HNO Production Research Articles

Nitrous acid in the urban area of Rome

Nitrous acid (HNO 2) and a large variety of other components were simultaneously measured in the city centre of Rome (Italy) during the NITROCAT ground based field experiment in May/June 2001. The highest HNO 2 concentrations were found under high-pressure conditions with high nocturnal atmospheric stability and high values of pollutants. After night time formation and accumulation up to 2 ppb HNO 2 were observed. The measurements confirm that during the first hours after sunrise, when hydroxyl radical (OH) production rates from other sources (photolysis of ozone and formaldehyde (HCHO)) are slow, HNO 2 photolysis is the most important primary OH source in the lowest part of the troposphere; up to 1–4×10 7 OH cm −3 s −1 were estimated for that time from this source. This contributes considerably to the initiation of the photochemistry for the day. The unexpected high daytime concentrations of few hundred ppt observed by DOAS as well as by the two in situ wet collection techniques (wet denuder/IC, coil sampling/HPLC) possibly influence ozone chemistry during the entire day. The heterogeneous on-surface production of HNO 2 (and consequently of HNO 3) provides also a new-type acidity formation influencing directly the biosphere and the materials. About 20% of the total nitrite was found on atmospheric aerosols. The HNO 2 measurements agree well for the different in situ measurement techniques and the spatial integration DOAS simultaneously performed over several weeks in the real atmosphere and during reaction chamber experiments.

Kinetics of the OH + HCNO Reaction

The kinetics of the OH + HCNO reaction was studied. The total rate constant was measured by LIF detection of OH using two different OH precursors, both of which gave identical results. We obtain k = (2.69 +/- 0.41) x 10(-12) exp[(750.2 +/- 49.8)/T] cm(3) molecule(-1) s(-1) over the temperature range 298-386 K, with a value of k = (3.39 +/- 0.3) x 10(-11) cm(3) molecule(-1) s(-1) at 296 K. CO, H(2)CO, NO, and HNO products were detected using infrared laser absorption spectroscopy. On the basis of these measurements, we conclude that CO + H(2)NO and HNO + HCO are the major product channels, with a minor contribution from H(2)CO + NO.

Mechanism of pH-Dependent Decomposition of Monoalkylamine Diazeniumdiolates to Form HNO and NO, Deduced from the Model Compound Methylamine Diazeniumdiolate, Density Functional Theory, and CBS-QB3 Calculations

Isopropylamine diazeniumdiolate, IPA/NO, the product of the reaction of isopropylamine and nitric oxide, NO, decomposes in a pH-dependent manner to afford nitroxyl, HNO, in the pH range of 13 to above 5, and NO below pH 7. Theoretical studies using B3LYP/6-311+G(d) density functional theory, the polarizable continuum and conductor-like polarizable continuum solvation models, and the high-accuracy CBS-QB3 method on the simplified model compound methylamine diazeniumdiolate predict a mechanism involving HNO production via decomposition of the unstable tautomer MeNN+(O-)NHO-. The production of NO at lower pH is predicted to result from fragmentation of the amide/NO adduct upon protonation of the amine nitrogen.

Comparison of the NO and HNO Donating Properties of Diazeniumdiolates: Primary Amine Adducts Release HNO in Vivo

Diazeniumdiolates, more commonly referred to as NONOates, have been extremely useful in the investigation of the biological effects of nitric oxide (NO) and related nitrogen oxides. The NONOate Angeli's salt (Na(2)N(2)O(3)) releases nitroxyl (HNO) under physiological conditions and exhibits unique cardiovascular features (i.e., positive inotropy/lusitropy) that may have relevance for pharmacological treatment of heart failure. In the search for new, organic-based compounds that release HNO, we examined isopropylamine NONOate (IPA/NO; Na[(CH(3))(2)CHNH(N(O)NO]), which is an adduct of NO and a primary amine. The chemical and pharmacological properties of IPA/NO were compared to those of Angeli's salt and a NO-producing NONOate, DEA/NO (Na[Et(2)NN(O)NO]), which is a secondary amine adduct. Under physiological conditions IPA/NO exhibited all the markers of HNO production (e.g., reductive nitrosylation, thiol reactivity, positive inotropy). These data suggest that primary amine NONOates may be useful as HNO donors in complement to the existing series of secondary amine NONOates, which are well-characterized NO donors.

Discriminating formation of HNO from other reactive nitrogen oxide species

Nitroxyl (HNO) exhibits unique pharmacological properties that often oppose those of nitric oxide (NO), in part due to differences in reactivity toward thiols. Prior investigations suggested that the end products arising from the association of HNO with thiols were condition-dependent, but were inconclusive as to product identity. We therefore used HPLC techniques to examine the chemistry of HNO with glutathione (GSH) in detail. Under biological conditions, exposure to HNO donors converted GSH to both the sulfinamide [GS(O)NH 2] and the oxidized thiol (GSSG). Higher thiol concentrations generally favored a higher GSSG ratio, suggesting that the products resulted from competitive consumption of a single intermediate (GSNHOH). Formation of GS(O)NH 2 was not observed with other nitrogen oxides (NO, N 2O 3, NO 2, or ONOO −), indicating that it is a unique product of the reaction of HNO with thiols. The HPLC assay was able to detect submicromolar concentrations of GS(O)NH 2. Detection of GS(O)NH 2 was then used as a marker for HNO production from several proposed biological pathways, including thiol-mediated decomposition of S-nitrosothiols and peroxidase-driven oxidation of hydroxylamine (an end product of the reaction between GSH and HNO) and N G-hydroxy- l-arginine (an NO synthase intermediate). These data indicate that free HNO can be biosynthesized and thus may function as an endogenous signaling agent that is regulated by GSH content.

Kinetics and mechanisms for reactions of HNO with CH3 and C6H5 studied by quantum‐chemical and statistical‐theory calculations

AbstractKinetics and mechanisms for the reactions of HNO with CH3 and C6H5 have been investigated by ab initio molecular orbital (MO) and transition‐state theory (TST) and/or Rice‐Ramsperger‐Kassel‐Marcus/Master Equation (RRKM/ME) calculations. The G2M(RCC, MP2)//B3LYP/6‐31G(d) method was employed to evaluate the energetics for construction of their potential energy surfaces and prediction of reaction rate constants. The reactions R + HNO (R = CH3 and C6H5) were found to proceed by two key product channels giving (1) RH + NO and (2) RNO + H, primarily by direct abstraction and indirect association/decomposition mechanisms, respectively. As both reactions initially occur barrierlessly, their rate constants were evaluated with a canonical variational approach in our TST and RRKM/ME calculations. For practical applications, the rate constants evaluated for the atmospheric‐pressure condition are represented by modified Arrhenius equations in units of cm3 mol−1 s−1 for the temperature range 298–2500 K: κ1A = 1.47 × 1011T0.76 exp[−175/T], κ2A = 8.06 × 103T2.40 exp[−3100/T], κ1B = 3.78 × 105T2.28 exp[230/T], and κ2B = 3.79 × 109T1.19 exp[−4800/T], where A and B represent CH3 and C6H5 reactions, respectively. Based on the predicted rate constant at 1 atm pressure for R + HNO → RNO + H, we estimated their reverse rate constants for R + HNO production from H + RNO in units of cm3 mol−1 s−1: κ−2A′ = 7.01 × 1010 T0.84 exp[120/T] and κ−2B′ = 2.22 × 1019 T−1.01 exp[−9700/T]. The heats of formation at 0 K for CH3NO, CH3N(H)O, CH3NOH, C6H5N(H)O, and C6H5NOH have been estimated to be 18.6, 18.1, 22.5, 47.2, and 50.7 kcal mol−1 with an estimated ±1 kcal mol−1 error. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 37: 261–274, 2005

Mechanisms of HNO and NO Production from Angeli's Salt: Density Functional and CBS-QB3 Theory Predictions

The mechanism of decomposition of Angeli's salt, Na(2)N(2)O(3), was explored with B3LYP and CBS-QB3 computational methods. Angeli's salt produces both nitroxyl (HNO) and nitric oxide (NO), depending upon the pH of the solution. These calculations show that protonation on N(2), while less favorable than O protonation, leads spontaneously to HNO production, while diprotonation at O(3) leads to NO generation. K(a) values for protonation at different centers and rate constants have been found which reproduce experimental data satisfactorily.

Nuclear Factor-κB and Mitogen-activated Protein Kinases Mediate Nitric Oxide-enhanced Transcriptional Expression of Interferon-β

Mitogen-activated protein (MAP) kinase and nuclear factor-kappaB (NF-kappaB) activation are critical for initiating the transcriptional expression of cytokines, cell adhesion molecules, and other factors in the macrophage immune response. Nitric oxide (NO), an endogenous free radical, is a product of macrophages that mediates inflammatory and cytotoxic processes in the immune system. Here we report the effects of NO on MAP kinase signaling and NF-kappaB activation in lipopolysaccharide (LPS)-stimulated RAW 264.7 macrophages and correlate these effects to the induction target genes, including interferon-beta (IFN-beta) and IkappaB-alpha. LPS alone induced a rapid phosphorylation of the stress-activated MAP kinases: c-Jun N-terminal kinase (JNK) and p38. Simultaneous treatment with LPS and the NO donor, diethylamine NONOate (DEA/NO), enhanced and prolonged JNK and p38 phosphorylation. Similarly, DEA/NO prolonged the LPS-induced degradation of the NF-kappaB inhibitory subunit, IkappaB-alpha, despite an increase in IkappaB-alpha mRNA levels. Whereas DEA/NO alone was sufficient to induce JNK and p38 phosphorylation, it was not sufficient to cause IkappaB-alpha degradation. The enhancement of IkappaB-alpha degradation by DEA/NO correlated with an increase in the nuclear levels of the p50 and p65 subunits and DNA-binding activity determined by electrophoretic mobility shift assay. DEA/NO and an additional NO donor, MAHMA/NO, are further demonstrated to enhance the transcriptional expression of the IFN-beta gene. The results suggest a role for NO in enhancing and propagating inflammatory conditions and the immune response.

Economic and ecological effects of the coproduction of nitric acid and electric and thermal power using steam-gas technologies

Nitric acid (HNO 3 ) is a high-tonnage product of the chemical industry, which has come into widespread use in various processes of chemical technology, especially in the mineral-fertilizer industry. The annual world production of HNO 3 has reached 60 million tons [1, 2], and is tending to increase. The production of nitric acid in countries of the former USSR is approximately 17 million tons/year. With such a massive product yield, problems of the optimal design and operation of production and power plants are basic from the standpoint of operating costs and ecology; this is associated with the following specifics of this production process: • a large amount of the heat liberated in the process, including high-temperature heat (the heat of exothermal reactions with allowance for condensation and dilution of the acid amounts to 7,149 MJ/ton of HNO 3 ); and • a large amount of compressed air required for the production process (oxygen and ammonia are raw materials for the production of HNO 3 ) and post-production tail gas discharged to the environment (4.75 tons of air/ton of HNO 3 , and 3.73 tons of tail gas/ton of HNO 3 ). Let us examine a method of reducing operating costs, which utilizes the heat of the exothermal chemical reactions and which is more effective than that of classical systems employed for the production of HNO 3 . This is possible when the production process is combined with the steam-gas process used for the production of electric power and effective heat. In the classic scheme employed to produce nitric acid with a single pressure (Fig. 1), the machinery consists of a compressor, which supplies air for the catalytic oxidation of ammonia to nitric oxide (NO) and its conversion to nitrogen dioxide (NO 2 ) in an absorption column, where nitric acid HNO 3 is formed with the participation of water, and also a tail-gas expander (approximately 98% of nitrogen, 2% of oxygen, and from 50 to 100 ppm of NO x ) for driving the compressor. A condensing steam turbine, which is supplied with steam from a waste-heat boiler incorporated in a series of heat exchangers for the process-gas cooling system, serves as an additional drive of the air compressor. The temperature distribution of the tail gas in th is cycle (Fig. 2) depends on the design assumptions with respect to the distribution of heat output for the gas and steam cycles i n the power system of the plant producing the HNO 3 , i.e., above all, for the steam turbine and expander, as well as for the amount of heating and process steam output externally (so-called export). The method used to extract the NO x from the exhaust gas to support the requirements for environmental protection may exert a significant influence on the output distribution of these cycles. In modern HNO 3 production, two principal methods are basically used for the catalytic reduction of the NO x : selective ammonia (SCR), and also natural gas [3]. The chemical reactions in both methods are exothermic; moreover, the temperature rise of the exhaust gas (SCR method) is only 10°K (for an optimal temperature range of from 230 to 330°C). Reduction of the NO x by natural gas using catalysts with favorable metals provides for an increase of approximately from 200 to 300°K when

Observations of HNO 2 in the polluted winter atmosphere: possible heterogeneous production on aerosols

Measurements of HNO 2 and NO 2 were obtained in Christchurch, New Zealand, during the winter of 1997, using differential optical absorption spectroscopy (DOAS). HNO 2 concentrations ranged from below 50 ppt to 2.9 ppb and were found to be correlated with those of NO 2. The highest HNO 2 values occurred during the night when general pollution levels, particularly those of suspended particulate matter, were also high. The aerosol surface density in the light path was estimated from the light attenuation measured by the spectroscopic system, and a strong correlation between HNO 2/NO 2 and the aerosol surface density was observed. This correlation suggests that significant heterogeneous chemical production of HNO 2 may occur through reactions of NO 2 on aerosol surfaces. This hypothesis is further supported by a detailed analysis of selected pollution episodes where the HNO 2/NO 2 ratio was highly correlated with short-term changes of the aerosol density during episodes with consistently high NO 2 concentrations. The observed HNO 2 concentrations are also consistent with recent studies of the oxidation of NO 2 to HNO 2 on aerosol surfaces. The evidence for heterogeneous production of HNO 2 on aerosol surfaces is limited, however, by the lack of data on inversion layer height which dominates trace gas concentrations in the boundary layer.

Production and removal of aerosol in a polluted fog layer: model evaluation and fog effect on PM

A radiation fog physics, gas- and aqueous-phase chemistry model is evaluated against measurements in three sites in the San Joaquin Valley of California (SJV) during the winter of 1995. The measurements include for the first time vertically resolved fog chemical composition measurements. Overall the model is successful in reproducing the fog dynamics as well as the temporal and spatial variability of the fog composition (pH, sulfate, nitrate, and ammonium concentrations) in the area. Sulfate production in the fog layer is relatively slow (1–4 μg m −3 per fog episode) compared to the episodes in the early 1980s because of the low SO 2 concentrations in the area and the lack of oxidants inside the fog layer. Sulfate production inside the fog layer is limited by the availability of oxidants in the urban areas of the valley and by SO 2 in the more remote areas. Nitrate is produced in the rural areas of the valley by the heterogeneous reaction of N 2O 5 on fog droplets, but this reaction is of secondary importance for the more polluted urban areas. The gas-phase production of HNO 3 during the daytime is sufficient to balance the nitrate removed during the nighttime fog episodes. Entrainment of air from the layer above the fog provides another source of reactants for the fog layer. Wet removal is one of most important processes inside the fog layer in SJV. We estimate based on the three episodes investigated during IMS95 that a typical fog episode removes 500–2000 μg m −2 of sulfate, 2500–6500 μg m −2 of nitrate, and 2000–3500 μg m −2 of ammonium. For the winter SJV valley the net fog effect corresponds to reductions in ground ambient concentrations of 0.05–0.2 μg m −3 for sulfate, 3–6 μg m −3 for total nitrate, and 1–3 μg m −3 for total ammonium.

Quantitative study of the formation of inorganic chemical species following corona discharge. II. Effect of SO 2 traces on the production of HNO 2 and HNO 3 in a humid atmosphere

The effect of sulfur dioxide traces on the formation of nitrous and nitric acid resulting from exposure to corona discharge in a composition-controlled, humid atmosphere was investigated. The production of NO 2 − and NO 3 − at the trace level was found to increase linearly with the corona discharge time, electric current intensity and quantity of electricity, but it was significantly lower in the presence of SO 2 traces. This decrease is attributed to the oxidation of SO 2 into sulfuric acid by OH radicals produced by corona discharge. The formation of S0 4 2− ions depends on the quantity of electricity and the amount of SO 2 introduced in the atmosphere, while the formation of HSO 3 − ions is a function of the electric wind and diffusion at air-water interface.

The budget of oxidised nitrogen species in orographic clouds

The transformation of NO x as it passed through a hill-top cap cloud was investigated by measuring (i) NO x (NO and NO 2) and particulate nitrate concentrations on both sides of the hill, (ii) nitrite and nitrate in cloud, and (iii) nitrous and nitric acid concentrations below cloud base. Results from four periods during April and May 1993 are presented as part of a EUROTRAC GCE (Ground-based Cloud Experiment) experimental campaign at Great Dun Fell, in Cumbria, England. The overall change in NO x in all four periods was less than 20%. On 22 April the air flow was from west to east, and NO x concentrations were very much larger than particulate nitrate concentrations. There was evidence for loss of NO x and production of nitrous acid as air passed through the cloud. During May the air flow was from east to west; NO x concentrations were much smaller, and similar to concentrations of particulate nitrate. Differences in NO x concentrations before and after cloud sometimes showed a loss of NO x which was greater than the combined measurement uncertainty. Changes in particulate nitrate concentrations were close to the combined measurement errors. Concentrations of nitrate in cloud, however, were greater than could be accounted for by particles alone, suggesting a significant input of HNO 3 Measurements below cloud showed that as much as 25% of the cloud nitrate could be released as HNO 3 as cloud droplets evaporated. These field measurements show that chemical processing of oxidised nitrogen does occur in clouds, involving consumption of NO x and production of gaseous HNO 3 as cloud droplets evaporate. The methods used to measure particulate nitrate concentrations, however, were not adequate to construct a complete budget of oxidised nitrogen across the hill.

Quantitative study of the formation of inorganic chemical species following corona discharge—I. Production of HNO 2 and HNO 3 in a composition-controlled, humid atmosphere

Nitrous and nitric acid formed after exposure to a corona discharge in a composition-controlled humid atmosphere were collected in an aqueous liquid phase at room temperature. It was found that the production of NO 2 − and NO 2 − ions at the trace level increased linearly with the corona discharge time, electric current intensity and quantity of electricity. The relative amount of nitrates formed was larger than that of nitrites.

Missing chemistry of reactive nitrogen in the upper stratospheric polar winter

Data from the CLAES on UARS indicate that a significant mechanism for production of HNO3 in the middle to upper stratosphere is missing from the chemical reaction set currently used by atmospheric models. Measured HNO3 in the polar vortex is strongly enhanced relative to the extra‐vortex at 1200 K potential temperature (near 3 mbar) in January, 1992. The HNO3 vertical profile shows this enhancement forms a secondary altitude maximum from about 10 to 2 mbar (800‐1500 K). A chemistry/transport model (CTM) simulation of this period produces no increase of HNO3 in the vortex near 3 mbar and no secondary maximum in the HNO3 profile. Furthermore, the CTM produces relatively high N2O5 in the vortex, with a vertical peak near 3 mbar, while both CLAES and ISAMS show a shallow minimum there. The implication of this comparison is that some unmodeled process is acting to enhance HNO3 and reduce N2O5 at high latitudes in the winter middle and upper stratosphere. Heterogeneous conversion of N2O5 to HNO3 on hydrated ion clusters is proposed as a possibility for the missing mechanism.

The diurnal variation of hydrogen, nitrogen, and chlorine radicals: Implications for the heterogeneous production of HNO2

In situ measurements of hydrogen, nitrogen, and chlorine radicals obtained through sunrise and sunset in the lower stratosphere during SPADE are compared to results from a photochemical model constrained by observed concentrations of radical precursors and environmental conditions. Models allowing for heterogeneous hydrolysis of N2O5 on sulfate aerosols agree with measured concentrations of NO, NO2, and ClO throughout the day, but fail to account for high concentrations of OH and HO2 observed near sunrise and sunset. The morning burst of [OH] and [HO2] coincides with the rise of [NO] from photolysis of NO2, suggesting a new source of HOx that photolyzes in the near UV (350 to 400 nm) spectral region. A model that allows for the heterogeneous production of HNO2 results in an excellent simulation of the diurnal variations of [OH] and [HO2].

Thermal deNOx: no HNO at room temperature

HNO production is predicted by the reaction sequence NH 2 + NO → HN 2 + OH, HN 2 + NO → HNO + N 2 in the Miller mechanism for the thermal deNOx process. A search was made for the HNO molecule in the reaction system NH 2 + NO at room temperature using diode laser infrared kinetic spectroscopy to search for NH stretch absorptions of HNO. No HNO attributable to the deNOx process was observed. Sensitivity calibration measurements set an upper bound of 1% for the conversion of NH 2 into HNO.

Verification of a mathematical model for aerosol nitrate and nitric acid formation and its use for control measure evaluation

A mathematical model for the formation of atmospheric nitric acid and aerosol nitrate has been developed and employed to study the effect of emission controls. Based on a Lagrangian formulation of the atmospheric diffusion equation, the model computes nitric acid concentrations from a description of daytime photochemical reactions and night-time reactions involving NO 3 and N 2O 5. Ammonium nitrate formation is computed at a thermodynamic equilibrium between HNO 3 and NH 3, and heterogeneous reactions between HNO 3 and preexisting aerosol are considered. The accuracy of the air quality model's predictions is verified by comparison to O 3, NO 2, HNO 3, NH 3, aerosol nitrate and PAN measurements made for this purpose in California's South Coast Air Basin during the period of 30–31 August 1982. Examination of emission control alternatives shows that reduction in NO x emissions yields a nearly proportional decrease in total inorganic nitrate levels (HNO 3 + aerosol nitrates). Reduction in NH 3 emissions suppresses aerosol nitrate formation, resulting in higher HNO 3 levels. Control of organic species emissions by the amounts expected in Los Angeles in future years causes a partial shift away from PAN formation toward greater production of HNO 3. Emission control strategies can be formulated that include a combination of controls on NO x organic gases and NH 3 emissions that will achieve a greater reduction in HNO 3, aerosol nitrate and O 3 levels than a strategy predicated on control of only a single precursor species.

Alpha radiation induced production of HNO 3 during dissolution of Pu compounds (1)

Air-equilibrated suspensions of 238Pu and 239Pu compounds in dilute salt solutions produced HNO 3 at a rate which increased with the H + concentration.

A nitrite-reducing enzyme from Nitrosomonas europaea Preliminary characterization with hydroxylamine as electron donor

1. A soluble enzyme which catalyzes the reduction of nitrite in the presence of hydroxylamine has been extracted from Nitrosomonas cells and partially purified. 2. The hydroxylamine-nitrite reductase was also able to utilize leuco-pyocyanine as an electron donor. 3. The enzyme had a pH optimum for HNO 2 reduction of 5.75 and approximate K m values for HNO 2 and NH 2OH of 1.6 mM and 0.24 M, respectively. 4. The net evolution of approx. 1 mole of gas and disappearance of 1.8 moles of hydroxylamine occurred per mole of nitrite utilized during the reaction. The compounds N 2O and NO were identified as the products of nitrite reduction. 5. Nitrite reduction by hydroxylamine was inhibited 50% by 2 μM diethyl-dithiocarbamate, 8 μM α,α′-dipyridyl, 2×10 −4 M KCN or 1.5 mM NaN 3. 6. The partially purified enzyme fraction contained mammalian cytochrome c oxidase, hydroxylamine oxidase, hydroquinone oxidase and NH 2OH-cytochrome c reductase activity and catalyzed the production of HNO 2 from NH 2OH. 7. The rate of O 2 utilization coupled to hydroxylamine oxidation was inhibited in the presence of nitrite, whereas the rate of aerobic hydroxylamine disappearance was stimulated approx. 100% in the presence of nitrite. 8. Hydroxylamine-nitrite reductase (hydroxylamine:nitrite oxidoreductase) appears to involve the combined action of Nitrosomonas hydroxylamine dehydrogenase and nitrite reductase.