Lifetime Of NO Research Articles

A Mechanism for the STEVE Continuum Emission

AbstractWe describe a mechanism to explain the subauroral emission feature called STEVE (Strong Thermal Emission Velocity Enhancement), with a focus on its continuum spectrum. Spacecraft observations show that emissions co‐occur with typically invisible plasma flows known as subauroral ion drifts. If these flows are fast enough, nitrogen molecules are vibrationally excited by collisions with ions, overcoming the activation energy of the N2+O→NO+N reaction. The resulting NO combines with ambient O, producing NO2 and spectrally broad light. Importantly, this mechanism also produces N, which reduces the lifetime of NO from hours to seconds and thus explains why the emission is confined to a discrete arc. The predicted emission altitude ( 130 km) and occurrence conditions ( 4‐km/s flows) match well with observations. We simulate this mechanism using a simple photochemical model to demonstrate its validity. This mechanism is initiated by fast ion flows and is thus distinct from auroral and airglow processes.

Chemical and meteorological influences on the lifetime of NO<sub>3</sub> at a semi-rural mountain site during PARADE

Abstract. Through measurements of NO2, O3 and NO3 during the PARADE campaign (PArticles and RAdicals, Diel observations of mEchanisms of oxidation) in the German Taunus mountains we derive nighttime steady-state lifetimes (τss) of NO3 and N2O5. During some nights, high NO3 (∼ 200 pptv) and N2O5 (∼ 1 ppbv) mixing ratios were associated with values of τss that exceeded 1 h for NO3 and 3 h for N2O5 near the ground. Such long boundary-layer lifetimes for NO3 and N2O5 are usually only encountered in very clean/unreactive air masses, whereas the PARADE measurement site is impacted by both biogenic emissions from the surrounding forest and anthropogenic emissions from the nearby urbanised/industrialised centres. Measurement of several trace gases which are reactive towards NO3 indicates that the inferred lifetimes are significantly longer than those calculated from the summed loss rate. Several potential causes for the apparently extended NO3 and N2O5 lifetimes are examined, including additional routes to formation of NO3 and the presence of a low-lying residual layer. Overall, the most likely cause of the anomalous lifetimes are related to the meteorological conditions, though additional NO3 formation due to reactions of Criegee intermediates may contribute.

Detection of Nitric Oxide by Electron Paramagnetic Resonance Spectroscopy: Spin-Trapping with Iron-Dithiocarbamates.

Electron paramagnetic resonance (EPR) spectroscopy is the ideal methodology to identify radicals (detection and characterization of molecular structure) and to study their kinetics, in both simple and complex biological systems. The very low concentration and short life-time of NO and of many other radicals do not favor its direct detection and spin-traps are needed to produce a new and persistent radical that can be subsequently detected by EPR spectroscopy.In this chapter, we present the basic concepts of EPR spectroscopy and of some spin-trapping methodologies to study NO. The "strengths and weaknesses" of iron-dithiocarbamates utilization, the NO traps of choice for the authors, are thoroughly discussed and a detailed description of the method to quantify the NO formation by molybdoenzymes is provided.

Radiative lifetimes of NO A Σ2+(v′=,1,2) and the electronic transition moment of the A Σ2+−X Π2 system

Improved measurements of the radiative lifetimes of NO A Σ2+(v′=0,1,2) are presented and used to update the absolute electronic transition moment for the NO γ bands. The pressure-dependent fluorescence decay rate was measured in a low-pressure, room-temperature, flow cell containing dilute mixtures of NO in N2 using time-resolved laser-induced fluorescence excited with a picosecond laser and detected with a microchannel-plate photomultiplier tube. Fluorescence decay rates were determined using an analysis procedure that accounted for the electronic response of the detection system and measurement noise. Radiative lifetimes were determined from an extrapolation of the measured decay rates to zero pressure. In comparison with prior measurements of these radiative lifetimes, the improved experimental approach and analysis procedure result in a significant improvement in the measurement precision. The accuracy of the fluorescence decay-rate measurements was confirmed by independent measurements using time-correlated single-photon counting and time-resolved probing of laser-excited population in A Σ2+ using 266 nm photoionization and charge detection. The measured radiative lifetimes are 192.6±0.2 ns for v′=0, 186.2±0.4 ns for v′=1, and 179.4±0.7 ns for v′=2. The measured lifetimes are shown to be in outstanding agreement with those predicted by an electronic transition moment that is identical in form to the function recommended by Luque and Crosley [J. Chem. Phys. 111, 7405 (1999)] after appropriate rescaling. This rescaling does not affect the agreement of the transition moment function with the previously reported vibrational branching ratios and improves agreement with previously reported absolute oscillator strength measurements. Based on the rescaled transition moment, updated values of absolute transition probabilities in the NO A Σ2+−X Π2 system are presented.

PHOTOLYSIS AND LIFETIME OF NO2, N2O AND HNO3 USING ANALYTICAL SOFTWARE PROGRAM

In this research photolysis of NO 2, N 2 O and HNO 3 for vast range of altitudes was investigated using the absorption cross-section data provided by NASA. The calculations were made using a special software computer program. Also the lifetimes of NO 2, N 2 O and HNO 3 were calculated. The investigation revealed that the lifetime due to photolysis will be nearly steady and short for NO 2, and will be as long (as there is no overlap with solar fluxes below 50 km altitude) for N 2 O . As for nitric acid HNO 3 the lifetime started to increase from 1 day at 25 km altitude to 10 days at the surface of the earth.

Collisional quenching of NO A Σ2+(v′=) between 125 and 294 K

We report measurements of the temperature-dependent cross sections for the quenching of fluorescence from the A (2)Sigma(+)(v(')=0) state of NO for temperatures between 125 and 294 K. Thermally averaged cross sections were measured for quenching by NO(X (2)Pi), N(2), O(2), and CO in a cryogenically cooled gas flow cell. Picosecond laser-induced fluorescence was time resolved, and the thermally averaged quenching cross sections were determined from the dependence of the fluorescence decay rate on the quencher-gas pressure. These measurements extend to lower temperature the range of previously published results for NO and O(2) and constitute the first reported measurements of the N(2) and CO cross sections for temperatures below 294 K. Between 125 and 294 K, a negative temperature dependence is observed for quenching by NO, O(2), and CO, implicating collision-complex formation in all three cases. Over the same temperature range, a constant, nonzero cross section is measured for quenching by N(2). Updated empirical models for the temperature dependence of the cross sections between 125 and 4500 K are recommended based on weighted least-squares fits to the current low-temperature results and previously published measurements at higher temperature. The results of over 250 measurements presented here indicate that the collisionless lifetime of NO A (2)Sigma(+)(v(')=0) is approximately 192 ns.

Vibrational level dependence of lifetime of NO 2 in the [formula omitted]2B 2 state

The vibrational level dependence of the lifetime of NO 2 D ̃ 2B 2 has been investigated by using LIF, hole-burning, and photofragment excitation methods. The predissociation rates for the vibrational levels estimated from the line profiles increase sharply with excitation energy even blow the second dissociation limit to form NO and O( 1D). The occurrence of the dissociation pathway into NO and O( 1D) via the D ̃ 2B 2 states is confirmed by the observation of the appearance thresholds to form various J″-levels of NO( 2Π 1/2, v″=0), which accord with the calculated dissociation limits. The dissociation mechanism is discussed based on the energy dependence of predissociation rates and O( 1D) quantum yields.

Kinetics of the reactions of nitrogen dioxide with glutathione, cysteine, and uric acid at physiological pH

Nitrogen dioxide (NO 2 •) is a key biological oxidant. It can be derived from peroxynitrite via the interaction of nitric oxide with superoxide, from nitrite with peroxidases, or from autoxidation of nitric oxide. In this study, submicromolar concentrations of NO 2 • were generated in < 1 μs using pulse radiolysis, and the kinetics of scavenging NO 2 • by glutathione, cysteine, or uric acid were monitored by spectrophotometry. The formation of the urate radical was observed directly, while the production of the oxidizing radical obtained on reaction of NO 2 • with the thiols (the thiyl radical) was monitored via oxidation of 2,2′-azino-bis-(3-ethylthiazoline-6-sulfonic acid). At pH 7.4, rate constants for reaction of NO 2 • with glutathione, cysteine, and urate were estimated as ∼ 2 × 10 7, 5 × 10 7, and 2 × 10 7 M −1 s −1, respectively. The variation of these rate constants with pH indicated that thiolate reacted much faster than undissociated thiol. The dissociation of urate also accelerated reaction with NO 2 • at pH > 8. The thiyl radical from GSH reacted with urate with a rate constant of ∼ 3 × 10 7 M −1 s −1. The implications of these values are: (i) the lifetime of NO 2 • in cytosol is < 10 μs; (ii) thiols are the dominant ‘sink’ for NO 2 • in cells/tissue, whereas urate is also a major scavenger in plasma; (iii) the diffusion distance of NO 2 • is ∼ 0.2 μm in the cytoplasm and < 0.8 μm in plasma; (iv) urate protects GSH against depletion on oxidative challenge from NO 2 •; and (v) reactions between NO 2 • and thiols/urate severely limit the likelihood of reaction of NO 2 • with NO• to form N 2O 3 in the cytoplasm.

The biological lifetime of nitric oxide: Implications for the perivascular dynamics of NO and O2

Endothelial nitric oxide (nitrogen monoxide) is synthesized at the intravascular/extravascular interface. We previously have reported the intravascular half-life of NO, as a result of consumption by erythrocytes, as approximately 2 ms. We report here studies designed to estimate the lifetime of NO in the parenchymal (extravascular) tissue and describe the implications of these results for the distribution of NO and oxygen concentration gradients away from the blood vessel. The rate of consumption of NO by parenchymal cells (hepatocytes) linearly depends on both NO and O(2) concentration. We estimate that the extravascular half-life of NO will range from 0.09 to > 2 s, depending on O2 concentration and thus distance from the vessel. Computer modeling reveals that this phenomenon, coupled with reversible NO inhibition of cellular mitochondrial oxygen consumption, substantially extends the zone of adequate tissue cellular oxygenation away from the blood vessel, with an especially dramatic effect during conditions of increased tissue work (oxygen consumption). This represents a second action of NO, in addition to vasodilation, in enhancing tissue cellular respiration and provides a possible physiological function for the known reversible inhibition of mitochondrial respiration by low concentrations of NO.

The biological lifetime of nitric oxide: Implications for the perivascular dynamics of NO and O 2

Endothelial nitric oxide (nitrogen monoxide) is synthesized at the intravascular/extravascular interface. We previously have reported the intravascular half-life of NO, as a result of consumption by erythrocytes, as approximately 2 ms. We report here studies designed to estimate the lifetime of NO in the parenchymal (extravascular) tissue and describe the implications of these results for the distribution of NO and oxygen concentration gradients away from the blood vessel. The rate of consumption of NO by parenchymal cells (hepatocytes) linearly depends on both NO and O 2 concentration. We estimate that the extravascular half-life of NO will range from 0.09 to &gt; 2 s, depending on O 2 concentration and thus distance from the vessel. Computer modeling reveals that this phenomenon, coupled with reversible NO inhibition of cellular mitochondrial oxygen consumption, substantially extends the zone of adequate tissue cellular oxygenation away from the blood vessel, with an especially dramatic effect during conditions of increased tissue work (oxygen consumption). This represents a second action of NO, in addition to vasodilation, in enhancing tissue cellular respiration and provides a possible physiological function for the known reversible inhibition of mitochondrial respiration by low concentrations of NO.

Ionization by energetic protons in Thermosphere‐Ionosphere Electrodynamics General Circulation Model

Originating in the magnetosphere and precipitating into the high‐latitude ionosphere, energetic protons in the keV energy range are a common auroral phenomenon and can represent an important energy source for the auroral atmosphere. In global models describing the ionosphere‐thermosphere interaction, keV protons have always been neglected or treated as if they were electrons. Here we investigate the effect of keV protons on both the ionospheric and thermospheric composition in the E region on a planetary scale. We present a parameterization of electron and ion production rates induced by an incident proton beam as a fast computational scheme for use in global models. The incident proton beam is assumed to have a Maxwellian distribution with characteristic energies between 1 and 20 keV. The parameterization is validated against a full proton transport code. By including these parameterized electron and ion production rates in a one dimension‐in‐space (1D‐in‐space) Thermosphere‐Ionosphere Global Mean Model, we show that proton precipitation can cause a significant enhancement of the electron density, the major ion (O2+ and NO+) densities, and the nitric oxide density. As a result, the conductivities in the E region are also greatly increased. Using the Thermosphere‐Ionosphere Electrodynamics General Circulation Model (TIE‐GCM), we show that the proton precipitation, when added to the normal electron aurora, causes a large increase (up to 70%) in electron, , and NO+ densities over much of the auroral oval. The NO density is affected in a larger area owing to the long lifetime of NO on the nightside. This first study of the influence of protons on a planetary scale clearly shows the significant impact that auroral keV protons can have on the ionospheric and thermospheric composition and the need to include proton precipitation in global models.

Climatic forcing of nitrogen oxides through changes in tropospheric ozone and methane; global 3D model studies

A three-dimensional global chemical tracer model and a radiation transfer model have been used to study the role of NO x emissions for radiative forcing of climate. Through production of tropospheric O 3, NO x emissions lead to positive radiative forcing and warming. But by affecting the concentration of OH radicals, NO x also reduces the levels of CH 4, thereby giving negative forcing and cooling. The lifetime of NO x varies from hours to days, giving large spatial variations in the levels of NO x . We have selected geographical regions representing different chemical and physical conditions, and chemical and radiative effects of reducing NO x emissions by 20% in each region are studied. Due to nonlinearities in the O 3 chemistry as well as differences in convective activity, there are large geographical differences in the effect of NO x on O 3 as well as variations in the annual profile of the changes. The effect of NO x emissions on methane is also found to depend on the localisation of the emissions. The calculated ozone and methane forcing are of similar magnitude but of opposite sign. The methane effect acts on a global scale with a delay of approximately a decade, while the ozone effect is of regional character and occurs during weeks.

The passive transport of NO x emissions from aircraft studied with a hierarchy of models

The passive transport of aircraft emissions of nitrogen oxides (NO x = NO + NO 2) has been studied with a hierarchy of models ranging from two-dimensional and three-dimensional chemistry transport models up to three-dimensional models of the general circulation. The sink of NO x was parameterized by an exponential decay process with a globally constant half-lifetime of 10 days. By performing a simple experiment the importance of the various transport processes has been studied. The three-dimensional models show that the monthly mean volume mixing ratio of NO x varies by a factor of three in the longitudinal direction and the temporal variability is of the order of 30%. In view of the nonlinearity of the chemical processes leading to ozone formation in the presence of NO x this implies that the assessment of the effects of subsonic aircraft emissions of NO x should be done with three-dimensional models. Vertical redistribution by convection strongly affects the maximum NO x mixing ratio at cruise altitudes, but due to the limited lifetime of NO x of the order of ten days the most important contribution to the mixing ratio at a certain level usually stems from emissions around that level. The strong static stability in the stratosphere hampers significant dispersion of the subsonic aircraft emissions above the height where the emissions take place for the lifetimes considered here. Some model deficiencies and biases have been identified and discussed. Examples are the oscillatory signature of NO x distributions obtained with a spectral advection scheme, the strong diffusion of one of the GCMs into the polar regions, and the too intense interhemispheric exchange of one of the two-dimensional CTMs. For the vertical redistribution of the emissions it may be necessary to include not only updrafts but also downdrafts in the convective parametrization of the transport model.

Model overestimates of NOy in the upper stratosphere

Stratospheric NOy profiles from the Garcia‐Solomon two‐dimensional model are compared to observed profiles from the Upper Atmosphere Research Satellite (UARS) and the Atmospheric Trace Molecule Spectroscopy Experiment (ATMOS). The model consistently overestimates NOy in the upper stratosphere beyond the range of uncertainty in the satellite data. The relatively short lifetime of NOy in this region suggests a largely photochemical explanation for the discrepancy. Uncertainties in the photochemical production of NOy from N2O strongly influence stratospheric NOy profiles, but this influence decreases with increasing height in the upper stratosphere. Photochemical loss of NOy is controlled by the NO photolysis rate and the reaction rates of N + NO and N + O2. All these rates are subject to substantial uncertainties that probably contribute to the discrepancy between model and observations.

Lifetimes of Rydberg states in ZEKE experiments. III. Calculations of the dc electric field dependence of predissociation lifetimes of NO

Results are presented of calculations on the experimentally observed lifetime enhancement of high principal quantum number nf(N+=2) and np(N+=0) Rydberg states of the NO molecule in small dc electric fields. A Hund’s case (d) molecular Hamiltonian is introduced, which describes intramolecular interactions between low angular momentum Rydberg states as a result of core penetration and l mixing caused by the electric field. Eigenstates of the molecule in the electric field are obtained by diagonalization of the Hamiltonian and an effective decay time is determined which describes the multiexponential decay of the superposition of (Stark) states which is excited experimentally. The calculations reproduce the striking onset of the lifetime enhancement of the np(N+=0) series, which was observed experimentally. Both for the nf(N+=2) and np(N+=0) Rydberg series, core penetration by low-l states leads to extensive interseries coupling for several values of the principal quantum number.

Enhancements in the lifetimes of NO Rydberg states in dc electric fields: Implications for zero-electron-kinetic-energy photoelectron spectroscopy experiments.

Lifetimes of NO p- and f-orbital Rydberg states (n=40--122) have been measured under near field-free conditions as well as in the presence of small dc electric fields. The field causes an increase in the observed lifetimes, which is attributed to Stark mixing of the predissociative p and f orbitals with high-l orbital angular momentum states. The results indicate that under the conditions existing in high-resolution zero-electron-kinetic-energy (ZEKE) photoelectron spectroscopy experiments, the ZEKE Rydberg states are l mixed.

Scale problems in global tropospheric chemistry modeling: Comparison of results obtained with a three-dimensional model, adopting longitudinally uniform and varying emissions of NO X and NMHC

As a consequence of the non-linear behavior of the chemistry of the atmosphere and because of the short lifetime of NO X in the atmosphere, two-dimensional models do not give an adequate description of the production and destruction rates of O 3 and the global distributions of the concentrations of O 3 and OH. The errors which result were estimated by running a 3-D model both with longitudinally uniform and varying anthropogenic NO and NMHC input rates. It is shown that the latter lead to much lower O 3 and especially OH concentrations. The effects are particularly pronounced in the tropics and in the mid-latitude regions of the northern hemisphere. This affects estimates of the atmospheric sink of CH 4 and especially deductions about its latitudinal distribution.

The radiative lifetime of NO(b 4Σ −)

Laser-induced fluorescence has been used to measure the radiative lifetimes and self-quenching rate coefficients for the NO(b 4Σ −) state in vibrational levels ν=2−5. Excitation of NO(b) utilized direct b←X pumping at 192–206 nm, with detection of the NO(b 4Σ − →a 4Π) Ogawa bands at 780–960 nm. The lifetimes lie in the 4.2–7.5 μs range, higher levels resulting in shorter lifetimes, and quenching by NO occurs at close to collision frequency.

Radiative lifetime measurements of vibrationally excited states of NO + (X 1Σ +)

The radiative lifetimes of NO + (X 1Σ +, v=1, …, 5) have been measured using an FT/ICR instrument equipped with pulsed valves. NO + (X 1Σ +, v) is state-selectively formed by REMPI on NO and detected by a state-selective charge-transfer reaction with a neutral monitor gas. Recording the monitor ion signal as a function of the NO + (X 1Σ +, v) radiative relaxation time yields radiative lifetimes of 90, 49, 30, 25 and 19 ms for v= 1, 2, 3, 4 and 5, respectively. these results are in good agreement with recent theoretical calculations from several research groups.

Radiative relaxation of NO + (X, v = 1−4)

Radiative lifetimes of NO + (X, v=1–4) has been determined using the monitor ion technique in a triple cell ICR spectrometer with Fourier transform detection. Correction of the measured lifetimes for radiative cascades and quenching is discussed in detail. The corrected lifetimes are in very good agreement with the best available theoretical data.