O2 Density Research Articles

Controlling the oxygen species density distributions in the flowing afterglow of O2/Ar–O2 surface-wave microwave discharges

The evolution of species densities along a reactor radially positioned on an O2 surface-wave microwave discharge is investigated by means of modelling with the aim to define the density tuning possibilities. The validity of the models is shown by the comparison of the calculated and measured axial distribution of O-atoms. The calculations revealed that due to the perpendicular injection of the plasma into the reactor, the gas temperature is close to the room temperature in most of it, except for a 5 cm region around the inlet. It is shown that the pressure drop along the discharge tube, which results in the change of pressure in the discharge region with the gas flow rate, induces the variation of the relative density of active species entering the reactor, where the pressure is kept constant. The surface recombination probability of atoms varies along the afterglow tube due to the surface temperature gradient, as well as due to the conditioning of the surface resulting from the continuous operation of the system. The system is shown to be very practical in applications where surfaces/porous materials are to be treated homogeneously by pumping active species through them, since by tuning the gas flow rate equidensity surfaces can be obtained in the case of the two most abundant species, the O-atoms and O2(a) molecules. In the case of O-atoms the densities obtained at the two pressures investigated, i.e. 100 and 50 Pa, are very similar, as well as their evolution along the reactor, while the density of O2(a) molecules decreases considerably with pressure.

Cold atmospheric plasma – A new technology for spacecraft component decontamination

Cold atmospheric plasma (CAP) based on the Surface Micro-Discharge (SMD) technology was investigated for inactivation of different bacteria and endospores. The used technique was developed to serve as an alternative method for the decontamination of spacecraft components based on the COSPAR planetary protection policy where currently the dry heat microbial reduction method is the only applicable way to satisfy the required demands. However it is known, that dry heat can thermally damage sophisticated components installed on the device. Therefore, the development of a low temperature sterilization system is one of the high priority issues for upcoming space missions in the extraterrestrial field. In the study presented here, the vegetative bacteria Escherichia coli and Deinococcus radiodurans and several types of bacterial endospores – including Bacillus atrophaeus, Bacillus safensis, Bacillus megaterium, Bacillus megaterium 2c1 and Bacillus thuringiensis E24 – were inactivated by exposing them indirectly i.e. only to the reactive gases produced by the SMD electrode at room temperature. The results showed a 5log inactivation for E. coli after 10min of exposure. In contrast D. radiodurans proved to be more resistant resulting in a reduction of 3log after exposure of 30min. More than 6log reductions were achieved for B. safensis, B. megaterium and B. megaterium 2c1 after 90min of exposure. Furthermore the applicability of the used CAP system for spacecraft decontamination according to the planetary protection policy was investigated. This included also the investigation of the inactivation homogeneity by the plasma gas, the control of the temperature at the area of interest, the measurement of the O3 density in the treatment region and the detailed investigation of the effects of the exposure on different materials.

Diagnostics of reactive oxygen species produced by microplasmas

Atmospheric pressure generation of reactive oxygen species (ROS) by microplasmas was experimentally studied. The remarkable stability of the microcathode sustained discharge (MCSD) allowed the operation of dc glow discharges, free from the glow-to-arc transition, in He/O2/NO mixtures at atmospheric pressure. Absolute densities of the main ROS were measured by different optical diagnostics: singlet delta oxygen (O2(a 1Δg)) by infrared emission and vacuum ultraviolet absorption in the effluent, ozone (O3) by ultraviolet absorption in the effluent, and atomic oxygen inside the discharge by two-photon absorption laser induced fluorescence. The effect of different parameters, such as gas flow and mixture, and discharge current, on the production of these ROS was studied. High ROS densities up to 1016 cm−3 were achieved. It is shown that the density ratio of O2(a 1Δg) to O3 can be finely tuned in the range [10−3–10+4], through the values of discharge current and NO concentration, and that high O2(a 1Δg) and O3 densities can be transported over distances longer than 50 cm. The MCSD is, thus, a very suitable tool for the continuous production at atmospheric pressure of large fluxes of O2(a 1Δg) and O3, useful to a wide range of applications, notably in plasma medicine.

Exospheric O2 densities at Europa during different orbital phases

Europa's exosphere is a mixture of different species among which sputtered H2O and H2 dominate in the highest altitudes and O2, formed mainly by radiolysis of ice and subsequent release of the produced molecules, prevails at lower altitudes. Europa's O2 exosphere has been demonstrated through both observation and simulation-based techniques to be spatially non-uniform. In the present study we investigate Europa's exospheric O2 characteristics under the external conditions that are likely in the Jupiter's magnetospheric environment, applying the Europa Global model of Exospheric Outgoing Neutrals (EGEON, Plainaki et al., 2012) for different configurations between the positions of Europa, Jupiter and the Sun. We demonstrate for the first time that the spatial distribution of Europa's exosphere is explicitly time-variable due to the time-varying relative orientations of solar illumination and the incident plasma direction. We show that the O2 release efficiency depends both on solar illumination and plasma impact direction. The modeled densities at different orbital phases of Europa are compared, a posteriori, with the analysis results from two observations in order to validate the model. Using the outputs of EGEON we also calculate the supply of neutral oxygen atoms of exospheric origin to Europa's neutral cloud.

Atomic oxygen TALIF measurements in an atmospheric-pressure microwave plasma jet with in situ xenon calibration

Two-photon absorption laser-induced fluorescence (TALIF) is used to measure the absolute density of atomic oxygen (O) in a coaxial microwave jet in ambient air at atmospheric pressure, operated with a mixture of He and a few per cent of air. The TALIF signal is calibrated using a gas mixture containing Xe. A novel method to perform calibration in situ, at atmospheric pressure, is introduced. The branching ratios of several Xe mixtures are reported, to enable us to perform the Xe calibration without the need for a vacuum vessel. The O densities are measured spatially resolved, and as a function of admixed air to the He, and microwave power. The electron density and temperatures are measured using Thomson scattering, and the N2 and O2 densities are measured using Raman scattering. O densities are found to have a maximum of (4–6) × 1022 m−3, which indicate that O2 is close to fully dissociated in the plasma. This is confirmed by the Raman scattering measurements. O is found to recombine mainly into species other than O2 in the afterglow, which is suggested to consist of O3 and oxidized components of NO.

Nighttime photochemical model and night airglow on Venus

The photochemical model for the Venus nighttime atmosphere and night airglow (Krasnopolsky, 2010, Icarus 207, 17–27) has been revised to account for the SPICAV detection of the nighttime ozone layer and more detailed spectroscopy and morphology of the OH nightglow. Nighttime chemistry on Venus is induced by fluxes of O, N, H, and Cl with mean hemispheric values of 3×1012, 1.2×109, 1010, and 1010cm−2s−1, respectively. These fluxes are proportional to column abundances of these species in the daytime atmosphere above 90km, and this favors their validity. The model includes 86 reactions of 29 species. The calculated abundances of Cl2, ClO, and ClNO3 exceed a ppb level at 80–90km, and perspectives of their detection are briefly discussed. Properties of the ozone layer in the model agree with those observed by SPICAV. An alternative model without the flux of Cl agrees with the observed O3 peak altitude and density but predicts an increase of ozone to 4×108cm−3 at 80km. Reactions H+O3 and O+HO2 that may excite the OH nightglow have equal column rates. However, the latter is shifted to 92–94km, and the models agree better with the nightglow observations if O+HO2 does not contribute to the OH excitation. Schemes for quenching of the OH vibrational quanta by CO2 are chosen to fit the observed band distribution in the Δv=1 sequence at 2.9μm. The models agree with all observational constraints for the mean nighttime atmosphere. Analytic relationships between the nightglow intensities, the ozone layer, and the input fluxes of atomic species are given. The model results are compared with those of three-dimensional models for the Venus thermosphere.

Arrays of microplasmas for the controlled production of tunable high fluxes of reactive oxygen species at atmospheric pressure

The atmospheric-pressure generation of singlet delta oxygen (O2(a 1Δg)) by microplasmas was experimentally studied. The remarkable stability of microcathode sustained discharges (MCSDs) allowed the operation of dc glow discharges, free from the glow-to-arc transition, in He/O2/NO mixtures at atmospheric pressure. From optical diagnostics measurements we deduced the yield of O2(a 1Δg). By operating arrays of several MCSDs in series, O2(a 1Δg) densities higher than 1.0 × 1017 cm−3 were efficiently produced and transported over distances longer than 50 cm, corresponding to O2(a 1Δg) partial pressures and production yields greater than 5 mbar and 6%, respectively. At such high O2(a 1Δg) densities, the fluorescence of the so-called O2(a 1Δg) dimol was observed as a red glow at 634 nm up to 1 m downstream. Parallel operation of arrays of MCSDs was also implemented, generating O2(a 1Δg) fluxes as high as 100 mmol h−1. In addition, ozone (O3) densities up to 1016 cm−3 were obtained. Finally, the density ratio of O2(a 1Δg) to O3 was finely and easily tuned in the range [10−3–10+5], through the values of the discharge current and NO concentration. This opens up opportunities for a large spectrum of new applications, making this plasma source notably very useful for biomedicine.

Electrical properties of atomic layer deposited Al2O3 with anneal temperature for surface passivation

The electrical characteristics of Al2O3 layers prepared by the atomic layer deposition technique using O3, H2O, and plasma O2, as oxidants are investigated through capacitance–voltage measurements of metal–insulator–semiconductor capacitors. Particular emphasis is placed on the properties of thermal annealed Al2O3 for surface passivation. Capacitance measurements at flatband voltage before and after the application of constant voltage stress in the inversion regime indicate that the charge trapping and hysteresis behavior of the capacitors are more dominant at low temperature annealing. Positive flatband voltage shifts due to negative charge tunneling are also observed under both negative and positive bias voltage polarities. The interface trap densities of O3 and plasma O2-based Al2O3 samples at 450°C decrease by an order of magnitude with increasing annealing temperature, approaching the interface trap density levels in the 1011eV−1cm−2 range. However, H2O-based Al2O3 doesn't change considerably. The interface trap density distribution shows that H2O-based Al2O3/Si annealed over 400°C has depassivated defects, similar to those observed in SiO2/Si interfaces. A comparison of the emitter saturation current density and the interface defect density shows that the interface density at the midgap is not so useful in predicting interface recombination after corona charging.

Theoretical and experimental density of (U, Gd)O2 and (U, Er)O2

An analytical expression is obtained for calculating the theoretical density of a stoichiometric, equilibrium, solid solution of the type U1–y R y O2 for uranium-gadolinium and uranium-erbium oxide fuel with different initial Gd2O3 or Er2O3 content. It is shown that the theoretical density of oxide fuel, containing a rare-earth oxide of the type R2O3, determined on the basis of the x-ray density is 0.03 g/cm3 higher and 0.02 g/cm3 lower than the computed density of (U, Gd)O2 and (U, Er)O2, respectively. It is found that the density of sintered uranium-gadolinium oxide pellets with an equilibrium solid solution of the type (U, Gd)O2 is 96–98% with initial Gd2O3 mass fraction to 3.35% of the theoretical value and 98–99% with 5% and higher.

Study on Plasma Agent Effect of a Direct-Current Atmospheric Pressure Oxygen-Plasma Jet on Inactivation of E. coli Using Bacterial Mutants

Biosensors of single-gene knockout mutants and physical methods using mesh and quartz glass are employed to discriminate plasma agents and assess their lethal effects generated in a Direct-Current atmospheric-pressure oxygen plasma jet. Radicals generated in plasma are determined by optical emission spectroscopy, along with the O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> density measurement by UV absorption spectroscopy. Besides, thermal effect is investigated by an infrared camera. The biosensors include three kinds of Escherichia coli (E. coli) K-12 substrains with their mutants, totalling 8 kinds of bacteria. Results show that oxidative stress plays a main role in the inactivation process. Rather than superoxide O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-</sup> , neutral reactive oxygen species such as O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> and O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">a</i> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sup> <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Δ</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">g</sub> ) are identified as dominant sources for oxidative stress. In addition, DNA damage caused by oxidation is found to be an important destruction mechanism.

A Computational Study of Radio Frequency Atmospheric Pressure Discharge in Nitrogen and Oxygen Mixture Gases

The characteristics of radio frequency atmospheric pressure discharge in nitrogen and oxygen mixture gases are investigated by using a one-dimensional fluid model. The model consists of equations of particle continuity, Poisson's equation, and the electron energy equation. The effect of the concentrations of O2 in N2 on the discharge characteristics is analyzed. The results show that when the concentration of O2 in N2 is less than 12%, as the amount of O2 grows, the electron density and the N+4 ion density decrease; the main negative particles are electrons. When the concentration of O2 in N2 is greater than 12%, the electron density and the N+4 ion density increase with the increasing admixture of oxygen; the main negative particle is the O− ion. Moreover, the O− ion density, the O+2 ion density, the electron temperature and the mixture gases electronegativity increase with growth of O2 in the range from 4% to 20% and with density of O2 in N2.

不同秧苗素质和移栽密度条件下臭氧胁迫对水稻光合作用、物质生产和产量的影响

Rising tropospheric ozone concentration constrained plant growth and thus result in yield loss of rice.However little is known about response of growth and yield of rice to elevated ozone concentration under different cultivation measures.By using an advanced FACE(Free Air gas Concentration Enrichment) system,hybrid rice cultivar shanyou 63 was grown at ambient(A-O3) and elevated ozone concentrations(E-O3,ambient×1.5).At transplanting,week seedlings(no tillers) and robust seedlings(with 2 tillers) were selected and planted with 3 spacing levels: low plant density(16 hills/m2),medium(24 hills/m2) and high plant density(32 hills/m2).Results showed as follows: Ozone stress decreased the SPAD value,net photosynthetic rate(Pn),stomatal conductivity(Gs) and transpiration rate(Tr) of flag leaves,but there was no significant effect on intercellular CO2 concentration(Ci) or leaf temperature(Tl).There was no significant ozone effect on dry matter production before jointing stage.However,elevatedsignificantly reduced dry matter production from jointing to heading stage and from heading to maturity stage by 13% and 29%,respectively.As a result,reduced dry matter accumulation at maturity stage and significant yield reduction were observed at harvest.The analysis of variance showed that seedling quality by O3 interaction was not significant,but significant interactions were detected between O3 and plant density for yield.The above results indicate that ozone stress significantly inhibited photosynthesis of rice during late growth stage,which result in reduced dry matter production and yield loss of rice.Ozone-induced yield loss could be mitigated by appropriately increasing plant density.

A model of the generation and transport of ozone in high-tension nozzle driven corona inside a novel diode

The genesis and transport of ozone (O(3)) are investigated in a novel plasma diode and described in this paper. The innovative cathode (K) of this axial symmetric diode which operated at the high voltage (φ(0)), has a large number of sharpened nozzles located on different radial planes of its central tubular-mast and is encircled by the anode (A). The nozzles played the dual role of oxygen (O(2)) injection as well as creation of high electric field (E) in the A-K gap, enabled the formation of a cold corona. Electrons in the corona under the influence of E moved towards anode, collided with O(2) and created the O radicals. O in turn joined the free O(2) and formed O(3). The evolution of O(3) here is modeled in various O(2) pressure (P), electron density (n(e)), and temperature (T) in terms of the major reaction modes involving e, O, O(2), and O(3). Typical steady state O(3) density attained so in P ~ bar, n(e) ~ 10(15) m(-3) and T ~ 300 K is over 10(25) m(-3) and that of O lower ~10(20) m(-3). Both the O and O(3) densities increased with an enhanced n(e) of avalanche multiplications in corona. O(3) increased also with a higher P but the temporal O reversed in trend midway and reduced with P towards the steady state. A sharp decline in diode resistance with smaller A-K gap induced finite discharge current and led to the undesired heating of corona. It is shown that the O(3) density reduced with the temperature rise but O density reduced with the T rise up to 500 K and then rose modestly with the further T increase.

Microwave plasma source operating with atmospheric pressure air-water mixtures

The overall performance of a surface wave driven air-water plasma source operating at atmospheric pressure and 2.45 GHz has been analyzed. A 1D model previously developed has been improved in order to describe in detail the creation and loss processes of active species of interest. This model provides a complete characterization of the axial structure of the source, including the discharge and the afterglow zones. The main electron creation channel was found to be the associative ionization process N + O → NO+ + e. The NO(X) relative density in the afterglow plasma jet ranges from 1.2% to 1.6% depending on power and water percentage, according to the model predictions and the measurements. Other types of species such as NO2 and nitrous acid HNO2 have also been detected by mass and Fourier Transform Infrared spectroscopy. The relative population density of O(3P) ground state atoms increases from 8% to 10% in the discharge zone when the input microwave power increases from 200 to 400 W and the water percentage from 1% to 10%. Furthermore, high densities of O2(a1Δg) singlet delta oxygen molecules and OH radicals (1% and 5%, respectively) can be achieved in the discharge zone. In the late afterglow the O2(a1Δg) density is about 0.1% of the total density. This plasma source has a flexible operation and potential for channeling the energy in ways that maximize the density of active species of interest.

The OH Venus nightglow spectrum: Intensity and vibrational composition from VIRTIS—Venus Express observations

Limb spectra of the OH nightglow emission corresponding to the Δv=1 and Δv=2 sequences have been collected with the VIRTIS infrared imaging spectrograph on board Venus Express between April 2006 and October 2008. A detailed statistical analysis shows that the peak intensity and altitude of the two vibrational sequences are significantly correlated, with a mean intensity ratio of the two sequences of 0.38±0.37. The altitude of the maximum of the Δv=2 emission is located ∼1km lower than Δv=1. A spectral analysis shows that the Δv=1 sequence is composed at 44.6% by the (1–0) band, 9.3% by the (3–2) band and 7.1% by the (4–3) band. The Δv=2 emission is best fitted if solely including the (2–0) band.A non-LTE model of OH vibrational population by the O3+H reaction including radiative and collisional relaxation has been used to compare the expected spectral distribution, the altitude of the emission peak and the emission rate under different assumptions on the quenching processes to those observed with VIRTIS. The adopted carbon dioxide, atomic oxygen and ozone densities are based on recent Venus Express remote sensing measurements. We find that the “Sudden Death” quenching scheme by CO2 produces inadequate spectral distribution between the various bands and insufficient airglow brightness. Instead, the observed spectral distribution and the total emission intensity are reasonably well reproduced with the Single Quantum jump model, an O density profile peaking at 103.5km with a maximum value of 1.9×1011cm−3, a O3 density profile peaking at 5.8×106cm−3 at 96.5km and a H density profile close to 108cm−3 between 90 and 120km, in agreement with several photochemical models.

Modeling the chemical kinetics of atmospheric plasma for cell treatment in a liquid solution

Low temperature atmospheric pressure plasmas have been known to be effective for living cell inactivation in a liquid solution but it is not clear yet which species are key factors for the cell treatment. Using a global model, we elucidate the processes through which pH level in the solution is changed from neutral to acidic after plasma exposure and key components with pH and air variation. First, pH level in a liquid solution is changed by He+ and He(21S) radicals. Second, O3 density decreases as pH level in the solution decreases and air concentration decreases. It can be a method of removing O3 that causes chest pain and damages lung tissue when the density is very high. H2O2, HO2, and NO radicals are found to be key factors for cell inactivation in the solution with pH and air variation.

Preparation of polytetrafluoroethylene porous membrane based composite alkaline exchange membrane with improved tensile strength and its fuel cell test

A strategy to improve the alkaline exchange membrane tensile strength was introduced based on porous PTFE and quaternized polyvinyl benzyl chloride (qPVBz/OH−). A thin PTFE film was used as the support to prepare the composite AAEM to improve the mechanical strength. Tensile stress tests showed 51.1 MPa which was twice that of the pure anion exchange membrane qPVBz/OH−. SEM observations showed that the pores of the PTFE were successfully filled with qPVBz/OH− polymer and there was no structure defects in the cross-section of the resultant membrane. The synthesized composite membrane had very good thermal stability. The through plane ionic conductivity was in the range of 1.65 × 10−2 to 2.2 × 10−2 S cm−1 in the temperature range of 25 °C–60 °C. The power density of H2 and O2 fuel cell gave 162 mW cm−2.

Reply to comment by J. Marra on “Measuring primary production rates in the ocean: Enigmatic results between incubation and non‐incubation methods at Station ALOHA”

Reply to comment by J. Marra on “Measuring primary production rates in the ocean: Enigmatic results between incubation and non‐incubation methods at Station ALOHA”

Unexpected O and O3 production in the effluent of He/O2 microplasma jets emanating into ambient air

Microplasma jets are commonly used to treat samples in ambient air. The effect of admixing air into the effluent may severely affect the composition of the emerging species. Here, the effluent of a He/O2 microplasma jet has been analyzed in a helium and in an air atmosphere by molecular beam mass spectrometry. First, the composition of the effluent in air was recorded as a function of the distance to determine how fast air admixes into the effluent. Then, the spatial distribution of atomic oxygen and ozone in the effluent was recorded in ambient air and compared with measurements in a helium atmosphere. Additionally, a fluid model of the gas flow with reaction kinetics of reactive oxygen species in the effluent was constructed. In ambient air, the O density declines only slightly faster with distance compared with a helium atmosphere. In contrast, the O3 density in ambient air increases significantly faster with distance compared with a helium atmosphere. This unexpected behavior cannot be explained by simple recombination reactions of O atoms with O2 molecules. A reaction scheme involving the reaction of plasma-produced excited species of unknown identity with ground state O2 molecules is proposed as a possible explanation for these observations.

Quantifying the relationship between the measurement precision and specifications of a UV/visible sensor on a geostationary satellite

To investigate the feasibility of new satellite observations, including air quality (AQ) observations from geostationary (GEO) orbit, it is essential to link the measurement precision (ε) with sensor specifications in advance. The present study attempts to formulate the linkage between ε and specifications of a UV/visible sensor (signal-to-noise ratio (SNR), full width at half maximum (FWHM) of the slit function, and sampling ratio (SR)) on a GEO satellite. A sophisticated radiative transfer model (JACOSPAR) is used to calculate synthetic radiance spectra that would be measured by a UV/visible sensor observing the atmosphere over Tokyo (35.7°N, 139.7°E) from GEO orbit at 120°E longitude. The spectra, modified according to given sensor specifications, are analyzed by the differential optical absorption spectroscopy technique to estimate the ε for slant column densities of O3 and NO2. We find clear relationships: for example, the ε of the O3 slant column density (molecules cm−2) and SNR at 330nm are linked by the equation log(ε)=−1.06·log(SNR)+20.71 in the UV region, and the ε of the NO2 slant column density and SNR at 450nm are linked by log(ε)=−0.98·log(SNR)+18.00, at a FWHM=0.6nm (for the Gaussian slit function) and SR=4. The relationships are mostly independent of other specifications (e.g., horizontal and temporal resolutions), as they affect ε primarily through SNR, providing constraints in determining the optimal SNR (and alternatively FWHM and SR) for similar UV/visible sensors dedicated for AQ studies.