High NO Research Articles

Study on revision of standard limits for nitrogen dioxide in "Standards for indoor air quality（GB/T 18883-2022）" in China

Nitrogen dioxide (NO2) is an important indoor air pollutant, with both outdoor and indoor sources contributing to indoor NO2 exposure levels. Considering the association of high NO2 exposure with adverse health effects, the Standards for indoor air quality (GB/T 18883-2022) have been revised to further restrict indoor NO2 limit values. The 1-h average concentration limit value for NO2 has been reduced from 0.24 mg/m3 to 200 μg/m3.This study analyzed the technical contents related to the determination of the limits of indoor NO2 in Standards for Indoor Air Quality (GB/T 18883-2022), including source, exposure level, health effects, and the process and evidence basis for determining the limit value. It also proposed prospects for the direction for the implementation of the indoor NO2 standard.

Evaluation of nitrous oxide emission during ammonia retention from simulated industrial wastewater by microaerobic activated sludge process

Considering the reciprocating processes of nitrogen gas (N2) fixation to ammonia (NH4-N) and NH4-N removal to N2 through nitrification and denitrification during wastewater treatment, a microaerobic activated sludge process (MAS) is proposed in this study as a pretreatment to retain NH4-N from high-strength nitrogenous wastewater for further NH4-N recovery through membrane technology, that is, inhibit nitrification, with sufficient removal of total organic carbon (TOC). With DO and pH control, the 3-reactor bench-scale MAS systems successfully realized an NH4-N retention rate of over 80 %, with TOC removal rates of over 90 %. In addition, the emissions of carbon dioxide (CO2) and nitrous oxide (N2O) during MAS were evaluated. The total N2O emissions were 407 and 475 mg-N/day when pH was controlled at 6.2 (S1) and 6.8 (S2), respectively, with average emission factors to total nitrogen load over 2 % in both systems. Also, the global warming potential of N2O is one order of magnitude larger than that of CO2, indicating the significance of N2O in the MAS process. Therefore, the mechanisms of N2O emission from each reactor were investigated. The first reactor, where most of the TOC was adsorbed, emitted only 1.98 % (S1) and 2.43 % (S2) of the total N2O emissions through the denitrification of nitrite and nitrate (NOx) from the return sludge. The second reactor emitted 79.9 % (S1) and 69.0 % (S2) of the total N2O with the emission rates the same order of magnitude as the NOx production rates. Multiple pathways were considered to contribute to the high N2O emissions, and biotic NH2OH oxidation was one potential pathway at pH 6.2. Finally, the third reactor emitted 9.98 % (S1) and 16.8 % (S2) of the total N2O by nitrifier denitrification. Overall, this study showed that the large N2O emissions under nitrification-inhibiting conditions of the MAS process owed to the incomplete nitrification under acidic conditions and large abundances of denitrifiers. On the other hand, the lower N2O emissions at pH 6.2 evidenced the potential N2O mitigation under slightly more acidic conditions, underlining the necessity of further study on N2O mitigation when adapting to the trend of NH4-N recovery.

Impact of NO2 emissions from household heating systems with wall-mounted gas stoves on indoor and ambient air quality in Chinese urban areas

Nitrogen dioxide (NO2) has been discussed as a typical indoor pollutant for decades. As an increasingly popular heating method, household heating system (HHS) with wall-mounted natural gas stoves has led to a continuous increase in the emission of NO2. The absence of legal regulations and strict limits for NO2 emissions from wall-mounted gas stoves has led to a significant exceedance of indoor NO2 concentrations beyond the permissible value. However, this issue is rarely taken into consideration. In this study, we present the first report on NO2 emissions from wall-mounted gas stoves for household heating and their impact on indoor and ambient air quality in Chinese urban areas based on in-situ measurements and numerical simulations. On heating days, the observed indoor NO2 concentration is within 80-200 μg/m3, much higher than the outdoor atmospheric concentration. With a low emission grade of the wall-mounted gas stoves, it is estimated that >10 % of residents in a typical residential building area are exposed to a high NO2 concentration of >200 μg/m3, and >50 % of residents are exposed to a concentration of >80 μg/m3. In addition, the indoor NO2 concentration shows an obvious non-uniform distribution with the floor in residential buildings. The NO2 emission from residential natural gas heating also shows an obvious impact on the microenvironment around buildings, which is primarily determined by the emission grade of the stoves. The findings highlight that HHS has become a non-negligible source of indoor NO2 pollution in China. It is urgently necessary to formulate NO2 emission limit standards for wall-mounted gas stoves in Chinese urban areas and upgrade traditional natural gas heaters with efficient emission reduction technologies.

Methanol (M85) Port Fuel-Injected Spark Ignition Motorcycle Engine Development—Part 1: Combustion Optimization for Efficiency Improvement and Emission Reduction

<div>Limited fossil fuel resources and carbonaceous greenhouse gas emissions are two major problems the world faces today. Alternative fuels can effectively power internal combustion engines to address these issues. Methanol can be an alternative to conventional fuels, particularly to displace gasoline in spark ignition engines. The physicochemical properties of methanol are significantly different than baseline gasoline and fuel mixture-aim lambda; hence methanol-fueled engines require modifications in the fuel injection parameters. This study optimized the fuel injection quantity, spark timing, and air–fuel ratio for M85 (85% v/v methanol + 15% v/v gasoline) fueling of a port fuel-injected single-cylinder 500 cc motorcycle test engine. Comparative engine performance, combustion, and emissions analyses were performed for M85 and baseline gasoline. M85-fueled engine exhibited improved combustion characteristics such as higher peak in-cylinder pressure, heat release rate, and cumulative heat release due to higher flame speed and the effect of fuel oxygen. The brake thermal efficiency increased by up to 23% at lower loads and 8% at higher loads for M85 fueling. Carbon monoxide was reduced by 11.4–94% and 46.1–94.4% for M85 w.r.t. baseline gasoline at 2500 and 3500 rpm, respectively, at varying engine loads. Hydrocarbon emissions showed mixed trends for M85 w.r.t. baseline gasoline. Nitric oxide emissions were 4–90.2% higher for M85 w.r.t. baseline gasoline at 2500 rpm, at varying engine loads; however, mixed trends were observed at 1500 and 3500 rpm. Carbon monoxide, hydrocarbons, and nitric oxide emissions were 4.6, 38.9, and 84.3% lower for M85 than baseline gasoline during idling. Overall the M85-fueled motorcycle engine emitted fewer harmful pollutants, indicating its superior environmental sustainability, except for slightly higher NO emission.</div>

Estimate of near-surface NO2 concentrations in Fenwei Plain, China, based on TROPOMI data and random forest model.

Nitrogen dioxide (NO2) concentration is a crucial indicator of ground-level air quality, and elevated concentrations can adversely affect human health and the atmospheric environment. In this study, we utilized Tropospheric Monitoring Instrument (TROPOMI) tropospheric NO2 vertical column density data (VCD) and multi-source geographic data to establish a random forest regression (RF) model that accurately estimates NO2 concentrations near the ground in the Fenwei Plain. The model addresses the inherent limitations of traditional ground-based monitoring and provides data support for analyzing regional pollution spatial and temporal characteristics. (1) The RF model based on TROPOMI and geographic data demonstrates high estimation accuracy, with monthly average RF model fit and validation coefficient of determination (R2) reaching 0.949 and 0.875, respectively. (2) A complex nonlinear relationship exists between near-surface NO2 concentration and multi-source geographic data. The RF model's estimations reveal clear seasonal and regional variations in near-surface NO2 concentration. Concentrations are generally highest in winter, followed by spring and autumn, and lowest in summer. The high NO2 concentrations are primarily mainly distributed in the plains and river valleys with low elevation and dense population density. The model estimation results also indicate that the estimated effect is better when the NO2 concentration fluctuates less and anthropogenic emission reduction measures significantly impact the NO2 concentration near the ground. (3) The population exposure risk results indicate that most cities in the Fenwei Plain face varying exposure risks. These findings offer valuable insights for regional NO2 pollution management.

Binary Metal-Oxide Active Sites Derived from Cu-Doped MIL-88 with Enhanced Electroactivity for Nitrate Reduction.

Nitrate-to-ammonia electrochemical conversion is important for decreasing water pollution and increasing the production of valuable ammonia. However, achieving high ammonium production without undesirable byproducts is difficult. Cu-doped MIL-88-derived bimetallic oxide catalysts with electrocatalytically active Fe-O-Cu bridges, which have high NO3- adsorption energy and facilitate N-intermediate hydrogenation, are developed for NH4+ production. Cu doping promotes hybridization between the O 2p of NO3- and Fe-Cu 3d, facilitating the adsorption and reduction of NO3- with a low Tafel slope (62.1 mV dec-1) and high ammonia yield (1698.8 μg·h-1·cm-2). The cathode efficiency is stable for seven cycles. Cu adjacent to Fe sites inhibits hydrogen evolution, promotes NO3- adsorption, and decreases the intermediate adsorption energy barrier. This study provides new opportunities for fabricating diverse binary metal oxides with new interfaces as efficient cathode materials for selective electroreduction.

Molecular Cloning, Expression and Transport Activity of SaNPF6.3/SaNRT1.1, a Novel Protein of the Low-Affinity Nitrate Transporter Family from the Euhalophyte Suaeda altissima (L.) Pall.

The SaNPF6.3 gene, a putative ortholog of the dual-affinity nitrate (NO3-) transporter gene AtNPF6.3/AtNRT1.1 from Arabidopsis thaliana, was cloned from the euhalophyte Suaeda altissima. The nitrate transporting activity of SaNPF6.3 was studied by heterologous expression of the gene in the yeast Hansenula (Ogataea) polymorpha mutant strain Δynt1 lacking the original nitrate transporter. Expression of SaNPF6.3 in Δynt1 cells rescued their ability to grow on the selective medium in the presence of nitrate and absorb nitrate from this medium. Confocal laser microscopy of the yeast cells expressing the fused protein GFP-SaNPF6.3 revealed GFP (green fluorescent protein) fluorescence localized predominantly in the cytoplasm and/or vacuoles. Apparently, in the heterologous expression system used, only a relatively small fraction of the GFP-SaNPF6.3 reached the plasma membrane of yeast cells. In S. altissima plants grown in media with either low (0.5 mM) or high (15 mM) NO3-; concentrations, SaNPF6.3 was expressed at various ontogenetic stages in different organs, with the highest expression levels in roots, pointing to an important role of SaNPF6.3 in nitrate uptake. SaNPF6.3 expression was induced in roots of nitrate-deprived plants in response to raising the nitrate concentration in the medium and was suppressed when the plants were transferred from sufficient nitrate to the lower concentration. When NaCl concentration in the nutrient solution was elevated, the SaNPF6.3 transcript abundance in the roots increased at the low nitrate concentration and decreased at the high one. We also determined nitrate and chloride concentrations in the xylem sap excreted by detached S. altissima roots as a function of their concentrations in the root medium. Based on a linear increase in Cl- concentrations in the xylem exudate as the external Cl- concentration increased and the results of SaNPF6.3 expression experiments, we hypothesize that SaNPF6.3 is involved in chloride transport along with nitrate transport in S. altissima plants.

Unravelling spatiotemporal N2O dynamics in an urbanized estuary system using natural abundance isotopes

Estuaries are strong sources of N2O to the atmosphere; yet we still lack insights into the impact of their biogeochemical dynamics on the emissions of this powerful greenhouse gas. Here, we investigated the spatiotemporal dynamics of the N cycle in an estuary with a focus on the emission mechanisms and pathways of N2O. By coupling N2O isotopocule analysis and substrate NO3− isotope analysis, we found that nutrient availability, oxygen level, salinity gradient and temperature variation were major drivers of the N2O emissions from the Scheldt Estuary. In winter, lower temperature and higher O2 concentration diminished denitrification rates and reduction of N2O to N2, while both were enhanced in warmer summer, causing higher fraction of reduced N2O. As a result, we found comparable N2O fluxes and dissolved concentrations between the two seasons. Decrease in salinity level and increase in NO3− concentration accelerated N2O production when moving upstream of the estuary where more urbanization and higher NO3− from wastewater discharges were found. However, these drivers had no significant effect on the fraction of N2O derived by either denitrification or nitrification and/or fungal denitrification since the fractional proportion of these pathways showed no spatiotemporal variations, remaining around 89 % and 11 %, respectively. These findings challenge the conventional notion that N2O fluxes are generally higher in summer because of higher denitrification rates while confirming that denitrification is the most important pathway of N2O production in the estuaries. Furthermore, our study highlight the importance of combining various isotope analyses to gain in-depth understanding about N2O emission pathways and N cycling in dynamic systems like estuaries.

Groundwater hydrogeochemistry and non-carcinogenic health risk assessment in major river basins of Punjab, India.

The Indian Punjab state is drained by the four rivers, along with a well-connected network of canals, and is now dealing with a slew of water quality issues and problems. In this study, basin-wise hydrogeochemical modelling of 323 groundwater samples and identification of NO3- and F- enrichment pathways in aquifer systems of Punjab were studied using different plots and multivariate statistics. To evaluate the groundwater quality and human health risks, an entropy-based water quality index and Monte Carlo simulation were used, respectively. Spatial distribution of NO3- indicated that its very high values were prominent in parts of southwestern Punjab falling under LSRB, along with few pockets in eastern and northeastern Punjab falling under MSRB and GRB. High NO3- values (> 45.0mg/L) were found in 15.0% of Ravi River Basin (RRB) groundwater samples, 22.86% of Beas River Basin (BRB), 23.52% of Middle Sutlej River Basin (MSRB), 36.9% of Lower Sutlej River Basin (LSRB), and 21.31% of Ghaggar River Basin (GRB). The spatial distribution of NO3- revealed elevated concentrations (> 100mg/L) in the southwestern part of Punjab, particularly in LSRB and localized pockets in the eastern and northeastern areas of Punjab within MSRB and GRB. High F- concentration (> 1.5mg/L) was observed in 15.12% and 21.31% groundwater samples of LSRB and GRB, respectively. Spatially southern parts falling under LSRB and GRB reflected high F- content (> 1.5mg/L) in groundwater. In LSRB, evaporative and anthropogenic processes influence the groundwater quality. The results of interionic relationships and statistical analysis revealed that NO3- has anthropogenic origin and that is being aggravated by leaching,the evaporation processes, animal excreta, septic tanks and irrigation return flows in LSRB and GRB, while F- is geogenic in nature. Hazard index (HI) values in 14.63%, 22.2%, 24.6%, 49.58%, and 34.42% samples for adults and 21.95%, 27.7%, 42.0%, 72.3%, and 52.46% samples for children were higher than unity in RRB, BRB, MSRB, LSRB, and GRB, respectively. The basin-wise demarcation of various groundwater quality parameter and assessment of human health risk would be of significance for the management of water resources.

Threshold-like effect of soil NO3− concentrations on denitrification product N2O/(N2O+N2) ratio is mediated by soil pH

The interactive effects of soil pH and nitrate (NO3−) availability on denitrification-derived nitrous oxide (N2O) and dinitrogen (N2) emissions, as well as N2O/(N2O + N2) product ratio (N2Oi) remain difficult to evaluate. Here, we consecutively monitored denitrification-derived N2O and N2 emissions with different soil pH and NO3− concentrations by using the artificial 15N gas flux method in combination with a global meta-analysis of 458 observations to illustrate the interactive effects of soil pH and NO3− availability on N2Oi. Isotopic data indicated that pH adjustment through liming significantly and nonlinearly reduced N2Oi and increased cumulative N2 emissions. Liming decreased cumulative N2O emissions by approximately threefold in low NO3− treatments (p < 0.01), while at high NO3− treatments liming showed no effect. The meta-analysis revealed a logarithmic relationship between N2Oi and increasing soil NO3− concentrations across different soil pH levels, indicating a threshold-like effect of NO3− concentrations on the reduction of N2O during denitrification. The threshold NO3− concentration tends to raise with increasing soil pH. Hence, there were significant interaction effects of soil pH and soil NO3− concentration on the N2Oi value. The present study emphasizes the need to consider soil pH and NO3− concentration interaction effects on denitrification for proposing the effective mitigation practices of denitrification-derived soil N2O emissions.

Undercovering the role of physicochemical properties of amides in two-phase absorbent systems for ship exhaust pollutant removals

The use of two-phase absorbents containing amides to treat ship pollutants is a new research solution that can achieve high NO oxidation rates and NO2 absorption rates. This paper studies the physicochemical properties of five different amides and their relationship with the desulfurization and denitrification processes. It was found that nitrous acid molecules undergo an isomerization rearrangement in the amide and combine in a more stable form during the NOx absorption process. The polarity and viscosity of the amide are more critical than the min ESP value in removing pollutants. The high polarity and low viscosity of DBA (N,N-Dibutylacetamide) provide dual advantages, facilitating the interaction between the organic and aqueous phases, as well as enhancing the mass transfer process and the combination of an inorganic acid. The system containing DBA achieved removal efficiencies of 99.6% for SO2, 86.33% for NO, and 86.3% for NOx in 10 min. Overall, this study provides valuable insights into the use of organic-containing two-phase absorbents to reducing ship exhaust pollution.

Periodic Defect Engineering of Iron-Nitrogen-Carbon Catalysts for Nitrate Electroreduction to Ammonia.

Iron-nitrogen-carbon single atom catalyst (SAC) is regarded as one of the promising electrocatalysts for NO3 - reduction reaction (NO3 RR) to NH3 due to its high activity and selectivity. However, synergistic effects of topological defects and FeN4 active moiety in Fe-N-C SAC have rarely been investigated. By performing density functional theory (DFT) calculations, 13 defective graphene FeN4 with 585, 484, and 5775 topological line defects are constructed, yielding 585-68-FeN4 with optimal NO3 RR catalytic activity, high selectivity, as well as robust anti-dissolution stability. The high NO3 RR activity on 585-68-FeN4 is well explained by the high valence state of Fe center as well as asymmetric charge distribution on FeN4 moiety influenced by 5- and 8-member rings. This DFT work provides theoretical guidance for engineering NO3 RR performance of iron-nitrogen-carbon catalysts by modulating periodic topological defects.

Bimetallic atom synergistic covalent organic framework for efficient electrochemical nitrate reduction

Electrochemical reduction has emerged as an effective method to remove nitrate from industrial wastewater. Nevertheless, this method has been largely restricted by the lack of low-cost and efficient electrocatalysts. Here, we demonstrate a porous two-dimensional covalent organic framework (2D COF) material as a promising electrocatalyst, which is obtained via a Schiff base reaction by combining copper phthalocyanine with bipyridine sites for precise copper coordination. The bidentate coordinated COF material has a robust framework and stable chemical property, allowing the isolated Cu sites to be embedded into the regular pores with controlled and uniformly dispersed active centers. The well-defined design of the reaction monomers makes the COF material to trap nitrate ions more easily from aqueous solution. By rationally combining the synergistic effect of 2D COF and Cu active sites, the CuTAPc-CuBPy-COF electrocatalyst shows much higher nitrate reduction efficiency than CuTAPc-BPy-COF under low superpotential and different nitrate concentrations. The high NO3− conversion (90.3 %) and NH3 selectivity (69.6 %) are achieved. To our best acknowledge, this is the first demonstration of bi-copper-based COF material for NO3−RR electrocatalysis, which provides a new direction for the rational design of COFs as significant electrocatalysts for nitrate reduction.

Chemical kinetic and behavior study of the cracked gas of H2/N2 and DME addition on ammonia combustion in lean-burn condition

The comparisons between the cracked gas and DME addition with a certain proportion on combustion behaviors are studied. A mechanism for the prediction of ammonia/H2/DME is updated based on the previously developed one. Since it is important to use a simplified mechanism in 3D numerical simulations, mechanism simplification is conducted, resulting in one with 72 species and 459 reactions. The premixed laminar flame simulations indicate that both the fuel cracking with hydrogen production and DME addition with a small amount can enhance laminar burning velocity (LBV) and extend lean-burn limit. NO is increased with hydrogen or DME addition due to the chemical and thermal effects, and comparatively, adding cracked gas leads to lower NO generation for the same blending ratio. The 3D simulated results shows that a sudden increase of HNO for DME addition during the combustion induces a higher NO formation relatively to that for hydrogen addition.

Study on denitrification of hydroponic wastewater reverse osmosis concentrate using sulfur-autotrophic denitrification

Hydroponic agriculture is one of the sectors that generate the highest amounts of nitrogen-containing wastewater. Sulfur-autotrophic denitrification is considered a promising technology due to its stable and excellent denitrification performance, cost-effectiveness, and operational advantages. In order to investigate the denitrification performance and the contribution of the filter layer under high NO3--N concentration (600 mg·L−1), this experiment designed a denitrification system using Na2S2O3 as an electron donor. The results showed that the reactor achieved the highest denitrification efficiency with a hydraulic retention time of 12 h, pH of 7, and sulfur to nitrogen ratio of 2, maintaining a stable NO3--N removal efficiency of 99%. The majority of NO3--N was removed by the bottom filter layer (0–300 mm), accounting for 86% of the total denitrification. The microbial community in the lower part of the filter column was dominated by Proteobacteria, with relatively high abundances of the genera Chryseobacterium, Thiobacillus, and Sulfurimonas. Similarly, the microbial community structure in the upper filter layer was dominated by Proteobacteria, with an increased abundance of the genus Chryseobacterium and a significant reduction in the abundance of Sulfurimonas. The study indicates that SAD can achieve stable and efficient denitrification of wastewater from hydroponic reverse osmosis concentrate. Moreover, higher NO3--N concentrations can influence the bacterial community structure within the reactor.

Numerical Study on the Combustion Properties of Ammonia/DME and Ammonia/DMM Mixtures

Ammonia (NH3) is considered a promising zero-carbon fuel and was extensively studied recently. Mixing high-reactivity oxygenated fuels such as dimethyl ether (DME) or dimethoxymethane (DMM) with ammonia is a realistic approach to overcome the low reactivity of NH3. To study the combustion characteristics of NH3/DMM and NH3/DME mixtures, we constructed a NH3/DMM chemical mechanism and tested its accuracy using measured laminar burning velocity (LBV) and ignition delay time (IDT) of both NH3/DMM and NH3/DME mixtures from the literature. The kinetic analysis of NH3/DMM flames using this mechanism reveals that the CH3 radicals generated from the oxidation of DMM substantially affects the oxidation pathway of NH3 at an early stage of flame propagation. We investigated the formation of nitrogen oxides (NOx) in NH3/DMM and NH3/DME flames and little difference can be found in the NOx emissions. Using NH3/DMM flames as an example, the peak NOx emissions are located at an equivalence ratio (φ) of 0.9 and a DMM fraction of 40% in the conditions studied. Kinetic analysis shows that NOx emission is dominated by NO, which primarily comes from fuel nitrogen of NH3. The addition of DMM at 40% significantly promotes the reactive radical pool (e.g., H, O, and OH) while the maintaining a high concentration of NO precursors (e.g., HNO, NO2, and N2O), which results in a high reaction rate of NO formation reaction and subsequently generates the highest NO emissions.

Pyrimidine-5-carbonitrile derivatives as sprout for CQDs proveniences: Antitumor and anti-inflammatory potentiality

A comparative study is proposed to show the effect of variation in the heteroatoms in the main skeleton of CQDs proveniences, on their affinity for nucleation of CQDs, as anti-inflammatory and anticancer drugs. Heterocyclic-based CQDs sprout was successfully exploited for preparation of three CQDs proveniences, named as; 2-(2,5-dimethoxyphenyl)-4,6-dioxo-6,11-dihydro-4H-pyrimido[2,1-b] quinazoline-3-carbonitrile (compound A), 2-(2,5-dimethoxyphenyl)-4,6-dioxo-4H,6H-benzo[e]pyrimido[2,1-b][1,3]oxazine-3-carbonitrile (compound S) and 2-(2,5-dimethoxyphenyl)-4,6-dioxo-4H,6H-benzo[e]pyrimido[2,1-b][1,3] thiazine-3-carbonitrile (compound T). Chemical formulas of CQDs proveniences & CQDs were verified via FTIR, 1HNMR, 13CNMR & XRD. Particle size of TM-CQDs, A-CQDs, S-CQDs &T-CQDs were estimated to be 3.7 ± 1.4, 4.6 ± 1.6, 5.9 ± 1.6 nm and 3.0 ± 1.3 nm, respectively. All of CQDs proveniences & CQDs were examined for their affinity as anti-inflammatory drugs via Griess assay. CQDs ingrained from TM (TM-CQDs) were detected with the highest NO inhibition% by increasing its concentration from 10 up to 100 μM to be 40 % to 89 %, respectively. Moreover, their anti-tumor performance against MCF-7: breast Adenocarcinoma cell line was approved via sulforhodamine B assay, whereas, IC50 was evaluated for TM-CQDs, A-CQDs, S-CQDs and T-CQDs to be 38.16, 36.09, 100 and 100 μg/ml, respectively.

Matching fertilization with available soil water storage to tackle the trade-offs between high yield and low N2O emissions in a semi-arid area: Mechanisms and solutions

Matching fertilization with available soil water storage to tackle the trade-offs between high yield and low N2O emissions in a semi-arid area: Mechanisms and solutions

High NO2 sensing for room temperature: A multifunctional hydrophobic sensitive layer with compatible flexible and ultraviolet activated

High NO2 sensing for room temperature: A multifunctional hydrophobic sensitive layer with compatible flexible and ultraviolet activated

Prediction of NOx emissions and pathways in premixed ammonia-hydrogen-air combustion using CFD-CRN methodology

Ammonia-hydrogen blends have gained significance as they are carbon-free energy-dense fuels. However, NOx emissions have been a significant concern. In this study, the emissions from the premixed combustion of 70/30VOL.% NH3/H2 blend is studied using the computational fluid dynamics (CFD)- chemical reactor network (CRN) approach. The velocity, temperature, and species field are first obtained using CFD, based on which, a network consisting of perfectly stirred reactors (PSR) and plug flow reactor (PFR) is constructed. Three mechanisms have been implemented in the CRN to predict the NO and N2O emissions. It is shown that the trend of NOx is correctly predicted by the CRN over a wide range of equivalence ratios (φ) of 0.65–1.2 as compared to the authors’ recently published experimental data. It is demonstrated that a single CRN (based on the CFD for a specific φ) can be run to cover the range of φ = 0.65 to 1.2 b y scaling the temperature input to each reactor of the CRN. To contrast the NO pathways at different φ, quantitative reaction pathway diagrams (QRPD) are constructed, and dominant production and consumption pathways of NO for lean and rich combustion are established. The shifts in reaction pathways with φ are noted and found to be governed by OH, O, and H radicals. Next, the effect of stoichiometry on these radicals is established. Finally, the experimental trend of high NO close to stoichiometric combustion and high N2O in very lean combustion along with their respective pathways are explained.