Nitric Oxide Mole Research Articles

Quantum-cascade-laser-absorption-spectroscopy diagnostic for temperature, pressure, and NO X 2 Π 1/2 at 500 kHz in shock-heated air at elevated pressures.

The design, validation, and application of a quantum-cascade-laser-absorption-spectroscopy diagnostic for measuring gas temperature, pressure, and nitric oxide (NO) in high-temperature air are presented. A distributed-feedback quantum-cascade laser (QCL) centered near 1976c m -1 was used to scan across two transitions of NO in its ground electronic state (X 2 Π 1/2). A measurement rate of 500kHz was achieved using a single QCL by: (1) performing current modulation through a bias-tee, and (2) targeting closely spaced transitions with a large difference in lower-state energy. The diagnostic was validated in a mixture of 95% argon and 5% NO, which was shock-heated to ≈2000 to 3700K. The average mean percent differences between laser-absorption-spectroscopy (LAS) measurements and predictions from shock-jump relations for temperature, pressure, and NO mole fraction were 3.1%, 4.1%, and 6.5%, respectively. The diagnostic was then applied to characterize shock-heated air at high temperatures (up to ≈5500K) and high pressures (up to 12atm) behind either incident or reflected shocks. The LAS measurements were compared to theoretical predictions from shock-jump relations, pressure sensors mounted in the wall of the shock tube, and equilibrium values of the NO mole fraction. The average mean percent differences between LAS measurements and their aforementioned reference values were 3.2%, 10.8%, and 10.4% for temperature, pressure, and NO mole fraction, respectively. Last, a comparison between a measured NO mole fraction time history and a time-stepped homogeneous reactor simulation performed using two different chemical kinetics mechanisms is presented.

Quantitative laser-induced fluorescence of NO in ammonia-hydrogen-nitrogen turbulent jet flames at elevated pressure

Ammonia is a very promising carbon-free fuel, but its combustion is prone to generate a large amount of harmful nitric oxide (NO). Designing NO reduction strategies for ammonia flames requires computational fluid dynamics and accurate kinetic mechanisms. However, there are currently no available experimental data that can be used to validate models describing chemistry-turbulence interactions in ammonia flames. This study introduces two non-premixed turbulent jet flames that emulate some features of the cracked ammonia combustion at 5 bar, relevant to micro gas turbines. These ammonia-hydrogen-nitrogen jet flames feature well-controlled boundary conditions and are particularly amenable to modeling. A one-dimensional NO laser-induced fluorescence (NO-LIF) method was implemented and combined with 1-D Raman spectroscopy to measure the NO mole fraction quantitatively. To avoid laser absorption by ammonia, excitation in the A2Σ+−X2Π (0–1) band near 236 nm was chosen instead of the more conventional (0–0) band near 226 nm. Due to the unsteady nature of turbulent jet flames, offline NO-LIF measurements are not useful, and undesirable interferences from Rayleigh scattering and oxygen LIF were instead quantified and removed using the temperature and major species mole fractions measured with Raman spectroscopy. NO quantification algorithms were optimized and validated first with a laminar NH3–H2–N2 counterflow flame, and then applied to the turbulent jet flames. Results show that a large amount of NO (∼1500 ppm) is produced in the NH3–H2–N2 jet flames. Increasing the ammonia cracking ratio from 14% to 28% reduces the NO concentration in laminar and turbulent NH3–H2–N2 flames. Data also shows that turbulence smear effects of differential diffusion. To the best of our knowledge, this is the first available database featuring quantitative measurements of spatially-resolved NO mole fraction in turbulent NH3–H2–N2 flames at a practically-relevant pressure. This unique database can be used in the future to validate turbulent combustion models for such flames.

Simultaneous detection of three chemical species (NO, O, O2) using a single broadband femtosecond laser

Simultaneous nitric oxide (NO) laser-induced fluorescence (LIF), atomic oxygen (O) two-photon LIF (TPLIF), and molecular oxygen (O2) LIF were demonstrated using a single broadband femtosecond (fs) laser in methane- and hydrogen-fueled flames. An amplified Ti:Sapphire laser with ∼80-fs pulse duration was used to pump an optical parametric amplifier (OPA) to generate 226.1-nm pulses having 2.3 nm (∼450 cm−1) bandwidth to excite all three species simultaneously. The specific excitation transitions are NO A-X (0,0) system, O 3p3P←←2p3P two-photon transition, and O2B3Σu−−X3Σg− Schumann-Runge system. Detailed emission characterization was performed using a 1D imaging spectrometer to identify suitable emission bands for interference-free detection of each species. A simultaneous detection system consisting of a visible and a UV camera provided the optimal detection of all three species. Imaging studies revealed high concentrations of NO, O, and O2 at the edge of the flame cone of Bunsen flames because NO and O are produced at the hot flame front. O2 LIF signal was present only at the flame front because of the strong temperature dependence of the O2 Schumann-Runge system. Direct imaging of O TPLIF enabled single-shot as well as high-fidelity shot-averaged line images in stable laminar flames. Equivalence ratio scans in the CH4/air Hencken flames showed good agreements for O and O2 with Cantera equilibrium predictions performed using GRI-Mech 3.0. Although the NO measurements deviated from the equilibrium calculations on the fuel-rich side, it agreed well with previously reported NO LIF measurements in a similar flame. This discrepancy is likely due to Prompt NO, which was not considered in the simulation. NO LIF measurements as a function of height-above-the-burner in the H2/air Hencken flames agreed well with calculated NO mole fractions using the UNICORN flame code. The present study lays the foundation for single-laser imaging of three critical flame species in NO formation pathways in combustion systems.

Tropospheric and stratospheric NO retrieved from ground-based Fourier-transform infrared (FTIR) measurements

Abstract. Nitric oxide (NO) is a key active trace gas in the atmosphere, which contributes to form harmful ozone in the troposphere and to the destruction of ozone in the stratosphere. In this study, we present the NO retrieval from ground-based Fourier-transform infrared (FTIR) solar absorption spectrometry measurements at a polluted site (Xianghe, China) and a background site (Maïdo, Reunion Island). The degree of freedom (DOF) of the NO retrieval is 2.3±0.4 (1σ) at Xianghe and 1.3±0.1 at Maïdo. By looking at the FTIR NO retrievals at Xianghe and Maïdo, we find that the stratospheric NO partial column is large in summer as compared to winter at both sites, and the seasonal variation in the FTIR stratospheric NO partial columns is consistent with that observed by the co-located Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) satellite measurements. A large diurnal variation in the stratospheric NO partial column is observed by the FTIR measurements at Maïdo, with an increase from the early morning to about 14:00 local time and a decrease thereafter. Due to the low NO concentration near the surface, the FTIR NO retrieval is only sensitive to the stratosphere at Maïdo. The high NO mole fraction near the surface at Xianghe allows us to derive tropospheric and stratospheric NO partial columns separately, although the tropospheric column is very difficult to retrieve in summer (June–August) because of the high water vapor abundance. A good correlation is found between the NO observed by the FTIR measurements and other air pollutants (NO2 and CO) in the troposphere at Xianghe. It is the first study of a successful analysis of NO in the troposphere from a ground-based FTIR site. The tropospheric and stratospheric NO retrieval might be possible at other potential FTIR sites inside or near large cities with enhanced levels of NO near the surface.

Experimental and kinetic modeling study of NO formation in premixed CH4+O2+N2 flames

The nitric oxide (NO) formation in methane (CH 4 ) flames has been widely investigated, with quite a few kinetic mechanisms available in the literature. However, studies have shown that there are often discrepancies between the simulations using various mechanisms and the experimental results. To elucidate reactions leading to these discrepancies, experiments were designed to measure the NO formation in the post flame zone of CH 4 +O 2 +N 2 flames with the oxygen ratio, x O 2 = O 2 /(O 2 +N 2 ), varying from 0.2 to 0.27. The experiments were carried out on a heat flux burner at atmospheric pressure and 298 K using saturated Laser-induced fluorescence. The equivalence ratio, ϕ , was changed from 0.7 to 1.6. The corresponding laminar burning velocity, S L , for each condition was also measured using the heat flux method. A comparison was made for the present experimental data and simulation results using the Konnov, Glarborg, NOMecha 2.0, and San Diego mechanisms, and none of them well reproduced the new NO experimental data for all investigated conditions. Numerical analyses show that the increment of NO mole fraction in stoichiometric and fuel-lean flames when the x O 2 increases is mostly defined by the thermal-NO production, which is found to be over-predicted, especially by the Konnov and San Diego mechanisms. The rate constant of reaction NO+N = N 2 +O was derived as k = 1.529 × 10 13 T − 0.0027 exp ( 185.41 [ c a l / m o l e ] R T ) cm 3 / mol s over 225–2400 K temperature range. The rate constants of four reactions controlling CH mole fraction profiles and prompt-NO formation were updated based on the analysis of the literature data that yields an improved performance of the Konnov mechanism.

NO and OH* emission characteristics of very-lean to stoichiometric ammonia–hydrogen–air swirl flames

One of the main concerns regarding ammonia combustion is its tendency to yield high nitric oxide (NO) emissions. Burning ammonia under slightly rich conditions reduces the NO mole fraction to a low level, but the penalties are poor combustion efficiency and unburnt ammonia. As an alternative solution, this paper reports the experimental investigation of premixed swirl flames fueled with ammonia-hydrogen mixtures under very-lean to stoichiometric conditions. A gas analyzer was used to measure the NO mole fraction in the flame and post flame regions, and it was found that low NO emissions (as low as 100 ppm) in the exhaust were achieved under very lean conditions (ϕ ≈ 0.40). Low NO emission was also possible at higher equivalence ratios, e.g. ϕ = 0.65, for very large ammonia fuel fractions (XNH3 > 0.90). 1-D flame simulations were performed to elaborate on experimental findings and clarify the observations of the chemical kinetics. In addition, images of OH* chemiluminescence intensity were captured to identify the flame structure. It was found that, for some conditions, the OH* chemiluminescence intensity can be used as a proxy for the NO mole fraction. A monotonic relationship was discovered between OH* chemiluminescence intensities and NO mole fraction for a wide range of ammonia-hydrogen blends (0.40 < ϕ < 0.90 and 0.25 < XNH3 < 0.90), making it possible to use the low-cost OH* chemiluminescence technique to qualify NO emission of flames fueled with hydrogen-enriched ammonia blends.

Instantaneous planar measurements of nitric oxide concentration in a turbulent n-heptane spray flame

Instantaneous and mean nitric oxide (NO) concentrations are measured in a turbulent, lifted, n-heptane jet spray flame at an atmospheric pressure using planar laser-induced fluorescence (PLIF). The flame-front is simultaneously located using OH-PLIF. The NO excitation line with the least temperature-quenching dependence is selected, and the associated NO-LIF dependence is corrected. LIF optimization and data reduction are based on previous work [Mulla et al. Combust. Flame 203 (2019) 217–229] where the NO-LIF signal was simulated at the spray flame condition (temperature and gas composition from LES) using a spectroscopic model. In the present work, to reduce interferences from polycyclic aromatic hydrocarbons (PAH) and soot, the detection bandwidth is progressively reduced from broadband (F6), intermediate (F3), to narrowband (F1). F6 results in a significant interference, while F1 contains the least interference. Instantaneous NO mole fraction (χNO) is deduced from F1 dataset using a novel instant-wise mapped interference subtraction approach (F1-Inst). The conditional mean NO concentrations derived from F6, F3, F1, and F1-Inst are in agreement (within uncertainty limits); however, F1-Inst appears to be the most reliable. Instantaneous flame-structure (OH) and NO concentration fields are analyzed. The spray flame structure consists of the inner (B1) and outer (B2) flame branches. Local extinctions are observed along B1. Small-scale (<1 mm) extinctions do not alter the NO concentration, whereas large-scale extinctions result in a sharp (50–100%) χNO drop, possibly due to a reduced temperature. Instantaneous χNO along B2 shows a sharp growth until 55 mm height above burner (HAB), beyond which the growth saturates. The deceleration of NO growth and χNO reduction near the sooting region is most likely due to the soot-radiation induced temperature drop. Mean χNO along B1 measures ∼ 25 ppm with a small axial variation (20–30 ppm). Expected lower temperature and nearly constant χNO with residence time suggest the nitrous oxide and prompt NO formations routes. Mean χNO in the outer diffusion branch (B2) increases from 35 ppm at the flame-base to 75 ppm at 60 mm HAB. The NO growth and potentially high temperature in B2 indicate the thermal route of NO formation.

Quantitative imaging of nitric oxide concentration in a turbulent n-heptane spray flame

The present work reports quantitative planar imaging of Nitric Oxide (NO) concentration in a dilute spray flame at atmospheric pressure, contributing to CORIA Rouen Spray Burner (CRSB) database. Mean NO mole fraction (χNO) is measured using planar laser-induced fluorescence (PLIF) technique, while the flame front is located simultaneously using OH-PLIF. An optimum NO excitation scheme is selected to minimize temperature-quenching dependence based on LIF simulations. Furthermore, the temperature and collisional quenching effects on NO fluorescence are corrected by using the temperature and gas composition obtained from large eddy simulation performed in previous work [Proc. Combust. Inst., 36 (2017), 2567-2575]. Additionally, interference in NO-PLIF from polycyclic aromatic or unburned hydrocarbon fluorescence is corrected by detuned (NO off-transition) signal subtraction. The spatial distribution of χNO is discussed in the context of a spray flame topology, which exhibits two distinct branches. The results suggest the formation of prompt NO on the inner composite branch (fuel-lean and non-premixed) and thermal NO on the outer pure non-premixed branch. χNO at 60 mm height above burner measures 33 ppm near the inner branch, and 75 ppm around the outer branch.

Nitric oxide formation in lean, methane-air stagnation flames at supra-atmospheric pressures

Increasingly stringent regulations are imposed on nitric oxide (NO) due to its numerous, direct and indirect, deleterious effects on human health and the environment. A better control of the post-flame temperature field to contain the thermal (Zel’dovich) route resulted in significant reductions of engine emissions. An improved knowledge of the chemistry and rate of the secondary prompt, NNH, and N2O pathways is now required to decrease nitric oxide emissions further. For this effort, NO laser-induced fluorescence (LIF) measurements are presented for lean (ϕ=0.7), jet-wall, stagnation, premixed flames at pressures of 2, 4, and 8 atm. For all cases, the NO-LIF signal increases rapidly through the flame front, and relatively slowly in the post-flame region where the temperature is too low to sustain the thermal pathway. Nitric oxide mole fractions are inferred from the measurements and show that the pressure has a very weak, monotonic, adverse effect on NO formation. Reaction pathway analyses are applied to flame simulations performed with a thermochemical model capturing the general trends of the data to assess the contribution of each NO formation route. For all cases, the N2O pathway, which proceeds mostly in the flame front region, dominates. This route produces slightly larger amounts of NO at higher pressures, but the variation appears very limited when considering the termolecular nature of its initiation reaction. The thermal route is predicted to progress slowly in the post-flame region, which causes a shallow increase in the NO mole fraction. The NNH and prompt pathways generate small amounts of NO, and their contributions reduce with the pressure. Overall, the thermochemical model predicts that the formation of NO is relatively unaffected by the pressure, which is consistent with the experiments. The experimental dataset reported in this work is made available for the development of thermochemical models.

First evaluation of a multicomponent flue gas cleaning concept using chlorine dioxide gas – Experiments on chemistry and process performance

This work has investigated a multi-pollutant flue gas cleaning concept based on oxidation using chlorine dioxide (ClO2) gas with subsequent absorption. The chlorine dioxide gas converts the relatively insoluble nitric oxide (NO) to the more soluble nitrogen dioxide (NO2). This makes a downstream wet scrubbing process feasible for simultaneous removal of sulphur oxides (SOx) and nitrogen dioxide (NO2).An experimental evaluation of the proposed process using chlorine dioxide gas has been performed on a laboratory scale. The experimental setup, designed and built by Akzo Nobel, consists of a reactor for oxidation, a flue gas condenser and a wet scrubber. The results show that ClO2 gas oxidises NO with high efficiencies under a wide range of process conditions, also in the presence of sulphur dioxide (SO2). The more ClO2 gas is added, the higher the degree of NO oxidation and the total nitrogen oxides (NOx) removal efficiency becomes. The results also show that the presence of water strongly increases the removal of SO2, which is believed to be an effect of liquid phase nitrogen-sulphur interactions. The absorption solution, sodium carbonate and sodium sulphite, is efficient in removing NOx (especially NO2) from the oxidised flue gas. The total NOx reduction at 0.6 ClO2:NO mole ratio and subsequent wet scrubbing is between 79% and 94%, depending on the process conditions used. The total SO2 reduction in the scrubber is between 97% and 100% independent of ClO2 gas addition. Furthermore, the total NOx balance shows that the major part of the NOx is converted to nitrate in the condensate liquor and as nitrite in the absorption solution. A higher ClO2 gas addition and a higher reactor temperature convert more of the NOx to nitrite in the absorption solution.

Experimental study and modelling of NOx formation in high pressure counter-flow premixed CH4/air flames

Nitric oxide (NO) is an atmospheric pollutant responsible for the destruction of the ozone layer and the creation of photochemical smog. As a result, NOx emissions from combustion sources are regulated in most industrialised countries. The need to control NOx emissions while also promoting more efficient use of fossil energy resources requires a better understanding of combustion processes, especially the chemical kinetics of NOx formation. NO formation in high-pressure flames is a research area of great practical interest as high pressure exists in practically all power-generation and propulsion engines and it is known that pressure influences the combustion chemistry. In the present work, NO mole fraction profiles were measured by Laser Induced Fluorescence in laminar high pressure (up to 0.7MPa) counter-flow lean CH4/air (E.R.=0.7) flames. Inherent problems linked to the application of the NO LIF technique in high pressure environment were addressed. The experimental NO profiles were then compared with modelling using the OPPDIF code and the three detailed kinetic mechanisms: the GDFkin®3.0_NCN mechanism developed by Lamoureux et al. and the two mechanisms from the Gas Research Institute: GRImech 2.11 and GRImech 3.0. A kinetic analysis based on rate of production/consumption analyses was performed to better understand the differences between the three mechanisms. Finally, the GRImech3.0 mechanism was modified with three updated prompt-NO submechanisms proposed in the literature and the consequences on the N-containing species mole fractions predictions are discussed.

Emission Control System for Nitrogen Oxides Using Enhanced Oxidation, Scrubbing, and Biofiltration

Nitric oxide (NO) constitutes about 90% of the nitrogen oxide (NOx) species in the flue gases emitted from combustion processes, but NO is difficult to remove in existing scrubbers due to its low solubility. NO may be oxidized with hydrogen peroxide (H2O2) into soluble species that can be partially removed in wet scrubbers simultaneously with sulfur dioxide (SO2) and biofilters located downstream of the scrubber can increase the removal efficiency. This article presents the results of a bench-scale evaluation of such an integrated system combining enhanced oxidation, scrubbing, and biofiltration. Main components of the bench-scale system consisted of a quartz tube in a furnace to simulate the NO oxidation stage and two vertical packed bed cylinders constituting the scrubber and the biofilter. Inlet synthetic gas had a concentration of 50 ¼L/L of NO. Overall removal efficiency by the integrated system was in the range of 53% to 93% with an average of 79%, absorption accounted for 43% and biofiltration for 36% of the total removal. Key parameters in the operation of the system are the H2O2:NO mole ratio, the reaction temperature, the liquid to gas flow ratio, and the biofilter residence time. Experimental results suggest a path for optimization of the technology focusing simultaneously in minimizing H2O2 use in the enhanced oxidation stage, reducing water consumption in the scrubber stage and balancing the residence times in the three stages of the integrated system.

Antimicrobial Activity of the Iron-Sulfur Nitroso Compound Roussin's Black Salt [Fe4S3(NO)7] on the Hyperthermophilic ArchaeonPyrococcus furiosus

The iron-sulfur nitroso compound [Fe(4)S(3)(NO)(7)](-) is a broad-spectrum antimicrobial agent that has been used for more than 100 years to combat pathogenic anaerobes. Known as Roussin's black salt (RBS), it contains seven moles of nitric oxide, the release of which was always assumed to mediate its cytotoxicity. Using the hyperthermophilic archaeon Pyrococcus furiosus, it is demonstrated through growth studies, membrane analyses, and scanning electron microscopy that nitric oxide does not play a role in RBS toxicity; rather, the mechanism involves membrane disruption leading to cell lysis. Moreover, insoluble elemental sulfur (S(0)), which is reduced by P. furiosus to hydrogen sulfide, prevents cell lysis by RBS. It is proposed that S(0) also directly interacts with the membranes of P. furiosus during its transfer into the cell, ultimately for reduction by a cytosolic NADPH sulfur reductase. RBS is proposed to be a new class of inorganic antimicrobial agent that also has potential use as an inert cell-lysing agent.

Fluorescence Determination of Nitric Oxide Production in Stimulated and Activated Platelets

Nitric oxide (NO) is quantitatively determined in platelets prior to, and after, stimulation with adenosine triphosphate (ATP) or activation with adenosine diphosphate (ADP). Platelets obtained from the whole blood of rabbits were loaded with the fluorescence probe diaminodifluorofluorescein diacetate (DAF-FM DA), and the subsequent NO production was measured as a fluorescent benzotriazole. Experiments were performed to determine the effect of probe concentration and probe incubation time in the platelets prior to measurement of the fluorescence. This information, combined with the method of multiple standard additions, was then employed to determine the moles of intracellular NO in the platelets (2.7 +/- 0.3) x 10(-16) mol of NO/platelet and the basal level of extracellular NO in the platelet sample (9.9 +/- 2.2) x 10(-18) mol of NO/platelet. Moreover, this method was used to quantitatively determine the amount of NO released from platelets whose NO production was stimulated with ATP (a nitric oxide synthase stimulus) or ADP, a substance known to result in NO production through platelet aggregation. When stimulated with ATP, the NO released from the platelets was determined to be (2.0 +/- 0.1) x 10(-17) mol of NO/platelet. When activated with ADP, the platelets released (2.8 +/- 0.3) x 10(-17) mol of NO/platelet. The difference between the extracellular basal levels of NO and that after stimulation with either ATP or ADP is in agreement with current estimates of NO release from platelets. Therefore, we conclude that a fluorescence determination of NO using the DAF family of probes, in combination with the method of multiple standard additions, can be employed to quantitatively determine the basal levels of NO in platelets, as well as the amount of NO released from stimulated and/or activated platelets.

Quantitative in-cylinder NO-LIF imaging in a realistic gasoline engine with spray-guided direct injection

Limiting the in-cylinder nitric oxide (NO) formation is a crucial task in the development of engines with gasoline direct injection. Exhaust gas aftertreatment requires storage catalysts that tolerate a maximum NO flux only, and the frequency of energy consuming catalyst regeneration cycles is directly correlated with engine-out NO. We present quantitative in-cylinder imaging measurements of NO mole fractions in a gasoline engine with spray-guided direct injection using laser-induced fluorescence (LIF). The optical engine design was kept close to that of a serial four-cylinder engine. Optical access was achieved via sapphire windows, requiring only minor modifications to the engine block. The engine was operated with commercial gasoline and fired continuously. The data interpretation applies the spectral simulation tool LIFSim to calculate pressure, temperature, and gas-composition dependencies of the LIF signal. Temperature-dependent CO 2 absorption cross-sections are used to correct for laser and signal attenuation. A sensitivity analysis of the quantitative NO concentrations on the different parameters entering the evaluation is presented. The LIF measurements are compared to results from in-cylinder fast gas sampling through a modified spark plug. The two techniques show good quantitative agreement. The LIF measurements are also compared to charge-averaged working-cycle-resolved NO chemiluminescence measurements in the exhaust port. NO-LIF imaging results are presented for stratified engine operation with different levels of exhaust gas recirculation (EGR), showing the large impact of EGR on in-cylinder NO formation.

Nitric Oxide Prevents Tumor Necrosis Factor α–Induced Rat Hepatocyte Apoptosis by the Interruption of Mitochondrial Apoptotic Signaling Through S-Nitrosylation of Caspase-8

Mitochondrial cytochrome c release plays a critical role in apoptotic signal cascade after the activation of cell surface death receptors. We investigated the role played by nitric oxide (NO) in mitochondrial apoptotic signaling in tumor necrosis factor α (TNF-α) plus actinomycin D (TNF-α/ActD)-induced apoptosis. NO produced either by S-nitroso-N-acetyl-DL-penicillamine (SNAP) or inducible NO synthase (iNOS) prevented TNF-α/ActD-induced apoptosis in hepatocytes and also inhibited both caspase-8–like (IETDase) and caspase-3–like protease (DEVDase) activity as well as mitochondrial cytochrome c release. Recombinant human (rh) caspase-8 induced the cleavage of the cytochrome c–effluxing factor Bid and cytochrome c release from purified mitochondria in the reconstitution system with Bid+/+ cytosol, but not with Bid−/− cytosol. The addition of SNAP and the caspase-8 inhibitor Ac-IETD-fmk inhibited caspase-8–dependent Bid cleavage and cytochrome c release. The inhibitory effect of NO on caspase-8 was reversed by dithiothreitol (DTT). Furthermore, rh-caspase-8 was found to be modified by S-nitrosylation with 1.7 moles of NO bound per mole of enzyme. Treatment of hepatocytes with interleukin 1β (IL-1β) plus interferon gamma (IFN-γ), which induced iNOS expression and NO production, suppressed TNF-α/ActD-induced Bid cleavage and mitochondrial cytochrome c release. The NOS inhibitor NG-monomethyl-L-arginine (NMA) inhibited the protective effects of IL-1β and IFN-γ. The liver-specific NO donor V-PYRRO/NO also inhibited in vivo elevation of IETDase activity, Bid cleavage, and mitochondrial cytochrome c release in the livers of rats injected with TNF-α plus D-galactosamine. Our results indicate that one mechanism by which NO protects hepatocytes from TNF-α/ActD-induced apoptosis is via the interruption of mitochondrial apoptotic signaling through S-nitrosylation of caspase-8.(Hepatology 2000;32:770-778.)

Measurement and modeling of nitric oxide release rates for nitric oxide donors.

An accurate model of the nitric oxide (NO)-release rate is essential for predicting the temporal NO-release rate and resulting NO concentrations for NO donors. Knowledge of the NO-release rate and/or the NO concentration is beneficial for assessing the physiological or pathological effects of NO on cell systems. This study describes a method to measure the temporal NO-release rate from NO donor compounds utilizing a modified ultrafiltration cell. For this study, the NO-release rates of spermine NONOate and diethylamine NONOate were measured and kinetically modeled at pH 7.4 and 37 degrees C. An advantage of this method is that complete dissolution of the NONOate was not necessary for modeling the NO-release rate. One model parameter, which is the number of moles of NO released per mole of decomposed NONOate, is 1.7 +/- 0.1 and 1.5 +/- 0.2 for spermine and diethylamine NONOate, respectively. The other model parameter, which is the NONOate first-order decomposition rate constant, is 0.019 +/- 0.002 min-1 and 0.47 +/- 0.10 min-1 for spermine and diethylamine NONOate, respectively, as determined from NO concentration profiles. The decomposition rate constant measured by spectrophotometry was consistent with the above value for spermine NONOate but was approximately half the above value for diethylamine NONOate. Preliminary experiments using spectrophotometry showed that for both NONOates the decomposition activation energy was approximately 100 kJ/mol. The NO-release rate model for spermine NONOate was applied to a model for predicting the NO concentration in oxygenated solution. The NO concentration was measured in phosphate buffer, culture medium, and Tyrode's solution. Excellent agreement was observed between experimental and predicted NO concentrations.

NO x adsorption on char in presence of oxygen and moisture

The char produced from a subbituminous coal is a cheap and effective adsorbent to remove nitrogen oxides (NO x) from flue gas. This paper addresses the NO x adsorption on char in the presence of oxygen and moisture since there are both water vapor and oxygen present in flue gas. The experimental results of this study show that nitric oxide (NO) is catalytically oxidized to nitrogen dioxide (NO 2) on the char surface. When the oxygen concentration in the feed gas is greater than 5% and H 2O concentration is less than 1%, the moles of NO x removed from the feed gas per 100 moles of carbon are almost independent of concentrations of oxygen and water in the feed gas. The breakthrough time of NO increased and that of NO 2 decreased slightly with an increase in the concentration of oxygen. When moisture is present, a part of the adsorbed NO 2 is further converted into nitric acid which is adsorbed on char. The amount of NO x adsorbed as HNO 3 increases as both oxygen and moisture concentration in the feed gas increase. The removal of NO x was almost independent of water vapor concentration in the feed gas (0.23–0.95% by volume) probably due to the fact that the promotion effect of water vapor on NO x adsorption was balanced by the inhibition effect.

Nitric oxide reduction in the freeboard of a fluidized bed coal combustor

Nitric oxide mole fractions of 650 to 1350 ppm were observed in the combustion productsnear the bed surface during fluidized combustion of bitminous coal. Reduction of NO to N 2 in the freeboard above the bed decreased NO to the characteristically low levels (80–400 mol ppm) observed in the exhaust from fluidized bed combustors. The experimentally measured variations of NO with height in the freeboard are compared with the predictions of a semi-empirical model in which NO reduction is assumed to occur by reaction with entrained coal char. The concentration of char particles is determined from measured bed properties using mechanistic models for the initial particle flux at the bed surface and the motion of particles in the freeboard. The nitric oxide reduction predicted by the model is in good agreement with the reduction observed in five of the six sets of measurements.