CO2 Absorption Band Research Articles

The Near-infrared CO Absorption Band as a Probe to the Innermost Part of an AGN-obscuring Material

Abstract We performed a systematic analysis of the 4.67 μm CO ro-vibrational absorption band toward nearby active galactic nuclei (AGNs) and analyzed the absorption profiles of 10 nearby galaxies collected from the AKARI and Spitzer spectroscopic observations that show the CO absorption feature by fitting a plane-parallel local thermal equilibrium gas model. We found that CO gas is warm (200–500 K) and has a large column density ( ). The heating of the gas is not explicable by either UV heating or shock heating because these processes cannot represent the large column densities of the warm gas. Instead, X-ray photons from the nuclei, which can produce large columns of warm gas with up to , are the most convincing power source. The hydrogen column density estimated from the CO band is smaller than that inferred from X-ray observations. These results indicate that the region probed by the near-infrared CO absorption is in the vicinity of the nuclei and is located outside the X-ray emitting region. Furthermore, the covering factors of nearly unity required by the observed deep absorption profiles suggest that the probed region is close to the continuum source, which can be designated as the inner rim of the obscuring material around the AGN.

Potential of Spaceborne Lidar Measurements of Carbon Dioxide and Methane Emissions from Strong Point Sources

Emissions from strong point sources, primarily large power plants, are a major portion of the total CO2 emissions. International climate agreements will increasingly require their independent monitoring. A satellite-based, double-pulse, direct detection Integrated Path Differential Absorption (IPDA) Lidar with the capability to actively target point sources has the potential to usefully complement the current and future GHG observing system. This initial study uses simple approaches to determine the required Lidar characteristics and the expected skill of spaceborne Lidar plume detection and emission quantification. A Gaussian plume model simulates the CO2 or CH4 distribution downstream of the sources. A Lidar simulator provides the instrument characteristics and dimensions required to retrieve the emission rates, assuming an ideal detector configuration. The Lidar sampling frequency, the footprint distance to the emitting source and the error of an individual measurement are of great importance. If wind speed and direction are known and environmental conditions are ideal, an IPDA Lidar on a 500-km orbit with 2 W average power in the 1.6 µm CO2 absorption band, 500 Hz pulse repetition frequency, 50 m footprint at sea level and 0.7 m telescope diameter can be expected to measure CO2 emission rates of 20 Mt/a with an average accuracy better than 3% up to a distance of 3 km away from the source. CH4 point source emission rates can be quantified with comparable skill if they are larger than 10 kt/a, or if the Lidar pulse repetition frequency is augmented.

Bias assessment of lower and middle tropospheric CO<sub>2</sub> concentrations of GOSAT/TANSO-FTS TIR version 1 product

Abstract. CO2 observations in the free troposphere can be useful for constraining CO2 source and sink estimates at the surface since they represent CO2 concentrations away from point source emissions. The thermal infrared (TIR) band of the Thermal and Near Infrared Sensor for Carbon Observation (TANSO) Fourier transform spectrometer (FTS) on board the Greenhouse Gases Observing Satellite (GOSAT) has been observing global CO2 concentrations in the free troposphere for about 8 years and thus could provide a dataset with which to evaluate the vertical transport of CO2 from the surface to the upper atmosphere. This study evaluated biases in the TIR version 1 (V1) CO2 product in the lower troposphere (LT) and the middle troposphere (MT) (736–287 hPa), on the basis of comparisons with CO2 profiles obtained over airports using Continuous CO2 Measuring Equipment (CME) in the Comprehensive Observation Network for Trace gases by AIrLiner (CONTRAIL) project. Bias-correction values are presented for TIR CO2 data for each pressure layer in the LT and MT regions during each season and in each latitude band: 40–20° S, 20° S–20° N, 20–40° N, and 40–60° N. TIR V1 CO2 data had consistent negative biases of 1–1.5 % compared with CME CO2 data in the LT and MT regions, with the largest negative biases at 541–398 hPa, partly due to the use of 10 µm CO2 absorption band in conjunction with 15 and 9 µm absorption bands in the V1 retrieval algorithm. Global comparisons between TIR CO2 data to which the bias-correction values were applied and CO2 data simulated by a transport model based on the Nonhydrostatic ICosahedral Atmospheric Model (NICAM-TM) confirmed the validity of the bias-correction values evaluated over airports in limited areas. In low latitudes in the upper MT region (398–287 hPa), however, TIR CO2 data in northern summer were overcorrected by these bias-correction values; this is because the bias-correction values were determined using comparisons mainly over airports in Southeast Asia, where CO2 concentrations in the upper atmosphere display relatively large variations due to strong updrafts.

Temperature dependence of collisional induced absorption (CIA) bands of CO2 with implications for Venus’ atmosphere

The intensity and temperature dependence of four CO2 collision induced absorption (CIA) bands in two spectral regions, 1100–1600 cm−1 and 2500–3200 cm−1 have been investigated. The measurements have been performed with a Fourier Transform InfraRed (FT-IR) spectrometer operating in a wide spectral range, from 350 to 25000 cm−1 (0.4 to 28.5 µm) with a spectral resolution of 2 cm−1, interfaced with a high pressure-high temperature (HP-HT) absorption cell with an optical path of about 2 cm. While the integrated band intensity of allowed bands shows a linear dependence versus density, the collision-induced integrated band intensity increases quadratically with the density, due to the absorption by pairs of molecules, which allows identifying the CIA bands unambiguously. While below 300 K the binary integrated absorption coefficients exhibit a pronounced temperature dependence due to the presence of dimers, a much weaker temperature dependence has been found above 300 K. The results are important for the radiative transfer calculations of Venus’ atmosphere. The integrated band intensities of the studied bands have been calculated for Venus’ atmosphere from 40 km down to the surface by extrapolating the binary integrated absorption coefficients to the relevant temperatures.

Sensitive and broadband measurement of dispersion in a cavity using a Fourier transform spectrometer with kHz resolution.

Optical cavities provide high sensitivity to dispersion since their resonance frequencies depend on the index of refraction. We present a direct, broadband, and accurate measurement of the modes of a high finesse cavity using an optical frequency comb and a mechanical Fourier transform spectrometer with a kHz-level resolution. We characterize 16000 longitudinal cavity modes spanning 16 THz of bandwidth in terms of center frequency, linewidth, and amplitude. Using the center frequencies we retrieve the group delay dispersion of the cavity mirror coatings and pure N2 with 0.1 fs2 precision and 1 fs2 accuracy, as well as the refractivity of the 3ν1 + ν3 absorption band of CO2 with 5 × 10-12 precision. This opens up for broadband refractive index metrology and calibration-free spectroscopy of entire molecular bands.

Open-path dual comb spectroscopy to an airborne retroreflector.

We demonstrate a new technique for spatial mapping of multiple atmospheric gas species. This system is based on high-precision dual-comb spectroscopy to a retroreflector mounted on a flying multi-copter. We measure the atmospheric absorption over long open-air paths to the multi-copter with comb-tooth resolution over 1.57 to 1.66 pm, covering absorption bands of CO2, Cm, H2O and isotopologues. When combined with GPS-based path length measurements, a fit of the absorption spectra retrieves the dry mixing ratios versus position. Under well-mixed atmospheric conditions, retrievals from both horizontal and vertical paths show stable mixing ratios as expected. This approach can support future boundary layer studies as well as plume detection and source location.

ATR-FTIR study of the interaction of CO2 with bacterial cellulose-based membranes

Bacterial cellulose (BC) was used as an active material for fabrication of the membrane for CO2 capture. The BC-membrane is further modified with silk fibroin protein and ZnO nanoparticles in order to increase the number of sites that may bind CO2. The interaction of the CO2 with the membranes was investigated by means of ATR-FTIR spectroscopy. The argon purged membranes were used as the control samples. After pressurizing the membranes in CO2 at 3bar, FTIR spectra were recorded and compared to the spectra of the controls. The interaction of the membrane materials with CO2 were studied by examining two regions of the spectra: 740–610cm−1 (bending vibrations of CO2) and 2400–2320cm−1 (asymmetric stretching vibrations of CO2). The envelope of the bending mode peak in 740–610cm−1 region is resolved into particular peaks and the appearance of the additional line at 654cm−1 suggested that the absorption bands of CO2 alters because of the Lewis acid-base type of interaction with membranes. The changes in the region of asymmetric stretching vibrations of CO2 were even more pronounced after pressurization. The presence of the number of different sites (active groups) for the CO2 adsorption reflected in the appearance of several additional asymmetric stretching peaks. Also, due to the entrapment of the CO2 in the membrane, a typical CO asymmetric stretching vibration line at ∼2340cm−1 is shifted towards lower frequencies. The analysis of the results suggested that there is a strong interaction of CO2 with BC membrane, which is additionally improved by its modification with silk fibroin and ZnO nanoparticles. From the results of CO2 permeation experiment, the basic BC membrane, silk fibroin-modified BC membrane and ZnO nanoparticles-modified BC membrane exhibited the CO2 permeability of 2.73, 2.69 and 2.66 Barrer, respectively.

Night side distribution of SO2 content in Venus’ upper mesosphere

In this paper we present the first night side distribution of SO2 content in Venus’ upper mesosphere (altitudes from 85 to 105km). The dataset is based on the SPICAV UV stellar occultation experiment which took place onboard ESA's Venus Express (VEX) orbiter in 2006–2014. The UV channel of SPICAV spectrometer detected absorption bands of SO2 and CO2 in the spectral range 180–300nm with a resolution of 1–2nm while stellar light was occulted by the mesosphere. Altitude profiles of sulfur dioxide's volume mixing ratio (VMR) could be retrieved in the upper part of the mesosphere covering the whole night side on Venus. In parallel, we have reprocessed the terminator UV solar occultations dataset (Belyaev et al., 2012. Icarus 217, 740–751) in the same altitude range and extended its statistics until 2014. On average the SO2 VMR increases with altitude from 10–30 ppb at 85km to 100–300 ppb at 100km in both regimes of occultation. The midnight SO2 abundance appears to be 3–4 times higher than in the terminator region: 150–200ppbv versus 50pppv at altitude around 95km. These new results were compared with the distribution of oxygen atoms, which are tracers of the global subsolar-antisolar (SS-AS) circulation at ∼100km (the data provided by Soret et al., 2012 Icarus, 217, 849–855). The night time behavior looks similar for SO2 molecules and O atoms with a correlation coefficient Rcorr= 0.73. Moreover, the retrieved SO2 enrichment above 85km appears to correlate with the density of H2SO4 droplets (Luginin et al., 2016; Icarus 277, 154–170).

The 2 µm spectrum of the auroral emission in the polar regions of Jupiter

We report observations of the high (R ∼ 18000) and medium (R ∼ 5900) resolution, near-infrared spectra of Jupiter’s polar regions with the GNIRS instrument at the Gemini North telescope. The observations correspond to the area of main auroral oval in the South and the main spot of the Io footprint in the North. We detected and assigned 18 emission lines of the H3+, 2ν2 → 0 overtone band in the region from 4800 to 4980 cm−1 and 5 additional lines in the extended low-resolution spectrum. We use our new modelling scheme, ATMOF to remove telluric absorption bands of CO2 that feature strongly in the 2 µm region. The H2 1-0 S(1), S(2) and S(3) emission lines are also detected in the observed spectral region. We found the rotational temperature and column density of H3+ emission at the peak intensity for both northern and southern auroral regions to be the same within the measurement errors (Trot ∼ 950K and N(H3+) ∼ 4.5× 1016 m−2). The estimates of Trot from H2 are consistent within much higher uncertainties with temperatures derived from H3+ emissions. We derived the profiles of the H3+ emissivity and ion density for both auroral regions providing the first such measurement for the emission associated with the main spot of the Io footprint. We also found a number of weaker lines in the high-resolution spectra that could be associated with emission from high excitation levels in neutral iron, which could be deposited in Jupiter’s atmosphere as a result of meteor ablation.

Spatial distribution of atmospheric CO2 absorption detected around 2 µm on the reflectance spectra derived from Hyperion images

ABSTRACTThis study explores the detectability of atmospheric carbon dioxide (CO2) absorption at the short wave infrared bands of Hyperion EO-1 hyperspectral images. Two CO2 absorption bands at around 2.002–2.012 and 2.052 µm, respectively, were identified on the reflectance spectra derived from the images. Considering the principle of differential optical absorption spectroscopy (DOAS) and assuming the O2-A band around 0.762 µm as reference, the spatial variation of the column density was estimated for Kolkata, a region around 22° 31′ N 88° 21′ E. The ratio of the individual absorption depth of CO2 to that of O2, instead of the ratio of their column density, was found to be more suitable to express the spatial distribution of CO2 concentration over short distance, of the order of metres. The methodology was validated with Orbiting Carbon Observatory-2 (OCO-2) data. The work suggests the inclusion of 2–3 narrowband channels corresponding to O2-A and CO2 absorptions in future moderate resolution multispectral sensors in order to facilitate the monitoring of atmospheric CO2.

Vibrational spectroscopy and dynamics of W(CO)6 in solid methane as a probe of lattice properties.

Methane solids present more than one accessible crystalline phase at low temperature at zero pressure. We trap W(CO)6 in CH4 and CD4 matrices between 8 and 35 K to probe the interaction between an impurity and its surrounding molecular solid under various physical conditions. Linear and nonlinear vibrational spectroscopies of W(CO)6 highlight different kinds of interaction and reveal new and remarkable signatures of the phase transition of methane. The structures in the absorption band of the antisymmetric CO stretching mode exhibit a clear modification at the transition between phase II and phase I in CH4 and motional narrowing is observed upon temperature increase. The vibrational dynamics of this mode is probed in stimulated photon echo experiments performed with a femtosecond IR laser. A short component around 10 ps is detected in the population relaxation lifetime in the high temperature phase of solid CH4 (phase I) and disappears at lower temperatures (phase II) where the vibrational lifetime is in the hundreds of ps. The analysis of the nonlinear time-resolved results suggests that the short component comes from a fast energy transfer between the vibrational excitation of the guest and the lattice in specific families of sites. Such fast transfers are observed in the case of W(CO)6 trapped in CD4 because of an energy overlap of the excitation of W(CO)6 and a lattice vibron. In solid CH4, even when these V-V transfers are not efficient, pure dephasing processes due to the molecular nature of the host occur: they are temperature dependent without a clear modification at the phase transition.

IR emitting Dy3+ doped chalcogenide fibers for in situ CO2 monitoring in high pressure microsystems

This paper reports the carbon dioxide detection in silicon-Pyrex high pressure microfluidic devices mimicking geological conditions encountered in deep saline aquifers using an in situ infrared optical sensor. The middle infrared source inserted inside the microchannel is based on infrared emission from Dy3+ sulfide glass fibers. The broad emission of the Dy3+ doping in infrared fibers is used to directly probe the CO2 thanks to the perfect overlap between the rare earth emission centered at 4.4μm and the CO2 absorption band located at 4.3μm. CO2 and water were clearly distinguished when using segmented flow on chip at pressures ranging from 4.5 to 6MPa. These results demonstrate the feasibility of the infrared optical detection of other gases displaying absorption bands in the middle infrared domain for further developments of gas sensors, which can find applications in geological media monitoring and microfluidics.

Liver Status Assessment by Spectrally and Time Resolved IR Detection of Drug Induced Breath Gas Changes

The actual metabolic capacity of the liver is crucial for disease identification, liver therapy, and liver tumor resection. By combining induced drug metabolism and high sensitivity IR spectroscopy of exhaled air, we provide a method for quantitative liver assessment at bedside within 20 to 60 min. Fast administration of 13C-labelled methacetin induces a fast response of liver metabolism and is tracked in real-time by the increase of 13CO2 in exhaled air. The 13CO2 concentration increase in exhaled air allows the determination of the metabolic liver capacity (LiMAx-test). Fluctuations in CO2 concentration, pressure and temperature are minimized by special gas handling, and tracking of several spectrally resolved CO2 absorption bands with a quantum cascade laser. Absorption measurement of different 12CO2 and 13CO2 rotation-vibration transitions in the same time window allows for multiple referencing and reduction of systematic errors. This FLIP (Fast liver investigation package) setup is being successfully used to plan operations and determine the liver status of patients.

Weakening the C[sbnd]C bond: On the behavior of glyoxylic acid on Pt(111) and its vicinal surfaces

Adsorption and oxidation of glyoxylic acid (GA) on platinum single crystals were investigated by spectroelectrochemical techniques. Among basal planes, Pt(111) is taken as a model surface for reactivity studies in order to point out the CC bond breaking. For a standard GA concentration (0.1M), self-poisoning by adsorbed CO (COads) is the main process dominating the positive-going sweep. The presence of (110) steps on (111) terraces contribute in the CC bond cleavage, leading to CO formation, while (100) steps do not show a significant effect. Poison stripping allows GA oxidation in a lower potential range in the negative-going sweep. By working with different GA concentrations (10−5–0.1M), surface blockage is hindered, pointing out an alternative reaction pathway, where GA is oxidized in a poison-free surface. Fourier transform infrared spectroscopy (FTIR) experiments allowed the identification of CO2, formic (FA) and oxalic acid (OA) as main products of GA oxidation. We highlight an activity peak at 0.01M GA, concomitant to the presence of CO2 absorption bands at lower potentials (0.2V). The formation of CO2 at potentials where CO cannot be oxidized suggests a change in the preferential reaction pathway, where GA is completely oxidized through an active intermediate distinct to COads.

Lidar reflectance from snow at 2.05 μm wavelength as measured by the JPL Airborne Laser Absorption Spectrometer.

We report airborne measurements of lidar directional reflectance (backscatter) from land surfaces at a wavelength in the 2.05 μm CO₂ absorption band, with emphasis on snow-covered surfaces in various natural environments. Lidar backscatter measurements using this instrument provide insight into the capabilities of lidar for both airborne and future global-scale CO₂ measurements from low Earth orbit pertinent to the NASA Active Sensing of CO₂ Emissions over Nights, Days, and Seasons mission. Lidar measurement capability is particularly useful when the use of solar scattering spectroscopy is not feasible for high-accuracy atmospheric CO₂ measurements. Consequently, performance in high-latitude and winter season environments is an emphasis. Snow-covered surfaces are known to be dark in the CO₂ band spectral regions. The quantitative backscatter data from these field measurements help to elucidate the range of backscatter values that can be expected in natural environments.

Measurements of Atmospheric CO2Column in Cloudy Weather Conditions using An IM-CW Lidar at 1.57 Micron

This study evaluates the capability of atmospheric CO2 column measurements under cloudy conditions using an airborne intensity-modulated continuous-wave integrated-path-differential-absorption lidar operating in the 1.57-m CO2 absorption band. The atmospheric CO2 column amounts from the aircraft to the tops of optically thick cumulus clouds and to the surface in the presence of optically thin clouds are retrieved from lidar data obtained during the summer 2011 and spring 2013 flight campaigns, respectively.

Supported Sulfated Zirconia Catalysts for Isomerization of n-hexane

Sulfated zirconia catalysts supported on SiO2 and Al2O3 were prepared and studied. Phase composition of the catalysts, acidic properties in CO adsorption, and textural characteristics were assessed. Activity of the catalysts in isomerization of n-hexane was measured. Alumina was shown to be a promising support for the synthesis of such catalysts. A new step of additional sulfation after platinum deposition was proposed for the synthesis of alumina-supported catalysts. It was found that strong Lewis acid sites with CO absorption bands at 2210 and 2224 cm-1 are formed in the catalysts. The yield of the sum of hexane isomers for the alumina-supported catalysts reached 80wt.%.

Spectroscopic constraints on CH3OH formation: CO mixed with CH3OH ices towards young stellar objects.

The prominent infrared absorption band of solid CO - commonly observed towards young stellar objects (YSOs) - consists of three empirically determined components. The broad 'red component' (2136 cm-1, 4.681 μm) is generally attributed to solid CO mixed in a hydrogen-bonded environment. Usually, CO embedded in the abundantly present water is considered. However, CO:H2O mixtures cannot reproduce the width and position of the observed red component without producing a shoulder at 2152 cm-1, which is not observed in astronomical spectra. Cuppen et al. showed that CO:CH3OH mixtures do not suffer from this problem. Here, this proposition is expanded by comparing literature laboratory spectra of different CO-containing ice mixtures to high-resolution (R = λ/Δλ = 25000) spectra of the massive YSO AFGL 7009S and of the low-mass YSOL1489 IRS. The previously unpublished spectrum of AFGL 7009S shows a wide band of solid 13CO, the first detection of 13CO ice in the polar phase. In this source, both the 12CO and 13CO ice bands are well fitted with CO:CH3OH mixtures, while respecting the profiles and depths of the methanol bands at other wavelengths, whereas mixtures with H2O cannot. The presence of a gradient in the CO:CH3OH mixing ratio in the grain mantles is also suggested. Towards L1489 IRS, the profile of the 12CO band is also better fitted with CH3OH-containing ices, although the CH3OH abundance needed is a factor of 2.4 above previous measurements. Overall, however, the results are reasonably consistent with models and experiments about formation of CH3OH by the hydrogenation of CO ices.

Fast spatially resolved exhaust gas recirculation (EGR) distribution measurements in an internal combustion engine using absorption spectroscopy.

Exhaust gas recirculation (EGR) in internal combustion engines is an effective method of reducing NOx emissions while improving efficiency. However, insufficient mixing between fresh air and exhaust gas can lead to cycle-to-cycle and cylinder-to-cylinder non-uniform charge gas mixtures of a multi-cylinder engine, which can in turn reduce engine performance and efficiency. A sensor packaged into a compact probe was designed, built and applied to measure spatiotemporal EGR distributions in the intake manifold of an operating engine. The probe promotes the development of more efficient and higher-performance engines by resolving high-speed in situ CO2 concentration at various locations in the intake manifold. The study employed mid-infrared light sources tuned to an absorption band of CO2 near 4.3 μm, an industry standard species for determining EGR fraction. The calibrated probe was used to map spatial EGR distributions in an intake manifold with high accuracy and monitor cycle-resolved cylinder-specific EGR fluctuations at a rate of up to 1 kHz.

Highly efficient tunable mid-infrared optical parametric oscillator pumped by a wavelength locked, Q-switched Er:YAG laser.

A highly efficient and stable mid-infrared optical parametric oscillator is demonstrated, pumped by an electro-optic Q-switched Er:YAG laser with operating wavelength locked at 1645 nm by a volume Bragg grating. The oscillator, based on MgO-doped periodically poled lithium niobate (MgO:PPLN) crystal, yields a maximum overall average output power in excess of 1 W, corresponding to a conversion efficiency of 35.5% and a slope efficiency of 43.6%. The signal and idler wavelengths of the OPO are around ~2.7 μm and ~4.3 μm, respectively, corresponding to the two peak absorption bands of CO(2). Lasing characteristics of the oscillator, including the time evolution of the pump, signal and idler pulses at different pump power levels, are also investigated. Temperature tuning of the MgO:PPLN crystal gives signal and idler ranges of 2.67 to 2.72 μm and 4.17 to 4.31 μm, respectively.