Chemiluminometric measurement of atmospheric ozone with photoactivated chromotropic acid

A highly sensitive, robust, fast, affordable measurement system based on interfacial gas-liquid chemiluminescence (CL) on a wetted transparent screen directly on top of a miniature photomultiplier tube provides the basis of an attractive method for ozone (O(3)). Alkaline chromotropic acid (CA, 4,5-dihydroxynaphthalene-2,7-disulfonic acid) chemiluminesces upon exposure to ozone. No light emission is observed from exposure of alkaline CA to NO(2) or H(2)O(2). However, response to ozone is highly dependent on the age and storage condition of the CA solution. As such, quantitative analysis will require frequent calibration, and the method will not be attractive. We have discovered that photoactivation plays the key role in producing (a) compound(s) from chromotropic acid that appear(s) to be the primary agent(s) responsible for the CL reaction with O(3). We thus devised a method wherein a flowing solution of CA (that is stable in neutral/acidic solutions) is rendered alkaline and then exposed for a few seconds on-line to UV radiation. The solution then reacts with ozone on a screen consisting of an "invisible" nylon stocking that provides for low liquid residence time and high light throughput and results in an LOD of 40 pptv, a determination range at least up to 230 ppbv, and 10-90% and 90-10% response times of 130 and 80 ms, respectively. Intra- and interday repeatabilities at the same concentration were 0.32 and 3.8% in relative standard deviation. On the basis of aging, CL, chromatography, and chromatography-mass spectrometry studies, we suggest that the primary CL-active species are likely dimeric semiquinone species derived from CA by a series of radical reactions.     

Determination of the calibration factor of polysulphone film UV dosemeters for terrestrial solar radiation.

Polysulphone film is used as a personal UV dosemeter in dermatological or epidemiological studies. The relative efficiency of this detector does not exactly match the action spectrum as proposed by the International Commission on Non-Ionizing Radiation Protection (ICNIRP) and to which the UV dose and exposure limits refer. Therefore, the calibration of the dosemeter depends on the spetrum. In the present paper the variation of the calibration factor for terrestrial solar UV spectra is analysed on the basis of a two year observation period at a site near Munich. Germany. A detailed error estimation is included. It is shown that the variation of the calibration factor within this class of spectra is the main contribution to the total uncertainty of the dose determination, which can be up to 40%. The shape of the spectrum of terrestrial solar UV radiation is mainly determined by the total ozone column and the solar elevation angle. It is shown how the calibration depends on these two parameters and how this additional information can help to reduce the measurement error to a residual uncertainty of 17%. Exposure studies of terrestrial solar UV radiation using polysulphone film as a dosemeter would gain in accuracy if total ozone column values at the study's site could be measured or taken from satellite or weather service data. The interpretation of the magnitude of the dose uncertainty depends on the further use of these data.     

Assessment of the ultraviolet radiation field in ocean waters from space-based measurements and full radiative-transfer calculations

Quantitative assessment of the UV effects on aquatic ecosystems requires an estimate of the in-water radiation field. Actual ocean UV reflectances are needed for improving the total ozone retrievals from the total ozone mapping spectrometer (TOMS) and the ozone monitoring instrument (OMI) flown on NASA's Aura satellite. The estimate of underwater UV radiation can be done on the basis of measurements from the TOMS/OMI and full models of radiative transfer (RT) in the atmosphere-ocean system. The Hydrolight code, modified for extension to the UV, is used for the generation of look-up tables for in-water irradiances. A look-up table for surface radiances generated with a full RT code is input for the Hydrolight simulations. A model of seawater inherent optical properties (IOPs) is an extension of the Case 1 water model to the UV. A new element of the IOP model is parameterization of particulate matter absorption based on recent in situ data. A chlorophyll product from ocean color sensors is input for the IOP model. Verification of the in-water computational scheme shows that the calculated diffuse attenuation coefficient Kd is in good agreement with the measured Kd.     

Decomposition of two haloacetic acids in water using UV radiation, ozone and advanced oxidation processes

The decomposition of two haloacetic acids (HAAs), dichloroacetic acid (DCAA) and trichloroacetic acid (TCAA), from water was studied by means of single oxidants: ozone, UV radiation; and by the advanced oxidation processes (AOPs) constituted by combinations of O(3)/UV radiation, H(2)O(2)/UV radiation, O(3)/H(2)O(2), O(3)/H(2)O(2)/UV radiation. The concentrations of HAAs were analyzed at specified time intervals to elucidate the decomposition of HAAs. Single O(3) or UV did not result in perceptible decomposition of HAAs within the applied reaction time. O(3)/UV showed to be more suitable for the decomposition of DCAA and TCAA in water among the six methods of oxidation. Decomposition of DCAA was easier than TCAA by AOPs. For O(3)/UV in the semi-continuous mode, the effective utilization rate of ozone for HAA decomposition decreased with ozone addition. The kinetics of HAAs decomposition by O(3)/UV and the influence of coexistent humic acids and HCO(3)(-) on the decomposition process were investigated. The decomposition of the HAAs by the O(3)/UV accorded with the pseudo-first-order mode under the constant initial dissolved O(3) concentration and fixed UV radiation. The pseudo-first-order rate constant for the decomposition of DCAA was more than four times that for TCAA. Humic acids can cause the H(2)O(2) accumulation and the decrease in rate constants of HAAs decomposition in the O(3)/UV process. The rate constants for the decomposition of DCAA and TCAA decreased by 41.1% and 23.8%, respectively, when humic acids were added at a concentration of 1.2mgTOC/L. The rate constants decreased by 43.5% and 25.9%, respectively, at an HCO(3)(-) concentration of 1.0mmol/L.     

Oxidation of methyl methacrylate from semiconductor wastewater by O3 and O3/UV processes

This study investigated the oxidation of methyl methacrylate (MMA) by sole ozonation and ozone/UV treatments. The semi-batch ozonation experiments were proceeded under different reaction conditions to study the effects of ozone dosage and UV radiation on the oxidation of MMA. The experimental results indicated that both the oxidation of MMA by the sole ozonation and O3/UV processes can completely decompose MMA to form the following intermediates within 30 min reaction time. To increase the applied ozone dosage can significantly raise the removal efficiency of MMA. However, the mineralization of MMA via the direct oxidation reaction of molecular ozone was slow, while introducing the UV radiation can promote the mineralization rate of MMA. In addition, the pH value of the oxidized solution in the O3/UV treatment decreased lower than that in the sole ozonation treatment of about 1 unit. The possible scheme of the decomposition pathway of MMA under the ozonation process is proposed in this study. Formic acid and acetic acid were found to be the main ozonated intermediates.     

Decomposition of 2-naphthalenesulfonate in electroplating solution by ozonation with UV radiation

This study investigates the ozonation of 2-naphthalenesulfonate (2-NS) combined with UV radiation in the electroplating solution. 2-NS is commonly used as a brightening and stabilization agent in the electroplating solution. Semibatch ozonation experiments were conducted under various reaction conditions to study the effects of ozone dosage and UV radiation on the oxidation of 2-NS. The concentrations of 2-NS were analyzed at specified time intervals to elucidate the decomposition of 2-NS. Total organic carbon (TOC) is chosen as a mineralization index of the ozonation of 2-NS. In addition, values of pH and oxidation reduction potential were continuously measured in the course of experiments. As a result, the nearly complete mineralization of 2-NS via the ozonation treatment can be achieved. The mineralization of 2-NS is found accelerated by the introduction of UV radiation and has a distinct relationship with the consumption of applied ozone. These results can provide useful information for the proper removal of 2-NS in the electroplating solution by the ozonation with UV radiation.     

Decomposition of dimethyl phthalate in an aqueous solution by ozonation with high silica zeolites and UV radiation

This study investigates the enhanced ozonation of dimethyl phthalate (DMP), which is a pollutant of concern in water environments, with high silica zeolites and ultraviolet (UV) radiation. Semibatch ozonation experiments are performed under various reaction conditions to examine the effects of inlet gas ozone concentration, high silica zeolite dosage, and UV radiation intensity on the decomposition of DMP. The complete removal of DMP can be efficiently achieved via both O(3) and O(3)/UV treatments. Note that the presence of high silica zeolites accelerates the decomposition rate of DMP in the O(3) process. On the other hand, the removal efficiencies of both chemical oxygen demand (COD) and total organic carbons (TOC) are significantly enhanced by employing the ozonation combined with UV radiation. The O(3)/UV process is also advantageous for the utilization efficiency of fed ozone especially in the late ozonation period. Furthermore, the correlation between the COD removal percentage (%) and the mole ratio of ozone consumed to the DMP treated (mol mol(-1)) is obtained. The clear-cut removal relationship of the TOC with COD during the ozonation of DMP has also been presented. Consequently, the results evaluate the flexibility of ozonation system associated with high silica zeolites and UV radiation for the removal of DMP and provide the useful information in engineering application.     

Surface combustion microengines based on photocatalytic oxidations of hydrocarbons at room temperature

The concept of a surface combustion microengine that is fuelled by volatile hydrocarbons at room temperature is demonstrated on a microcantilever covered with a thin layer of titanium oxide (TiO(2)). Exposing this microengine to ultraviolet (UV) radiation and hydrocarbon vapor produces controlled bending of the microcantilever as a result of differential stress produced by photocatalytic oxidation of organic molecules on the TiO(2) coating. Compared to the motion generated solely by UV radiation or hydrocarbon adsorption, the unique photocatalytic-mechanical effects in the presence of UV and hydrocarbon produce more work and exhibit fast response. The surface combustion based microengines would require less maintenance in minimally controlled field environment and could be potentially used in construction of miniature movable machines, conversion of solar and chemical energy to mechanical work, when extended to a large array of microcantilevers. We believe such microengines can be fuelled by a variety of molecules or mixtures due to the generally favorable photocatalytic reactivity of TiO(2), thus potentially offering a broad approach for mechanical work generation from multiple energy sources.     

An overview of geoengineering of climate using stratospheric sulphate aerosols

We provide an overview of geoengineering by stratospheric sulphate aerosols. The state of understanding about this topic as of early 2008 is reviewed, summarizing the past 30 years of work in the area, highlighting some very recent studies using climate models, and discussing methods used to deliver sulphur species to the stratosphere. The studies reviewed here suggest that sulphate aerosols can counteract the globally averaged temperature increase associated with increasing greenhouse gases, and reduce changes to some other components of the Earth system. There are likely to be remaining regional climate changes after geoengineering, with some regions experiencing significant changes in temperature or precipitation. The aerosols also serve as surfaces for heterogeneous chemistry resulting in increased ozone depletion. The delivery of sulphur species to the stratosphere in a way that will produce particles of the right size is shown to be a complex and potentially very difficult task. Two simple delivery scenarios are explored, but similar exercises will be needed for other suggested delivery mechanisms. While the introduction of the geoengineering source of sulphate aerosol will perturb the sulphur cycle of the stratosphere signicantly, it is a small perturbation to the total (stratosphere and troposphere) sulphur cycle. The geoengineering source would thus be a small contributor to the total global source of 'acid rain' that could be compensated for through improved pollution control of anthropogenic tropospheric sources. Some areas of research remain unexplored. Although ozone may be depleted, with a consequent increase to solar ultraviolet-B (UVB) energy reaching the surface and a potential impact on health and biological populations, the aerosols will also scatter and attenuate this part of the energy spectrum, and this may compensate the UVB enhancement associated with ozone depletion. The aerosol will also change the ratio of diffuse to direct energy reaching the surface, and this may influence ecosystems. The impact of geoengineering on these components of the Earth system has not yet been studied. Representations for the formation, evolution and removal of aerosol and distribution of particle size are still very crude, and more work will be needed to gain confidence in our understanding of the deliberate production of this class of aerosols and their role in the climate system.     

Sulfur mustard destruction using ozone, UV, hydrogen peroxide and their combination

Numerous methods are used for destruction of sulfur mustard. Oxidation is one of those methods. There have been only limited data concerning application of the advanced oxidation technologies (AOTs) for mustard destruction available before. In this study sulfur mustard oxidation rate depending on kind of the oxidative system and process parameters used was assessed using selected AOT. The following were selected for mustard oxidation: ozone (O(3)), UV light (UV), hydrogen peroxide (H(2)O(2)); double systems: UV/O(3), UV/H(2)O(2), and O(3)/H(2)O(2); a triple system: O(3)/H(2)O(2)/UV and Fenton reaction. Effectiveness of the selected AOT methods has been evaluated and the most suitable one for mustard destruction was chosen. Using ozone in various combinations with hydrogen peroxide and UV radiation mustard can be destroyed much quicker comparing to the classical oxidizers. Fast mustard oxidation (a few minutes) occurred in those systems where ozone alone was used, or in the following combinations: O(3)/H(2)O(2), O(3)/UV and O(3)/H(2)O(2)/UV. When those advanced oxidation technologies are used, mustard becomes destroyed mainly in course of the direct oxidation with ozone, and reactions of mustard with radicals formed due to ozone action play a secondary role. Rate of sulfur mustard oxidation in the above mentioned ozone-containing oxidative systems decreases with pH value increasing from 2 to 12. Only when pH value of reaction solutions is close to pH 5, mustard oxidation rate is minimal, probably due to "disappearance" of radicals participating in oxidation in this pH. Sulfur mustard can be most effectively destroyed using just ozone in pH 7. In that case mustard destruction rate is only slightly lower than the rate achieved in optimal conditions, and the system is the simplest.     

Comparison of different advanced oxidation processes (AOPs) in the presence of perovskites

The efficacy of the oxidation systems: O3, UV radiation, O3/UV radiation, O3/perovskite, UV radiation/perovskite, O3/UV radiation/perovskite, H2O2/UV radiation, H2O2/UV radiation/perovskite, has been investigated by using pyruvic acid as probe compound. Under the operating conditions used, the combination of UV radiation and hydrogen peroxide (with or without perovskites) leads to the fastest pyruvic acid removal while the best results in terms of mineralization degree are obtained when combining O3/UV radiation/perovskite. The effect of the variables: inlet ozone (15-75 mg L(-1)) and initial pyruvic acid (10(-3) to 10(-2)M) concentrations, catalyst load (0.01-1.5 g L(-1)) and pH (2-9) was investigated for the photocatalytic ozonation. The most influencing parameter was the ozone concentration fed to the photoreactor. A zero order was observed for pyruvic acid concentration and close to zero for catalyst load. Some deactivation is observed after reusing the catalyst, likely due to leaching of the active phase.     

A novel ozone detection at room temperature through UV-LED-assisted ZnO thick film sensors

In this work a novel ozone detection at room temperature (RT) has been investigated. Two functional materials, ZnO and (W_0.9Sn_0.1)O_3 − x (WS10) oxides, have been synthesized to prepare thick film gas sensors, both used in conventional heated mode as well as at RT assisted by UV irradiation. As a source of light, a light emitting diode (LED) of 400 nm peak wavelength was used. Under typical operating conditions of the UV-LED, the radiation flux density ? over the sensor was of about 5 · 10¹⁷ photons/cm². Powders and films have been characterized by means of TG-DTA, SEM, TEM and XRD. Finally, electrical measurements have been performed on sensing films with the aim to compare conductive properties, surface barrier heights and ozone sensing features with and without UV irradiation. Despite the fact that two types of conventional heated sensors offered quite similar results with respect to ozone sensing, it turned out that, at RT and with the assistance of UV light, ZnO behaved excellently fast detecting ozone at concentrations down to 10 ppb, while for WS10 under the same operating conditions an opposite result was observed, i.e. very low response and long response time.     

Forming wrinkled stiff films on polymeric substrates at room temperature for stretchable interconnects applications

Periodically wrinkled stiff thin films on elastomeric substrates have been found extensive applications, such as in stretchable electronics. This paper presents a cost-effective and simple method to form wrinkled stiff SiO_x thin films on polydimethylsiloxane (PDMS) substrates at room temperature by ultraviolet/ozone (UV/O) radiation on pre-strained PDMS. Systemic studies have been conducted to understand the dependence of the wavy profile on the PDMS pre-strain, UV/O exposure time, and PDMS modulus. The mechanics analysis has been verified to be quantitatively or qualitatively accurate by experimental comparisons. The wrinkled SiO_x/PDMS system is stretchable and provides a wavy mold for stretchable electrodes. The constant electrical resistance during mechanical stretching shows the stretchability of this system.     

Degradation of carbofuran by using ozone, UV radiation and advanced oxidation processes.

The degradation of carbofuran (2,3-dihydro-2,2-dimethylbenzofuran-7-yl methylcarbamate), a frequently used carbamate derivative pesticide that is considered a priority pollutant, is carried out in batch reactors by means of single oxidants: ozone, UV radiation and Fenton's reagent; and by the advanced oxidation processes (AOPs) constituted by combinations of ozone plus UV radiation, UV radiation plus H(2)O(2), and UV radiation plus Fenton's reagent (photo-Fenton system). For all these reactions, the apparent pseudo-first-order rate constants are evaluated in order to compare the efficiency of each process. In addition and by means of a competition kinetic model, the rate constants for the reaction of carbofuran with ozone and with hydroxyl radicals are also determined. The improvement in the decomposition levels of carbofuran reached by the combined processes in relation to the single oxidants, due to the generation of the very reactive hydroxyl radicals, is also established in every process. For the oxidant concentrations applied, the most effective process in removing carbofuran was the photo-Fenton system.     

Kinetic modelling of aqueous atrazine ozonation processes in a continuous flow bubble contactor

The ozonation of atrazine in different waters (ultrapure and surface waters) has been studied in continuous bubble contactors with kinetic modelling purposes. Three ozonation processes have been considered: ozonation alone and combined with hydrogen peroxide or UV radiation. The kinetic models are based on a molecular and free radical mechanism of reactions, reaction rate and mass transfer data and non-ideal flow analysis models for gas and water phases through the contactors (the tanks in series model and the dispersion model). The models predict well the experimental concentrations of atrazine, dissolved ozone and hydrogen peroxide both at non-steady state and steady state regimes. From both experimental and calculated results, atrazine conversions are observed to be highly dependent on the nature of water where ozonation is carried out. As far as removal of atrazine and oxidation intermediates are concerned, ozone combined with UV radiation resulted in the most effective ozonation process among the three studied.     

Characterization of an ultraviolet and a vacuum-ultraviolet irradiance meter with synchrotron radiation

We have constructed and characterized a simple probe that is suitable for accurate measurements of irradiance in the UV to the vacuum UV spectral range. The irradiance meter consists of a PtSi detector located behind a 5-mm-diameter aperture. The probe was characterized at various wavelengths ranging from 130 to 320 mm by use of continuously tunable synchrotron radiation from the Synchrotron Ultra-violet Radiation Facility III. We determined the irradiance responsivity by scanning a small monochromatic beam over the active area of the irradiance meter and measuring its response on a grid with regular spacing. The angular response was also determined and shown to be suitable for applications such as photolithography. In addition, we studied the radiation damage using a 157-nm excimer laser and found that the irradiance meter can endure more than 100 J/cm2 of 157-nm radiation before a noticeable change occurs in its responsivity. Many industrial applications such as UV curing, photolithography, or semiconductor chip fabrication that require accurate measurement of the irradiance would benefit from having such a stable, accurate LTV irradiance meter.     

Dust in the Earth system: the biogeochemical linking of land,air and sea

Understanding the response of the Earth's climate system to anthropogenic perturbation has been a pressing priority for society since the late 1980s. However, recent years have seen a major paradigm shift in how such an understanding can be reached. Climate change demands analysis within an integrated 'Earth-system' framework, taken to encompass the suite of interacting physical, chemical, biological and human processes that, in transporting and transforming materials and energy, jointly determine the conditions for life on the whole planet. This is a highly complex system, characterized by multiple nonlinear responses and thresholds, with linkages often between apparently disparate components. The interconnected nature of the Earth system is wonderfully illustrated by the diverse roles played by atmospheric transport of mineral 'dust', particularly in its capacity as a key pathway for the delivery of nutrients essential to plant growth, not only on land, but perhaps more importantly, in the ocean. Dust therefore biogeochemically links land, air and sea. This paper reviews the biogeochemical role of mineral dust in the Earth system and its interaction with climate, and, in particular, the potential importance of both past and possible future changes in aeolian delivery of the micro-nutrient iron to the ocean. For instance, if, in the future, there was to be a widespread stabilization of soils for the purpose of carbon sequestration on land, a reduction in aeolian iron supply to the open ocean would occur. The resultant weakening of the oceanic carbon sink could potentially offset much of the carbon sequestered on land. In contrast, during glacial times, enhanced dust supply to the ocean could have 'fertilized' the biota and driven atmospheric CO(2) lower. Dust might even play an active role in driving climatic change; since changes in dust supply may affect climate, and changes in climate, in turn, influence dust, a 'feedback loop' is formed. Possible feedback mechanisms are identified, recognition of whose operation could be crucial to our understanding of major climatic transitions over the past few million years.     

Initial in-orbit results from a low-cost atmospheric ozone monitor operating on board the FASat-Bravo microsatellite

In 1994, a collaborative programme was set up between the University of Surrey and the Chilean Air Force to design and build a low-cost 50 kg microsatellite with instrumentation capable of monitoring the distribution and concentration of stratospheric ozone, particularly over Chilean territory. This resulted in the joint design and development of the ozone-layer monitoring experiment (OLME), which was flown on board the resultant FASat-Bravo microsatellite, launched in July 1998 into an 820 km altitude Sun-synchronous orbit. The nadir-pointing OLME measures the solar ultraviolet light backscattered from the atmosphere in four spectral bands. From these raw radiometric data, total column ozone concentrations can be deduced. Since the launch, a series of high-spatial-resolution measurements have been made over Chilean scientific stations, while continuous low-spatial-resolution measurements have been used to provide global coverage. To date, the University of Surrey has concentrated on these global measurements, and has used a simplified ozone retrieval algorithm to check the results qualitatively against ozone maps produced by NASA's Earth Probe Total Ozone Mapping Spectrometer (TOMS) payload. These initial results look promising, with apparently good correlation between the two datasets. A novel, more-complex retrieval algorithm has been applied to the high-resolution data, and early results have shown agreement with the TOMS.     

Effect of oxidation on surface-enhanced Raman scattering activity of silver nanoparticles: a quantitative correlation

We quantitatively studied, using X-ray photoelectron spectroscopy (XPS), oxidation of substrate-immobilized silver nanoparticles (Ag NPs) in a wide range of conditions, including exposure to ambient air and controlled ozone environment under UV irradiation, and we correlated the degree of silver oxidation with surface-enhanced Raman scattering (SERS) enhancement factors (EFs). The SERS activity of pristine and oxidized Ag NPs was assessed by use of trans-1,2-bis(4-pyridyl)ethylene (BPE) and sodium thiocynate as model analytes at the excitation wavelength of 532 nm. Our study showed that the exposure of Ag NPs to parts per million (ppm) level concentrations of ozone led to the formation of Ag(2)O and orders of magnitude reduction in SERS EFs. Such an adverse effect was also notable upon exposure of Ag NPs under ambient conditions where ozone existed at parts per billion (ppb) level. The correlated XPS and SERS studies suggested that formation of just a submonolayer of Ag(2)O was sufficient to decrease markedly the SERS EF of Ag NPs. In addition, studies of changes in plasmon absorption bands pointed to the chemical enhancement as a major reason for deterioration of SERS signals when substrates were pre-exposed to ambient air, and to a combination of changes in chemical and electromagnetic enhancements in the case of substrate pre-exposure to elevated ozone concentrations. Finally, we also found UV irradiation and ozone had a synergistic effect on silver oxidation and thus a detrimental effect on SERS enhancement of Ag NPs and that such oxidation effects were analyte-dependent, as a result of inherent differences in chemical enhancements and molecular binding affinities for various analytes.     

Extreme-ultraviolet radiation filtering by freestanding transmission gratings

Measurement of energetic neutral atoms fluxes in space requires efficient suppression of exceptionally strong background extreme-ultraviolet (EUV) and UV radiation. Diffraction filters make it possible to separate (transmit) charged and neutral particles from the background radiation (which would be suppressed). Recently developed freestanding transmission gratings look especially promising for implementation in a new family of diffraction EUV/UV filters. The first results of our experimental study of filtering properties of freestanding transmission gratings with a period of 200 nm are presented. The grating transmission was measured in the 52-131-nm wavelength range, and grating polarization properties were determined at 58.4 nm. It is shown that transmission gratings can be used efficiently as filters and polarizers in the EUV/UV spectral range.