O2 Absorption Research Articles

Whey Protein Film with Oxygen Scavenging Function by Incorporation of Ascorbic Acid

Residual O(2) in a package headspace can be removed by an O(2)-absorbing sachet, which can be harmful if swallowed by the consumer, or by a chemically-active plastic packaging film, which is difficult to recycle. An edible, O(2)-absorbing film would avoid these disadvantages. The objective of our research was to assess the O(2)-scavenging potential of an edible whey protein isolate (WPI) film incorporating ascorbic acid (AA). AA at 0.05, 0.1, or 0.2 M was added to 5% (w/w) heat-denatured WPI film-forming solutions with WPI : glycerol (Gly) ratio of 1: 1.00, 1: 0.80, or 1: 0.67. The pH of solutions was then adjusted to 3.5 (below pK(a1) of AA), to stabilize AA against oxidation, before film casting. The mechanical properties, O(2) permeabilities, and thermal transitions of films were measured. Activation of the O(2)-scavenging function of the AA-incorporated films was accomplished by adjustment of the films to pH ≥ 7. O(2)-scavenging ability of AA-incorporated WPI films was determined by measuring residual O(2) in the headspace of a high-barrier container. Incorporation of AA into WPI film decreased film tensile strength and further reduced O(2) permeability at each WPI : Gly ratio. AA-containing films adjusted to pH ≥ 7 demonstrated O(2) absorption proportional to AA content, consistent with theoretical O(2)-scavenging capacity. Thermal transition measurements indicated that AA was involved in WPI structural modification and decreased the degradation temperature of WPI-based film. The demonstrated O(2)-scavenging function, improved O(2) barrier and acceptable mechanical properties of AA-incorporated films indicate potential commercial usefulness. Ascorbic acid-incorporated whey protein film with oxygen scavenging function can be used to extend shelf lives of a wide variety of oxygen-sensitive products by eliminating headspace oxygen as well as oxygen permeating through the packaging wall over time. Edible oxygen-scavenger film has the advantages of avoiding both accidental consumption and nonrecyclability of conventional oxygen scavenger systems.

Effect of preparative methods on electrical and electrochemical performance of lanthanum strontium manganite

The electrochemical performance of La0.8Sr0.2MnO3:Ce0.8Gd0.2O2 composite cathode was investigated for solid oxide fuel cell applications. Sol–gel, combustion, and solid-state syntheses yielded rhombohedral La0.8Sr0.2MnO3, whereas mechanochemical process gave cubic structure. X-ray diffraction results established good chemical stability of La0.8Sr0.2MnO3 with Ce0.8Gd0.2O2 composite cathode. Combustion synthesis was found best among all preparative methods on the basis of lowest area specific resistance 0.70 Ω cm2 at 800 °C. The activation energy E a = 1.09 ± 0.01 eV indicated absorption of O2 and was the rate-limiting process of cathode.

MAMAP – a new spectrometer system for column-averaged methane and carbon dioxide observations from aircraft: retrieval algorithm and first inversions for point source emission rates

Abstract. MAMAP is an airborne passive remote sensing instrument designed to measure the dry columns of methane (CH4) and carbon dioxide (CO2). The MAMAP instrument comprises two optical grating spectrometers: the first observing in the short wave infrared band (SWIR) at 1590–1690 nm to measure CO2 and CH4 absorptions, and the second in the near infrared (NIR) at 757–768 nm to measure O2 absorptions for reference/normalisation purposes. MAMAP can be operated in both nadir and zenith geometry during the flight. Mounted on an aeroplane, MAMAP surveys areas on regional to local scales with a ground pixel resolution of approximately 29 m × 33 m for a typical aircraft altitude of 1250 m and a velocity of 200 km h−1. The retrieval precision of the measured column relative to background is typically ≲1% (1σ). MAMAP measurements are valuable to close the gap between satellite data, having global coverage but with a rather coarse resolution, on the one hand, and highly accurate in situ measurements with sparse coverage on the other hand. In July 2007, test flights were performed over two coal-fired power plants operated by Vattenfall Europe Generation AG: Jänschwalde (27.4 Mt CO2 yr−1) and Schwarze Pumpe (11.9 Mt CO2 yr−1), about 100 km southeast of Berlin, Germany. By using two different inversion approaches, one based on an optimal estimation scheme to fit Gaussian plume models from multiple sources to the data, and another using a simple Gaussian integral method, the emission rates can be determined and compared with emissions reported by Vattenfall Europe. An extensive error analysis for the retrieval's dry column results (XCO2 and XCH4) and for the two inversion methods has been performed. Both methods – the Gaussian plume model fit and the Gaussian integral method – are capable of deriving estimates for strong point source emission rates that are within ±10% of the reported values, given appropriate flight patterns and detailed knowledge of wind conditions.

Improving transmission calculations for the Edwards–Slingo radiation scheme using a correlated‐k distribution method

AbstractA new version of the Edwards–Slingo (ES) radiation scheme is developed using the correlated‐k distribution (CKD) method. The work is conducted based on the line‐by‐line radiative transfer scheme GENLN2. A dataset of new ozone absorption cross‐section in the ultraviolet spectrum and new oxygen collision‐induced continuum data have been implemented in both the GENLN2 and new ES schemes. In order to improve the efficiency of the ES scheme, a new technique is proposed in this work to optimize the k distribution and a new method is used to deal with the gaseous overlapping absorption in a spectral band. The accuracy of the scheme is improved by replacing the scaling function used in the ES scheme with a pre‐determined look‐up table for consideration of the pressure and temperature dependency of the absorption oefficients. The number of spectral bands and number of absorbing species are both increased in the new scheme for better resolution of the spectral variation of absorbing species, aerosols and clouds. However, this does not increase the computational cost. Instead, it is reduced substantially compared with the previous version of the code. The treatment of transmission in the short‐wave spectrum is improved by implementing the absorbing species of CH4, N2O and O2 collision‐induced continuum absorption which are not included in the ES scheme. New O3 absorption cross‐section data in the ultraviolet spectrum measured by the European Space Agency are used to generate the CKD spectral data in the short‐wave spectral bands. These data have a temperature dependency and better spectral resolution. The irradiance and heating rate determined by the new scheme are tested against the same variables determined by GENLN2. It has been shown that the new scheme produces results more accurate than the ES scheme. Copyright © 2011 Royal Meteorological Society

Remote sensing of tropospheric aerosol using UV MAX-DOAS during hazy conditions in winter: Utilization of O4 Absorption bands at wavelength intervals of 338–368 and 367–393 nm

Abstract Multi Axis Differential Optical Absorption Spectroscopy (MAX-DOAS) measurements were taken during 12 hazy days in December 2006 in Fresno, USA. We obtained vertical distributions of aerosol extinction coefficients (AECs) and aerosol optical depths (AODs) at UV wavelengths of 353 and 380 nm by applying a recently developed aerosol retrieval algorithm based on O 4 slant column densities (SCDs) from MAX-DOAS measurements. A linear correlation coefficient (R) of 0.74 (0.73) was obtained between surface PM 2.5 concentrations and AECs at 353 (380) nm within the 0–1 km layer under hazy conditions. AODs obtained from MAX-DOAS measurements were validated by comparison with those measured by a collocated sunphotometer. AODs derived at both wavelengths were overestimated under the hazy atmospheric conditions compared with those retrieved from sunphotometer measurements. A coefficient of determination ( R 2 ) of 0.58 (0.79) was obtained for AODs at 353 (380) nm from MAX-DOAS and sunphotometer during the hazy period, and AODs obtained using MAX-DOAS agreed with sunphotometer data within 50% and 40% for the different wavelengths, respectively.

Diode laser-based cavity ring-down instrument for NO<sub>3</sub>, N<sub>2</sub>O<sub>5</sub>, NO, NO<sub>2</sub> and O<sub>3</sub> from aircraft

Abstract. This article presents a diode laser-based, cavity ring-down spectrometer for simultaneous in situ measurements of four nitrogen oxide species, NO3, N2O5, NO, NO2, as well as O3, designed for deployment on aircraft. The instrument measures NO3 and NO2 by optical extinction at 662 nm and 405 nm, respectively; N2O5 is measured by thermal conversion to NO3, while NO and O3 are measured by chemical conversion to NO2. The instrument has several advantages over previous instruments developed by our group for measurement of NO2, NO3 and N2O5 alone, based on a pulsed Nd:YAG and dye laser. First, the use of continuous wave diode lasers reduces the requirements for power and weight and eliminates hazardous materials. Second, detection of NO2 at 405 nm is more sensitive than our previously reported 532 nm instrument, and does not have a measurable interference from O3. Third, the instrument includes chemical conversion of NO and O3 to NO2 to provide measurements of total NOx (= NO + NO2) and Ox (= NO2 + O3) on two separate channels; mixing ratios of NO and O3 are determined by subtraction of NO2. Finally, all five species are calibrated against a single standard based on 254 nm O3 absorption to provide high accuracy. Disadvantages include an increased sensitivity to water vapor on the 662 nm NO3 and N2O5 channels and a modest reduction in sensitivity for these species compared to the pulsed laser instrument. The in-flight detection limit for both NO3 and N2O5 is 3 pptv (2 σ, 1 s) and for NO, NO2 and O3 is 140, 90, and 120 pptv (2 σ, 1 s) respectively. Demonstrated performance of the instrument in a laboratory/ground based environment is better by approximately a factor of 2–3. The NO and NO2 measurements are less precise than research-grade chemiluminescence instruments. However, the combination of these five species in a single instrument, calibrated to a single analytical standard, provides a complete and accurate picture of nighttime nitrogen oxide chemistry. The instrument performance is demonstrated using data acquired during a recent field campaign in California.

Pound-Drever-Hall-locked, frequency-stabilized cavity ring-down spectrometer

We describe a high sensitivity and high spectral resolution laser absorption spectrometer based upon the frequency-stabilized cavity ring-down spectroscopy (FS-CRDS) technique. We used the Pound-Drever-Hall (PDH) method to lock the probe laser to the high-finesse ring-down cavity. We show that the concomitant narrowing of the probe laser line width leads to dramatically increased ring-down event acquisition rates (up to 14.3 kHz), improved spectrum signal-to-noise ratios for weak O(2) absorption spectra at λ = 687 nm and substantial increase in spectrum acquisition rates compared to implementations of FS-CRDS that do not incorporate high-bandwidth locking techniques. The minimum detectable absorption coefficient and the noise-equivalent absorption coefficient for the spectrometer are about 2×10(-10) cm(-1) and 7.5×10(-11) cm(-1)Hz(-1/2), respectively.

Methane emission from living tree wood

The time courses of CO2, CH4, and H2 accumulation and O2 absorption at the exposure of trunk wood samples taken from living trees of birch (Betula pendula Roth.), bird cherry tree (Padus avium Mill.), and pine (Pinus sylvestris L.) in the closed volume were studied. The activity of these processes at different temperatures (from 5 to 55°C) was also examined. The main components of gas exchange in all three tree species were O2 absorption and CO2 evolution. The fluxes of these gases were equal. In experiments with dehydration-hydration of wood samples, the intrawood origin of “woody” methane was established. Emission of CH4 and H2 from the wood depended on temperature. The temperature dependence of CH4 emission was similar to the temperature dependence of wood respiration. The high correlation between CO2, CH4, and H2 release and O2 absorption was noted. The relationships between these gas-exchange parameters were not species-specific. Temperature maxima of CH4 emission and the respiratory activity coincided. This implies that the highest methane emission should be expected in the period of the growth season most favorable for tree physiology. For the wood from all tree species, the ratio between released CH4 and CO2 volumes was close to 1: 160. This means that the annual methane emission from living tree is about 2 Mt C, attaining 4% of total methane emission from the territory of North Eurasia. However, taking into account a temperature dependence of methane exchange between the vegetation cover and atmosphere, we can expect that, at global climate warming, methane emission volume might be substantial.

Vacuum ultraviolet spectroscopic properties of KSrPO4:Tb3+

KSrPO4:Tb3+ phosphors were prepared by a solid-state method and their photoluminescence properties were investigated under vacuum ultraviolet excitation. In the excitation spectrum monitoring at 544nm, the band in the region of 120–162nm can be attributed to be the overlap of host absorption and charge transfer transition of O2−→Tb3+, and the band ranging from 162 to 300nm was assigned to the f–d transition of Tb3+. The photoluminescence spectrum shows that the phosphors exhibited a strong green emission around 544nm corresponding to the 5D4→7F5 transition of Tb3+ under the excitation of 147nm. Optimal emission intensity was obtained when x=7% in KSr1-xPO4:xTb3+ and the luminescent chromaticity coordinates were calculated to be (x=0.317, y=0.522) for KSr0.93PO4:7%Tb3+.

Absorption of atmospheric oxygen by agitated weakly alkaline solutions of surfactants

Volumetric analysis of the decomposition kinetics of sodium hydroxymethylsulfinate was performed to study the absorption of atmospheric oxygen by surfactant solutions agitated in various modes at 353 K. The application of the Danchwerts model of surface renewal made it possible to evaluate the contribution made by changes in driving forces in the stages of O2 absorption and solvation to the overall effect of accelerated gas absorption. The intensifying influence of surfactants on the process of oxygen absorption, manifested in an immobile fluid and at slow solution agitation rates, is eliminated by the oppositely directed changes in the mass transfer and solubility of oxygen at the phase boundary in the transition and turbulent flow modes.

Atomic Force Microscopy and X-Ray Photoelectron Spectroscopy Study on the Surface and Interface States of Liq and ITO Films

An understanding of the surface and interface states of the organic material and the underlying andoe material is meaningful for organic light-emitting devices (OLEDs). The 8-Hydroxyquinolinolatolithium (Liq) was deposited on indium-tin-oxide (ITO) coated glass by traditional vacuum evaporation.The thickness of Liq is about 120nm. The morphology, surface and interface electron states of the Liq and the underlying ITO have been investigated with the utilization of the atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) technology. AFM observation indicated that Liq grows in the shape of an asymmetrically-distributed island, with each island resembling a round hillock and different size. The Liq film is not very uniform and teemed with many pinholes and cracks.The analysis on XPS spectra of the surface of the Liq/ITO samples shows that, the core-levels of Li1s, C1s, N1s, O1s, In3d5/2, and Sn3d5/2, spectra slightly shift towards lower binding energy with the increase of the sputtering time, which may be caused by the effect of oxygen, indium and tin in ITO diffusing into Liq layer and the argon ions beam with energy. Coordination bond between Li atoms and N atoms does not exist in Liq, which is the main reason why Liq is the blue electroluminescent material. The C atoms mainly bond to C, N and O atoms, forming C-C, C-N=C and C-O bonds, respectively. And there is a speculation of the existence of contaminated C atoms in the surface of ITO, while the O atoms basically originate from quinolate rings and the absorption of O2 and H2O. At the interface N and O, In and Sn interact to some extent, which probably affects the emitting colour of Liq based OLEDs. The analysis of surface of In3d and Sn3d spectrum by XPS provides additional evidence of the existence of cracks and pinholes in Liq layer, leading to much absorption of air molecules.

Remote sounding of atmospheric pressure profile from space, part 1: principle

The molecular oxygen absorption band near 0.762 µm can be used for remote sounding of atmospheric pressure profiles. Atmospheric O2 absorption, atmospheric molecular multi-scattering, extinction of atmospheric aerosols, bi-reflection at the earth surface, the atmospheric refractive effect and the global curvature are taken into account to establish an atmospheric radiation transfer equation. By means of an accurate O2 atmospheric transmittance model and a mean atmospheric transmittance model the remote sounding equation of surface pressure from space suitable to clear sky field of view is derived. At last, a pure physical retrieval method is given and the atmospheric pressure profile can be deduced.

MAX-DOAS measurements in southern China: retrieval of aerosol extinctions and validation using ground-based in-situ data

Abstract. We performed MAX-DOAS measurements during the PRiDe-PRD2006 campaign in the Pearl River Delta region 50 km north of Guangzhou, China, for 4 weeks in June 2006. We used an instrument sampling at 7 different elevation angles between 3° and 90°. During 9 cloud-free days, differential slant column densities (DSCDs) of O4 (O2 dimer) absorptions between 351 nm and 389 nm were evaluated for 6 elevation angles. Here, we show that radiative transfer modeling of the DSCDS can be used to retrieve the aerosol extinction and the height of the boundary layer. A comparison of the aerosol extinction with simultaneously recorded, ground based nephelometer data shows excellent agreement.

An experimental study on the relation between lung volume and pulmonary blood flow

The purpose of this study was to elucidate whether or not the reduction of lung volume is related to the mechanism of blood flow reduction in the atelectatic lung. In adult mongrel dogs, whose main stem bronchus in the thoracotomized lung was obstructed, the change of blood flow in the lung containing N2 was compared with that in the collapsed lung. 1) Under a low partial pressure of O2 in the broncho-alveolar system by obstruction of the main stem bronchus, the blood flow did not change, even when the N2 volume in the lung was varied. Therefore, the change of blood flow in the collapsed lung is not attributable to the reduction of lung volume. 2) The lung blood flow increased when the partial pressure of O2 in the broncho-alveolar system was elevated by infusion of O2 into the collapsed lung, and it decreased with the subsequent O2 absorption leading to lung collapse. Therefore, the change of lung blood flow is due to the change of intraalveolar partial pressure of O2. 3) The reduction of blood flow in the atelectatic lung is caused by hypoxic pulmonary vasoconstriction, and is not influenced by the reduction of lung volume due to the lung collapse.

LP-DOAS测量乙二醛时大气中干扰吸收的去除

When measuring glyoxal directly in the atmosphere by Long Path Differential Optical Absorption Spectroscopy(LP-DOAS),the analysis of glyoxal strongly suffers from the cross interference of other absorbers or structure(Xe lamp-structure,H2O,O4 and NO2 absorption).The retrieval method of glyoxal-the elimination of interfering absorption or structure was studied.The Xe lamp-structure will change nonlinearly resulted from the change of pressure broadening and Doppler Broadening with the change of of Xe lamp pressure or temperature.The different lamp reference spectra detected at different time were interpolated to eliminate lamp structure and the resulting residual structures caused by an incorrect elimination were a factor of three below the detection limit of glyoxal;high amount of H2O in the atmosphere cause the nonlinear absorption of H2O and the observed band shape to vary with the column density of H2O.Two H2O absorption spectra with higher and lower column density were interpolated to eliminate nonlinear H2O absorption and the resulting residual structures caused by an incorrect elimination were ten times below the detection limit of glyoxal.In addition,the strong absorption of interfering species NO2 and O4 were also accurately removed.Low detection limit(0.15 ppbv)and low systematic errors(~10 %)were achieved by the accurate elimination of interfering structures.In the end,glyoxal was routinely detected during the daytime on the outskirts of Guangzhou,where mixing ratios ranged from less than detection limit(0.15 ppbv)to 1.66 ppbv.The variation and range of glyoxal concentration detected agreed well with the results reported.

O2 density and temperature profiles retrieving from direct solar Lyman-alpha radiation measurements

The resonance transition 2P-2S of the atomic hydrogen (Lyman-alpha emission) is the strongest and most conspicuous feature in the solar EUV spectrum. The Lyman-alpha radiation transfer depends on the resonance scattering from the hydrogen atoms in the atmosphere and on the O2 absorption. Since the Lyman-alpha extinction in the atmosphere is a measure for the column density of the oxygen molecules, the atmospheric O2 density and temperature profiles can be calculated thereof. A detector of solar Lyman-alpha radiation was manufactured in the Stara Zagora Department of the Solar-Terrestrial Influences Laboratory (STIL). Its basic part is an ionization camera, filled in with NO. A 60 V power supply is applied to the chamber. The produced photoelectric current from the sensor is fed to a two-channel amplifier, providing analog signal. The characteristics of the Lyman-alpha detector were studied. It passed successfully all tests and the results showed that the so-designed instrument could be used in rocket experiments to measure the Lymanalpha flux. From the measurements of the detector, the Lyman-alpha vertical profile can be obtained. Programs are created to compute the O2 density, atmospheric power and temperature profiles based on Lymanalpha data. The detector design appertained to ASLAF project (Attenuation of the Solar Lyman-Alpha Flux), a scientific cooperation between STIL—Bul.Acad.Sci., Stara Zagora Department and the Atmospheric Physics Group at the Department of Meteorology (MISU), Stockholm University, Sweden. The joint project was part of the rocket experiment HotPay I, in the ALOMAR eARI Project, EU’s 6th Framework Programme, Andøya Rocket Range, Andenes, Norway. The project is partly financed by the Bulgarian Ministry of Science and Education.

Plateau and Transpulmonary Pressure With Elevated Intra-Abdominal Pressure or Atelectasis

ARDSnet standards limit plateau pressure (Pplat) to reduce ventilator induced lung injury (VILI). Transpulmonary pressure (Ptp) [Pplat-pleural pressure (Ppl)], not Pplat, is the distending pressure of the lung. Lung distention can be affected by increased intra-abdominal pressure (IAP) and atelectasis. We hypothesized that the changes in distention caused by increases in IAP and atelectasis would be reflected by Ptp but independent of Pplat. In Yorkshire pigs, esophageal pressure (Pes) was measured with a balloon catheter as a surrogate for Ppl under two experimental conditions: (1) high IAP group (n=5), where IAP was elevated by CO2 insufflation in 5 mm Hg steps from 0 to 30 mm Hg; and (2) Atelectasis group (n=5), where a double lumen endotracheal tube allowed clamping and degassing of either lung by O2 absorption. Lung collapse was estimated by increases in pulmonary shunt fraction. High IAP: Sequential increments in IAP caused a linear increase in Pplat (r2=0.754, P<0.0001). Ptp did not increase (r2=0.014, P=0.404) with IAP due to the concomitant increase in Pes (r2=0.726, P<0.0001). Partial Lung Collapse: There was no significant difference in Pplat between the atelectatic (21.83+/-0.63 cm H2O) and inflated lung (22.06+/-0.61 cmH2O, P<0.05). Partial lung collapse caused a significant decrease in Pes (11.32+/-1.11 mm Hg) compared with inflation (15.89+/-0.72 mm Hg, P<0.05) resulting in a significant increase in Ptp (inflated=5.97+/-0.72 mm Hg; collapsed=10.55+/-1.53 mm Hg, P<0.05). Use of Pplat to set ventilation may under-ventilate patients with intra-abdominal hypertension and over-distend the lungs of patients with atelectasis. Thus, Ptp must be used to accurately set mechanical ventilation in the critically ill.

Determination of aerosol properties from MAX-DOAS observations of the Ring effect

Abstract. The first quantitative comparison of MAX-DOAS observations of the Ring effect with model simulations is presented. It is performed for a large variety of viewing geometries (solar zenith angles: 45° to 90°, elevation angles: 3°, 6°, 10°, 18°, 90°; three different azimuth angles), which allows a comprehensive test of our capabilities to measure and simulate the Ring effect. In addition to the Ring effect, also the observed O4 absorptions (optical densities) and radiances are compared with model simulations. In general good agreement is found for all measured quantities. From several sensitivity studies it is found that for most measurement situations, the aerosol optical depth has usually the strongest influence on the observed quantities, but also other aerosol properties like e.g. the vertical distribution have a significant effect. In some aspects, the qualitative dependence of the Ring effect on aerosol properties is similar to that of the O4 absorption. This can be understood, since both quantities depend strongly on the light path length in the lower atmosphere. However, since the Ring effect depends also on the properties of the scattering processes, in specific cases observation of the Ring effect can provide complementary information to that retrieved from the O4 observations. This is e.g. possible for measurements at small relative azimuth angles, from which information on the aerosol phase function can be derived. Observations at large solar zenith angle might allow the retrieval of stratospheric aerosol properties, even in cases with very low aerosol optical depths. In addition, Ring effect observations in zenith direction are rather sensitive to the aerosol optical depth (in contrast to O4 observations), which might allow to retrieve information on aerosol properties from existing zenith UV data sets prior to the MAX-DOAS era.

A Multiwavelength Differential Imaging Experiment for the High Contrast Imaging Testbed

ABSTRACTWe discuss the results of a multiwavelength differential imaging lab experiment with the High Contrast Imaging Testbed (HCIT) at the Jet Propulsion Laboratory. The HCIT combines a Lyot coronagraph with a Xinetics deformable mirror in a vacuum environment to simulate a space telescope in order to test technologies and algorithms for a future exoplanet coronagraph mission. At present, ground-based telescopes have achieved significant attenuation of speckle noise using the technique of spectral differential imaging (SDI). We test whether ground-based SDI can be generalized to a nonsimultaneous spectral differential imaging technique (NSDI) for a space mission. In our lab experiment, a series of five filter images centered around the O2(A) absorption feature at 0.762 μm were acquired at nominal contrast values of 10-6, 10-7, 10-8, and 10-9. Outside the dark hole, single differences of images improve contrast by a factor of ∼6. Inside the dark hole, we found significant speckle chromatism as a function of wavelength offset from the nulling wavelength, leading to a contrast degradation by a factor of 7.2 across the entire ∼80 nm bandwidth. This effect likely stems from the chromatic behavior of the current occulter. New, less chromatic occulters are currently in development; we expect that these new occulters will resolve the speckle chromatism issue.

Six years of total ozone column measurements from SCIAMACHY nadir observations

Abstract. Total O3 columns have been retrieved from six years of SCIAMACHY nadir UV radiance measurements using SDOAS, an adaptation of the GDOAS algorithm previously developed at BIRA-IASB for the GOME instrument. GDOAS and SDOAS have been implemented by the German Aerospace Center (DLR) in the version 4 of the GOME Data Processor (GDP) and in version 3 of the SCIAMACHY Ground Processor (SGP), respectively. The processors are being run at the DLR processing centre on behalf of the European Space Agency (ESA). We first focus on the description of the SDOAS algorithm with particular attention to the impact of uncertainties on the reference O3 absorption cross-sections. Second, the resulting SCIAMACHY total ozone data set is globally evaluated through large-scale comparisons with results from GOME and OMI as well as with ground-based correlative measurements. The various total ozone data sets are found to agree within 2% on average. However, a negative trend of 0.2–0.4%/year has been identified in the SCIAMACHY O3 columns; this probably originates from instrumental degradation effects that have not yet been fully characterized.