Light Absorption Measurements Research Articles

Preparation of environmentally resistant conductive silica-based polymer hybrids containing tetrathiafulvalene–tetracyanoquinodimethane charge-transfer complexes

We report the preparation of conductive glasses based on organic−inorganic hybrids that contain charge-transfer (CT) complexes of tetrathiafulvalene (TTF) and 7,7,8,8-tetracyanoquinodimethane (TCNQ). Using poly(vinylpyrrolidone) as the organic component, the hybrid materials were prepared with various concentrations of CT complexes. From a series of evaluations, including light absorption and X-ray diffraction (XRD) measurements and microscopy observations, it was confirmed that CT complexes form in the materials and are well dispersed. The hybrids that were synthesized with relatively large loading amounts of CT complexes exhibited a conductivity level similar to that of a semiconductor (∼10−1 S cm−1). In addition, the conductivity of the synthesized hybrids was maintained during heating and changed negligibly after exposure to water. We report the preparation of the conductive glasses based on organic−inorganic hybrids containing charge-transfer (CT) complexes with tetrathiafulvalene and 7,7,8,8-tetracyanoquinodimethane. The synthesized hybrids with relatively larger amounts of the loaded CT complexes can show the conductivity level similarly as a semiconductor (∼10−1 S cm−1). In addition, it was shown that the conductivity of the synthesized hybrids can be maintained during heating and dipping into water.

The artefacts of radiochromic film dosimetry with flatbed scanners and their causation by light scattering from radiation-induced polymers

Optical experiments and theoretical considerations have been undertaken in order to understand the causes of the ‘orientation effect’ and the ‘parabola effect’, the artefacts impairing the desired light absorption measurement on radiochromic EBT3 films with flatbed scanners. EBT3 films exposed to doses up to 20.9 Gy were scanned with an Epson Expression 10000XL flatbed scanner in landscape and portrait orientation. The horizontally and vertically polarized light components of the scanner were determined, and another Epson Expression 10000XL flatbed scanner was disassembled to examine its optical components. The optical properties of exposed and unexposed EBT3 films were studied with incident polarized and unpolarized white light, and the transmitted red light was investigated for its polarization and scattering properties including the distribution of the scattering angles. Neutral density filters were studied for comparison. Guidance was sought from the theory of light scattering from rod-like macromolecular structures. The drastic dose-dependent variation of the transmitted total light current as function of the orientation of front and rear polarizers, interpreted by light scattering theory, shows that the radiation-induced polymerization of the monomers of EBT3 films produces light scattering oscillators preferably polarized at right angles with the coating direction of the film. The directional distribution of the scattered light is partly anisotropic, with a preferred scattering plane at right angles with the coating direction, indicating light scattering from stacks of coherently vibrating oscillators piled up along the monomer crystals. The polyester carrier film also participates in these effects. The ‘orientation’ and ‘parabola’ artefacts due to flatbed scanning of radiochromic films can be explained by the interaction of the polarization-dependent and anisotropic light scattering from exposed and unexposed EBT3 films with the quantitative difference between the scanner's horizontally and vertically polarized light supply and with the limited directional acceptance of the scanner's light recording system.

SU‐E‐T‐37: An Optical Investigation Into the Polarization and Scattering Effects Underlying the Artifacts of Radiochromic Film Dosimetry with Commercial Flatbed Scanners

Purpose:This study aims to investigate the optical properties of radiochromic EBT3 films on exposure to polarized incident light.Methods:An optical table setup was used to investigate the properties of exposed and unexposed EBT3 films. The films were placed with their long side horizontally and illuminated with polarized incident white light. The polarization of light with the electrical vector pointing vertically is referred to as 0°, accordingly horizontal orientation corresponds to 90°. The light transmission was measured depending on the polarization angle of the incident light and the polarization of a polarizer in front of the detector. Secondly, the scattering properties of exposed and unexposed films were measured by placing a plane convex lens behind the films and a screen in its focal plane. Thereby, the distribution of the scattering angles appears as an intensity map on the screen. The distributions of scattering angles caused by EBT3 films and by neutral density filters were compared.Results:EBT3 films show a strong dependence of the light transmission on the polarization of the incident light. With both polarizers parallel, a peak transmission was found at 90° orientation of the polarizers. With the rear polarizer at right angles with the front polarizer, peak transmissions were found at front polarizer orientations 45° and 135°. The scattering appears to be anisotropic with a preference direction parallel to the long side of the film. The portion of scattered light and the half value scattering angle both increase with the dose on the film.Conclusion:EBT3 films show dose dependent changes in polarized light transmission and anisotropic light scattering. These effects impair the light absorption measurements on exposed films performed with commercial flatbed scanners and are causing the well‐known artifacts of radiochromic film dosimetry with flatbed scanners, the “orientation effect” and the “parabola effect”.

Seasonal dynamics of light absorption by chromophoric dissolved organic matter (CDOM) in the NW Mediterranean Sea (BOUSSOLE site)

We analyze a two-year time-series of chromophoric dissolved organic matter (CDOM) light absorption measurements in the upper 400m of the water column at the BOUSSOLE site in the NW Mediterranean Sea. The seasonal dynamics of the CDOM light absorption coefficients at 440nm (acdom(440)) is essentially characterized by (i) subsurface maxima forming in spring and progressively reinforcing throughout summer, (ii) impoverishment in the surface layer throughout summer and (iii) vertical homogeneity in winter. Seasonal variations of the spectral dependence of CDOM absorption, as described by the exponential slope value (Scdom), are characterized by highest values in summer and autumn at the surface and low values at the depths of acdom(440) subsurface maxima or just below them. Variations of acdom(440) are likely controlled by microbial digestion of phytoplankton cells, which leads to CDOM production, and by photochemical destruction (photobleaching), which leads to CDOM degradation. Photobleaching is also the main driver of Scdom variations. Consistently with previous observations, acdom(440) for a given chlorophyll a concentration is higher than expected from Case I waters bio-optical models. The total non-water light absorption budget shows that surface waters at the BOUSSOLE site are largely dominated by CDOM during all seasons but the algal bloom in March and April. These results improve the knowledge of CDOM absorption dynamics in the Mediterranean Sea, which is scarcely documented. In addition, they open the way to improved algorithms for the retrieval of CDOM absorption from field or satellite radiometric measurements.

Nanowire antenna absorption probed with time-reversed fourier microscopy.

Understanding light absorption in individual nanostructures is crucial for optimizing the light-matter interaction at the nanoscale. Here, we introduce a technique named time-reversed Fourier microscopy that enables the measurement of the angle-dependent light absorption in dilute arrays of uncoupled semiconductor nanowires. Because of their large separation, the nanowires have a response that can be described in terms of individual nanostructures. The geometry of individual nanowires makes them behave as nanoantennas that show a strong interaction with the incident light. The angle-dependent absorption measurements, which are compared to numerical simulations and Mie scattering calculations, show the transition from guided-mode to Mie-resonance absorption in individual nanowires and the relative efficiency of these two absorption mechanisms in the same nanostructures. Mie theory fails to describe the absorption in finite-length vertical nanowires illuminated at small angles with respect to their axis. At these angles, the incident light is efficiently absorbed after being coupled to guided modes. Our findings are relevant for the design of nanowire-based photodetectors and solar cells with an optimum efficiency.

Optical multi-sensor for simultaneous measurement of absorbance, turbidity, and fluorescence of a liquid

We have built a novel optical multi-sensor apparatus (MSA) for the measurement of light absorption, scattering and fluorescence either separately or simultaneous from a liquid. From the measured data it is possible to calculate different optical properties of liquid samples, such as absorbance and turbidity. The MSA is a portable device which is an advantage considering different field applications. The MSA was tested in laboratory conditions using well-known reference liquids. Data obtained with the MSA were compared with data obtained with a commercial spectrophotometer, fluorometer and a nephelometer, respectively. Relatively good correlations between the data of MSA and the three commercial devices were found. It is proposed that MSA is a potential device for monitoring changes of process liquids and liquid products in industry.

Photoresponsive cellulose fibers by surface modification with multifunctional cellulose derivatives

Eucalyptus bleached kraft pulp fibers were modified by adsorption of novel bio-based multifunctional cellulose derivatives in order to generate light responsive surfaces. The cellulose derivatives used were decorated with both cationic groups (degree of substitution, DS of 0.34) and photoactive groups (DS of 0.11 and 0.37). The adsorption was studied by UV–vis spectroscopy, surface plasmon resonance (SPR) and time-of-flight secondary ion mass spectroscopy (ToF-SIMS). The adsorption isotherms followed the Freundlich model and it turned out that the main driving force for the adsorption was electrostatic interaction. Moreover, strong indications for hydrophobic interactions between the fibers and the derivatives and the derivatives themselves were found. ToF-SIMS imaging revealed an even distribution of the derivatives on the fiber surfaces. The modified fibers underwent fast photocrosslinking under UV-irradiation as demonstrated by light absorbance and fluorescence measurements. Thus, our results proved that the modified fibers exhibited light-responsive properties and can potentially be used for the manufacture of smart bio-based materials.

Attribution of aerosol light absorption to black carbon and volatile aerosols

We investigated the contribution of volatile aerosols in light-absorption measurement by three filter-based optical instruments [aethalometer, continuous light-absorption photometer (CLAP), and continuous soot monitoring system (COSMOS)] at Gosan Climate Observatory (GCO) from February to June 2012. The aerosol absorption coefficient (σ abs) and the equivalent black carbon (BC) mass concentration (M BC) measured by the aethalometer and CLAP showed good agreement with a difference of 9%, which is likely due to the instrumental uncertainty. However, σ abs and M BC measured by the COSMOS with a heated inlet were found to be approximately 44 and 49% lower than those measured by the aethalometer and CLAP under ambient conditions, respectively. This difference can be attributed to the light absorption by the volatile aerosols coexisting with the BC. Even considering inherent observational uncertainty, it suggests that approximately 35-40% difference in the σ abs and M BC can be contributed by volatile aerosols. Increase in the difference of M BC measured by the aethalometer and COSMOS with the increasing thermal organic carbon (OC) measured by Sunset OC/EC analyzer further suggests that the filter-based optical instruments without the use of a heater are likely to enhance the value of σ abs and M BC, because this sample air may contain both BC and volatile aerosols.

Dependence of the Absorption and Optical Surface Plasmon Scattering of MoS2 Nanoparticles on Aspect Ratio, Size, and Media

The optical and electronic properties of suspensions of inorganic fullerene-like nanoparticles of MoS2 are studied through light absorption and zeta-potential measurements and compared to those of the corresponding microscopic platelets. The total extinction measurements show that, in addition to excitonic peaks and the indirect band gap transition, a new peak is observed at 700-800 nm. This spectral peak has not been reported previously for MoS2. Comparison of the total extinction and decoupled absorption spectrum indicates that this peak largely originates from scattering. Furthermore, the dependence of this peak on nanoparticle size, shape, and surface charge, as well as solvent refractive index, suggests that this transition arises from a plasmon resonance.

Indium–chlorine and gallium–chlorine tetrasubstituted phthalocyanines in a bulk system, Langmuir monolayers and Langmuir–Blodgett nanolayers – Spectroscopic investigations

The paper deals with spectroscopic characterization of metallic phthalocyanines (Pc’s) (indium and gallium) complexed with chlorine and substituted with four benzyloxyphenoxy peripheral groups in bulk systems, 2D Langmuir monolayers and Langmuir–Blodgett nanolayers. An influence of the molecular structure of dyes (the presence of metal and of substitutes attached to the phthalocyanine macroring) on the in situ measurements of light absorption is reported. Molecular arrangement of the phthalocyanine molecular skeleton in the Langmuir monolayers on water substrate and in the Langmuir–Blodgett nanolayers is evaluated. A comparison of the light absorption spectra of the phthalocyanine monolayers with the spectra of the dyes in solution supports the existence of dye aggregates in the monolayer. It was shown that the type of dye aggregates (oblique and H types) depends markedly on the dye molecular structures. The NIR-IR, IR reflection–absorption and Raman spectra are also monitored for Langmuir–Blodgett nanolayers in non-polarized and polarized light. It was shown that the dye molecules in the Langmuir–Blodgett layers are oriented nearly vertically with respect to a gold substrate.

Sources and light absorption of water-soluble organic carbon aerosols in the outflow from northern China

Abstract. High loadings of anthropogenic carbonaceous aerosols in Chinese air influence the air quality for over one billion people and impact the regional climate. A large fraction (17–80%) of this aerosol carbon is water-soluble, promoting cloud formation and thus climate cooling. Recent findings, however, suggest that water-soluble carbonaceous aerosols also absorb sunlight, bringing additional direct and indirect climate warming effects, yet the extent and nature of light absorption by this water-soluble "brown carbon" and its relation to sources is poorly understood. Here, we combine source estimates constrained by dual carbon isotopes with light-absorption measurements of water-soluble organic carbon (WSOC) for a March 2011 campaign at the Korea Climate Observatory at Gosan (KCOG), a receptor station in SE Yellow Sea for the outflow from northern China. The mass absorption cross section at 365 nm (MAC365) of WSOC for air masses from N. China were in general higher (0.8–1.1 m2 g−1), than from other source regions (0.3–0.8 m2 g−1). However, this effect corresponds to only 2–10% of the radiative forcing caused by light absorption by elemental carbon. Radiocarbon constraints show that the WSOC in Chinese outflow had significantly higher fraction fossil sources (30–50%) compared to previous findings in S. Asia, N. America and Europe. Stable carbon (δ13C) measurements were consistent with aging during long-range air mass transport for this large fraction of carbonaceous aerosols.

Estimation of the Deposited Aerosol Particles in Baghdad City, using Image Processing Technique

ABSTRACT In this study, an algorithm was developed to measure the volume and the covered area by the dust particles, and the radius of dust particle deposited for different time hours of the day. Slices transparent glass has been used to collect samples of dust particle deposited for different time of the day in Rusafa area of Baghdad city, were taken digital image of the samples through an optical microscope (EYEPIECE 10X). What have been noticeable are the difference in radii and areas of dust particles deposited as well as the difference in the density of dust particles for each slice according to time that put the slice to deposition. this paper, Keywords Dust particle, Atmospheric Aerosols. 1. INTRODUCTION Air pollution is one of the important problems in latest decades, with increasing use of fuels from oil and natural gas in various fields of life, spread in the environment many air pollutants such as gases resulting from industrial activities or different modes of transport [1].Air pollutants are classified according to the nature of its presence into two main groups: gaseous pollutants and aerosols. An example of gaseous pollutants and hydrocarbons that exist in the form of organic compounds may be gaseous, liquid or solid, such as sulfur oxides, nitrogen oxides and carbon [2]. The aerosol pollutants other are divided into solid and liquid non-permanent, such as the normal dust and pollen. Aerosol sooner or later precipitates out of the air but gases, containing space which launches it and act like the air and will not precipitate [3]. Aerosol light-absorption measurements are important for health, climate, and visibility applications [4]. Michael D. King et al. (1999) [5] Studied the advantages and disadvantages systems of Remote sensing for aerosol application, Where no one sensor system is capable of providing totally unambiguous information. Also a careful intercomparison of derived products from different sensors, to gather with comprehensive network of ground-based sun photometer and sky radiometer systems. W.Partrick Arnottet. al.(2005)[4] exploited the aerosol optics use in experiment develop a model-based calibration scheme for the 7-wavelength aethalometer, and the photo acoustic instrument operating at 532nm is used to evaluate the filter loading effect caused by aerosol light absorption and multiple scattering theory is used to analytically obtain a filter-loading correction function. G. J. Wong et al. (2007) [6] Studied the temporal development for air quality, was develop the image processing technique for enhancing the capability of an internet video surveillance (IVS) camera for real time air quality monitoring, in this technique could to detect particulate mater with diameter less than 10 micrometers(PM10).Xiaolei Yu et. al. (2011) [7] introduced a relationship between aerosol anthropogenic component and air quality in the city of Wuhan, by used satellite remote sensing. A. Bagatet. al. (2013) [8] exploit the aerosol optical depth, Angstrom exponent, single scattering albedo, and polarized phase function have been retrieved from polarized sun-photometer measurements for atmosphere. Where the Angstrom exponent has a meaningful variations respect to the changes in the complex refractive index of the aerosol, and the polarized phase function shows a moderate negative correlation respect to aerosol optical depth and single scattering albedo, so polarized phase function became regarded as a key parameter to characterize the aerosol. In measuring system will be introduced for determine radius, covered area by deposited aerosol particle and deposited aerosol particle volume as a function of day time, will be calculated by using image analysis and computer algorithms.

Complexation of DNA with ruthenium organometallic compounds: the high complexation ratio limit.

Interactions between DNA and ruthenium organometallic compounds are studied by using visible light absorption and circular dichroism measurements. A titration technique allowing for the absolute determination of the advancement degree of the complexation, without any assumption about the number of complexation modes is developed. When DNA is in excess, complexation involves intercalation of one of the organometallic compound ligands between DNA base pairs. But, in the high complexation ratio limit, where organometallic compounds are in excess relative to the DNA base pairs, a new mode of interaction is observed, in which the organometallic compound interacts weakly with DNA. The weak interaction mode, moreover, develops when all the DNA intercalation sites are occupied. A regime is reached in which one DNA base pair is linked to more than one organometallic compound.

A filter-based light-absorption measurement with polar photometer: Effects of sampling artefacts from organic carbon

In this work, light-absorption measurements were carried out on quartz-fibre and PTFE (i.e. Teflon®) filters using a home-made polar photometer in order to assess the role of organic sampling artefacts on optical measurements. Filter-based light-absorption instruments are generally operated with quartz/glass-fibre filter tapes and – as far as we know – currently there are no systematic studies on the sampling artefacts affecting the light absorption coefficient measurements. In this work, particulate matter (PM) samples were collected in Milan (Italy) during different sampling campaigns with the aim of (1) validating the polar photometer; (2) comparing the absorption properties measured on PM collected on different filter media; (3) investigating the causes of the observed differences.The polar photometer was demonstrated to give aerosol light absorption coefficients (σap in Mm−1) fully comparable to those obtained by a Multi-Angle Absorption Photometer (MAAP) when using quartz-fibre filters to collect atmospheric particles. The aerosol light absorption coefficients determined on samples collected in parallel on quartz-fibre and PTFE filters showed significant differences (about 40%). These differences were much lower (i.e. 8%) when the quartz-fibre filter sampling line was equipped with a denuder to remove organic gases from the incoming air stream evidencing a relevant role of organic sampling artefacts in light absorption measurements by filter-based systems.

Physical–chemical characterisation of the particulate matter inside two road tunnels in the São Paulo Metropolitan Area

Abstract. The notable increase in biofuel usage by the road transportation sector in Brazil during recent years has significantly altered the vehicular fuel composition. Consequently, many uncertainties are currently found in particulate matter vehicular emission profiles. In an effort to better characterise the emitted particulate matter, measurements of aerosol physical and chemical properties were undertaken inside two tunnels located in the São Paulo Metropolitan Area (SPMA). The tunnels show very distinct fleet profiles: in the Jânio Quadros (JQ) tunnel, the vast majority of the circulating fleet are light duty vehicles (LDVs), fuelled on average with the same amount of ethanol as gasoline. In the Rodoanel (RA) tunnel, the particulate emission is dominated by heavy duty vehicles (HDVs) fuelled with diesel (5% biodiesel). In the JQ tunnel, PM2.5 concentration was on average 52 μg m−3, with the largest contribution of organic mass (OM, 42%), followed by elemental carbon (EC, 17%) and crustal elements (13%). Sulphate accounted for 7% of PM2.5 and the sum of other trace elements was 10%. In the RA tunnel, PM2.5 was on average 233 μg m−3, mostly composed of EC (52%) and OM (39%). Sulphate, crustal and the trace elements showed a minor contribution with 5%, 1%, and 1%, respectively. The average OC : EC ratio in the JQ tunnel was 1.59 ± 0.09, indicating an important contribution of EC despite the high ethanol fraction in the fuel composition. In the RA tunnel, the OC : EC ratio was 0.49 ± 0.12, consistent with previous measurements of diesel-fuelled HDVs. Besides bulk carbonaceous aerosol measurement, polycyclic aromatic hydrocarbons (PAHs) were quantified. The sum of the PAHs concentration was 56 ± 5 ng m−3 and 45 ± 9 ng m−3 in the RA and JQ tunnel, respectively. In the JQ tunnel, benzo(a)pyrene (BaP) ranged from 0.9 to 6.7 ng m−3 (0.02–0.1‰ of PM2.5) whereas in the RA tunnel BaP ranged from 0.9 to 4.9 ng m−3 (0.004–0. 02‰ of PM2.5), indicating an important relative contribution of LDVs emission to atmospheric BaP. Real-time measurements performed in both tunnels provided aerosol size distributions and optical properties. The average particle count yielded 73 000 cm−3 in the JQ tunnel and 366 000 cm−3 in the RA tunnel, with an average diameter of 48 nm in the former and 39 nm in the latter. Aerosol single scattering albedo, calculated from scattering and absorption observations in the JQ tunnel, indicates a value of 0.5 associated with LDVs. Such single scattering albedo is 20–50% higher than observed in previous tunnel studies, possibly as a result of the large biofuel usage. Given the exceedingly high equivalent black carbon loadings in the RA tunnel, real time light absorption measurements were possible only in the JQ tunnel. Nevertheless, using EC measured from the filters, a single scattering albedo of 0.31 for the RA tunnel has been estimated. The results presented here characterise particulate matter emitted from nearly 1 million vehicles fuelled with a considerable amount of biofuel, providing a unique experimental site worldwide.

Fibronectin alters the rate of formation and structure of the fibrin matrix

Plasma fibronectin is a vital component of the fibrin clot; however its role on clot structure is not clearly understood. The goal of this study was to examine the influence of fibronectin on the kinetics of formation, structural characteristics and composition of reconstituted fibrin clots or fibrin matrices. Fibrin matrices were formed by adding thrombin to 1, 2 or 4mg/ml fibrinogen supplemented with 0–0.4mg/ml fibronectin. The rate of fibrin matrix formation was then monitored by measuring light absorbance properties at different time points. Confocal microscopy of fluorescein conjugated fibrinogen was used to visualize the structural characteristics of fibrin matrices. The amount of fibronectin in fibrin matrices was determined through electrophoresis and immunoblotting of solubilized matrices. Fibronectin concentration positively correlated with the initial rate of fibrin matrix formation and with steady state light absorbance values of fibrin matrices. An increase in fibronectin concentration resulted in thinner and denser fibers in the fibrin matrices. Electrophoresis and immunoblotting showed that fibronectin was covalently and non-covalently bound to fibrin matrices and in the form of high molecular weight multimers. The formation of fibronectin multimers was attributed to cross-linking of fibronectin by trace amounts Factor XIIIa. These findings are novel because they link results from light absorbance studies to microcopy analyses and demonstrate an influence of fibronectin on fibrin matrix structural characteristics. This data is important in developing therapies that destabilize fibrin clots.

Use of in vivo chlorophyll fluorescence to estimate photosynthetic activity and biomass productivity in microalgae grown in different culture systems

In vivo chlorophyll fluorescence associated to Photosystem II is being used to evaluate photosynthetic activity of microalgae grown in different types of photobioreactors; however, controversy on methodology is usual. Several recommendations on the use of chlorophyll fluorescence to estimate electron transport rate and productivity of microalgae grown in thin-layer cascade cultivators and methacrylate cylindrical vessels are included. Different methodologies related to the measure of photosynthetic activity in microalgae are discussed: (1) measurement of light absorption, (2) determination of electron transport rates versus irradiance and (3) use of simplified devices based on pulse amplitude modulated (PAM) fluorescence as Junior PAM or Pocket PAM with optical fiber and optical head as measuring units, respectively. Data comparisons of in vivo chlorophyll fluorescence by using these devices and other PAM fluorometers as Water- PAM in the microalga Chlorella sp. (Chlorophyta) are presented. Estimations of carbon production and productivity by transforming electron transport rate to gross photosynthetic rate (as oxygen evolution) using reported oxygen produced per photons absorbed values and carbon photosynthetic yield based on reported oxygen/carbon ratio are also shown. The limitation of ETR as estimator of photosynthetic and biomass productivity is discussed. Low cost:quality PAMs can promote monitoring of chlorophyll fluorescence in algal biotechnology to estimate the photosynthetic activity and biomass productivity.

Light absorption by secondary organic aerosol from α‐pinene: Effects of oxidants, seed aerosol acidity, and relative humidity

AbstractIt is well known that light absorption from dust and black carbon aerosols has a warming effect on climate while light scattering from sulfate, nitrate, and sea salt aerosols has a cooling effect. However, there are large uncertainties associated with light absorption and scattering by different types of organic aerosols, especially in the near‐UV and UV spectral regions. In this paper, we present the results from a systematic laboratory study focused on measuring light absorption by secondary organic aerosols (SOAs) generated from dark α‐pinene + O3 and α‐pinene + NOx + O3 systems in the presence of neutral and acidic sulfate seed aerosols. Light absorption was monitored using photoacoustic spectrometers at four different wavelengths: 355, 405, 532, and 870 nm. Significant light absorption at 355 and 405 nm was observed for the SOA formed from α‐pinene + O3 + NO3 system only in the presence of highly acidic sulfate seed aerosols under dry conditions. In contrast, no absorption was observed when the relative humidity was elevated to greater than 27% or in the presence of neutral sulfate seed aerosols. Organic nitrates in the SOA formed in the presence of neutral sulfate seed aerosols were found to be nonabsorbing, while the light‐absorbing compounds are speculated to be aldol condensation oligomers with nitroxy organosulfate groups that are formed in highly acidic sulfate aerosols. Overall, these results suggest that dark α‐pinene + O3 and α‐pinene + NOx + O3 systems do not form light‐absorbing SOA under typical atmospheric conditions.

Al‐Modified Zinc Oxide Nanorods for Photoelectrochemical Water Oxidation

AbstractThe photoassisted water oxidation by a range of electrodeposited Al‐modified zinc oxide nanorod arrays (NRAs) has been explored in a standardised photoelectrochemical cell. The nanorods were prepared by electrodeposition onto fluorine‐doped tin oxide glass substrates from warm aqueous solutions of zinc nitrate and aluminium nitrate. Photoluminescence measurements suggested that the nanorods have a very low concentration of defects that could act as centres for undesired charge recombination. The effect of NRA aluminium modification, morphology and optical properties as well as the presence of sputtered i‐ZnO and aluminium‐doped ZnO seeding layers on the catalytic performance of the films were investigated. Water oxidation was observed under 1 Sun illumination even at very low applied potentials (0 V vs. Ag/AgCl at pH 9.2). The pure ZnO nanorods yielded a relatively high photocurrent of 0.52 mA cm–2 (at 1 V vs. Ag/AgCl). Al modification of the sputtered seeding layer and/or the NRAs did not change the performance significantly. The photocurrent was further increased by exchanging the sputtered ZnO seeding layer for a galvanostatically deposited seeding layer. In this case the photocurrent increased to 0.74 mA cm–2 (at 1 V bias). Light absorbance and IPCE measurements indicated that although all NRAs absorb well in the UV region, light conversion does not extend greatly into the visible region. To address the issue of rapid photodegradation during water oxidation catalysis, the effect of electrolyte pH was explored by using phosphate and borate buffers with a view to improving photocurrent and long‐term stability. A borate buffer at pH 9.2 was found to be the most suitable. In this case, the photocurrent of undoped ZnO and aluminium‐doped ZnO NRA films was sustained at a high level on continuous illumination with a reduction of less than 10 and 30 %, respectively, over 1 hour, as opposed to almost complete deactivation after 20 min as observed in 0.1 M Na2SO4 (pH 6). These results indicate that the ZnO NRAs presented here have the potential to become viable photoelectrocatalysts for water oxidation.

Evaluation of scatter corrections for ac-9 absorption measurements in coastal waters

Determinations of inherent optical properties of natural waters are fundamental in marine optical research. In situ measurements of light absorption are mostly obtained with an instrument that uses a reflective tube design to reduce concomitant errors induced by light scattering (ac-9, WETLabs Inc.). The remaining, generally still substantial, error is commonly corrected using one of a number of different approaches, each of which is based on a set of assumptions. Until now, the errors in these measurements have only been theoretically examined using Monte Carlo modeling Leymarie et al. (2010). The study presented here used a lab-based point source integrating cavity absorption meter (PSICAM) which avoids scattering errors. The PSICAM data were used to evaluate the absorption determination with an ac-9 in coastal waters for each of the scattering correction approaches. The results showed that the assumption of negligible absorption at wavelengths >700 nm is not valid in coastal waters and that, as a result, ac-9 measurements strongly underestimate absorption at longer wavelengths (>600 nm). An empirical relationship between uncorrected (for scattering) ac-9 measurements and the true absorption at 715 nm was included in the correction scheme; this improved the quality of ac-9 data at longer wavelengths but showed overestimation at shorter wavelengths. However, additional inclusion of a scatter correction for the ac-9 attenuation measurement resulted in a significant improvement of the proportional scatter error correction across the spectrum. Despite these innovations, variations in scattering properties can, combined with low absorption at specific wavelengths, result in relatively large percentage errors for individual measurements.