Absorption Cross Sections Of CO2 Research Articles

Measurement of absorption cross sections of Co2+:MgAl2O4 crystals with transition of Co2+ ions along two orthogonal directions.

The nonlinear transmission curves of the Co2+:MgAl2O4 crystal at 1.5 µm are experimentally measured by the pump-probe technique. The measurement results demonstrate that the transition into the near-infrared absorption band is polarized not only along the C3 local symmetry axis, but also along the direction perpendicular to the C3 axis, arising from the distortion of oxygen tetrahedrons about the Co2+ ions along the four C3 local symmetry axes. The obtained saturation curves are analyzed using a theoretical model taking into account the transition of Co2+ ions along two orthogonal directions. The ground-state absorption cross sections for polarization parallel and perpendicular to the C3 axis are calculated to be 3.4×10-19cm2 and 2.6×10-20cm2, respectively. The excited-state absorption cross section for polarization parallel to the C3 axis is estimated to be4.2×10-20cm2.

Relationship Between the Ozone and Water Vapor Columns on Mars as Observed by SPICAM and Calculated by a Global Climate Model

AbstractOzone (O3) in the atmosphere of Mars is produced following the photolysis of CO2 and is readily destroyed by the hydrogen radicals (HOx) released by the photolysis and oxidation of water vapor. As a result, an anti‐correlation between ozone and water vapor is expected. We describe here the O3‐H2O relationship derived from 4 Martian years of simultaneous observations by the SPICAM spectrometer onboard the Mars Express spacecraft. A distinct anti‐correlation is found at high latitudes, where the O3 column varies roughly with the −0.6 power of the H2O column. The O3 and H2O columns are uncorrelated at low latitudes. To evaluate our quantitative understanding of the Martian photochemistry, the observed O3‐H2O relationship is then compared to that predicted by a global climate model with photochemistry. For identical model and observed abundances of H2O, the model underpredicts observed ozone by about a factor of 2 relative to SPICAM when using the currently recommended gas‐phase chemistry. Sensitivity studies employing low‐temperature CO2 absorption cross sections, or adjusted kinetics rates, do not solve this bias. Taking into account potential heterogeneous processes of HOx loss on clouds leads to a significant improvement, but only at high northern latitudes. More broadly, the modeled ozone deficits suggest that the HOx‐catalyzed photochemistry is too efficient in our simulations. This problem is consistent with the long‐standing underestimation of CO in Mars photochemical models, and may be related to similar difficulties in modeling O3 and HOx in the Earth's upper stratosphere and mesosphere.

Temporally resolved two dimensional temperature field of acoustically excited swirling flames measured by mid-infrared direct absorption spectroscopy.

The detailed understandings of temperature profiles and flow-flame interaction in unsteady premixed swirling flames are crucial for the development of low emission turbine engines. Here, a phase-locked tomographic reconstruction technique measuring the large absorption cross section of CO2 at its mid-infrared fundamental band around 4.2 μm is used to acquire the flame temperature and in situ CO2 volume fraction distribution in a turbulent premixed swirling flame under different levels of external acoustic forcing amplitude. The temporally resolved temperature field variation reveals large temperature fluctuation in unsteady premixed swirling flames produced near the nozzle exit due to vortex-driven mixing of surrounding cold gas. The temperature fluctuation quickly dissipates when moving downstream of the flame with the flow velocity of the burnt gas. The accurate high temporal resolution thermodynamic measurements of the phase-locked tomographic thermometry technique reported in this work can be generally applied to periodic reacting flows.

VUV-absorption cross section of carbon dioxide from 150 to 800 K and applications to warm exoplanetary atmospheres

Context. Most exoplanets detected so far have atmospheric temperatures significantly higher than 300 K. Often close to their star, they receive an intense UV photons flux that triggers important photodissociation processes. The temperature dependency of vacuum ultraviolet (VUV) absorption cross sections are poorly known, leading to an undefined uncertainty in atmospheric models. Similarly, data measured at low temperatures similar to those of the high atmosphere of Mars, Venus, and Titan are often lacking. Aims. Our aim is to quantify the temperature dependency of the VUV absorption cross sections of important molecules in planetary atmospheres. We want to provide high-resolution data at temperatures prevailing in these media, and a simple parameterisation of the absorption in order to simplify its use in photochemical models. This study focuses on carbon dioxide (CO2). Methods. We performed experimental measurements of CO2 absorption cross sections with synchrotron radiation for the wavelength range (115–200 nm). For longer wavelengths (195–230 nm), we used a deuterium lamp and a 1.5 m Jobin-Yvon spectrometer. We used these data in our one-dimensional (1D) thermo-photochemical model in order to study their impact on the predicted atmospheric compositions. Results. The VUV absorption cross section of CO2 increases with the temperature. The absorption we measured at 150 K seems to be close to the absorption of CO2 in the fundamental ground state. The absorption cross section can be separated into two parts: a continuum and a fine structure superimposed on the continuum. The variation in the continuum of absorption can be represented by the sum of three Gaussian functions. Using data at high temperature in thermo-photochemical models significantly modifies the abundance and the photodissociation rates of many species in addition to CO2, such as methane and ammonia. These deviations have an impact on synthetic transmission spectra, leading to variations of up to 5 ppm. Conclusions. We present a full set of high-resolution (Δλ = 0.03 nm) absorption cross sections of CO2 from 115 to 230 nm for temperatures ranging from 150 to 800 K. A parameterisation allows us to calculate the continuum of absorption in this wavelength range. Extrapolation at higher temperature has not been validated experimentally and therefore should be used with caution. Similar studies on other major species are necessary to improve our understanding of planetary atmospheres.

Fabrication and spectral properties of hot-pressed Co:MgAl2O4 transparent ceramics for saturable absorber

Cobalt-doped magnesium aluminate spinel (Co:MgAl2O4) could be the most effective saturable absorber (SA) for Q-switching solid-state lasers operating at 1.5 μm. Using LiF as the sintering aid, highly transparent Co:MgAl2O4 ceramics were fabricated by hot pressing (HP) of the commercial spinel and the co-precipitated Co:MgAl2O4 powder mixture. The optical properties of Co:MgAl2O4 ceramics were investigated, and the ground state absorption cross section (σgas) of Co2+ was calculated from the curve of the absorption coefficient. For the Co:MgAl2O4 ceramics hot-pressed at 1600 °C for 2 h under 30 MPa with 1 wt.% LiF addition, the in-line transmittance reaches about 77% at 1000 nm and 1700 nm, and the ground state absorption cross section of Co2+ is 2.55 × 10−19 cm2 at the wavelength of 1540 nm, which is promising as a saturable absorber for solid-state pulse laser operating at 1.5 μm.

VUV-absorption cross section of CO2at high temperatures and impact on exoplanet atmospheres

Ultraviolet (UV) absorption cross sections are an essential ingredient of photochemical atmosphere models. Exoplanet searches have unveiled a large population of short-period objects with hot atmospheres, very different from what we find in our solar system. Transiting exoplanets whose atmospheres can now be studied by transit spectroscopy receive extremely strong UV fluxes and have typical temperatures ranging from 400 to 2500 K. At these temperatures, UV photolysis cross section data are severely lacking. Our goal is to provide high-temperature absorption cross sections and their temperature dependency for important atmospheric compounds. This study is dedicated to CO2, which is observed and photodissociated in exoplanet atmospheres. We performed these measurements for the 115 - 200 nm range at 300, 410, 480, and 550 K. In the 195 - 230 nm range, we worked at seven temperatures between 465 and 800 K. We found that the absorption cross section of CO2 is very sensitive to temperature, especially above 160 nm. Within the studied range of temperature, the CO2 cross section can vary by more than two orders of magnitude. This, in particular, makes the absorption of CO2 significant up to wavelengths as high as 230 nm, while it is negligible above 200 nm at 300 K. To investigate the influence of these new data on the photochemistry of exoplanets, we implemented the measured cross section into a 1D photochemical model. The model predicts that accounting for this temperature dependency of CO2 cross section can affect the computed abundances of NH3, CO2, and CO by one order of magnitude in the atmospheres of hot Jupiter and hot Neptune.

High-temperature measurements of VUV-absorption cross sections of CO2and their application to exoplanets

UV absorption cross sections are an essential ingredient of photochemical atmosphere models. Exoplanet searches have unveiled a large population of short-period objects with hot atmospheres, very different from what we find in our solar system. Transiting exoplanets whose atmospheres can now be studied by transit spectroscopy receive extremely strong UV fluxes and have typical temperatures ranging from 400 to 2500 K. At these temperatures, UV photolysis cross section data are severely lacking. Aims. Our goal is to provide high-temperature absorption cross sections and their temperature dependency for important atmospheric compounds. This study is dedicated to CO2, which is observed and photodissociated in exoplanet atmospheres. We also investigate the influence of these new data on the photochemistry of some exoplanets. We performed these measurements for the 115 - 200 nm range at 300, 410, 480, and 550 K. In the 195 - 230 nm range, we worked at seven temperatures between 465 and 800 K. We implemented the measured cross section into a 1D photochemical model. For wavelengths > 170 nm, the wavelength dependence of ln(cross-section_CO2(wavelength, T)x1/Qv(T)) can be parametrized with a linear law. Thus, we can interpolate cross-section_CO2(wavelength, T) at any temperature between 300 and 800 K. Within the studied range of temperature, the CO2 cross section can vary by more than two orders of magnitude. This, in particular, makes the absorption of CO2 significant up to wavelengths as high as 230 nm. The absorption cross section of CO2 is very sensitive to temperature. The model predicts that accounting for this temperature dependency of CO2 cross section can affect the computed abundances of NH3, CO2, and CO by one order of magnitude in the atmospheres of hot Jupiter and hot Neptune. This effect will be more important in hot CO2-dominated atmospheres.

The ACOS CO<sub>2</sub> retrieval algorithm – Part II: Global X<sub>CO<sub>2</sub></sub> data characterization

Abstract. Here, we report preliminary estimates of the column averaged carbon dioxide (CO2) dry air mole fraction, XCO2, retrieved from spectra recorded over land by the Greenhouse gases Observing Satellite, GOSAT (nicknamed "Ibuki"), using retrieval methods originally developed for the NASA Orbiting Carbon Observatory (OCO) mission. After screening for clouds and other known error sources, these retrievals reproduce much of the expected structure in the global XCO2 field, including its variation with latitude and season. However, low yields of retrieved XCO2 over persistently cloudy areas and ice covered surfaces at high latitudes limit the coverage of some geographic regions, even on seasonal time scales. Comparisons of early GOSAT XCO2 retrievals with XCO2 estimates from the Total Carbon Column Observing Network (TCCON) revealed a global, −2% (7–8 parts per million, ppm, with respect to dry air) XCO2 bias and 2 to 3 times more variance in the GOSAT retrievals. About half of the global XCO2 bias is associated with a systematic, 1% overestimate in the retrieved air mass, first identified as a global +10 hPa bias in the retrieved surface pressure. This error has been attributed to errors in the O2 A-band absorption cross sections. Much of the remaining bias and spurious variance in the GOSAT XCO2 retrievals has been traced to uncertainties in the instrument's calibration, oversimplified methods for generating O2 and CO2 absorption cross sections, and other subtle errors in the implementation of the retrieval algorithm. Many of these deficiencies have been addressed in the most recent version (Build 2.9) of the retrieval algorithm, which produces negligible bias in XCO2 on global scales as well as a ~30% reduction in variance. Comparisons with TCCON measurements indicate that regional scale biases remain, but these could be reduced by applying empirical corrections like those described by Wunch et al. (2011b). We recommend that such corrections be applied before these data are used in source sink inversion studies to minimize spurious fluxes associated with known biases. These and other lessons learned from the analysis of GOSAT data are expected to accelerate the delivery of high quality data products from the Orbiting Carbon Observatory-2 (OCO-2), once that satellite is successfully launched and inserted into orbit.

Surface abundance change in vacuum ultraviolet photodissociation of CO2 and H2O mixture ices

Photodissociation of amorphous ice films of carbon dioxide and water co-adsorbed at 90 K was carried out at 157 nm using oxygen-16 and -18 isotopomers with a time-of-flight photofragment mass spectrometer. O((3)P(J)) atoms, OH (v = 0) radicals, and CO (v = 0,1) molecules were detected as photofragments. CO is produced directly from the photodissociation of CO(2). Two different adsorption states of CO(2), i.e., physisorbed CO(2) on the surface of amorphous solid water and trapped CO(2) in the pores of the film, are clearly distinguished by the translational and internal energy distributions of the CO molecules. The O atom and OH radical are produced from the photodissociation of H(2)O. Since the absorption cross section of CO(2) is smaller than that of H(2)O at 157 nm, the CO(2) surface abundance is relatively increased after prolonged photoirradiation of the mixed ice film, resulting in the formation of a heterogeneously layered structure in the mixed ice at low temperatures. Astrophysical implications are discussed.

Impact of UV absorption by CO 2 and H 2O on no lif inhigh-pressure combustion applications

The influence of UV light absorption by hot CO2 and H2O is evaluated for laser-induced fluorescence(LIF) measurements of NO in high-pressure combustors. UV lasers are ubiquitously used to measure LIF from species like NO, OH, HCO, and O2, as well as Raman and Rayleigh scattering in combusting environments. However, attenuation of the laser probe and/or signal by optical absorption from major combustion species is seldom considered. In this paper, we show that neglecting UV attenuation by major product species like CO2 may lead to large errors in combustion measurements. Absorption cross sections between 190 and 320 nm are measured in shock-heated CO2 and H2O at temperatures ranging from 900 to 3050 K. The absorption cross section of CO2 has strong temperature dependence and increases by 4 orders of magnitude at 193 nm between 300 and 2000 K. The measured temperature-dependen tabsorption spectra for CO2 and H2O are fit to an empirical function to provide a tool for facile assessment of potential errors and quantitative corrections for UV combustion diagnostics. LIF measurements of NO in a high-pressure burner and an internal combustion engine are adjusted for CO2 and H2O absorption to demonstrate the importance of these corrections.

Ultraviolet Absorption Spectra of Carbon Dioxide and Oxygen at Elevated Temperatures

Measurements of ultraviolet absorption spectra in lean and stochiometric premixed C2H4/O2 flames have been performed with different flame temperatures (1400–1700 K). The spectra of the light transmitted through the flame were measured in the 200–270 nm range by using as an incoherent broadband light source the plasma kernel of optical breakdown generated by a focused pulsed laser beam. Measurements were performed far downstream of the main flame zone in a region where the concentrations of flame products reach equilibrium values. CO2 and O2 are the major absorbing species, and their absorption cross sections at flame temperature have been evaluated by changing the flame conditions and thus obtaining different concentration of these species at the flame exit. At temperatures above 1500 K there is strong absorption (σa > 10−20 cm2) due to both CO2 and O2 in the 200–230 nm range. A clear increase can be seen in absorption of both CO2 and O2 with increasing temperature. CO2 absorption cross sections also show a different dependence with respect to temperature for the different wavelengths.

A Photochemical Model of the Martian Atmosphere

The factors governing the amounts of CO, O2, and O3 in the martian atmosphere are investigated using a minimally constrained, one-dimensional photochemical model. We find that the incorporation of temperature-dependent CO2 absorption cross sections leads to an enhancement in the water photolysis rate, increasing the abundance of OH radicals to the point where the model CO abundance is smaller than observed. Good agreement between models and observations of CO, O2, O3, and the escape flux of atomic hydrogen can be achieved, using only gas-phase chemistry, by varying the recommended rate constants for the reactions CO + OH and OH + HO2 within their specified uncertainties. Similar revisions have been suggested to resolve discrepancies between models and observations of the terrestrial mesosphere.The oxygen escape flux plays a key role in the oxygen budget on Mars; as inferred from the observed atomic hydrogen escape, it is much larger than recent calculations of the exospheric escape rate for oxygen. Weathering of the surface may account for the imbalance. Quantification of the escape rates of oxygen and hydrogen from Mars is a worthwhile objective for an upcoming martian upper atmospheric mission.We also consider the possibility that HOx radicals may be catalytically destroyed on dust grains suspended in the atmosphere. Good agreement with the observed CO mixing ratio can be achieved via this mechanism, but the resulting ozone column is much higher than the observed quantity. We feel that there is no need at this time to invoke heterogeneous processes to reconcile models and observations.

Absorption Cross Sections of O2 and CO2 Continua in the Schumann and Far-uv Regions

By means of a photoelectrical technique used in conjunction with a 3-m vacuum monochromator, the absorption cross section of the O2 continuum in the region 2350–1814 Å and the absorption cross section of CO2 in the region 2160–1718 Å have been measured. The cross section of the O2 continuum is 3.8 × 10−24 cm2 at 2350 Å; it slowly increases towards shorter wavelengths and reaches 10.7 × 10−24 cm2 at about 1980 Å, then increases very rapidly and reaches 7.1 × 10−22 cm2 at about 1814 Å. In the case of CO2, numerous discrete bands were found overlapping a weak continuum in the wavelength region below 1980 Å. The absorption cross section of the CO2 continuum is about 2 × 10−24 cm2 at 2100 Å; it gradually increases toward the shorter wavelength side, and reaches about 4 × 10−24 cm2 at 2000 Å. The continuum rises rapidly at 2000 Å and its value is 1.19 × 10−20 cm2 at 1718 Å. Origins of the continua of both O2 and CO2 are briefly discussed.

Absorption Cross Sections of Carbon Dioxide and Carbon Monoxide in the Vacuum Ultraviolet

Absorption cross sections of CO2 and CO in the region from 1306 A to 374 A have been measured. The absorption spectrum of CO2 consists of strong resonance bands between 1306 A and 700 A, with one of them at 923 A showing an unusually large cross section of 117×10—18 cm2. A continuum with bands superimposed on it was observed to start at about 860 A or 14.4 ev which corresponded to the first ionization potential of CO2. From 700 A toward shorter wavelengths, the contour of the continuum was better defined and smooth with a broad maximum of 36×10—18 cm2 at 550 A and a total f-value of 4.4. The CO absorption between 1306 A and 955 A was less than 10—18 cm2. Prominent resonance bands appeared at 924 A and extended to 600 A. An absorption continuum could be identified between 876 A and 374 A showing maximum values of σ≃19×10—18 cm2 between 750 A and 550 A with perhaps a small dip of 15×10—18 cm2 at 644 A. The f-value of this continuum was 2.8.