Fate Of NO Research Articles

Nitrate-consuming processes in a petroleum-contaminated aquifer quantified using push–pull tests combined with 15N isotope and acetylene-inhibition methods

Nitrate consumption in aquifers may result from several biogenic and abiotic processes such as denitrification, assimilatory NO 3 − reduction, dissimilatory NO 3 − reduction to ammonium (DNRA), or abiotic NO 3 − (or NO 2 −) reduction. The objectives of this study were to investigate the fate of NO 3 − in a petroleum-contaminated aquifer, and to assess the feasibility of using single-well push–pull tests (PPTs) in combination with 15N isotope and C 2H 2 inhibition methods for the quantification of processes contributing to NO 3 − consumption. Three consecutive PPTs were performed in a monitoring well of a heating oil-contaminated aquifer in Erlen, Switzerland. For each test, we injected 500 l of test solution containing 0.5 mM Br − as conservative tracer and either 0.5 mM unlabeled NO 3 − or ∼0.3 mM 15N-labeled NO 3 − as reactant. Test solutions were sparged during preparation and injection with either N 2, Ar or 10% C 2H 2 in Ar. After an initial incubation period of 1.5–3.2 h, we extracted the test solution/groundwater mixtures from the same location and measured concentrations of relevant species including Br −, NO 3 −, NO 2 −, N 2O, N 2, and NH 4 +. In addition, we determined the 15N contents of N 2, N 2O, NH 4 +, and suspended biomass from 15N/ 14N isotope-ratio measurements. Average total test duration was 50.5 h. First-order rate coefficients ( k) were computed from measured NO 3 − consumption, N 2– 15N production and N 2O– 15N production. From measured NO 3 − consumption we obtained nearly identical estimates of k for all PPTs with small 95% confidence intervals, indicating good reproducibility and accuracy for the tests. Estimates of k from N 2– 15N production and N 2O– 15N production indicated that denitrification accounted for only 46–49% of observed NO 3 − consumption. Production of N 2– 15N in the presence of C 2H 2 was observed during one of the tests, which may be an indicator for abiotic NO 3 − reduction. Moreover, 15N isotope analyses confirmed occurrence of assimilatory NO 3 − reduction (0.58 at.% 15N in suspended biomass) and to a smaller extent DNRA (up to 4 at.% 15N in NH 4 +). Our results indicated that the combination of PPTs, 15N-isotope and C 2H 2 inhibition methods provided improved information on denitrification as well as alternative fates of NO 3 − in this aquifer.

Contribution of Nitric Oxide to the Apoptotic Process in Human B Cell Chronic Lymphocytic Leukaemia

B cell chronic lymphocytic leukaemia (B-CLL) is characterised by defective apoptosis that cannot be explained solely on the basis of the known chromosomal abnormalities. We and other have now reported that the leukemic cells spontaneously display the inducible isoform of nitric oxide synthase, iNOS. Inhibition of the iNOS pathway leads to increased apoptosis of the tumoral cells in vitro, indicating that the endogenous release of NO contributes to their resistance to the normal apoptotic process. The factors that induce the expression of iNOS in vivo in the leukemic cells are not yet identified. Yet, as interaction of B-CLL leukemic cells with bone marrow stromal cells promotes their survival, the involvement of adhesion molecules and integrins may be suspected. The engagement of CD23 stimulates iNOS activation in the tumoral cells, suggesting that in vivo interaction of CD23 with one of its recognised lig-ands may contribute to iNOS induction. A role for CD40-CD40 ligand interaction may also be hypothesised.The mechanisms involved in the anti-apoptotic role of NO are not fully understood, but may implicate the inhibition of caspase activity, hence the impairment of the Fas pathway. In addition, the mitochondrial membrane potential disruption appears to be a NO-sensitive step in the apoptosis cascade. The presence of a NOS displaying anti-apoptotic properties has now been recognised in different cell types, including various leukaemia. A better knowledge of the mechanisms governing the ultimate fate of NO, anti-versus pro-apoptotic would allow the development of new therapeutic approaches for the treatment of these diseases.

A study of nighttime nitrogen oxide oxidation in a large reaction chamber—the fate of NO 2, N 2O 5, HNO 3, and O 3 at different humidities

Inorganic reactions important for the nighttime chemistry of nitrogen oxides in surface air were studied. The experiments were performed in a new, large reaction chamber with a volume of 260 m 3 and a surface/volume ratio better than 1 m −1. The inner surface of the chamber is Teflon FEP. The formation of N 2O 5 and HNO 3 in ambient air with an initial content of ≈ 1.3 ppm NO 2 and ≈ 1.3 ppm O 3 was monitored at 8, 20, and 70% relative humidity for periods of up to five days. The mixing ratios of NO 2, N 2O 5, and HNO 3 were measured simultaneously by in-chamber FTIR absorption spectroscopy. O 3 and NO were measured by UV absorption and chemiluminescence. Model calculations for the nitrogen oxide/ozone system were performed. By comparison of the model calculations with the experimental data, the rate coefficients of two slow reactions, the unimolecular decomposition of NO 3 and the gas-phase formation of HNO 3 from N 2O 5 and water were determined. An upper limit for the rate coefficient for the unimolecular decomposition of NO 3 of ⩽ 1.4 × 10 −4s −1 was obtained, which corresponds to a lifetime of 120 min. The experiments provide evidence that the conversion of N 2O 5 with gaseous water to gas-phase HNO 3 is a superposition of two slow processes: a second-order reaction, N 2O 5 + H 2O, with a rate coefficient of 2.6( ± 0.1) × 10 −22cm 3 molecule −1s −1, and a third-order reaction, first order in N 2O 5 and second order in H 2O, with a rate coefficient of 2( ± 0.05) × 10 −39 cm 6 molecule −2s −1. The third-order process could be due to a reaction of N 2O 5 with water on the chamber walls or alternatively to a gas-phase reaction, possibly even with water dimers. The implications of both alternatives for the atmospheric lifetime of N 2O 5 with respect to its gas-phase conversion to HNO 3 are discussed.

Uptake of carbon dioxide from flue gas by microalgae

The technology under development seeks to provide affordable, and efficient methods for reducing carbon dioxide and other emissions from coal-fired electricity generation based on biological assimilation. Photosynthetic microorganisms such as microalgae, when grown in large outdoor ponds could use carbon dioxide from flue gas directly injected into the culture. This process requires land, water, sunlight and other nutrients. Currently, commercial production of photosynthetic microorganisms is used to produce high value products such as pigments. This work seeks to extend this technology to the energy field. Our results to date indicate that at least some microalgae can tolerate moderate levels of SO x and NO x in laboratory culture, and that a well-engineered outdoor pond can easily achieve in excess of 90% carbon dioxide trapping efficiency when presented with pure carbon dioxide. In laboratory culture experiments with simulated flue gas, the green alga Monoraphidium minutum could tolerate 200 ppm sulfur dioxide and 150 ppm nitric oxide. Some clues to fate of NO are found in the analyses of nitrite and nitrate concentrations in the culture medium during sparging with flue gas. Nitrite concentration in the culture media of flue gas treated cultures is much higher than in control cultures which did not receive sulfur dioxide and nitric oxide. This suggests that some of the NO may be dissolving and could be available as an N-source for the microalgae. Similarly, nitrate utilization is less in flue gas treated cultures, but cell growth is unaffected, again suggesting that N-metabolism is tied to flue gas tolerance. Overall, these results demonstrate that this type of simulated flue gas is tolerated very well by microalgae, and is an excellent substrate for their growth. Culture pH remains quite stable during these experiments indicating that sulfur dioxide is not likely to be a problem under this sparging regime, at least as far as its effect on culture pH.

95/01732 Impact of air staging and the fate of NO and N 2O in a circulating fluidized-bed combustor

95/01732 Impact of air staging and the fate of NO and N 2O in a circulating fluidized-bed combustor

Impact of air staging on the fate of NO and N 2O in a circulating fluidized-bed combustor

This paper presents an experimental investigation of the influence of combustion-air staging on the formation and reduction of NO and N 2O from coal combustion, carried out in a 6.2-m-tall and 0.161-m i.d. circulating fluidized-bed (CFB) combustor. The main operating parameters examined were secondary air ratio and air staging position. It was found that NO generated in the primary combustion zone could be effectively reduced in the secondary combustion zone. The effect of combustion-air staging on the N 2O emissions was found to be relatively small. The axial concentration profile of N 2O along the CFB furnace, however, could be significantly influenced by the air staging position. Detailed analyses were made of the chemistry of NO and N 2O formation and reduction under combustion-air staging conditions. It was revealed that the axial distribution of NO and N 2O along the CFB furnace could be the combined effect of initial distribution of intermediate coal-N, coal combustion performance and furnace hydrodynamics. Unlike traditional approaches, in which exhaust gases only are discussed, this paper for the first time introduces analyses of axial profiles of NO and N 2O in a CFB furnace under combustion-air staging conditions, which should provide a better understanding of the influence of combustion-air staging on NO and N 2O formation and reduction in a CFB furnace.

Penicillins and activity of nitrogen metabolism enzymes in plant tissue cultures

Since plant tissues grown in vitro are not indifferent to antibiotics added to the culture medium, effects of penicillin G (PG) and V (PV) on the uptake and metabolism of nitrogen were studied by following levels of activity of nitrate reductase (NR), glutamate dehydrogenase (GDH), glutamine synthetase (GS), glutamate synthase (GOGAT) and the fate of NO 3 − in the culture media, using callus tissue cultured during 14 days. In comparison to control both NR and GDH showed some degree of stimulation: higher levels of GS than in control were found up to day 10, with a reverse situation from that point till the end of treatment; activity of GOGAT was always lower in treated tissues, throughout the experiments; soluble protein contents were always higher in treated tissues. Uptake of NO 3 − was generally more intense in treated material, discounting an initial two days period during which the inverse was observed. Data obtained show that penicillins enhance certain metabolic pathways of cultured plant cells.

Regulation of nitrate assimilation by ammonium in soils and in isolated soil microorganisms

The regulation of NO − 3 assimilation by NH + 4 and amino acids was studied to better define the conditions under which raicrobial NO − 3 assimilation could be expected to take place in nature. The assay system was microbial isolates from soil and slurries of two soils enhanced in NO − 3 assimilating capacity by previous exposure to glucose for 18–24 h. The NO − 3 assimilation rate was monitored by a NO − 3 electrode and the inhibition determined by the change in rate following addition of NH + 4 or amino acids. NH + 4 inhibited (by 60%) NO − 3 assimilation immediately (< 1 min) and at very low NH + 4 concentrations (O.1 μg N g −1 soil). At higher NH + 4 concentrations (10 μg N g − soil) a second state of inhibition (80%) occurred after 5 min. The speed of the first inhibition stage suggests that the site of inhibition is the transport of NO − 3 into the cell. Asparagine was the only amino acid to act as rapidly and effectively as NH + 4 in the soil, and thus the amino acids are unlikely to be important regulators of NO − 3 assimilation in soils. Of the three soil isolates studied, Saccharomyces cerevisiae and Pseudomonas fluorescens responded to NH + 4 and amino acids in a manner similar to the soil but NO − 3 assimilation in the third organism, Azotobacter vinelandii, was generally insensitive to these N substrates in this short-term assay. Only high concentrations of NH + 4 caused a partial inhibition of NO − 3 assimilation in A. vinelandii. Due to the effectiveness of low NH + 4 concentrations in inhibiting NO − 3 assimilation in soils, microbial immobilization is not expected to be an important fate of NO − 3 unless there are NH + 4-free microsites in the soil.

屋内環境中の窒素酸化物に関する研究(その3) : 二酸化窒素の減衰過程に対する変動要因とその行方について

In this study, the variations of indoor-originated NO and NO_2 concentration in the test rooms were surveyed in detail with a chemiluminescent autoanalyzer. At first, some confusing factors on the sink rate of indoor NO_2 were investigated. In the second place, the fate of NO_2 consumed through the rapid decay in higher relative humidity was discussed. The experimental results are as follows: (1) Lighting such as natural light without direct sunbeam or fluorescent lamp, and small variation of air composition don't have any effect. Forced air mixing and repeated exposition to NO_2 of the interior material have little effect; such physical conditions may take effect where the surface reaction is outstanding. A large difference in the air volume of rooms seemed to bring about a small change in the sink rate of NO_2. Since ordinary variations of actual air volume of living rooms are not so large, such an influence may be negligible. (2) A certain part of NO_2 has been proved to be converted to NO through the decay process described above.

Mathematical modeling of the formation and transport of ammonium nitrate aerosol

A mathematical model describing the transport and formation of aerosol NH 4NO 3 is presented. Based on a vertically resolved Lagrangian trajectory formulation incorporating gas phase kinetics, NH 4NO 3 concentrations are computed at thermodynamic equilibrium with precursor HNO 3 vapor and NH 3 concentrations. Sensitivity analysis shows that NH 4NO 3 concentration predictions are strongly influenced by ambient temperature and NH 3 levels. A brief description of the NH 3 emissions inventory used in this study is included to indicate the important sources. The model was tested by comparison to ambient NH 3, NH 4 + and NO 3 − concentrations measured at El Monte, California during June 1974. Model results compare favorably with the ambient measurements and are used to explain trends in those measurements. An early morning nitrate peak develops as HNO 3 produced soon after sunrise reacts with NH 3 accumulated overnight. A second peak in nitrate concentration is predicted and observed at El Monte later in the day. Potential applications of this model to control strategy decisions and to study the fate of NO x are discussed.