Formation Of Nitrogen Dioxide Research Articles

Numerical and experimental analysis of the formation of nitrogen oxides in a non-premixed industrial gas burner

Nitrogen oxides (NOx) formation in a non-premixed industrial gas burner is analyzed with Reynolds-averaged Navier-Stokes (RANS) computational fluid dynamics, using the Flamelet Generated Manifold (FGM) approach for chemistry and the Reynolds stress model for turbulence closure. Analysis and validation of the numerical methodology use both the RANS and the Large Eddy Simulation methods to study the Sandia flame D experiment. Four regimes of the gas burner, differing by thermal power, are studied experimentally and numerically, comparing measured and computed flue gas temperature and emissions. The flow features leading to NOx formation are analyzed. At low power, most NOx formation occurs in the flame core, where temperatures are highest. At high power, a significant amount of NOx forms where a secondary stream of oxidizer meets the high-temperature burnt gas stream. The NOx formation rate is modeled either by summing the contributions of the main paths relevant to the studied problem or via two variants of the FGM scalar transport approach. One of these variants features a correction to the transported scalar approach that enables accounting for the effects of non-adiabatic phenomena, e.g. heat radiation, on NOx formation without increasing the look-up table dimensionality and the required memory usage. The correction is shown to improve emission predictions over the baseline model, although quantitative differences between predicted and measured emission levels remain significant. The approach computing the NOx formation rate as by summing contributions yields the best agreement with measurements when the thermal path predominates, and the formation of nitrogen dioxide is negligible.

Photochemically-induced protein tyrosine nitration in vitro and in cellula by 5-methyl-1,4-dinitro-1H-imidazole (DNI): synthesis and biochemical characterization

The photochemical nitrating agent 5-methyl-1,4-dinitro-1H-imidazole (DNI) has been recently described as an effective tool for nitrating tyrosine residues in proteins under 390 nm irradiation (Long T. et al., 2021). Herein, we describe the one-step synthesis of DNI from the precursor 4-methyl-5-nitro-1H-imidazole with good yield (66%) and high purity (>99%). Spectral analysis of DNI reveals two maximum peaks (228 and 290 nm) with maximum nitration yields and kinetics occurring at 290 nm. Electron paramagnetic resonance (EPR)- and mass spectrometry (MS)- spin trapping analysis evidenced the formation of nitrogen dioxide (•NO2) upon irradiation of DNI, implying the homolysis of the N–N bond in the DNI molecule. Irradiation of DNI at 290, 390 nm, or UVA light (315–400 nm), produced tyrosine nitration, with yields approaching ca. 30% with respect to DNI at 290 nm exposure. Indeed, using alpha-synuclein as a model protein, the main protein post-translational modification triggered by DNI was the generation of 3-nitrotyrosine as shown by MS analysis. Additionally, the formation of di-tyrosine was also observed. Finally, intracellular •NO2 production upon DNI photolysis in bovine aortic endothelial cells was evidenced by the nitration of the tyrosine analog probe p-hydroxyphenylacetic acid (PHPA) and cellular protein tyrosine nitration.

Gas and Propane Combustion from Stoves Emits Benzene and Increases Indoor Air Pollution.

Exposure pathways to the carcinogen benzene are well-established from tobacco smoke, oil and gas development, refining, gasoline pumping, and gasoline and diesel combustion. Combustion has also been linked to the formation of nitrogen dioxide, carbon monoxide, and formaldehyde indoors from gas stoves. To our knowledge, however, no research has quantified the formation of benzene indoors from gas combustion by stoves. Across 87 homes in California and Colorado, natural gas and propane combustion emitted detectable and repeatable levels of benzene that in some homes raised indoor benzene concentrations above well-established health benchmarks. Mean benzene emissions from gas and propane burners on high and ovens set to 350 °F ranged from 2.8 to 6.5 μg min-1, 10 to 25 times higher than emissions from electric coil and radiant alternatives; neither induction stoves nor the food being cooked emitted detectable benzene. Benzene produced by gas and propane stoves also migrated throughout homes, in some cases elevating bedroom benzene concentrations above chronic health benchmarks for hours after the stove was turned off. Combustion of gas and propane from stoves may be a substantial benzene exposure pathway and can reduce indoor air quality.

New Insights into the Role of Nitrite in the Degradation of Tetrabromobisphenol S by Sulfate Radical Oxidation.

Tetrabromobisphenol S (TBBPS) is a brominated flame retardant and a contaminant of emerging concern. Several studies found that sulfate radical (SO4•-) oxidation is effective to degrade TBBPS. Here, we demonstrate that the presence of nitrite (NO2-) at environmentally relevant levels causes dramatic changes in the kinetics and pathways of TBBPS degradation by SO4•-. Initially, NO2- suppresses the reaction by competing with TBBPS for SO4•-. At the same time, SO4•- oxidizes NO2- to form nitrogen dioxide radicals (NO2•), which actively react with some key TBBPS degradation intermediates, thus greatly altering the transformation pathway. As a result, 2,6-dibromo-4-nitrophenol (DBNP) becomes the primary TBBPS product. As TBBPS undergoes degradation, the released bromide (Br-) is oxidized by SO4•- to form bromine radicals and free bromine. These reactive bromine species immediately combine with NO2• or NO2- to form nitryl bromide (BrNO2) that in turn attacks the parent TBBPS, resulting in its accelerated degradation and increased formation of toxic nitrophenolic byproducts. These results show that nitryl halides (e.g., BrNO2 or ClNO2) are likely formed yet inadequately recognized when SO4•- is applied to remediate halogenated pollutants in the subsurface environment where NO2- is ubiquitously found. These insights further underscore the potential risks of the application of SO4•- oxidation for the remediation of halogenated compounds in realistic environmental conditions.

Экспериментальное определение удельного коэффициента образования диоксида азота при горении нитроцеллюлозной киноплёнки

Purpose. Pulmonotoxic substances (for example, nitrogen dioxide) are extremely hazardous for people during fires. These substances cause mucous membrane irritation and with prolonged exposure can lead to toxic pulmonary edema. However, fire load database which is used for calculating fire risks does not contain values of nitrogen dioxide formation distribution coefficient. Therefore, determining parameters of nitrogen dioxide formation during various substances and materials burning is a priority. The purpose of the study is to experimentally determine the partial density and distribution coefficient of nitrogen dioxide formation during cellulose nitrate film combustion in an enclosed volume. To achieve it an experimental installation for determining fire hazard of condensed materials during their thermal decomposition has been modified. Methods. Experimental methods of measuring and processing parameters of substances and raw materials burning as well as obtained results analysis methods are used. Findings. A technique for experimental calculation of nitrogen dioxide formation distribution coefficient has been developed and validity of obtained results approximation for real rooms has been justified. Values of distribution coefficient of forming nitrogen dioxide evolved during cellulose nitrate film combustion are experimentally obtained. Maximum weight of the above-mentioned film located in a room of a given volume at which NO2 partial density does not reach its critical or fatal value for people has been assessed. Research application field. Fire load database used when calculating fire risks, according to distribution coefficients of nitrogen dioxide formation during various substances andmaterials combustion has been expanded. Conclusions. The modified experimental installation for determining fire hazard of condensed materials during their thermal decomposition, as well as the developed method for experimental determination of nitrogen dioxide formation distribution coefficient make it possible to obtain data on nitrogen dioxide formation necessary for calculating fire risks in buildings and structures.

EFFECT OF MOISTURE ON NITROGEN DIOXIDE FORMATION IN LAMINAR FLAME OF NATURAL GAS

The paper contains the results of experimental studies of the effect of moisture on nitrogen dioxide formation and on oxidation of NO to NO2 in laminar premixed flame of natural gas. The water vapor is shown to be the third very influential participant, along with fuel and oxidizer, in the combustion process. Injection of moisture into the combustion zone has an effect due to the insertion of additional quantities of HO2- and OH– radicals into the process, which contributes to the intensification of the oxidation of NO to NO2. Introduction of the concept of the “excess moisture ratio” in the combustion process is proposed. The studies were executed at the laboratory installation in conditions of formation of the V-shaped laminar flame of natural gas behind a transverse cylindrical steel stabilizer, with determining the concentrations of flue gas components.

Recycling of Secondary cooper Waste

The process of dissolution of copper crumbs with nitric acid without superposition and with superposition of alternating current of industrial frequency is investigated. The main parameters of the process of copper dissolution by nitric acid in the absence of nitrogen dioxide formation are determined. The technology of electrolytic dissolution of copper with nitric acid is proposed.

Nitric oxide (NO): physiology and metabolism (lecture)

The chemical compound nitric oxide is a gas with chemical formula NO. It is one of the impotant signaling molecules, in the body of mammalians including humans, one of the few gaseous signaling molecules known. The NO molecule is a free radical, which is relevant to understanding its high reactivity. It reacts with the oxygen in air to form nitrogen dioxide. NO plays a key role in the regulation of numerous vital biological functions: immunology, cardiovascular system, peripheral nervous system, cell proliferation. Humans lose ability to produce NO with aging. Loss of endothelian NO function is associated with several cardiovascular disorders, including atherosclerosis. Dietary nitrate metabolism is dependent upon bacteria and stomach acid.

Comparison of efficacy of nitric oxide fumigation under nitrogen and carbon dioxide atmospheres in controlling granary weevil (Sitophilus granaries) and confused flour beetle (Tribolium confusum)

Nitric oxide (NO) was a recently discovered fumigant for postharvest pest control. Because NO reacts with oxygen (O2) spontaneously to form nitrogen dioxide (NO2), NO fumigation must be conducted under ultralow oxygen (ULO) atmospheres to preserve NO and nitrogen (N2) has been used to establish ULO atmospheres in NO fumigation studies in the past. However, carbon dioxide (CO2) can also be used to ULO atmospheres and CO2 fumigation was also reported to be effective in controlling certain insect pests and enhancing toxicity of some fumigants. In the present study, NO fumigations under ULO conditions established with N2 and CO2 were compared for effects against granary weevil, Sitophilus granaries, and confused flour beetle, Tribolium confusum. All life stages of the two insects were subjected to 12 h fumigation treatments with 0.5–1.0% NO at 25 °C under ULO established with CO2 (NO–CO2 treatments) and N2 (NO–N2 treatments). The most tolerant life stage for each species in each fumigation treatment was then fumigated with NO for 24 h fumigation at 25 °C to determine an effective treatment. There were no significant differences in mortalities of adults, larvae, and pupae at all NO concentrations between ULO conditions established with CO2 and N2 for either insect. NO–CO2 was, however, significantly less effective than NO–N2 against eggs of both species. Granary weevil pupae and confused flour beetle eggs were the most tolerant stages for each respective species to NO fumigation: >99% mortality of granary weevil pupae and confused flour beetle eggs were, however, achieved in the 24 h fumigation with 2% and 1% NO, respectively. This study showed that CO2 can be used to establish ULO atmospheres for NO fumigation, but did not significantly contribute to insect mortality.

Environmental Characteristics of Modern Systems of Domestic Use of Fuel. Part 1

The analysis of the environmental component of the processes of natural gas burning in atmospheric burners of domestic gas stoves has been carried out. The computational and experimental studies of the harmful substances formation by combustion of natural gas have been performed. The chemical equilibrium of the NO–O2–NO2 system was considered. The thermodynamic analysis of transformation of the system during a process of natural gas (methane-air mixture) combustion has been tested. Despite an essential (sometimes – by the order(s)) difference between the thermodynamically equilibrium concentration of the nitrogen oxides [NOx]eq and the local, actually measured values [NOx] = [NO] + [NO2], the [NO]eq values could be served as the qualitative indicators of actual values of [NOx] concentrations. In the combustion processes natural gas and other fuels combustion at high temperatures [NO] >> [NO2] for both equilibrium and measured concentrations. By moderate and low local temperatures up to 600 K the equilibrium concentration [NO2]eq → [NO]eq in order of magnitude. Under some compositions of burning mixture the correlation could be set as [NO2] >> [NO], resulting in great danger for the human health. With regard to the formation of particularly toxic NO2 effluents observed in some cases, an influence of the reaction temperature and the composition of the combustible mixture on the possibility of nitrogen dioxide formation in the combustion products have been analyzed. A methodology for the experimental study of the harmful emissions formation has been proposed while the computerized firing rig has been developed for studying the combustion of hydrocarbon gases in burners of household stoves. An influence of the coefficient of primary air excess on the СО, NO, NO2 formation has been revealed and the possibility of appearance the emissions of a high concentration of nitrogen dioxide has been demonstrated.

Analysis of nitrogen oxide emissions from modern vehicles using hydrogen or other natural and synthetic fuels in combustion chamber

The paper presents a calculated analysis of the equilibrium emission of nitrogen oxides on the exhaust of carburetor and diesel internal combustion engines. The temperature of fuel oxidation is assumed to be 1,400 °C while the pressure for carburetor and diesel engines is assumed to be 60 atm and 80 atm respectively. The studies have been carried out for natural and synthetic fuels such as hydrogen, ethanol, methanol, petroleum, diesel fuel and methane at the excess air coefficient corresponding to the fuel oxidation temperature of 1,400 °C. In the paper, the method for calculating the equilibrium composition based on the equilibrium constant and mass conservation equations has been applied. It is shown that with an increase in pressure from 1 atm to 60 atm for carburetor engines and up to 80 atm for diesel engines, the reaction of nitrogen dioxide formation may shift towards an increase in NO2. The formation of NO may be not affected by the increase in pressure by virtue of the fact that the reaction proceeds without changes in the amount. It has been determined that NO is the major atmospheric pollutant. However, it would be advisable to use more extensively the fuels characterized by the lowest output of nitrogen dioxide (methane and methanol), since nitrogen dioxide (NO2) related to the 2nd hazard class is appeared to be the most dangerous to humans. It has been revealed that the reduction in oxidation temperature using hydrogen as a fuel for electrochemical current generators may allow reducing nitrogen oxide emissions by more than an order of magnitude as compared to the best results for ICE.

Twelve-Hour Urine Collection Can Be Utilized to Estimate 24-Hour Total Urinary Nitrogen in Critically Trauma Patients

Abstract Patients suffering from trauma, burns, and sepsis are frequently in a hypermetabolic state, and as the majority of urinary nitrogen comes from amino acid metabolism, the determination of total urinary nitrogen (TUN) provides an accurate measurement of all nitrogen excreted in urine and can be used as an indicator of catabolic stress. To evaluate whether time of collection influences the performance of TUN test, 12-hour urine specimens were collected from ICU trauma patients and the 12-hour results were correlated with results from 24-hour collections. Two consecutive 12-hour urine samples were collected (06:00-18:00 hours and 18:00-06:00 hours) from surgical ICU patients. Total urinary nitrogen levels were measured in each 12-hour sample, as well as in a pooled sample (24 hours). Pyrochemiluminescence was used to determine TUN level on an Antek 9000N elemental analyzer. In this approach, the urine sample is completely oxidized at high temperature in a quartz pyrotube. Nitrogen is converted to nitric oxide (·NO), then mixed with O3 (ozone) to form nitrogen dioxide (NO2). Light is emitted and specific wavelengths between 650 and 900 nm were measured in a photomultiplier tube. The measured chemiluminescent emission is specific and proportional to the amount of nitrogen in the sample. Fifty 12-hour urine samples from 16 patients were collected. One patient was excluded from the study due to acute renal injury during the collection period. There was no significant observed circadian effect on measured TUN. The 12-hour TUN (g/total volume) was multiplied by 2 to compare to 24-hour TUN for statistical analysis. There was strong correlation between either day or night 12-hour TUN and corresponding pooled 24-hour TUN, with correlation coefficients ranging from 0.93 to 0.98 and regression slopes ranging from 0.98 to 1.01. No statistically significant difference was found between the 12-hour TUN and 24-hour TUN approaches. A 12-hour TUN collection was overall highly predictive of 24-hour TUN collection and has the advantage of convenience of sample collection and improved clinical efficiency. Serial 12-hour urine collection is therefore preferred for monitoring nitrogen balance and adjusting protein intake for critically ill ICU patients.

Analysis of Nitrogen Oxides Emission by Modern Vehicles when Used Hydrogen or Other Natural and Synthetic Fuels in Combustion Chamber

This paper presents calculated analysis of the equilibrium emission of nitrogen oxides at the exhaust of carburetor and diesel internal combustion engines. The temperature of the fuel oxidation process is assumed to be 1,400 °C, the pressure for carburetor and diesel engines to be 60 and 80 at, respectively. We have conducted studies for natural and artificial fuels: hydrogen, ethanol, methanol, gasoline, diesel fuel and methane with an excess air ratio corresponding to the oxidation temperature of fuels 1,400 °C. The method of calculating the equilibrium composition based on the equilibrium constant and the equations of mass conservation is applied. It is shown that with an increase in pressure from 1 to 60 bar for the carburetor engines and up to 80 bar for the diesel engines the reaction of nitrogen dioxide formation shifts towards an increase in NO2. Increasing the pressure has no effect on the formation of NO, since the reaction proceeds without changes in the volume. It is established that the main polluting atmospheric component is NO. However, it is advisable to make greater use of fuel with the lowest yield nitrogen dioxide (methane and methanol) because nitrogen dioxide (NO2) pertaining to the chemicals 2ndclass of danger is the most dangerous to humans. It is established that the reducing temperature of oxidation using hydrogen as fuel for electrochemical power generators allows us to reduce the emission of nitrogen oxides over an order of magnitude in comparison with the best results for internal combustion engines.

Experimental study on effects of combustion atmosphere and coal char on NO2 reduction under oxy-fuel condition

Nitrogen oxides (NOx) as the principal air pollutants are mainly from the combustion of fossil fuels. Oxy-fuel combustion is a promising clean coal technology, by which carbon dioxide (CO2) can be captured in large-scale and NOx emission can be reduced significantly. The formation of nitrogen dioxide (NO2) in oxy-fuel combustion exceeds that under traditional air condition. However, the specific studies on NO2 chemistry under oxy-fuel condition are still insufficient and the functional mechanisms of minerals and combustion atmosphere on NO2 reduction have yet to be fully understood. The objective of present study is to experimentally clarify the effects of combustion atmosphere and coal char on NO2 reduction in oxy-fuel combustion using a fixed-bed reactor. Experimental results showed that the decomposition of NO2 had a strong temperature dependence and the NO2 reduction rate showed a positive variation with temperature. The strength of catalytic activity in NO2 reduction to nitric oxide (NO) was Fe2O3 > MgO > CaO > Al2O3 > Na2CO3 > K2CO3 > SiO2. In addition, the increased concentrations of carbon monoxide (CO) and CO2 could promote the reduction of NO2, while the low content of CO2 only established a slight impact on NO2 reduction. However, the increase of oxygen (O2) concentration displayed an inhibition effect on NO2 reduction to a certain extent. The variation of atmosphere in oxy-fuel combustion generated a substantial influence on the creation and reduction of NO2. The char prepared in lower temperature exhibited a higher promotion effect on the consumption of NO2. Higher contents of fixed carbon and basic oxides had more obvious stimulation effects on NO2 reduction. Fixed carbon had a superior activity in NO2 reduction than ash. The kinetic analysis indicated that high content of CO and the presence of char could reduce the apparent activation energy of NO2 reduction. The present study can be helpful to improve the understanding of NO2 chemistry in oxy-fuel combustion.

Nitric oxide fumigation for control of western flower thrips and its safety to postharvest quality of fresh fruit and vegetables

Nitric oxide fumigation under ultralow oxygen conditions was studied for controlling western flower thrips and effects on postharvest quality of fresh fruit and vegetables. Four hour fumigation with 1.0% nitric oxide at 2°C and 3h fumigation with 2.0% nitric oxide at 5°C achieved complete control of the thrips. The 4h treatment was tested on 10 fresh fruit and vegetables including lettuce, broccoli, pepper, squash, tomato, apple, lemon, orange, peach, and pear. When the treatment was terminated by flushing with nitrogen to dilute nitric oxide before exposing the products to ambient air, the treatment had no negative impact on quality of the products. When the treatment was terminated by flushing with air to allow nitric oxide to reacts with oxygen in the air to form nitrogen dioxide, the treatment caused injuries to the majority of the fresh products. Fresh products with thick and robust skins were more tolerant than those with thin and delicate skins to nitric oxide fumigation. The 4h fumigation with 1.0% nitric oxide of strawberries at 2°C had positive impact on strawberry quality with enhanced firmness, brighter and richer color than the controls. The study demonstrated efficacy of nitric oxide fumigation in controlling western flower thrips, safety to fresh commodities, and benefits to postharvest quality of strawberries.

Detection of taggants in explosives on nanostructured metal/silver phthalocyanine chemiresistors: Influence of analyte photoactivation

Our work deals with detection of the two most widely used taggants in explosives (2-nitrotoluene and 2,3-dimethyl-2,3-dinitrobutane) on metal/silver phthalocyanine chemiresistors, when the analyte vapors are activated by ultraviolet radiation (λ=266nm). As the first step, morphological and electrical properties of gold, palladium and silver non-continuous layers deposited on silver phthalocyanine (AgPc) have been studied. Experiments monitored by SEM confirmed formation of metal clusters on organic surface if subthreshold amount of metal is deposited onto the AgPc layer (i.e. layer of equivalent thickness of 4nm for Pd, 5nm for Au and 8nm for Ag) and thermal stabilization follows.We demonstrated that metallic non-continuous layers on AgPc can be used for effective adjustment of chemiresistor's electrical resistance. Resistance of all modified sensors in reference atmosphere (synthetic air) − R0 − was effectively shifted by one to four orders of magnitude to lower values, so that cheaper devices and set-ups can be used for resistance measurements. Moreover, measurements of responses of Me/AgPc chemiresistors to 1ppm of NO2 revealed that the presence of metal reduces the sensor response time (τ90). On basis of optimal R0 and τ90 values, Pd(1nm)/AgPc chemiresistor was selected to be the most prospective for detection of taggants.Finally, the taggants were detected on Pd (1nm)/AgPc chemiresistor in two modes: without- or with- photoactivation. While the dc-response (Sdc) to 190ppm of non-activated 2-nitrotoluene vapors was negligible, on photoactivation we reached the value of Sdc=5.8. This significant improvement, which is attributed to the formation of nitrogen dioxide during photoactivation of 2-nitrotoluene, and also negligible interaction of sensor with water vapor as the most common interferent make our method applicable for early detection of tagged explosives in real “field” conditions. The Pd(1nm)/AgPc sensors exhibited excellent recovery after detection of photoactivated 2-NT. The recovery was achieved by thermal regeneration steps (sensor temperature switches from 40 °C to 120°C and vice-versa)

4種の拡散サンプラーを用いる札幌市における屋内外のガス状化学物質の実態調査

Gaseous chemical compounds such as carbonyls, volatile organic compounds (VOC), acid gases, basic gases, and ozone were measured in indoor and outdoor air of 40 houses throughout Sapporo city in the winter (January to March, 2012 and 2013) and summer (July to September, 2012) using four kinds of diffusive samplers. Almost all compounds in indoor air were present at higher levels in the summer than in the winter. The indoor concentrations of acetaldehyde and p-dichlorobenzene exceeded the Health, Labour and Welfare, Japan guideline in three and two houses, respectively. The mean concentrations of formaldehyde were 27 μg m−3 in the summer and 17 μg m−3 in the winter, and showed that the summer concentration was 1.6-fold higher than that in the winter. Nitrogen dioxide was present in extremely high concentrations in the winter, and it was suggested that the sources of nitrogen dioxide in indoor air are kerosene heaters, unvented gas stoves and heaters. Formic acid was generated by combustion because the nitrogen dioxide concentration in indoor air was well correlated with the formic acid concentration (correlation coefficient = 0.947). In outdoor air, the negative correlation between nitrogen dioxide and ozone was observed during the winter. It was suggested that the reaction of nitric oxide and ozone may influence the formation of nitrogen dioxide.

Oxidation of nitric oxide by atmospheric pressure plasma in a resonant plasma reactor

A novel non-equilibrium atmospheric-pressure-plasma generation system is proposed. The system discussed in this study is specifically designed for nitrogen oxide (NOx) gas treatment. A plasma is generated by a high-voltage radio-frequency (RF) electric field formed in the system that accumulates electromagnetic energy by resonance provided by a low-voltage power supply. With an input RF voltage of 100–200 V, a high voltage of 4k–8 kV at the same frequency can be formed on the powered electrode of the system under the resonance conditions. The plasma generator also serves as a plasma reactor, in which nitric oxide (NO) can be efficiently oxidized to form nitrogen dioxide (NO2) in the presence of oxygen (O2) at atmospheric pressure. It has been shown that, in terms of NO oxidation efficiency, the resonant plasma reactor proposed in this study is comparable or even superior to some of the previously proposed NO oxidation systems.

Nitrate–Nitrite–Nitric Oxide Pathway in Pulmonary Arterial Hypertension Therapeutics

Pulmonary arterial hypertension (PAH) is a disorder characterized by elevated vascular resistance in pulmonary arterioles. Progressive increases in pulmonary vascular resistance and pulmonary artery pressures result in right heart failure and reduced cardiac output. Patients experience progressive exertional dyspnea, right heart failure, syncope, and ultimately death. The common pathophysiological features of PAH include pulmonary vasoconstriction, intimal and smooth muscle proliferation, in situ thrombosis, and pathological remodeling of pulmonary arterial circulation. Although the origin of PAH is multifactorial, impairments in vasodilator (nitric oxide [NO] and prostaglandin signaling) and vasoconstrictor (endothelin-1, reactive oxygen species, angiotensin II) pathways underlie the evolution of early disease.1 Based on this knowledge, drugs that enhance the NO signaling pathways (phosphodiesterase 5 inhibitors), the prostenoids, and endothelin receptor blockers, have been developed and approved for PAH-specific therapy. Article see p 2922 Inhaled NO gas can alleviate vasoconstriction and may modulate cellular proliferative responses, but NO therapy is limited by the need for continuous inhalation, NO reactions with oxygen to form nitrogen dioxide, and special delivery devices. It is now appreciated that inorganic nitrite and nitrate are bio-transformed to NO via the nitrate-to-nitrite-to-NO pathway,2 leading to studies with inhaled nitrite as an alternative to NO gas inhalation.3,4 In this issue of Circulation , Baliga and colleagues5 investigate the nitrate-to-nitrite-to-NO pathway by studying the effects of oral nitrite and nitrate on preclinical mouse and rat models of PAH, and then attempt to characterize the enzymes that regulate bioconversion of nitrite to NO. They find that both nitrate and nitrite delivered in drinking water can prevent and reverse experimental PAH in the hypoxic and bleomycin mouse models, which is consistent with published models for in vivo conversion of nitrite to NO.6–8 They also provide unexpected evidence that eNOS may have nitrite reductase …

Numerical study of a butanol/heptane fuelled Homogeneous Charge Compression Ignition (HCCI) engine utilizing negative valve overlap

The calibration and comparison to experimental data of a parallel computing multi-zone combustion model for simulating operational characteristics of an n-butanol/n-heptane fuelled Homogeneous Charge Compression Ignition (HCCI) engine utilizing the negative valve overlap (NVO) technology is described. The model is calibrated using one experimentally characterized operating point and by taking into account the major features of NVO. The model simulations at other four operating points closely match the cylinder pressure trace and heat release rates of the experiments. The unburned hydrocarbon emission is predicted to a reasonable level while NOx (nitric oxide NO and nitrogen dioxide NO2) formation is under-predicted. The difficulty in mapping the NOx emission is attributed to the fact that the combustion model operates within the closed cycle period of engines and therefore does not capture the complexity of the charge stratification within the NVO equipped engine. Nevertheless, the trend of increasing NOx levels with the increasing fraction of butanol in the fuel mixture is captured and the model is able to predict the pressure, heat release rates, and combustion phasing for the three fuel blends tested.