Ozone Partial Pressure Research Articles

Kinetics of p-hydroxybenzoic acid photodecomposition and ozonation in a batch reactor

The decomposition of p-hydroxybenzoic acid, an important pollutant present in the wastewaters of the olive oil industry, has been carried out by a direct photolysis provided by a polychromatic UV radiation source, and by ozone. In both processes, the conversions obtained as a function of the operating variables (temperature, pH and ozone partial pressure in the ozonation process) are reported. In order to evaluate the radiation flow rate absorbed by the solutions in the photochemical process, the Line Source Spherical Emission Model is used. The application of this model to the experimental results provides the determination of the reaction quantum yields which values ranged between 8.62 and 81.43 l/einstein. In the ozonation process, the film theory allows to establish that the absorption process takes place in the fast and pseudo-first-order regime and the reaction is overall second-order, first-order with respect to both reactants, ozone and p-hydroxybenzoic acid. The rate constants are evaluated and vary between 0.18×10 5 and 29.9×10 5 l/mol s depending on the temperature and pH.

共存硫酸塩を含む強酸性ＭｎＳＯ４溶液中のオゾン酸化によって生成した沈殿のＸ線回折および放電特性

The incorporation of coexisting metal ion in the precipitates produced by ozone oxidation-precipitation in acidified MnSO4 solutions with an added sulfate was investigated for 15 elements (18 ionic species) by chemical analysis, X-ray diffraction and discharge curve measurement of the precipitates.The precipitates were formed in the stream of O3 - O2 gas mixture with ozone partial pressure of 2.7 × 10 - 3 atm at 70°C in the solutions of 1.0 M sulfuric acid, 0.1 M MnSO4 and other metal sulfate. A little incorporation in the γ -MnO2 based precipitate was detected for alkali metal ions, Mg, Cu, Co and Ni ions. Both Fe (II) and Fe (III) ions were captured in the precipitate and affected significantly the discharge curve of the precipitate. The precipitates formed in the presence of Ti, V or As showed a fairly high content of the coexisting element, X-ray diffraction peaks remarkably differing from those for γ -MnO2 and poor discharge behavior. These suggest possibility for Ti, V or As to be precipitated as some compounds with Mn rather than to be incorporated into the MnO2-based precipitate.

Atrazine removal by ozonation processes in surface waters

Atrazine (6‐chloro‐N‐ethyl‐N'‐isopropyl‐1,3,5‐triazinedyl‐2,4‐diamine) was treated with ozone alone and in combination with hydrogen peroxide or UV radiation in three surface waters. Experiments were carried out in two bubble reactors operated continously. Variables investigated were the ozone partial pressure, temperature, pH, mass flow ratio of oxidants fed: hydrogen peroxide and ozone and the type of oxidation including UV radiation alone. Residence time for the aqueous phase was kept at 10 min. Concentrations of some intermediates, including deethylatrazine, deisopropylatrazine and deethyldeisopropylatrazine, were also followed. The nature of water, specifically the alkalinity and pH were found to be important variables that affected atrazine (ATZ) removal. Surface waters with low alkalinity and high pH allowed the highest removal of ATZ to be reached. There was an optimum hydrogen peroxide to ozone mass flow ratio that resulted in the highest ATZ removal in each surface water treated. This optimum was above the theoretical stoichiometry of the process. Therefore, to reach the maximum removal of ATZ in a O3/H2O2 process, more hydrogen peroxide was needed in the surface waters treated than in ultrapure water under similar experimental conditions. In some cases, UV radiation alone resulted in the removal of ATZ higher than ozonation alone. This was likely due to the alkalinity of the surface water. Ozonation and UV radiation processes yield different amounts of hydrogen peroxide. Combined ozonations (O3/H2O2 and O3/UV) lead to ATZ removals higher than single ozonation or UV radiation but the formation of intermediates was higher.

Variations in ozone profiles during the period of solar proton events from October 19–31,1989

Ozone deepletion was the main effect revealed up to now after penetration of Solar Cosmic Rays (SCR) in the middle atmosphere. Making use of satellite data (collected from 19 to 31 October1989) to examine the ozone profiles we established: i.) The partial ozone pressure (POP) decreased between 23–25 km, ii.) POP increased between 18–19 km. The study was performed on the base of data about POP and temperature at altitudes 25.5 km, 24.5 km, 23.5 km, 19.5 km, 18.5 km and 11.5 km. The orbits of the satellite covered the belt 30°–90° N and 20°–40° E. Data about high energetic protons were taken from the Solar Geophysical Data (1989). The measurements were carried out with the Neutron Monitor in Kiel, Germany. Seven energy bins were herein used: 4.2–8.7 MeV, 8.7–14.5 MeV, 15–44 MeV, 39–82 MeV, 82–200 MeV, 110–500 MeV, 640–850 MeV.

Aerobic treatment of black olive wastewater and the effect of an ozonation stage

The reduction of the pollutant organic matter present in wastewaters generated in the black olive production process is studied by an aerobic degradation, and by the combination of two successive steps: an ozonation pretreatment followed by an aerobic degradation. In the single aerobic process, in addition to the biomass evolution which is followed during each experiment, the removal of the pollutant load is evaluated by means of global parameters which are directly related with the organic matter, as the chemical oxygen demand and the total phenolic compounds content. A kinetic study is performed by using the Monod model, which applied to the experimental data, provides the specific kinetic parameters of this model: the kinetic constant for the substrate decomposition rate, the cellular yield coefficient and the kinetic constant for the biomass decrease during the death phase of microorganisms. In the combined process, an ozonation pretreatment is conducted with experiments where the ozone partial pressure is varied, and an important reduction in the phenolic compounds is achieved. The kinetic parameters of the following aerobic degradation stage are also evaluated, and the effect of the chemical oxidation pretreatment on this biological stage is discussed.

On the role of the lower-stratospheric circulation to the vertical ozone structure

The examination of the role of the lower stratospheric circulation to the vertical ozone distribution, is attempted by using the vertical ozone profiles collected by balloon-borne sondes released at Athens, Greece (38°N, 24°E), throughout the period 1989–1997. The most pronounced special features of the ozone structure, such as lamination phenomenon, minimum of ozone partial pressure at the height region of 14–17 km and ozone minima at the height region of 20–25 km, have been used in order to create groups of relevant profiles. The occurrence of the above mentioned features, correlated with the circulation pattern, leads to the following preliminary results: a) Laminated features are associated with the north-northwest circulation in the lower stratosphere; b) The lower stratosphere's characteristic ozone minimum is related to the influence of the subtropical jet stream circulation; and c) The observed ozone depletion at the height region of 20–25 km, is characterized by the movement of the polar vortex to the mid-latitudes, resulting more intense north-western circulation above our experimental site.

A partial pressure monitor and controller for stable ozone flow from a silica gel trap

A new ozone trapping system designed for safe and consistent delivery to a reaction vessel is described. Silica gel is used to trap the ozone because of its known safety advantages over traps that store ozone in liquid form. The new design is free of any liquid baths, such as freon or flammable solvents. A circuit design for monitoring and controlling the ozone partial pressure of 6–25 Torr is also described.

Initial Delignification and Cellulose Degradation of Conventional and Ethanol-Assisted Ozonation

It has been proposed that the initial regime of pulp ozonation is a diffusion controlled process, due to the low solubility of ozone and its very fast reaction with lignin. However, whether the process is governed by diffusion on a fibre wall scale (macro diffusion control), on a (micro)fibril scale (micro diffusion control), or by reaction with lignin located on the fibre surface followed by diffusion control is an open question. In order to address this, a 31 kappa Hemlock kraft pulp impregnated with acidified (pH = 2.0) water or acidified (pH = 2.0) ethanol-water (70% w/w) was ozonated at high consistency in a differentially operated packed bed reactor. The cellulose degradation and pulp delignification rates were determined from the change in pulp viscosity and kappa number with ozonation time. Transmission electron microscopy (TEM) was used to visualize the lignin distribution of KMnO4 stained fibre walls. The TEM pictures clearly show reacted lighter regions at exposed fibre surfaces, which are sharply separated from unreacted darker areas inside the fibre wall. Therefore, these pictures support the macro diffusion theory. The macro diffusion theory was used to describe the progress of delignification and cellulose degradation as a sharp reaction front moving through the fibre wall from the external fibre surface towards the lumen. In agreement with this so called diffusion controlled shrinking core model, the present experimental results show that the delignification and cellulose degradation increase proportionally with the square root of the ozonation time. The effects of ozone partial pressure and ethanol-water impregnation on the delignification and cellulose degradation rates are also described.

Changes of Ozone Content at Middle Latitudes During Forbush Decreases in Cosmic Rays

The variations of total ozone at Alma-Ata (43°N, 76 °E) and ozone profiles obtained by balloon sounding at Tateno (36°N, 140°E), Wallops Island (38°N, 75°W) and Cagliari (39°N, 9°E) in the periods of Forbush decreases (FD) in galactic cosmic rays have been analysed. A decrease of total ozone was observed in the initial stage of the FD and an increase 10–11 days later. The average total deviations calculated using the superposed epoch method for 9 FD events are equal to 30 D. U. in the positive and to −18 D. U. in the negative phase. The changes of average ozone profiles, associated with 26 FD events, are more significant in the lower stratosphere and upper troposphere. The decrease of the partial ozone pressure at a height of 12–15 km is about 30 υmb. These vertical variations of ozone coincide with the average changes of the respective temperature profiles. A cooling, on the average, of 3°C was observed at 12–15 km, and a heating of 4°C below this level.

Applying mass transfer models for controlling organic compounds in ozonation process

Mass transfer plays a significant role in the ozonation process. The prediction models associated with the volumetric overall mass transfer coefficient (K La) and initial fractional ozone absorption (FOA 0) during the ozonation process were developed through the use of dimensional analysis. It was found that the volumetric overall mass transfer coefficient is the function of diffusivity, agitation speed, and gas flow rate, and the parameters in the K La equation are determined. Application of the prediction models for K La and FOA 0 would yield information to choose the most practically feasible operating parameters. The removability of total organic carbon (TOC) can be estimated based on the mass balance relationship and kinetic expression of TOC oxidation, during continuous laboratory ozonation of humic acid solution. The reaction rate constant averaged 0.0291 L/mg·min. The developed model in combination with the mass transfer and reaction kinetics can be used successfully in forecasting the most efficient agitation speed to control the formation of organic compounds. Also, the critical value of ozone partial pressure to achieve the highest TOC removability can be determined through the use of the above developed model.

Ozone-enhanced molecular beam deposition of nickel oxide (NiO) for sensor applications

For the deposition of nickel oxide (NiO) a molecular beam deposition process in an ozone atmosphere was developed. Pure gaseous ozone is received from a cooling system, which stores only O 3 at −78°C from a O 2/O 3 gas mixture stream, created with an ozone generator. The ozone is released by heating up the system to room temperature. For the deposition process nickel is evaporated while a constant ozone partial pressure is adjusted in the growth chamber. The reactive species of ozone reacts on the substrate surface with the impinging metal atoms to form the compound. This process was carried out in an ultra high vacuum (UHV) chamber to create pure nickel oxide films at room temperature and to study the fundamental layer properties for sensor applications. These films were characterized with respect to their stoichiometric and optical properties by Auger Electron spectroscopy and ellipsometry. The gas sensitivity of the films (as deposited and annealed) on various gases (H 2, NH 3, NO 2, SO 2, CO) was investigated by work function measurements.

Elimination pathways during water ozonation of volatile organochlorine compounds

Ozonation of trichloroethylene, TCE and 1,1,1 trichloroethane, TCA in water has been studied. The effect of gas flow rate, pH, ozone partial pressure and water nature has been investigated. These variables exert positive effects on the elimination rates. Gas flow rate effect is specially important in the case of TCA which, at 20 Lh‐1, is mainly transferred from the water to the air rather than being decomposed through ozonation. On the contrary, TCE is mainly oxidised through hydroxyl radicals. The rate constant of the TCE‐ozone direct reaction was found to be 17.1 M‐1s‐1 which confirms that direct ozonation represents a rather poor contribution (in most cases between 2 to 5%) of the total TCE elimination rate. Therefore, ozonation of these compounds is basically an advanced oxidation process due to the participation of hydroxyl radicals. At high gas flow rates (20 Lh‐1) ozonation rates of VOC elimination were similar in ultrapure laboratory and surface waters used, except for the case of TCE that at 2.5 Lh‐1 gas flow rate, decomposes in ultrapure water faster than in surface water.

Growth and Yield Response of Commercial Bearing-age ‘Casselman’ Plum Trees to Various Ozone Partial Pressures

Nursery stock of plum (Prunus salicina Lindel., cv. Casselman) was planted 1 Apr. 1988 in an experimental orchard at the Univ. of California Kearney Agricultural Center near Fresno, CA. Trees in this study were enclosed in open-top fumigation chambers on 1 May 1989, and exposed to three atmospheric ozone partial pressures (charcoal filtered air, ambient air, and ambient air + ozone) during the 1989 through 1992 growing seasons (typically 1 Apr. - 1 Nov.). A nonchamber treatment plot was used to assess chamber effects on tree performance. This study details the results of the exposures during the initial commercial bearing period (1991 through 1993) in this orchard. The mean 12-h (0800-2000 h Pacific Daylight Time [PDT]) ozone partial pressures during the experimental periods in the charcoal filtered, ambient, ambient + ozone, and nonchamber treatments averaged 0.031, 0.048, 0.091, and 0.056 {mu}Pa Pa{sup {minus}1} in 1991 and 1992, respectively. Fruit number per tree decreased as atmospheric ozone partial pressure increased from the charcoal filtered to ambient + ozone treatment, significantly affecting yield. Yield of plum trees averaged 23.6, 19.8, 13.7, and 17.9 kg tree{sup {minus}1} in 1991 and 1992 in the charcoal filtered, ambient, ambient + ozone, and nonchamber treatments, respectively.more » Only one out of the five original treatment plots was exposed to ozone treatments during the 1993 growing season. Yield of plum trees in this single replicate in 1993 was reduced by increased atmospheric ozone partial pressure. Yield of plum trees in the four remaining unexposed treatment plots in 1993 was 16.7, 17.9, and 16.0 kg tree{sup {minus}1} in the previous charcoal filtered, ambient, and ambient + ozone treatments respectively. The similarity in yield of the post-chamber treatments indicates that a change in air quality in the current growing season can affect yield of Casselman plum trees. 26 refs., 6 figs., 4 tabs.« less

Ozonation Kinetics of Phenolic Acids Present in Wastewaters from Olive Oil Mills

A kinetic study of the degradation by ozone of eight phenolic acids present in wastewaters from olive oil mills has been performed by using a competition kinetic method. The selected phenolic acids are: caffeic, p-coumaric, syringic, vanillic, 3,4,5-trimethoxybenzoic, veratric, p-hydroxybenzoic, and protocatechuic. The influence of the operating variables (temperature, pH, and ozone partial pressure in the gas stream) is established, and the stoichiometric ratios for the individual direct reactions between ozone and each acid are determined. Once the reaction rate constants are evaluated, they are correlated as a function of temperature and pH into kinetic expressions which are provided for every phenolic acid. The global process occurs in the fast and pseudo-first-order kinetic regime of absorption, a condition required by the competition model to be used.

Changes of the lower stratospheric ozone over Europe and Canada

Ozonesonde measurements from Europe arid Canada for the period 1973–1994, stratified to the height of the tropopause, were analyzed to estimate regional changes in stratospheric ozone. The calculations were performed for 1‐km layers from the actual tropopause up to 30 km and within ±4 km around the tropopause. The long‐term changes in ozone partial pressure are very similar for both regions, and ozone anomalies show many common features. Negative deviations of 15–25 nbar (or 10–20%) are clearly seen in 1976 (at 12–20 km), 1983 (at 17–22 km), 1985 and 1988 (at 18–25 km), 1989 and 1990 (at 12–20 km), and 1992 and 1993 (at 12–23 km). In January‐April 1995, negative deviations of 15–25 nbar (at 12–23 km) were observed again over the two regions, Trend estimations demonstrate that the strongest decline, in units of ozone partial pressure, takes place at 17–20 km over Europe in January‐April and for Canadian stations from March through June. For the period 1973–1994 the decline over both regions is 10–13 nbar per decade (or 5–10% per decade) and is ∼1.5 times larger for the shorter time interval 1979–1994. The estimation of trends as a function of altitude from the actual tropopause level reduces the relative error in the 7 to 13‐km layer by more than one third, which permits better understanding of the ozone changes in these critical altitudes. Using stratified ozone data around the height of the tropopause, the negative stratospheric winter‐spring trends became significant (10–15 nbar per decade or 12–17% per decade) at only 1–2 km above the tropopause.

Rate constant determination of ozone‐organic fast reactions in water using an agitated cell

Abstract Rate constants of the direct reaction between ozone and some organic pollutants (phenol and azo dyes) in water have been determined from experiments carried out in an agitated cell of known interfacial area. Kinetic equations derived from the Danckwerts model for gas to liquid absorption have been applied. By varying the ozone partial pressure, the regime of ozone absorption can be changed from instantaneous to fast. In the first case, the volumetric mass transfer coefficient was obtained, while in the second, the rate constant of the ozone‐organic direct reaction studied was determined. The procedure is recommended for ozonation reactions with rate constants in the range 102‐105 m3mol‐1S‐1.

On the relationship between vertical ozone distribution and the synoptic situation

The purpose of the paper is to provide a statistical view of the role of circulation patterns and the origin of low stratospheric air in connection with vertical ozone distribution below the ozone maximum, and also with the total ozone amount. Ozonesonde data from the aerological observatory of the Czech Hydrometeorological Institute (CHMI) Prague-Libus (50·0N, 14·7E) for January to April during the period 1979–1990 have been analyzed using an objective method to find the distribution of laminae in the vertical profile of the ozone partial pressure related to the different types of circulation patterns. The synoptic classification following Grosswetterlagen (GWL) was used, the parameters of the ozone profile such as number, magnitude, thickness and height of laminae, or the appearance of the large laminae were obtained for the individual types of GWL and used in other procedures. The total ozone data from the ozone observatory of CHMI in Hradec Kralove (50·2N, 15·8E) was also included together with the height of the tropopause and parameters of ozone profiles in the cluster analysis to investigate connections between the ozone distribution and circulation patterns (types of synoptic situation). The ozone “low-level index” (LLI), defined as the ratio of the integral amount of ozone in D.U. from the surface up to 50 hPa and total ozone were introduced to provide better information about ozone profile response to circulation patterns and thus provide a better grouping of similar types of GWL. The presented results imply the strong confirmation of the huge ozone laminae below the ozone maximum as the source of total ozone positive extremes under appropriate synoptic situations with the near location of the polar vortex edge, which could be used in common forecasts of atmospheric ozone as well as in remote sensing applications.

Kinetics of the bentazone herbicide ozonation

Abstract The kinetics of ozonation of the herbicide Bentazone (3‐isopropyl‐lH‐2,1,3‐benzothiadiazin‐4–3H‐one 2,2 dioxide) is studied, the experiments being carried out in a bubble reactor, and using a porous plate as gas sparger. The increases of temperature, ozone partial pressure, initial Bentazone concentration and pH values under 5 have a positive effect on the degradation rate. A consumption of 2 moles of ozone per mol of herbicide degraded is determined for the direct reaction. Following a model based in the film theory which is applied to the experimental data, the reaction orders with respect to both, ozone and Bentazone, and the rate constants are evaluated for the herbicide ozonation.

Stratospheric Aerosol and Gas Experiment II‐Umkehr ozone profile comparisons

This study compares 1789 pairs of ozone profiles derived from 1384 Umkehr observations at 14 different stations and 1163 Stratospheric Aerosol and Gas Experiment (SAGE) II profiles coincident within 1000 km and 14 hours between October 1984 and April 1989. The comparison indicates the following significant percentage differences (SAGE II‐Umkehr)/Umkehr with 2 × standard errors of the mean: Umkehr layer 4, (18.3±0.8)%; layer 5, (−1.6±0.4)%; layer 6, (−6.2±0.5)%; layer 7, (0.8±0.6)%; layer 8, (7.7±0.6)%; and layer 9, (12.0±1.1)%. Differences in layers 4 and 6 are due, at least in part, to inaccurate Umkehr climatologies. Average SAGE II/Umkehr differences in layers 5 through 9 at individual stations are generally less than 10%. While the Umkehr retrievals are known to be sensitive to aerosol interference, the mean layer 8 correction during the period of this study is estimated to be only 2% with large station‐to‐station variability. The correction in lower layers is smaller. We have chosen to ignore the small Umkehr aerosol correction in this study. The mean difference would decrease if Umkehr profiles were corrected for a priori profile effects calculated by DeLuisi et al. (1989a). However, using the newer Bass and Paur (1985) ozone absorption cross sections would tend to increase the differences at most levels. The profile of mean differences is similar to previously observed differences between Umkehr and solar backscattered ultraviolet (SBUV) observations. Comparing SAGE II/Umkehr differences to SAGE I/Umkehr differences at seven common stations shows a bias of −4% at the ozone peak (layer 4). This bias increases with altitude to 8% in layer 8 and 15% in layer 9, with SAGE II ozone partial pressures higher than or equal to those of SAGE I (version 6.1) relative to Umkehr in all layers above 4. A systematic upward reference‐altitude shift between 0.25 and 0.50 km for SAGE I, similar to the quoted uncertainty, would increase SAGE I ozone 4% to 8% in layer 8 and would result in similar SAGE and Umkehr ozone trends during the 1980s. Cross correlations of numerous variables associated with the Umkehr and SAGE II data sets show a minimum correlation between SAGE II and Umkehr ozone partial pressures in layers 5, 8, and 9. This correlation is a result similar to the one previously noted in other comparisons against Umkehr data. We discuss these minimum correlations in relationship to the seasonal cycle in ozone and synoptic scale variations at midlatitudes based on model results. Substantial differences between SAGE II and Umkehr exist in both the mean and the variability of ozone in layers 8 and 9. Substantial differences also exist in layer 6 where the Umkehr algorithm does not retrieve the low ozone values periodically observed by SAGE II during winter.

Electrochemical concentration cell ozone soundings at two sites during the Stratospheric Ozone Intercomparison Campaign

The Stratospheric Ozone Intercomparison Campaign (STOIC) was designed to compare proposed instruments for the Network for the Detection of Stratospheric Change (NDSC) with established measurement techniques. Ground‐based measurements were conducted at Table Mountain, California (34.4°N, 117.7°W), and rocket profiles were made at San Nicolas Island, California (33.3°N, 119.5°W). In an effort to estimate site‐to‐site differences during the intercomparison, daily soundings were made with balloon‐borne electrochemical concentration cell (ECC) ozonesondes at the two sites. Comparisons have been made of the mean values for the soundings at each site. The soundings showed small temperature differences between the two sites with the nighttime Table Mountain measurements up to 2°K cooler than the daytime San Nicolas Island temperatures. Day/night temperature corrections based on the emissivity and absorptivity of the thermistors in the balloon instruments can account for these apparent temperature differences. Ozone partial pressure profiles from the ECCs have been used to estimate atmospheric ozone variability during STOIC. Above 20 km, the lowest altitude for the STOIC comparisons, the average data sets from both sites showed standard deviations that were at or below the estimated 5–6% profile‐to‐profile repeatability for the ozonesondes. This indicates that atmospheric ozone variability was only of the order of a few percent above 20 km during the 2 weeks of the STOIC campaign. Above 20 km the ozone partial pressures over the Table Mountain site averaged 2.0% lower than over San Nicolas Island.