High OH Concentrations Research Articles

HOx radical regeneration in the oxidation of isoprene

We propose, and quantify from first principles, two novel HO(x)-regenerating unimolecular reactions in isoprene oxidation, which are estimated to yield in pristine tropical forest conditions about 0.7 HO(2) and 0.03 OH radicals per isoprene oxidized; it is further argued that the photolabile coproduct of HO(2) can be a major source of OH, with a yield of the order of 1. The newly proposed chemistry could provide a rationalization for the unexpectedly high OH concentrations often observed in forested environments, such as over the Amazon forest in the recent Gabriel campaign.

Formation and transport of oxidized reactive nitrogen, ozone, and secondary organic aerosol in Tokyo

Measurements of the major reactive nitrogen species (NOy)i (NOx, peroxyacyl nitrates, HNO3, and particulate nitrate (NO3−)), total reactive nitrogen (NOy), volatile organic compounds, OH and HO2, and organic aerosol were made near the urban center of Tokyo in different seasons of 2003–2004 to study the processes involving oxidized forms of reactive nitrogen and O3. Generally, NOx constituted the dominant fraction of NOy throughout the seasons. The NOx/NOy and HNO3/NOy ratios were lowest and highest, respectively, in summer, owing to the seasonally high OH concentration. The fraction of NOy that remained in the atmosphere after emission (RNOy) decreased with the decrease in the NOx/NOy ratio in summer and fall. It is likely that the median seasonal‐diurnal variations of Ox = O3 + NO2 were controlled by those of the background O3 levels, photochemical O3 formation, and vertical transport. Ox showed large increases during midday under stagnant conditions in mid‐August 2004. Their in situ production rates calculated by a box model were too slow to explain the observed increases. The high Ox was likely due to the accumulation of Ox from previous days in the upper part of the boundary layer (BL) followed by transport down to near the surface by mixing after sunrise. Considering the tight correlation between Ox and secondary organic aerosol (SOA), it is likely that SOA also accumulated during the course of sea‐land breeze circulation in the BL.

Atmospheric oxidation capacity sustained by a tropical forest

Terrestrial vegetation, especially tropical rain forest, releases vast quantities of volatile organic compounds (VOCs) to the atmosphere, which are removed by oxidation reactions and deposition of reaction products. The oxidation is mainly initiated by hydroxyl radicals (OH), primarily formed through the photodissociation of ozone. Previously it was thought that, in unpolluted air, biogenic VOCs deplete OH and reduce the atmospheric oxidation capacity. Conversely, in polluted air VOC oxidation leads to noxious oxidant build-up by the catalytic action of nitrogen oxides (NO(x) = NO + NO2). Here we report aircraft measurements of atmospheric trace gases performed over the pristine Amazon forest. Our data reveal unexpectedly high OH concentrations. We propose that natural VOC oxidation, notably of isoprene, recycles OH efficiently in low-NO(x) air through reactions of organic peroxy radicals. Computations with an atmospheric chemistry model and the results of laboratory experiments suggest that an OH recycling efficiency of 40-80 per cent in isoprene oxidation may be able to explain the high OH levels we observed in the field. Although further laboratory studies are necessary to explore the chemical mechanism responsible for OH recycling in more detail, our results demonstrate that the biosphere maintains a remarkable balance with the atmospheric environment.

309 POSTER Serum matrix metalloproteinase 1 (MMP1) as a prognostic marker in bone metastases (BM) treated with bisphosphonates

In this work, the aluminum–water reaction induced by Fe–B, Co–B and Ni–B particles was studied. The catalysts were mixtures of the metal boride and metallic particles. The chainlike Fe–B catalyst forms a network structure under the influence of an external magnetic field and has a large specific surface area. Aggregated particles of Co–B and Ni–B catalyst have small specific surface area. Catalytic activity in the initial corrosion of aluminum increases with increasing Fe–B content because of the large specific surface area and the formation of a micro galvanic cell. However, the amount of hydrogen generated slowly decreases with increasing amount of Co–B and Ni–B. The activity of Fe–B, Co–B and Ni–B in the initial Al/H2O reaction decreases in the order Fe–B > Ni–B > Co–B. The calculated apparent activation energies in the presence of Fe–B, Co–B and Ni catalysts are 38.2, 39 and 29.6 kJ mol−1, respectively. Aluminum is rapidly and completely corroded in a weakly alkaline solution (pH < 10) after consecutive additions of Al batches because of high concentrations of OH− in the local domain and an increase in the amount of Al(OH)3 precipitate.

Isoprene and monoterpene fluxes from Central Amazonian rainforest inferred from tower-based and airborne measurements, and implications on the atmospheric chemistry and the local carbon budget

Abstract. We estimated the isoprene and monoterpene source strengths of a pristine tropical forest north of Manaus in the central Amazon Basin using three different micrometeorological flux measurement approaches. During the early dry season campaign of the Cooperative LBA Airborne Regional Experiment (LBA-CLAIRE-2001), a tower-based surface layer gradient (SLG) technique was applied simultaneously with a relaxed eddy accumulation (REA) system. Airborne measurements of vertical profiles within and above the convective boundary layer (CBL) were used to estimate fluxes on a landscape scale by application of the mixed layer gradient (MLG) technique. The mean daytime fluxes of organic carbon measured by REA were 2.1 mg C m−2 h−1 for isoprene, 0.20 mg C m−2 h−1 for α-pinene, and 0.39 mg C m−2 h−1 for the sum of monoterpenes. These values are in reasonable agreement with fluxes determined with the SLG approach, which exhibited a higher scatter, as expected for the complex terrain investigated. The observed VOC fluxes are in good agreement with simulations using a single-column chemistry and climate model (SCM). In contrast, the model-derived mixing ratios of VOCs were by far higher than observed, indicating that chemical processes may not be adequately represented in the model. The observed vertical gradients of isoprene and its primary degradation products methyl vinyl ketone (MVK) and methacrolein (MACR) suggest that the oxidation capacity in the tropical CBL is much higher than previously assumed. A simple chemical kinetics model was used to infer OH radical concentrations from the vertical gradients of (MVK+MACR)/isoprene. The estimated range of OH concentrations during the daytime was 3–8×106 molecules cm−3, i.e., an order of magnitude higher than is estimated for the tropical CBL by current state-of-the-art atmospheric chemistry and transport models. The remarkably high OH concentrations were also supported by results of a simple budget analysis, based on the flux-to-lifetime relationship of isoprene within the CBL. Furthermore, VOC fluxes determined with the airborne MLG approach were only in reasonable agreement with those of the tower-based REA and SLG approaches after correction for chemical decay by OH radicals, applying a best estimate OH concentration of 5.5×106 molecules cm−3. The SCM model calculations support relatively high OH concentration estimates after specifically being constrained by the mixing ratios of chemical constituents observed during the campaign. The relevance of the VOC fluxes for the local carbon budget of the tropical rainforest site during the measurements campaign was assessed by comparison with the concurrent CO2 fluxes, estimated by three different methods (eddy correlation, Lagrangian dispersion, and mass budget approach). Depending on the CO2 flux estimate, 1–6% or more of the carbon gained by net ecosystem productivity appeared to be re-emitted through VOC emissions.

Effect of liquid property on adsorption and catalytic reduction of nitrate over hydrotalcite-supported Pd-Cu catalyst

This study focused on investigating the effect of liquid property on adsorption and catalytic reduction of nitrate over hydrotalcite-supported Pd-Cu catalyst. Batch experiments were conducted under specific operating conditions. It was found that nitrate ions were adsorbed apparently by hydrotalcite-supported Pd-Cu catalyst at different reaction temperature (10, 25 and 35 °C). Adsorption isotherms for NO 3 − were described by Langmuir's equation. Higher reaction temperature accelerated nitrate adsorption and reduction, and simultaneously decreased the accumulation of NO 2 − and NH 4 +. Nitrate adsorption and reduction were independent of the initial pH because of the high buffering capacity of hydrotalcite when the initial pH of solution was from 5.25 to 7.4. However, the dissolve of hydrotalcite-supported Pd-Cu catalyst at low initial pH (3.77) and higher concentration of OH − ions at high initial pH (10.74) decreased nitrate adsorption and reduction. When using various nitrate salts as a source of nitrate ions, nitrate adsorption and reduction removal efficiency decreased in the order: Fe 3+ > Mn 2+ > Mg 2+ > Ca 2+ > Na +, which was attributed to different affinity toward OH −. Co-existed cations in water with higher valence and lower crystal ionic radius and solubility constant of hydroxide showed stronger affinity toward OH − and consequently increased the concentration of active sites accessible to NO 3 − and NO 2 −. The competitive adsorption of Cl −, SO 4 2− and HCO 3 − with nitrate on the catalyst surface suppressed the adsorption and reduction of NO 3 −. Besides, few metals dissolved in neutral and alkaline solution. The activity of the hydrotalcite-supported Pd-Cu catalyst for nitrate reduction kept steady after repeated use.

Re-initiation phenomenon of gaseous detonation induced by shock reflection

The two-dimensional, time-dependent, reactive Navier–Stokes equations including the effects of viscosity, thermal conduction and molecular diffusion were solved to reveal the wave evolution and chemical dynamics involved in the re-initiation process. The computation was performed for hydrogen–oxygen–argon mixtures at the low initial pressure (8.00 kPa), using detailed chemical reaction model. The results show that, the decoupled leading shock reflects on the right wall of the vertical branch. High temperature and pressure behind the reflected shock induce the generation of hot spots and local explosion. Therefore, the re-initiation of gaseous detonation occurs. In the re-initiation area, there exist very high OH concentration and no H2 concentration. However, in front of reflected shock, there exist relatively high H2 concentration and no OH radicals. Additionally, the shock–flame interaction induces RM instability. This results in the fast mixing between hot reacted gas mixture and the relatively cold unreacted gas mixture and accelerates the chemical reactions. However, the shock–flame interaction contributes much less to the re-initiation, in contrast with shock reflection. The transition of leading shock from regular reflection to Mach reflection happens during the re-initiation. The computed evolution of wave structures involved in the re-initiation is qualitatively agreeable with that from the experimental schlieren images.

Roles of hydroxyl radical generating/scavenging mechanisms in pseudo polluted dew in reducing the foliar CO 2 assimilation rate and biomass production of Japanese red pine ( Pinus densiflora Sieb. et Zucc.) seedlings

Hydroxyl radical ( OH) is one of the most highly reactive of all active oxygen species. Aqueous-phase OH is photochemically generated in polluted dew droplets on needle surfaces of Japanese red pine ( Pinus densiflora Sieb. et Zucc., an evergreen coniferous tree) in declining pine forests. In former studies, we examined the effects of OH-generating mist solutions, which simulate polluted dew droplets, on needle ecophysiological traits of pine seedlings. Two types of solution with different OH-generating sources, i.e. the photo-Fenton reaction (H 2O 2-Fe-oxalate) and photolysis of HONO and NO 2 − [N(III)], had contrasting functional effects on needle gas exchange characteristics even though they had similar OH photoformation rates. In the present study, we investigated the effects of OH-generating mist solutions containing mixed-sources of OH (photo-Fenton and N(III)) on needle gas exchange and the biomass production of potted Japanese red pine seedlings. The N(III) and H 2O 2 concentrations of the OH-generating mist solutions were regulated to the same concentration (0, 25, 50, 75 or 100 μM, pH 5.2–5.3). Treated needles with the lowest photoformation rate and scavenging rate constant of OH had the smallest CO 2 assimilation rate ( A max) and needle conductance ( g n) of all treated pine seedlings. This suggests that the photoformation rate and scavenging rate constant do not always explain the ecophysiological disorders of pine needles subjected to OH-generating wet deposition. On the other hand, the calculated steady-state concentration of OH in the mist solutions was significantly negatively correlated with A max. In addition, pine seedlings with reduced A max showed suppressed biomass (dry weight) production. These results suggest that the OH concentration in the mist solutions is the decisive factor in explaining the negative effects of pseudo dew droplets not only on needle but also plant productivity. We propose that the deposition of polluted dew with chemical components and systems that result in a high OH concentration is one of the causes of growth decline of Japanese red pine.

Intercomparison of Two Hydroxyl Radical Measurement Techniques at the Atmosphere Simulation Chamber SAPHIR

At the atmosphere simulation chamber SAPHIR in Julich both Laser-Induced Fluorescence Spectroscopy (LIF) and Long-Path Differential Optical Laser Absorption Spectroscopy (DOAS) are operational for the detection of OH radicals at tropospheric levels. The two different spectroscopic techniques were compared within the controlled environment of SAPHIR based on all simultaneous measurements acquired in 2003 (13 days). Hydroxyl radicals were scavenged by added CO during four of these days in order to experimentally check the calculated precisions at the detection limit. LIF measurements have a higher precision (σ= 0.88×106 cm–3) and better time resolution (Δt = 60 s), but the DOAS method (σ= 1.24×106 cm–3, Δt = 135 s) is regarded as primary standard for comparisons because of its good accuracy. A high correlation coefficient of r = 0.95 was found for the whole data set highlighting the advantage of using a simulation chamber. The data set consists of two groups. The first one includes 3 days, where the LIF measurements yield (1 – 2) ×106 cm–3 higher OH concentrations than observed by the DOAS instrument. The experimental conditions during these days are characterized by increased NOx concentration and a small dynamic range in OH. Excellent agreement is found within the other group of 6 days. The regression to the combined data of this large group yields unity slope without a significant offset.

Monomolecular‐Layer Ba5Ta4O15 Nanosheets: Synthesis and Investigation of Photocatalytic Properties

AbstractMonomolecular‐layer perovskite Ba5Ta4O15 nanosheets with hexagonal structure have been synthesized by a hydrothermal method. The thickness of the nanosheets is about 1.1 nm, which corresponds to a monolayer of Ba5Ta4O15 molecules, with the lateral size ranging from 50 to 200 nm. The optimal conditions for the formation of the nanosheets are maintaining the reactants above 270 °C for 24 h. A dissolution–recrystallization mechanism is suggested based on observations of the factors that influence nanosheet formation, such as reaction time, temperature, and basicity. Formation of Ba5Ta4O15 nanosheets takes precedence over other nanostructures under high concentrations of OH– because the hindering effect of OH– ions on the c‐axis growth is strong. Thus, the extended growth rate of polyhedrons on one monolayer is much faster than the superposition rate of the monolayer, and the crystal grows more easily along the a‐ and b‐planes. The Ba5Ta4O15 nanosheets show a high photocatalytic activity in the degradation of Rhodamine B and gaseous formaldehyde. The layered perovskite probably affects the photocatalytic activity by promoting the charge separation and delocalization of photogenerated electrons and holes.

Impact of highly basic solutions on sorption of Cs + to subsurface sediments from the Hanford site, USA

The effect of caustic NaNO 3 solutions on the sorption of 137Cs to a Hanford site micaceous subsurface sediment was investigated as a function of base exposure time (up to 168 d), temperature (10°C or 50°C), and NaOH concentration (0.1 mol/L to 3 mol/L). At 10°C and 0.1 M NaOH, the slow evolution of [Al] aq was in stark contrast to the rapid increase and subsequent loss of [Al] aq observed at 50°C (regardless of base concentration). Exposure to 0.1 M NaOH at 10°C for up to 168 d exhibited little if any measurable effect on sediment mineralogy, Cs + sorption, or Cs + selectivity; sorption was well described with a two-site ion exchange model modified to include enthalpy effects. At 50°C, dissolution of phyllosilicate minerals increased with [OH]. A zeolite (tetranatrolite; Na 2Al 2Si 3O 10·2H 2O) precipitated in 0.1 M NaOH after about 7 days, while an unnamed mineral phase (Na 14Al 12Si 13O 51·6H 2O) precipitated after 4 and 2 days of exposure to 1 M and 3 M NaOH solutions, respectively. Short-term (16 h) Cs + sorption isotherms (10 −9–10 −2 mol/L) were measured on sediment after exposure to 0.1 M NaOH for 56, 112, and 168 days at 50°C. There was a trend toward slightly lower conditional equilibrium exchange constants (Δlog Na CsK c ∼ 0.25) over the entire range of surface coverage, and a slight loss of high affinity sites (15%) after 168 days of pretreatment with 0.1 M base solution. Cs + sorption to sediment over longer times was also measured at 50°C in the presence of NaOH (0.1 M, 1 M, and 3 M NaOH) at Cs + concentrations selected to probe a range of adsorption densities. Model simulations of Cs + sorption to the sediment in the presence of 0.1 M NaOH for 112 days slightly under-predicted sorption at the lower Cs + adsorption densities. At the higher adsorption densities, model simulations under-predicted sorption by 57%. This under-prediction was surmised to be the result of tetranatrolite precipitation, and subsequent slow Na → Cs exchange. At higher OH concentrations, Cs + sorption in the presence of base for 112 days was unexpectedly equal to, or greater than that expected for pristine sediment. The precipitation of secondary phases, coupled with the fairly unique mica distribution and quantity across all size-fractions in the Hanford sediment, appears to mitigate the impact of base dissolution on Cs + sorption.

Clay Mineralogical Transformations over Time in Hanford Sediments Reacted with Simulated Tank Waste

Buried waste storage tanks at the USDOE Hanford Reservation in Washington State have released solutions containing high concentrations of Na, OH, NO3, and Al into the vadose zone. When such solutions contact vadose zone sediments, mineral transformations will change the sediment matrix. We hypothesized that Si, dissolved from primary and secondary minerals, will combine with Al from the tank waste to form crystalline or poorly crystalline network silicates such as zeolites and feldspathoids. In this study, we characterized the colloidal (&lt;2 μm equivalent diam.) minerals formed when simulated tank solutions reacted with vadose zone Hanford sediments. Variables studied included simulated tank waste (STW) composition, reaction time, and temperature. Hanford sediments were reacted with a series of simulated tank solutions in batch experiments at 25 and 50°C for 1, 10, 25, 40, and 50 d. The mineralogical, structural, and chemical properties of the resulting colloidal fractions and bulk solutions were determined by x‐ray diffraction (XRD), Fourier transform infrared (FTIR), 27Al‐ and 29Si‐magic angle spinning‐nuclear magnetic resonance (MAS‐NMR), scanning electron microscopy (SEM), energy‐dispersive x‐ray analysis (EDAX), colorimetry, atomic absorption spectroscopy, and inductively coupled plasma–atomic emission spectroscopy (ICP–AES). Upon contact with STW, Si was released from the sediments and a portion was incorporated into poorly crystalline solids. The amount of poorly crystalline solids increased initially and reached maximum quantities between 0 and 25 d. Lability of minerals in the presence of NaOH followed the order quartz → kaolinite → illite. New secondary minerals, NO3–cancrinite, NO3–sodalite, and zeolite A, were formed at the expense of the original clay minerals. Zeolite A was labile and disappeared after about 25 d of reaction time. Cancrinite and sodalite, however, appeared to be stable and increased in abundance with time.

High levels of the hydroxyl radical in the winter urban troposphere

Measurements of the OH radical during winter show that noon‐time concentrations at an urban site in Birmingham are only a factor of 2 less than during summer at the same site, despite a factor of 15 reduction in OH production from the photolysis of ozone. Noon‐time concentrations of HO2 were similar for summer and winter. These high winter concentrations are quantitatively reproduced by a detailed box‐model, showing that the winter radical pool (OH, HO2, RO2) is sustained by reactions of unsaturated hydrocarbons with ozone and by the photolysis of carbonyls. The high OH concentrations show there is significant chemical processing of volatile organic compounds (VOCs) in winter at mid‐to‐high latitudes in the northern hemisphere where emissions are high.

Abundance and Partitioning of OH in a High-pressure Magmatic System: Megacrysts from the Monastery Kimberlite, South Africa

Concentrations of OH, and major and trace elements were determined in a suite of mantle-derived megacrysts that represent the crystallization products of a kimberlite-like magma at ~5 GPa and ~1400–1100°C. OH concentrations, determined by single-crystal Fourier transform infrared spectroscopy, display the following ranges (ppmw H2O): olivine 54–262, orthopyroxene 215–263, garnet 15–74, clinopyroxene 195–620, and zircon 28–34. High OH concentrations in olivine imply mantle conditions of origin, with limited H loss during ascent. OH is consistently correlated with megacryst composition, exhibiting trends with Mg-number that are similar to those of other minor and trace elements and indicating a record of high-pressure magmatic evolution. H substitution is not coupled to minor elements in olivine, but may be in ortho- and clinopyroxene. The OH–Mg-number trends of garnet and clinopyroxene show inflections related to co-precipitation of ilmenite, suggesting minor element (Ti) influence on OH partitioning. During differentiation, relative OH enrichment in clinopyroxene and olivine is consistent with proportional dependence on water activity, whereas that in garnet suggests a higher power-law dependence and/or influence of temperature. Inter-mineral distribution coefficients for OH between cpx, opx, olivine and zircon are thus constant, whereas partitioning between these minerals and garnet shows a factor 4–10 variation, correlated regularly with composition (and temperature). Calculation of solid–melt partition coefficients for H at 5 GPa over a range of magmatic evolution from 1380 to 1250°C yields: ol 0·0053–0·0046, opx 0·0093–0·0059, cpx 0·016–0·013, gt 0·0014–0·0003, bulk (garnet lherzolite–melt) 0·0063–0·0051. These are consistent with experimental studies and similar to values inferred from mid-ocean ridge basalt geochemistry, confirming the moderate incompatibility of H in mantle melting.

Luminescence in SiO 2 induced by MeV energy proton irradiation

Ion-induced luminescence was measured at room temperature for SiO 2 glasses with different OH concentration during irradiation by protons with 0.2–2 MeV energies. In addition to a prominent peak at 460 nm, characteristic peaks were detected at 390 and 650 nm, depending on the OH contents. For silica glasses with lower OH, the 390 nm luminescence appeared at a low dose and its intensity decreased quickly with an increase of the ion dose. The higher intensity for the 650 nm luminescence, related with the non-bridging oxygen hole centers, was found for higher OH concentration. On the other hand, the luminescence at 460 nm was not efficiently emitted from the silica glasses with higher OH when irradiated by MeV protons with low-electronic energy loss.

Distribution of hydrous components in jadeite of the Dabie Mountains

Two kinds of jadeite occur in the jadeite–quartzite from the Dabie Mountains, Eastern China: associated either with weak or strong deformation. The former shows a uniform composition while the latter shows both uniform and zoning composition. These jadeites were examined with infrared (IR) spectroscopy. All jadeite displays hydroxyl (OH) stretching bands, implying that hydrous components commonly exist in jadeite. The concentration of the hydrous components in the jadeite with weak deformation is homogenous, whereas the concentration of the hydrous components in strongly deformed samples is variable. The correlation between the intensity of OH-band absorbance and compositional zoning of jadeite with strong deformation indicates that Na-rich jadeite can accommodate more OH than Na-poor jadeite. Its interpretation is that there is more Na associated with greater OH availability in the initial crystallization environment. Our data of the comparatively high OH concentrations recorded in the core of the jadeite which contains relative high vacancies in M2 site imply that both OH content and the vacancies in M2 site could decrease during exhumation of the jadeite–quartzite. The decrease of OH solubility in jadeite would result in the formation of H 2O fluid during the early exhumation of UHP metamorphic rocks. The H 2O fluid transformed from OH during exhumation could trigger and enhance the early retrograde metamorphism of the host rocks and facilitate plastic deformation of jadeite grain by dislocation creep and diffusion creep.

Catalytic effect of Fe2+, Cu2+and UVA light on the electrochemical degradation of nitrobenzene using an oxygen-diffusion cathode

The electrochemical treatment of 100 mg L−1 nitrobenzene solutions in 0.05 M Na2SO4 in the pH range 2.0–4.0 at 25 °C has been comparatively studied in the presence of Fe2+, Cu2+ and/or UVA light as catalysts using an undivided cell with a Pt anode and an O2-diffusion cathode able to electrogenerate H2O2. A quite slow degradation is found for the solution with 1 mM Cu2+ due to the low production of oxidizing hydroxyl radical (OH˙) from anodic oxidation of water and the action of the Cu2+/Cu+ system. Electro-Fenton treatment with 1 mM Fe2+ leads to a high concentration of OH˙ in the medium from Fenton's reaction, but less than 70% of the nitrobenzene is mineralized since stable complexes of Fe3+ with products are formed. These complexes are quickly photodecomposed in the photoelectro-Fenton treatment of the same solution under UVA irradiation, leading to overall depollution at low currents. Complete degradation is also feasible using 1 mM Cu2+ and 1 mM Fe2+ at high current because OH˙ can slowly destroy the complexes between Cu2+ and intermediates. The positive synergetic effect of all catalysts allows the quickest nitrobenzene mineralization using 1 mM Cu2+ and 1 mM Fe2+ under UVA irradiation. The nitrobenzene decay always follows a pseudo-first-order reaction. Aromatic products such as o-nitrophenol, m-nitrophenol, p-nitrophenol and 4-nitrocatechol have been followed by reverse-phase chromatography. Nitrate ions are formed from oxidation of nitroaromatic products. Generated carboxylic acids such as maleic, fumaric and oxalic have been detected by ion-exclusion chromatography. The different evolution of complexes of oxalic with Cu2+ and Fe3+ explains the influence of the catalysts on nitrobenzene degradation.

Charging of ice-vapor interfaces: applications to thunderstorms

Abstract. The build-up of intrinsic Bjerrum and ionic defects at ice-vapor interfaces electrically charges ice surfaces and thus gives rise to many phenomena including thermoelectricity, ferroelectric ice films, sparks from objects in blizzards, electromagnetic emissions accompanying cracking in avalanches, glaciers, and sea ice, and charge transfer during ice-ice collisions in thunderstorms. Fletcher's theory of the ice surface in equilibrium proposed that the Bjerrum defects have a higher rate of creation at the surface than in the bulk, which produces a high concentration of surface D defects that then attract a high concentration of OH- ions at the surface. Here, we add to this theory the effect of a moving interface caused by growth or sublimation. This effect can increase the amount of ionic surface charges more than 10-fold for growth rates near 1 mm s-1 and can extend the spatial separation of interior charges in qualitative agreement with many observations. In addition, ice-ice collisions should generate sufficient pressure to melt ice at the contact region and we argue that the ice particle with the initially sharper point at contact loses more mass of melt than the other particle. A simple analytic model of this process with parameters that are consistent with observations leads to predicted collisional charge exchange that semiquantitatively explains the negative charging region of thunderstorms. The model also has implications for snowflake formation, ferroelectric ice, polarization of ice in snowpacks, and chemical reactions in ice surfaces

Combustion Behavior and Stability of Turbulent Premixed Flame

The combination of a premixed flame from the main burner and a diffusion flame from the pilot burner is often used for industrial low NOx burners. However, an oscillatory combustion can occur rather easily and is a big problem with this method. To investigate the problem, the correlations between combustion conditions and pressure fluctuation levels are studied on a swirling flow type combustor burning natural gas. It is found from the observation that an oscillatory combustion tends to occur for the case of having the wide region of higher OH concentration.

Flourescence and Temperature Measurements in an Actively Forced Swirl-Stabilized Spray Combustor

The effect of synchronized liquid fuel injection into combustion zones within excited air vortices in a small-scale model of a swirl-stabilized combustor was studied using planar laser induced fluorescence (PLIF) imaging of OH. Both the liquid fuel stream and airstream were forced at a normalized frequency of approximately 6. Air vortices were produced by acoustically forcing the airstream. The liquid fuel was modulated at the same frequency and injected at different phase angles relative to the air vortex formation. Air was forced at two levels, and both nonswirling and swirling flow situations (swirl number of 0.3) were considered. Instantaneous and phase-averaged PLIF images of OH and time-averaged temperature measurements were obtained for different phase differences between the two forcing signals. The PLIF images indicated that with forcing there was an increase in the radial distribution of the reaction zones and a decrease in the height of the flame above the nozzle exit for both nonswirling and swirling conditions. Swirl also produced better mixing along the radial direction for low forcing amplitudes. The phase difference between the two forcing signals produced a significant change in the reaction zones particularly at a low-forcing level and with swirl. The single-shot and phase-averaged PLIF images indicated that in the unforced swirling flow, high OH concentrations were obtained in two regions: an inner brush flame region and an outer flame-sheet-type region. The effect of the outer shear layer on combustion was enhanced by swirl, as the swirl increased the droplet dispersion away from the axis. With forcing, the mixing between the inner and outer regions is enhanced, and the time-averaged OH concentrations show that the primary combustion occurs in the inner core region of the flame.