Decrease In Ozone Concentration Research Articles

Application of Technical Kinetics for Macroscopic Analysis of Ozone Synthesis Process

The method of measuring the technical rate of ozone synthesis process, and the manner of utilizing the process rate for determining the boundary ozone contents in the reacting system has been presented. On the basis of macroscopic analysis of the process the reason causing the obtaining of the ozone concentration lower than that theoretically possible, has been pointed out. It is shown that an increase in temperature in the discharge gap does not inhibit the ozone-forming rate. The decrease in ozone concentration observed is a result of ozone intensive decomposition. However, under typical conditions of the process, the ozone decomposition is a result of the temperature in the microdischarge channels and not that of the gas or the cooling liquid.

A Study of Ozone Formation on the Surfaces of Electrodes

It had been previously thought that ozone production occurred in gaseous space, especially the space between electrodes. However, based on our research, we believe that may only be one of the ozone-producing processes. In this study, we aimed to confirm that a third body, which is present at the interface between oxygen gas and a metal electrode, works to compose ozone. Ozone was not observed in pure oxygen (400x10−6 Nm3/min flow rate) when electrical discharge was supplied after approximately 6 months. The concentration of ozone increased (approximately 0.07 ppm) when nitrogen (approximately 20x10−6 Nm3/min flow rate) was added to a gas-mixing chamber. A third body was required to produce ozone when an oxygen molecule and an oxygen atom collided. The same phenomenon was observed on the surface of a copper anode. A simulation confirmed this. Using an industrial ozone generator which utilized ceramic dielectrics and expanded metal electrodes, an increase in the temperature of the cooling water led to a proportional decrease in ozone concentration. After changing from the titanium electrode to a nickel electrode and an antimony electrode, we observed the difference in the enthalpy changes which were calculated using van't Hoff's formula. The antimony electrode increases the efficiency of the ozone generator to produce ozone. We have come to believe that ozone can be composed on the surface of a metal electrode.

Development of dielectric barrier discharge-type ozone generator constructed with piezoelectric transformers: effect of dielectric electrode materials on ozone generation

The dependence of ozone generation on the types of dielectric electrode material has been investigated using an ozone generator constructed with the piezoelectric transformer developed in our laboratory. The ozone generator is based on the excitation of the dielectric barrier discharge (DBD), which has the advantage of a compact configuration for generating ozone. Four kinds of dielectric materials are prepared for dielectric barrier electrodes. Electrical properties of the DBD and the ozone generation characteristics are investigated for the different dielectric materials. Differences in the discharge mode among the barrier electrode materials are recognized and discussed on the basis of the results of the Lissajous figures and voltage–current waveforms. During the continuous running of the generator, a temporal decrease in ozone concentration is observed owing to the temperature increase inside the reactor. Although the ozone generation characteristics are influenced by many properties of dielectrics, two important factors for achieving high-efficiency ozone generation are identified in this study. One is the use of a high-thermal conductivity material for the dielectric electrode, which functions well as a heat sink for transferring the generated heat to the outside through the material. The other factor is the control of the discharge mode. Our results show that the discharge mode that is considered as Townsend-like DBD is suitable for high-efficiency ozone generation.

Synchronous variations of the mass concentration of near-ground aerosol, nitrogen oxides, and ozone in the Moscow region

During 2007–2008 in the Moscow region, a cycle of complex observations of a number of gaseous and aerosol constituents of the atmosphere was performed. Incorporating the data of back trajectory analysis, we circumscribed a range of atmospheric situations when abrupt changes in the content of these variables were associated with long-range transport in the atmosphere. Primarily, this was due to an across-Moscow passage of warm atmospheric fronts of occlusion in Atlantic and Mediterranean maritime cyclones. In such situations, the abundances of NO2 and NO and aerosol mass concentrations simultaneously increase, while the ozone concentration decreases. This is accompanied by a marked decrease of the refractive index of the particle substance. The response of the parameter of aerosol condensation activity is not unique.

Degradation of caffeine and identification of the transformation products generated by ozonation

The ozonation of caffeine in water was performed at different pH values, including acidic conditions. Kinetic experiments were conducted by adding pulses of a concentrated caffeine solution to ozone saturated water. The results showed a rapid decrease of ozone concentration during the first 15 s after injection, followed by a gradual decline at a much slower rate. The data were fitted to a second order kinetic model with rate constants increasing from 0.25 to 1.05 M −1 s −1 for pH in the 3–10 range. The initial ozone consumption per mol of ozonated caffeine was greater at high pH values, reflecting a higher ozone decomposition rate. The decomposition of ozone was positively affected by the concentration of caffeine, an effect that could be attributed to the presence of a reaction intermediate from the ozonation of caffeine that behaved as a strong promoter of ozone decomposition. A study of the transformation products identified by liquid chromatography in combination with time-of-flight mass spectrometry was carried out, which permitted a tentative degradation pathway to be proposed and several persistent by-products to be identified at both pH 3 and 8. Most transformation products were the result of the opening of the imidazole ring after breaking caffeine’s N9C8 double bond.

Contributions of pollutants from North China Plain to surface ozone at the Shangdianzi GAW Station

Abstract. Regional ozone pollution has become one of the top environmental concerns in China, especially in those economically vibrant and densely populated regions, such as North China region including Beijing. To address this issue, surface ozone and ancillary data over the period 2004–2006 from the Shangdianzi Regional Background Station in north China were analyzed. Due to the suitable location and valley topography of the site, transport of pollutants from the North China Plain was easily observed and quantified according to surface wind directions. Regional (polluted) and background (clean) ozone concentrations were obtained by detailed statistic analysis. Contribution of pollutants from North China Plain to surface ozone at SDZ was estimated by comparing ozone concentrations observed under SW wind conditions and that under NE wind conditions. The average daily accumulated ozone contribution was estimated to be 240 ppb·hr. The average regional contributions to surface ozone at SDZ from the North China Plain were 21.8 ppb for the whole year, and 19.2, 28.9, 25.0, and 10.0 ppb for spring, summer, autumn, and winter, respectively. The strong ozone contribution in summer led to disappearance of the spring ozone maximum phenomenon at SDZ under winds other than from the NNW to E sectors. The emissions of nitrogen oxide in the North China plain cause a decrease in ozone concentrations in winter.

Ozone generation in positive and negative corona discharge fed by humid oxygen and carbon dioxide

The effect of humidity on ozone generation of positive and negative corona discharges fed by O2 and CO2 has been studied in the humidity range of 100–20 000 ppm. The experiments were carried out at an ambient temperature and pressure of 100 kPa. The increase in humidity of CO2 conspicuously suppressed the ozone generation in negative corona discharge at all values of the input energy densities into the discharge. The effect was less pronounced in oxygen. In contrast to decrease of ozone concentration observed in negative corona discharge, the presence of water both in O2 and CO2 acts catalytically. The ozone concentration has been found to increase remarkably (approximately 10 times) in oxygen, if the humidity was increased from 100 to 20 000 ppm. The dependence of ozone concentration on the gas humidity exhibited an extreme. The increase observed at humidity up to approximately 5000 ppm was followed by the marginal reduction in ozone concentration. Anyway, the values of this were considerably higher than those found in dry CO2. The effect of humidity on ozone concentration will be discussed in relation to plasma chemical processes in studied discharges and their macroscopic parameters.

PARIS project: Radiolytic oxidation of molecular iodine in containment during a nuclear reactor severe accident: Part 1. Formation and destruction of air radiolysis products—Experimental results and modelling

In case of a hypothetical severe accident in a nuclear LWR (light water reactor), the high radiation fields reached in the reactor containment building due to the release of fission products from the reactor core could induce air radiolysis. The air radiolysis products could, in turn, oxidise gaseous molecular iodine into aerosol–borne iodine–oxygen–nitrogen compounds. Thereby, this reaction involves a change of iodine speciation and a decrease of iodine volatility in the reactor containment atmosphere. Kinetic data were produced within the PARIS project on the air radiolysis products formation and destruction, and on their reaction with molecular iodine, with the objective of developing and validating existing kinetic models. The current paper includes the non-iodine tests of the PARIS project whose objective was to determine the rates of formation and destruction of air radiolysis products in the presence of both structural containment surfaces (decontamination coating (“paint”) and stainless steel), aerosol particles such as silver rich particles (issued from the control rods) in boundary conditions representative for LWR or PHEBUS facility containments. It is found that the air radiolysis products concentration increases with dose and tend to approach saturation levels at doses higher than about 1 kGy. This behaviour is more evident in oxygen/steam atmospheres, producing ozone, than in air/30% (v/v) steam atmospheres, the latter favouring the model-predicted on-going production of nitrogen dioxide even at very high doses. No significant effect of temperature, dose rate and hydrogen addition (4%, v/v) was observed. Furthermore, the inserted surfaces do not exhibit significant effects on the air radiolysis concentrations. However, these “non-noticeable influence” could be due to a masking of small effects by the appreciable scattering of the experimental air radiolysis product concentrations. The PARIS results are then analysed using two different kinetic models, an empirical and a mechanistic one. The kinetic constants within an empirical model including formation and destruction of air radiolysis products, derived from PARIS results, are in reasonable agreement with those determined previously for lower steam fractions. From the mechanistic model IODAIR-IRSN, it is concluded that ozone is the predominant air radiolysis product at low doses in air/steam atmospheres. At doses higher than 1 kGy, nitrogen dioxide becomes increasingly important, both due to an increase in its concentration and due to a simultaneous decrease in ozone concentration.

Recent Trends in Ozone and Particle Concentrations in the Sydney (Australia) Airshed

An overview is presented of changes in ground level ozone and atmospheric fine particles determined using ambient monitoring data collected at selected locations in Sydney, Australia. After removing seasonally, auto-regressive and moving average dependence from the selected time series, the trend of a selected series was modelled using the fractional long-term dependent component. The selected technique was able to detect the trend at a very small resolution. The method results were compared to the trends obtained using the Rao-Zurbenco method. For selected monitoring stations, between 1980 and 1993, there was a decrease in ozone concentrations followed by a slight increase between 1994 and 2002, and thereafter a stable concentration. Fine particle concentrations as measured by nephelometry, showed a significant decrease from 1980 to 1990, which stabilised beyond 1994.

Dynamics of ozone layer under Serbia and solar activity: Previous statement

The aim of this paper is to identify ozone layer dynamics under Serbian area, as well as possible relations of change in stratospheric ozone concentration with some parameters of solar activity. During the period 1979-2005, the statistical decrease of ozone concentration was noticed under Serbian territory cumulatively for 24.5 DU (7.2%), apropos 9.4 DU (2.8%) by decade. These changes are consistent with the changes in surrounding countries. From absolute minimum 1993, flexible trend of ozone layer pentad values validate hypotheses of its recovery. Correspondence of ozone thickness extreme period with Wolf's number and with the greatest volcanic eruptions shows that interannual variations of stratospheric ozone concentration are still in the function of natural factors above all, as are solar and volcanic activities. Investigation of larger number solar activity parameters shows statistically important antiphase synchronous between the number of polar faculae on the Sun and stratospheric ozone dynamics under Serbia. Respecting that relation between these two features until now isn't depicted, some possible causal mechanisms are proposed.

Evaluation of downer reactor performance by catalytic ozone decomposition

Radial distribution profiles of ozone concentrations were measured along an 8.50 m high and 0.09 m inside diameter gas/solid co-current down-flow circulating fluidized bed (downer) to characterize the reactor performance. Tests were conducted under a series of operating conditions at room temperature and near atmospheric pressure, with FCC particles as the bed material. Results show that the concentration distribution of the ozone tracer gas correlates well with the flow structure of the downer. There is quite a uniform radial distribution of ozone concentrations in the core region of all tested axial sections in the fully developed region of the downer, except for the near-wall region where there is a sharp decrease in ozone concentration. And there exists a relatively significant non-uniform distribution in the entrance acceleration region of the downer.

Gas-Phase Chemistry of α-Terpineol with Ozone and OH Radical: Rate Constants and Products

A bimolecular rate constant, kOH+alpha-terpineol, of (1.9 +/- 0.5) x 10(-10) cm3 molecule(-1) s(-1) was measured using gas chromatography/mass spectrometry and the relative rate technique for the reaction of the hydroxyl radical (OH) with alpha-terpineol (1-methyl-4-isopropyl-1-cyclohexen-8-ol) at (297 +/- 3) K and 1 atm total pressure. Additionally, a bimolecular rate constant, kO3+alpha-terpineol, of (3.0 +/- 0.2) x 10(-16) cm3 molecule(-1) s(-1) was measured by monitoring the first order decrease in ozone concentration as a function of excess alpha-terpineol. To better understand alpha-terpineol's gas-phase transformation in the indoor environment, the products of the alpha-terpineol + OH and alpha-terpineol + 03 reactions were also investigated. The positively identified alpha-terpineol/OH reaction products were acetone, ethanedial (glyoxal, HC(=O)C(=O)H), and 2-oxopropanal (methyl glyoxal, CH3C(=O)C(=O)H). The positively identified alpha-terpineol/O3 reaction product was 2-oxopropanal (methyl glyoxal, CH3C(=O)C(=O)H). The use of derivatizing agents O-(2,3,4,5,6-pentalfluorobenzyl)hydroxylamine (PFBHA) and N,O-bis(trimethylsilyl)trifluoroacetamide (BSTFA) clearly indicated that several other reaction products were formed. The elucidation of these other reaction products was facilitated by mass spectrometry of the derivatized reaction products coupled with plausible alpha-terpineol/OH and alpha-terpineol/O3 reaction mechanisms based on previously published volatile organic compound/ OH and volatile organic compound/O3 gas-phase reaction mechanisms.

A new fast stratospheric ozone chemistry scheme in an intermediate general‐circulation model. II: Application to effects of future increases in greenhouse gases

AbstractWhile chlorine loadings in the atmosphere are expected to decrease towards pre‐ozone‐hole levels by 2060, the greenhouse gases (GHGs) burden is rising continuously and may in turn significantly modify the stratospheric ozone layer.In this study, use is made of the new interactively coupled chemistry–general‐circulation model IGCMFASTOC to investigate in detail the response of stratospheric ozone to a specified increase in GHG concentrations between 1979 and 2060.The Intermediate General Circulation Model (IGCM) is a relatively fast general‐circulation model with parametrizations of an intermediate level of complexity, and the new chemistry scheme Fast STratospheric Ozone Chemistry (FASTOC) is an efficient input‐output model composed of pre‐computed nonlinear functions.A total of seven 14‐year time‐slice simulations are performed to allow for the separation of individual processes and the analysis of sensitivity to methane and stratospheric water‐vapour scenarios.In a basic scenario where all GHG concentrations increase (except stratospheric H2O) the total ozone column is found to increase at a global rate of 0.27 DU decade−1 with maxima in late winter–spring poles. This increase is merely the result of two opposing effects: (i) An increase of ozone concentration in the summer and tropical stratospheric region near 30–40 km which is passively advected into the polar‐night vortex between 40 and 20 km. This ozone increase is due to the slowing down of the NOx catalytic cycle caused by the cooling of the stratosphere resulting from increased GHG concentrations in the stratosphere. (ii) A decrease of ozone concentration in the same region which is also advected into the polar‐night vortex, due to enhanced NOx concentrations caused by the increased N2O concentrations. These two opposing effects are additive to a large degree, i.e. the sum of their individual effects is a good approximation of their total effect when the processes are acting together.A significant deviation from this additivity occurs inside the northern polar‐night vortex and to a lesser extent in the southern polar‐night vortex. Our analysis suggests that methane is mainly responsible for this feature. The impact of methane increase on ozone is confined to the high latitudes and is found to have a negative sign in the northern polar vortex when the stratospheric cooling is taken into account, and a positive sign when no stratospheric cooling is taken into account.The scenario where methane is kept at its 1979 level produces a global rate of increase of the ozone column of 9% above the basic scenario. The scenario where stratospheric H2O is increased by 50% leads to a global rate of increase of the ozone column of 70% above the basic scenario. Finally, in a scenario where CO2 is reduced to its 1979 level and the other GHGs involved in the ozone chemistry are increased as in the basic scenario, the global effect of GHGs on the ozone layer is to decrease it at a rate of 0.37 DU decade−1. Copyright © 2005 Royal Meteorological Society

Five-year measurements of ozone fluxes to a Danish Norway spruce canopy

Abstract Ozone concentrations and fluxes have been measured continuously during 5 years (1996–2000) by the gradient method in a Norway spruce dominated forest stand in West Jutland, Denmark, planted in 1965. The method has been validated against other methodologies and a relatively good relationship was found. The data are analysed to quantify diurnal, seasonal and yearly fluxes, and non-stomatal and stomatal removal are estimated. Monthly means of climatic data are shown, and day and night values of the aerodynamic resistance, ra, viscous sub-layer resistance, rb, and the surface or canopy resistance, rc, are presented. The yearly ozone deposition is approximately 126 kg ha−1. The canopy ozone uptake is highest during the day and during the summer. This is interpreted as increased stomatal uptake and physical and chemical reactions. The daily means of ozone concentration and fluxes averaged over 5 years correlate, but the correlation is primarily based on two different uncoupled processes outside and inside the stomates: (1) The ozone destruction in the canopy occurring outside the stomates is much influenced by temperature, light and humidity, e.g. surface reactions, NO- and VOC-emissions. (2) The same factors have a strong influence on the stomatal opening, e.g. midday and night closure. Thus, looking at diurnal variations, the diurnal ozone concentration and ozone flux do not correlate at all during the growing season. The maximum diurnal difference for the ozone concentration is a factor 1.3 and the maximum diurnal difference for the ozone flux is a factor 3. From dawn to ca. 8:00 the ozone deposition increases and the ozone concentration decreases. The yearly stomatal uptake of ozone is estimated to minimum 21% of the total deposition, being highest in May–August (30–33%) and lowest in November–February (4–9%). The physiological ozone uptake per leaf area is estimated to 0.33 g ozone m−2 y−1.

Global modeling of heterogeneous chemistry on mineral aerosol surfaces: Influence on tropospheric ozone chemistry and comparison to observations

Mineral aerosols can affect gas phase chemistry in the troposphere by providing reactive sites for heterogeneous reactions. We present here a global modeling study of the influence of mineral dust on the tropospheric photochemical cycle. This work is part of the Mineral Dust and Tropospheric Chemistry (MINATROC) project, which focussed on measurement campaigns, laboratory experiments, and integrative modeling. The laboratory experiments provide uptake coefficients for chemical species on mineral aerosol surfaces, which are used to compute the heterogeneous reaction rates in the model. The field measurements at Mount Cimone, northern Italy, provide trace gas and aerosol measurements during a Saharan dust episode and are used to evaluate the model. The simulations include the reactions between mineral dust aerosols and the gas‐phase species O3, HNO3, NO3, and N2O5. Under the conditions for the year 2000 the model simulates a decrease in global tropospheric ozone mass by about 5% due to the heterogeneous reactions on dust aerosols. The most important heterogeneous reaction is the uptake of HNO3 on the dust surface, whereby the direct uptake of ozone on dust is not important in atmospheric chemistry. The comparison of the model results to observations indicates that the model simulates well the aerosol mass transported into the Mediterranean during the dust events and the arrival of all major dust events that were observed during a 7 month period. The decrease in ozone concentration during dust events is better simulated by the model when the heterogeneous reactions are included.

Influence of Inversion Layers on the Distribution of Air Pollutants in Urban Areas

The air quality in urban areas is on the one hand determined by the intensity of emissions. On the other hand atmospheric dispersion and chemical transformation conditions as well as topographic location have great influence on the ambient air concentrations. Within, this study the correlation between pollutant concentrations and the dynamics of atmospheric barrier and mixing layers has been experimentally investigated by tethered balloon soundings.The most important barrier layer is the surface inversion. During clear sky it develops in the late afternoon and is dissolved by warm air from the heated ground in the morning. Emitted pollutants are kept beneath this inversion. But, at the same time, the component ozone is depleted below and stored above the layer within the so called `ozone reservoir layer'. During night elevated mountain sites are decoupled from the ground conditions and stay within this reservoir without a remarkable nocturnal decrease of ozone concentration. The regularly observed ground level ozone increase in the morning hours is firstly caused by down mixing from the reservoir. The conditions and dynamics are illustratively depicted by vertical profiles of the different components and diagrams of temperature and concentration isopleths over the height and the experiment time lasting over five days.

Heterophase Processes in the Formation of Antarctica's Spring Ozone Anomaly

A study demonstrates that accepted official values of the catalytic cycle with the participation of ClO in ozone destruction during the spring ozone anomaly in Antarctica (SOAA) usually is not adequately validated or confirmed by observational data. The strong inverse correlation between the mixing ratios for ozone and ClO observed during the SOAA period evidently can be attributed to the heterophase reactions of direct destruction of molecules of both chlorine nitrate and ozone on particle surfaces in polar stratospheric clouds. An increase in ClO concentration and decrease in ozone concentration during an SOAA period may be the result of a single factor causing temperature changes, and thus changes in the quantitative and qualitative parameters of polar stratospheric clouds.

Atmospheric mercury concentrations: measurements and profiles near snow and ice surfaces in the Canadian Arctic during Alert 2000

Gaseous elemental mercury (GEM) concentration measurements were made during the Alert 2000 campaign in Alert, Nunavut, Canada, between February and May 2000. GEM exhibits dramatic mercury depletion events (MDE) concurrently with ozone in the troposphere during the Arctic springtime. Using a cold regions pyrolysis unit, it was confirmed that GEM is converted to more reactive mercury species during the MDEs. It was determined that on average 48% of this converted GEM was recovered through pyrolysis suggesting that the remaining converted GEM is deposited on the snow surfaces. Samples collected during this campaign showed an approximate 20 fold increase in mercury concentrations in the snow from the dark to light periods. Vertical gradient air profiling experiments were conducted. In the non-depletion periods GEM was found to be invariant in the air column between surface and 1–2 m heights. During a depletion period, GEM was found to be invariant in the air column except at the surface where a noticeable increase in the GEM concentration was observed. Concurrent ozone concentration profiles showed a small gradient in the air column but a sharp decrease in ozone concentration at the surface. Other profile studies showed a 41% average GEM concentration difference between the interstitial air in the snow pack and ∼2 m above the surface suggesting that GEM is emitted from the snow pack. Further profile studies showed that during MDEs surface level GEM exhibits spikes of mercury concentrations that were over double the ambient GEM concentrations. It is thought that the solar radiation may reduce reactive mercury that is deposited on the snow surface during a MDE back to its elemental form which is then increasingly released from the snow pack as the temperature increases during the day. This is observed when wind speeds are very low.

Experimental investigations and modelling studies of ozone producing corona discharges

The ozone generation by negative corona discharge in coaxial cylindrical system of electrodes have been studied experimentally in Ar+O2 and N2+O2 mixtures. Both in argon and nitrogen mixtures with oxygen the monotonous decrease in ozone concentration [O3] was observed at decreasing oxygen content in mixtures and the constant input energy density η. The rate coefficients for the ozone generation and ozone decomposition were obtained by fitting experimentally measured data [O3]=f(η) with Vasiljev-Eremin formula. The calculated rate coefficient for ozone generation in N2+O2 mixtures at low content of oxygen (below 20%) was found considerably higher than that in Ar+O2 mixtures. Increase in the rate coefficients for ozone generation and decomposition was observed with decreasing content of oxygen in both mixtures. The experimental results are in qualitative agreement with the simple model incorporating five main chemical processes in mechanism of ozone generation.

Mid‐latitude marine boundary‐layer ozone destruction at visible sunrise observed at Cape Grim, Tasmania, 41°S

An analysis is made of 13 years of observations of ozone concentrations in the remote marine boundary layer at Cape Grim, Tasmania 41°S. These data reveal a decrease in ozone concentration in the first few hours following sunrise at a rate of around 0.1 ppb h−1 in mid‐summer and in mid‐winter. This ozone destruction phenomenon causes an asymmetry in the daily ozone loss rate with enhanced destruction following sunrise, is statistically distinguishable from the O3‐HOx destruction cycle that peaks at mid‐day, and occurs at similar rates in mid‐summer and in mid‐winter. The cause of this sunrise ozone decrease is examined using the conservation equation for ozone. We speculate that ozone destruction at sunrise arises due to halogen chemistry. The absence of sunrise ozone decrease in models of marine boundary‐layer photochemistry means that the ozone destruction rate in the remote marine boundary layer is underestimated by perhaps a factor of two.