of materials, while biochar can enhance the quality of organic fertilizer. The combination of these two conditioners may help decrease NH3 emissions and improve organic fertilizer quality. Therefore, this study investigates the effects of different doses of FeCl3 and BC on NH3 emissions and organic fertilizer quality during composting. The results demonstrated that Fe/BC co-conditioners reduced the accumulation of NH3 emissions during composting by 11.1–48.2%, increased the total nutrient content by 0.6–15.3%, and enhanced economic and environmental benefits by 0.1–23.6 $ t−1. At the high-temperature stage of composting, Fe/BC co-conditioners decreased the pH by 0.3–1.2, but there was no significant difference compared to the control at the end of composting, and they did not affect compost maturation. The structural equation model analysis suggested that the reduction in NH3 emissions was related to ammonia-oxidizing bacteria (AOB), NH4+–N, and total nitrogen (TN). As a result, the Fe/BC co-conditioners reduced NH3 emissions by lowering the pH at the beginning of composting and increasing the content of NH4+–N. This study concludes that Fe/BC co-conditioners could complement each other to significantly reduce NH3 emissions and improve the quality of organic fertilizers.Graphical

Application of Simultaneous and Coupled Thermal Analysis Techniques in Studies on the Melting Process, Course of Pyrolysis and Oxidative Decomposition of Fused Triazinylacetohydrazides.

The effect of the structure of promising antioxidant agents with prospective medical use, i.e., unsubstituted and para-substituted annelated triazinylacetic acid hydrazides, on their melting points, thermal stabilities, pyrolysis and oxidative decomposition stages and the type of volatiles emitted under heating with the use of DSC and TG/DTG/FTIR/QMS methods was evaluated and discussed. The melting point of the investigated compounds increased with an enhanced number of electrons (directly correlated with their molecular weight). Melting enthalpy values were determined and presented for all the studied compounds. The pyrolysis and oxidative decomposition processes of the analysed molecules consisted of several poorly separated stages, which indicated a multi-step course of the decomposition reactions. It was found that the thermal stability of the tested compounds depended on the type of substituent at the para position of the phenyl moiety or its absence. In both atmospheres used (air and helium), the thermal stability increased in relation to R as follows: -CH3 ≤ -OCH3 < -H < -OC2H5. In an inert atmosphere, it was higher by approx. 8-18 °C than in an oxidative atmosphere. The pyrolysis was connected with the emission of NH3, HCN, HNCO, HCONH2, HCHO, CO2, CO and H2O in the case of all the tested compounds, regardless of the substituent attached. In the case of the derivative containing the para-CH3 group, para-toluidine was an additional emitted aromatic product. In turn, emissions of aniline and alcohol (methanol or ethanol) for compounds with the para-OCH3 and para-OC2H5 groups, respectively, were confirmed. In oxidative conditions, the release of NH3, NO, HCN, HNCO, HCONH2, CO2, H2O and cyanogen (for all the compounds) and para-toluidine (for the para-CH3 derivative), aniline (for para-OCH3, para-OC2H5 and unsubstituted derivatives) and acetaldehyde (for the para-OC2H5 derivative) were clearly observed. No alcohol emissions were recorded for either compound containing the para-OCH3- or para-OC2H5-substitututed phenyl ring. These results confirmed that the pyrolysis and oxidative decomposition of the investigated annelated triazinylacetohydrazides occurred according to the radical mechanism. Moreover, in the presence of oxygen, the reactions of volatiles and residues with oxygen (oxidation) and the combustion process additionally proceeded.

Insights into national distribution of NH3 concentrations in Republic of Korea: findings from passive sampler observations and implications for sources and management.

Gas-phase NH3 is one of the significant contributors to secondary aerosol formation in the atmosphere, and it is a crucial consideration in any strategy aiming to reduce PM2.5 emissions. This study aimed to investigate the spatial distributions of NH3 in verity source areas in Republic of Korea using passive samplers. NH3 concentrations were observed at 45 locations over a period of approximately 35weeks, from June 2022 to February 2023. As a result, NH3 concentration was found to be more affected by local sources rather than long-distance influx from outside. The average concentration of NH3 observed in 7 source areas excluding the background area was all less than 20.91ppb, except for livestock sources. These results suggest that atmospheric NH3 concentrations are significantly influenced from livestock sources. In addition, in major cities, the need for NH3 management was confirmed to be more focused on emissions from automobiles and industrial complexes than emissions from livestock and farmland. Moreover, even for the same source, NH3 concentrations varied depending on the type of livestock species, breeding methods and scale, products produced, crops cultivated, and vehicle traffic volume. These findings indicate the importance of considering factors such as breeding methods and manure treatment practices in emission factors, and it is expected that the results can be used as basic data for NH3 emission estimation and management.

Experimental investigation of operating conditions on performance and emissions of spark ignition ammonia direct injection engine

Hydrogen, attracting attention as a future eco-friendly fuel, is difficult to handle and store because of its material characteristics; thus, ammonia has been proposed as an alternative. However, when only ammonia is utilized as the fuel, the operating range in which stable combustion is possible is limited because of the slow combustion speed and high minimum ignition energy. Here, to examine the applicability of ammonia as an engine fuel, an experiment was conducted based on changes in hydrogen energy ratios and operating conditions in a direct-injection ammonia combustion engine with hydrogen addition. The hydrogen energy ratio for stable operation is about 4.5 % at 1500 rpm under low-load operating conditions such as BMEP 0.2 MPa, and hydrogen must be supplied at a high energy ratio of 27.8 % in the case of a rated-power condition of 3800 rpm. The unburned NH3 and NOx emissions were high at 9285 ppm and 4870 ppm, respectively, under rated-power operating conditions.

Enhanced ammonia combustion by partial pre-cracking strategy in a gas turbine model combustor: Flame macrostructures, lean blowout characteristics and exhaust emissions

Cofiring with hydrogen presents a reasonable approach to achieve enhanced ammonia (NH3) combustion without introducing an extra carbon footprint. A promising strategy for NH3/H2 cofiring in gas turbines involves on-site partial pre-cracking of NH3 and burns of NH3/H2/N2 mixtures, eliminating additional hydrogen transportation and storage. This work investigates the effects of the pre-cracking ratio (γ) on flame macrostructures, lean blowout characteristics and exhaust emissions of the partially pre-cracked NH3 flames in a single-swirl gas turbine model combustor. Flow and flame macrostructures were captured using particle image velocimetry (PIV) and OH planar laser-induced fluorescence (OH-PLIF) measurements. Lean blowout limits (ϕLBO) were assessed under varying γ, and emissions at the burner outlet were measured using a Fourier transform infrared spectroscopic (FTIR) gas analyzer. Results show that as γ increases, the flame exhibits a shortened height, strengthened OH fluorescence, amplified core jet velocities and significantly reduced ϕLBO, indicating an effective enhancement of NH3 combustion by partial pre-cracking strategy. Nevertheless, NO and NO2 emissions exhibit a substantial increase with larger γ. Opposite trends of NO and NH3 emissions versus equivalence ratio (ϕ) suggest a trade-off between NO and NH3 emissions, with relatively low NO/NH3 window appearing under slightly-rich (ϕ = 1.0–1.1) conditions. Low NO emissions are also noted under ultra-lean conditions (ϕ = 0.4–0.5) with the penalty of high NH3 and N2O emissions, making it an unacceptable trade-off. Furthermore, the effect of N2 separation from the partially pre-cracked NH3 mixtures was evaluated at γ = 0.4. The results show deteriorating effects on NOx emissions, resulting in 13 % and 21 % increases in peak NO and NO2 emissions, respectively, which implies more feasibility to burn the partially pre-cracked NH3 in a direct manner rather than N2 separation.

Dominant contribution of combustion-related ammonium during haze pollution in Beijing

Aerosol ammonium (NH4+), mainly produced from the reactions of ammonia (NH3) with acids in the atmosphere, has significant impacts on air pollution, radiative forcing, and human health. Understanding the source and formation mechanism of NH4+ can provide scientific insights into air quality improvements. However, the sources of NH3 in urban areas are not well understood, and few studies focus on NH3/NH4+ at different heights within the atmospheric boundary layer, which hinders a comprehensive understanding of aerosol NH4+. In this study, we perform both field observation and modeling studies (the Community Multiscale Air Quality, CMAQ) to investigate regional NH3 emission sources and vertically resolved NH4+ formation mechanisms during the winter in Beijing. Both stable nitrogen isotope analyses and CMAQ model suggest that combustion-related NH3 emissions, including fossil fuel sources, NH3 slip, and biomass burning, are important sources of aerosol NH4+ with more than 60% contribution occurring on heavily polluted days. In contrast, volatilization-related NH3 sources (livestock breeding, N-fertilizer application, and human waste) are dominant on clean days. Combustion-related NH3 is mostly local from Beijing, and biomass burning is likely an important NH3 source (∼15%–20%) that was previously overlooked. More effective control strategies such as the two-product (e.g., reducing both SO2 and NH3) control policy should be considered to improve air quality.

Effect of fermentation materials reflux on gaseous emissions during perishable waste composting

Aiming at the problems of low bioconversion efficiency and serious secondary pollution of urban perishable waste (PW), fermentation materials reflux was applied in PW composting to investigate the effects of reflux modes on emission of ammonia (NH3), methane (CH4) and nitrous oxide (N2O) in this study. Before that, 20% was determined to be the optimal ratio of reflux in terms of the indicators of gaseous emissions and used in the current experiment. Five treatments including CK (no-reflux), T1 (reflux mature compost (MC), completely mixed with the initial material), T2 (reflux MC, 15% for initial mixing, 5% for surface covering), T3 (reflux MC, 10% for initial mixing, 10% for surface covering) and T4 (reflux thermophilic compost (TC) and MC, 15% TC for initial mixing, and 5% MC for surface covering). T2 reduced NH3 and CH4 emission by 52.9% and 40.11%, as a result of high temperature and inhibition of methanogens in the former stage. While T4 reduced the most N2O emission by 56.85% through the restraint of denitrification. In conclusion, the introduction of fermentation materials can accelerate the composting process, improve maturity, and mitigate greenhouse gas (GHG) emissions ranging from 27.61% to 58.05%, which can provide theoretical and technical support for rapid composting of urban PW in the future.

Life cycle assessment of hemp-based milk alternative production in Lower Saxony, Germany, based on a material flow analysis of a pilot scale

PurposeRecently, demand for plant-based milk products (PBMP) has increased for multiple reasons, such as the rapid population growth expected to reach 9.7 billion by 2050, health concerns such as lactose intolerance, nutritional aspects, ethical reasons, and environmental concerns. This leads to increased demand for food and competition for natural resources. Hemp-based milk is an emerging dairy alternative, and stakeholders in the supply chain are becoming increasingly interested in learning about the environmental effects of its production. This article aims for a comparative life cycle assessment of hemp-based and bovine milk with fat and protein correction to account for the differences in macronutrient content.MethodsThe cradle-to-factory gate LCA relied on experimental cultivation and milk production in Lower Saxony, Germany. Inventory was based on primary data from fields and the pilot plant of DIL e. V. and on literature and ecoinvent database to develop a life cycle assessment (LCA) model. The LCA was performed using Simapro 9.3 software and IMPACT 2002+ impact assessment method. The life cycle stages include cultivation, harvesting, and milk production. The study compared hemp-based milk to bovine milk based on 1 kg fat and protein-corrected milk (FPCM) as a functional unit (FU). Co-products are taken into consideration using mass-economic allocation.ResultsThe results showed that hemp cultivation accounted for the highest impact (99%) in the production chain of hemp milk production. The GWP of 1 kg of FPCM hemp-based milk is 0.42 kg CO2 eq. The energy consumption for 1 kg of FPCM hemp-based milk is 4.73 MJ (12.26% lower than bovine milk). The other main factors impacting hemp-based milk production were terrestrial ecotoxicity (6.444E2 kg TEG soil) and aquatic ecotoxicity (2.458E2 kg TEG water). Hemp fiber was the co-product with 40% of the allocated impacts. The results are sensitive to the changes in fat-protein contents, functional unit, and system boundaries. The results demonstrated that the impacts of hemp milk production were within the range indicated for other PBMP production and 51.7% lower than bovine milk production in terms of GWP. This range primarily stems from field emissions, fertilizer application, and machinery usage during cultivation and harvest.ConclusionThe results of the comparisons of bovine milk and hemp-based milk were dependable on the FU. The hemp-based milk has the potential to be a more sustainable alternative to bovine milk due to considerably lower impacts in impact categories—land occupation (99% lower than bovine milk), global warming (52% lower than bovine milk), and ionizing radiation (23% lower than bovine milk). It is primarily due to less use of agricultural machinery, less land requirement, and lower NH3 emissions than bovine milk in various stages of milk production.

Large Seasonal Variation in Nitrogen Isotopic Abundances of Ammonia Volatilized from a Cropland Ecosystem and Implications for Regional NH3 Source Partitioning.

Ammonia (NH3) volatilization from agricultural lands is a main source of atmospheric reduced nitrogen species (NHx). Accurately quantifying its contribution to regional atmospheric NHx deposition is critical for controlling regional air nitrogen pollution. The stable nitrogen isotope composition (expressed by δ15N) is a promising indicator to trace atmospheric NHx sources, presupposing a reliable nitrogen isotopic signature of NH3 emission sources. To obtain more specific seasonal δ15N values of soil NH3 volatilization for reliable regional seasonal NH3 source partitioning, we utilized an active dynamic sampling technique to measure the δ15N-NH3 values volatilized from maize cropping land in northeast China. These values varied from -38.0 to -0.2‰, with a significantly lower rate-weighted value observed in the early period (May-June, -30.5 ± 6.7‰) as compared with the late period (July-October, -8.5 ± 4.3‰). Seasonal δ15N-NH3 variations were related to the main NH3 production pathway, degree of soil ammonium consumption, and soil environment. Bayesian isotope mixing model analysis revealed that without considering the seasonal δ15N variation in soil-volatilized NH3 could result in an overestimate by up to absolute 38% for agricultural volatile NH3 to regional atmospheric bulk ammonium deposition during July-October, further demonstrating that it is essential to distinguish seasonal δ15N profile of agricultural volatile NH3 in regional source apportionment.

Insight into hydroxyl groups in anchoring Ir single–atoms on vacancy–deficient rutile TiO2 supports for selective catalytic oxidation of ammonia

High–performance catalysts are extremely required for controlling NH3 emission via selective catalytic oxidation (SCO), and the anchoring structural feature of active sites is a key prerequisite for developing them. This study confirms the importance of hydroxyl groups on vacancy–deficient reducible oxides as active groups. On the one hand, spontaneous atomic dispersion of active metal Ir is promoted by the abundant terminal hydroxyl groups. On the other hand, Ir cations anchor on the TiO2 surface through exchange with H+ in Ti–OH groups, and thus occupy the Brönsted acid sites. The adsorption strength of NH3 is another key factor affecting the reaction rate–determining step, namely NH3 dehydrogenation, which occurs at a faster rate in the coordinated L–NH3 rather than the ionic B–NH4+. Meanwhile, the coordinated L–NH3 significantly avoids the competitive adsorption of water vapor in the NH3–SCO reaction by reducing the number of hydrogen bonding. The TOF of preferred 0.8Ir/TiO2 sample is significantly higher than 0.2Ir/TiO2 sample, although Ir is almost always atomic dispersed. Finally, NH3 conversion is 85% in a wet circumstance (5% H2O) at 240 °C (GHSV = 85 000 h–1), with a N2 selectivity of up to 65% on 0.8Ir/TiO2 sample.

Enhancing pure NH3 combustion: Impacts of O2 enrichment under MILD conditions in a 20-kW semi-industrial scale furnace

This experimental work provides insights into the effects of oxygen (O2) enrichment on pure ammonia (NH3) combustion in a 20-kW semi-industrial scale furnace featuring an industrial-grade burner operated under MILD/Flameless conditions. The impact of O2 enrichment on the NH3 combustion stabilization, the flame and furnace temperature, the exhaust emissions, and the OH* chemiluminescence were explored. The tests were conducted by varying O2 concentration in the oxidizer stream from 21 % to 50 % and using two different oxidizer injectors to achieve average inlet velocities of 80 m/s and 150 m/s while keeping the inlet power and the total oxidizer mass flow rate constant. Stable flameless combustion with a distributed reaction zone and a consistent and uniform temperature profile throughout the combustion chamber was achieved with O2 enrichments higher than 34 %. Nevertheless, high levels of NH3 slips were observed, which were drastically reduced to negligible concentrations at higher O2 enrichments. On the contrary, NO emissions increased with the O2 fraction with an opposite non-linear trend compared to that of NH3 slip. An optimum trade-off between NOx emissions and NH3 slip was achieved by co-firing NH3 with O2=37 % with ID16 and 36 % with ID20 injector. This study also compares the behavior of pure O2-enriched NH3 combustion under flame and MILD combustion conditions to highlight the advantages of oxygen-enhanced NH3 flameless combustion. While operating in flame mode ensured a stable ammonia oxidation process already at low O2 enrichment=30 %, NO emissions and NH3 slips were significantly higher than those measured under MILD conditions. Finally, the impact of varying industrial load and the related heat balance on the NH3 slip was assessed at different levels of O2 enrichments at a fixed equivalence ratio. The overall results show that O2-enriched flameless ammonia combustion can simultaneously expand the range of stable combustion and reduce NO and NH3 emissions.

Comprehensive multi-gas study by means of fiber-enhanced Raman spectroscopy for the investigation of nitrogen cycle processes.

The extensive use of synthetic fertilizers has led to a considerable increase in reactive nitrogen input into agricultural and natural systems, resulting in negative effects in multiple ecosystems, the so-called nitrogen cascade. Since the global population relies on fertilization for food production, synthetic fertilizer use needs to be optimized by balancing crop yield and reactive nitrogen losses. Fiber-enhanced Raman spectroscopy (FERS) is introduced as a unique method for the simultaneous quantification of multiple gases to the study processes related to the nitrogen cycle. By monitoring changes in the headspace gas concentrations, processes such as denitrification, nitrification, respiration, and nitrogen fixation, as well as fertilizer addition were studied. The differences in concentration between the ambient and prepared process samples were evident in the Raman spectra, allowing for differentiation of process-specific spectra. Gas mixture concentrations were quantified within a range of low ppm to 100% for the gases N2, O2, CO2, N2O, and NH3. Compositional changes were attributed to processes of the nitrogen cycle. With help of multivariate curve resolution, it was possible to quantify N2O and CO2 simultaneously. The impact of fertilizers on N-cycle processes in soil was simulated and analyzed for identifying active processes. Thus, FERS was proven to be a suitable technique to optimize fertilizer composition and to quantify N2O and NH3 emissions, all with a single device and without further sample preparation.