Line narrowing effect on the retrieval of HF and HCl vertical profiles from ground-based FTIR measurements

Collision-induced line narrowing, which has been discovered in the 1950s and investigated thoroughly in the laboratory since then, has yet never been taken into account in the spectroscopic remote sensing of the atmosphere. This work investigates the effect of collision-induced line narrowing onto the retrieval of HCl and HF vertical profiles from ground-based solar absorption FTIR measurements made at the NDSC station of the Jungfraujoch (46.5^°N, 8^°E and 3580 m above see level). The retrievals are performed with the Atmosphit software, recently developed at the Université Libre de Bruxelles. It is presented in this paper for the first time and is validated against the widely used SFIT2 software. The impact of the line narrowing onto the retrieval of HCl and HF vertical profiles is examined relying on careful information content and error budget analyses. We report that the effect is relatively weak for HCl but significant for HF. Confirmation of the need to take the line narrowing into account for the retrieval of vertical profiles from ground-based FTIR spectra is given by comparison with data from the HALOE space borne instrument, rather insensitive to this spectroscopic effect.     

Effects of vertical grid discretization in infrared transmission modeling

The vertical spacing of a discretization used to model transmission in the mid-infrared spectral range was investigated. The forward model employed in this study is a part of an algorithm used to retrieve trace gas profiles from high-resolution ground-based solar absorption Fourier transform infrared (FTIR) spectra, however, the results have general applicability. A finely spaced retrieval grid was constructed and made progressively more sparse in the troposphere and in the stratosphere. The effect was quantified in terms of transmission differences with respect to the most fine discretization for a suite of molecules (H₂O, O₃, CO, CO₂, CH₄, N₂O, NO, NO₂, HCl, HF, HNO₃, ClONO₂, and N₂) in microwindows commonly used in FTIR spectroscopy. Systematic differences in modeled transmissions are apparent when coarser grid schemes are used for all species and microwindows, though some are below random noise levels typical of spectra recorded at Toronto. The most significant are H₂O and O₃ at 0.30-0.73% and 0.10-0.34%, respectively. CO (0.13%), ClONO₂ (0.84%), and HF (1.03%) are also influenced by the interference of H₂O, which is sensitive to temperature interpolation errors via the lower state energy of the particular H₂O transition. O₃ is a significant interference in CO (0.42%) and ClONO₂ (0.31%) microwindows, but its influence is felt primarily via interpolation errors in the O₃ number concentration profile introduced by the coarser grids. HCl and HF themselves show the next most significant response in transmission to coarser stratospheric grids (∼0.18%). Finally, considering transmission differences >0.1% as significant in typical measurements, we identify maximum tropospheric and stratospheric layer widths that still lead to negligible transmission errors as, respectively, 0.6 and 2.0 km. These numbers can vary depending on the band or transition of interest, the signal-to-noise ratio of the measurement and the use of significantly different a priori volume mixing ratio profiles.     

Near-infrared radiative transfer modelling with different CH4 spectroscopic databases to retrieve atmospheric methane total amount

Atmospheric methane content can be retrieved from measurements of solar radiation attenuated by the atmosphere in the near infrared spectral region where the space-borne and ground-based spectrometers carry out regular measurements. It is shown, in the present work, that the different spectroscopic databases can give significantly different results for both forward simulations of the atmospheric transmittance and the inverse problem solution to retrieve the CH₄ total content in the atmosphere using spectra measured by ground-based FTIR spectrometer in the near infrared spectral region. These discrepancies and the problem of the reduction of their influence on the atmospheric radiation transfer calculations are discussed. A comparison of atmospheric ground-based measured and simulated spectra, modelled with different CH₄ databases, is presented.     

Non-Voigt line-shape effects on retrievals of atmospheric ozone: Collisionally isolated lines

This paper addresses the question of errors in retrievals of vertical profiles of ozone from atmospheric spectra caused by assuming that the absorption lines have pure Voigt line shapes. The case of collisionally isolated transitions (no line mixing) is treated by considering only the effects of the speed dependence (SD) of the pressure broadening. The case of O₃ retrievals from a sequence of limb transmission spectra is first treated theoretically. The results show that the influence of SD is very small, leading to changes in the residuals and in the retrieved O₃ mixing ratios smaller than 1%. These findings are then confirmed by treating a series of spectra recorded by the ACE-FTS instrument. Similar exercises are also made for other observation techniques by treating simulated or measured limb and nadir emission spectra as well as ground-based solar and in-situ laser transmission data. All lead to the general conclusion that SD (and Dicke narrowing) can be neglected in retrievals of ozone amounts from recorded atmospheric spectra. Indeed, the biases caused in the ozone profiles by the use of pure Voigt line shapes still remain significantly smaller than the total error/uncertainty from other sources such as improper line intensities and widths, uncertainty in the instrument function, errors in the pressure and temperature profiles and so forth.     

Improving spectroscopic line parameters by means of atmospheric spectra: Theory and example for water vapor and solar absorption spectra

Current atmospheric remote sensing experiments measuring high resolution spectra apply instruments of similar quality as the laboratory experiments that are especially equipped to derive spectroscopic parameters. We propose a method that uses high quality atmospheric spectra to improve the spectroscopic parameterization. It is an optimal estimation method that applies the uncertainty ranges given in current spectroscopic databases as a priori covariance and the residuals between the simulated and measured atmospheric spectra as new measurements. We test the method by updating the current HITRAN parameters of 49 mid-infrared water vapor lines (situated in 15 spectral windows between 795 and ) by the information present in high quality ground-based Fourier transform infra-red (FTIR) spectra. We show that the application of a speed dependent Voigt line shape model is important. The updated water vapor parameterization, compared to the original one, leads to lower residuals, larger measurement information content, and better agreement between remotely sensed and coincident in situ water vapor profiles. Using the new line parameterization, a state-of-the-art ground-based FTIR system is able to monitor upper tropospheric water vapor amounts and middle/upper tropospheric HDO/H₂O ratios.     

O4对利用天顶散射光法测量大气组分含量的影响研究

通过实验证明是否考虑O₄的存在对利用天顶散射光测量大气组分含量的结果存在影响.介绍了天顶散射光的观测原理、实验仪器、测量方法、光谱处理以及浓度反演过程.用具体的实验数据说明考虑O₄在实验波段内的吸收能提高NO₂和O₃浓度反演结果的准确性.同时将观测得到的臭氧垂直柱密度与美国TOMS观测数据进行了对比. 关键词： 4')" href="#">O₄ 臭氧 天顶散射光 DOAS     

太阳光谱对高分辨吸收光谱反演大气CO2浓度影响的研究

以太阳光为辐射源的近红外波段高分辨率吸收光谱广泛应用于大气参数遥测.以CO2浓度反演为例,研究了太阳光谱分辨率的影响.利用美国AER公司编制的太阳光谱计算程序得到大气上界的理论计算太阳光谱作为辐射源,结合自行编制的高分辨率大气透过率模拟软件HRATS对大气中CO2平均浓度进行模拟反演.数值模拟计算结果表明,太阳光谱的准确度对浓度反演非常重要,特别是在超分辨光谱反演中异常重要,虽然反演浓度的偏差与观测分辨率没有明显的线性变化规律,但有趋势:观测分辨率的降低对太阳光谱分辨率的要求也降低,为了精确反演大气中CO2浓度,因此需要充分利用大气层顶的高分辨太阳辐射光谱数据.     

Ground-based solar absorption studies for the Carbon Cycle science by Fourier Transform Spectroscopy (CC-FTS) mission

Carbon cycle science by Fourier transform spectroscopy (CC-FTS) is an advanced study for a future satellite mission. The goal of the mission is to obtain a better understanding of the carbon cycle in the Earth's atmosphere by monitoring total and partial columns of CO₂, CH₄, N₂O, and CO in the near infrared. CO₂, CH₄, and N₂O are important greenhouse gases, and CO is produced by incomplete combustion. The molecular O₂ column is also needed to obtain the effective optical path of the reflected sunlight and is used to normalize the column densities of the other gases. As part of this advanced study, ground-based Fourier transform spectra are used to evaluate the spectral region and resolution needed. Spectra in the 3950–7140 cm^?1 region with a spectral resolution of 0.0042 cm^?1 recorded at Kiruna (67.84°N, 20.41°E, and 419 m above sea level), Sweden, on 1 April 1998, were degraded to the resolutions of 0.01, 0.1, and 0.3 cm^?1. The effect of spectral resolution on the retrievals has been investigated with these four Kiruna spectra. To obtain further information on the spectral resolution, optical components and spectroscopic parameters required by the future mission, high-resolution solar absorption spectra between 2000 and 15000 cm^?1 were recorded using Fourier transform spectrometers at Kitt Peak (31.9°N, 111.6°W, and 2.1 km above sea level), Arizona, on 25 July 2005 and Waterloo (43.5°N, 80.6°W, and 0.3 km above sea level), Ontario, on 22 November 2006 with spectral resolutions of 0.01 and 0.1 cm^?1, respectively. Dry air volume mixing ratios (VMRs) of CO₂ and CH₄ were retrieved from these ground-based observations. The HITRAN 2004 spectroscopic parameters are used with the SFIT2 package for the spectral analysis. The measurement precisions for CO₂ and CH₄ total columns are better than 1.07% and 1.13%, respectively, for our observations. Based on these results, a Fourier transform spectrometer (maximum spectral resolution of 0.1 cm^?1 or 5 cm maximum optical path difference (MOPD)) operating between 2000 and 15000 cm^?1 is suggested as the primary instrument for the mission. Further progress in improving the atmospheric retrievals for CO₂, CH₄, and O₂ requires new laboratory measurements of the spectroscopic line parameters.     

Selective synthesis of monoclinic and tetragonal phase LaVO<Subscript>4</Subscript> nanorods via oxides-hydrothermal route

Pure monoclinic (m-) and tetragonal (t-) LaVO₄ nanorods are successfully obtained via a facile oxides-hydrothermal method, in which V₂O₅ and La₂O₃ bulk powders are directly utilized as precursors without pretreatment. It is found that ethylenediamine tetraacetic disodium salt (EDTA) is a key factor for synthesizing t-LaVO₄. The as-obtained products are characterized by X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), and selected area electron diffraction (SAED). The FTIR spectra of VO₄ around 800 cm⁻¹ are suggested as an effective auxiliary means to identify the crystal phase of LaVO₄. UV–Visible spectra of LaVO₄ nanomaterials are obvious blue shift compared with the bulk m-LaVO₄ materials. The different photoluminescent properties of Eu³⁺ doped m- and t-LaVO₄ are demonstrated. A dissolution–precipitation mechanism is mainly responsible for the anisotropic morphology and phase control evolution of the LaVO₄ nanocrystals. The oxides-hydrothermal system is also applicable to prepare other pure LnVO₄ (Ln³⁺: Nd³⁺, Y³⁺, Sm³⁺) and doped LnVO₄ nanomaterials.     

The 2ν3 band of CH4 revisited with line mixing: Consequences for spectroscopy and atmospheric retrievals at 1.67 μm

This paper presents a study of absorption in N₂-broadened P and R manifolds of the 2ν₃ band of CH₄ near 6000 cm⁻¹ using high resolution laboratory and atmospheric spectra. This region is of prime importance for the retrieval of methane abundances in the Earth's atmosphere using ground-based or space-borne spectrometers. Recent laboratory investigations have been devoted to the methane spectroscopic parameters in this band, motivated by their previous poor knowledge and their increasing use by remote sensing experiments. In the absence of a better model, previous studies have used Voigt line shapes and thus purposely neglected line mixing (LM). In this paper, we first present direct comparisons between measured laboratory spectra and the results of a model which accounts for LM without adjusting any of the spectroscopic parameters. A good agreement is obtained and the results show that LM does have a significant influence on the shapes of P and R manifolds. Hence, most previously observed discrepancies were not due to improper broadening and shifting coefficients but to the neglect of this effect. This also confirms that widths and shifts derived in recent 2ν₃ band studies neglecting LM are “effective” and lack physical meaning, as suggested in a previous work [17] (Frankenberg et al., 2008). In a second step, the conclusions from the laboratory data are tested using ground-based atmospheric solar absorption spectra. The fit residuals obtained confirm the quality of the proposed model and evidence the impact of line mixing on CH₄ atmospheric spectra. The present results also confirm that laboratory and atmospheric spectra can alternatively be accurately modeled neglecting LM and using ad hoc broadening and shifting parameters. Conclusions of this exercise can be drawn from two perspectives. From the point of view of spectroscopy and understanding of processes, accurate line parameters will not be deduced from fits of laboratory measurements unless line-mixing effects are included in the spectral-shape model. In the meantime, and from the point of view of atmospheric retrievals, neglecting LM with suitable effective line parameters is convenient and accurate (within current retrieval uncertainties). Note that this is only true if this approach is not used for total pressures significantly above 1 atm (e.g. Jupiter).     

Infrared absorption cross sections for acetone (propanone) in the 3 μm region

Infrared absorption cross sections for acetone (propanone), CH₃C(O)CH₃, have been determined in the 3 μm spectral region from spectra recorded using a high-resolution FTIR spectrometer (Bruker IFS 125 HR) and a multipass cell with a maximum optical path length of 19.3 m. The spectra of mixtures of acetone with dry synthetic air were recorded at 0.015 cm⁻¹ resolution (calculated as 0.9/MOPD using the Bruker definition of resolution) at a number of temperatures and pressures (50-760 Torr and 195-296 K) appropriate for atmospheric conditions. Intensities were calibrated using three acetone spectra (recorded at 278, 293 and 323 K) taken from the Pacific Northwest National Laboratory (PNNL) IR database.     

Composition depth profiles of Bi3.15Nd0.85Ti3O12 thin films studied by X-ray photoelectron spectroscopy

In the present work, X-ray photoelectron spectroscopy (XPS) was used to investigate the composition depth profiles of Bi_3.15Nd_0.85Ti₃O₁₂ (BNT) ferroelectric thin film, which was prepared on Pt(1 1 1)/Ti/SiO₂/Si(1 0 0) substrates by chemical solution deposition (CSD). It is shown that there are three distinct regions formed in BNT film, which are surface layer, bulk film and interface layer. The surface of film is found to consist of one outermost Bi-rich region. High resolution spectra of the O 1s peak in the surface can be decomposed into two components of metallic oxide oxygen and surface adsorbed oxygen. The distribution of component elements is nearly uniform within the bulk film. In the bulk film, high resolution XPS spectra of O 1s, Bi 4f, Nd 3d, Ti 2p are in agreement with the element chemical states of the BNT system. The interfacial layer is formed through the interdiffusion between the BNT film and Pt electrode. In addition, the Ar⁺-ion sputtering changes lots of Bi³⁺ ions into Bi⁰ due to weak Bi-O bond and high etching energy.     

Analysis of XPS spectra of Fe and Fe ions in oxide materials

Samples of the iron oxides Fe_0.94O, Fe₃O₄, Fe₂O₃, and Fe₂SiO₄ were prepared by high temperature equilibration in controlled gas atmospheres. The samples were fractured in vacuum and high resolution XPS spectra of the fractured surfaces were measured. The peak positions and peak shape parameters of Fe 3p for Fe²⁺ and Fe³⁺ were derived from the Fe 3p XPS spectra of the standard samples of 2FeO·SiO₂ and Fe₂O₃, respectively. Using these parameters, the Fe 3p peaks of Fe₃O₄ and Fe_1−yO are analysed. The results indicate that high resolution XPS techniques can be used to determine the Fe²⁺/Fe³⁺ ratios in metal oxides. The technique has the potential for application to other transition metal oxide systems.     

Retrieval of ozone profile from ground-based measurements with polarization: A synthetic study

We perform a retrieval based on optimal estimation theory to retrieve the vertical distribution of ozone from simulated spectra in the Huggins bands. The model atmosphere includes scattering by aerosol as well as Rayleigh scattering. The virtual instrument is ground-based and zenith-viewing. Using this algorithm, we show that it is possible to retrieve the ozone profile provided that the spectral resolution is at least 0.2 nm and the signal to noise ratio greater than 500. Our synthetic retrievals suggest that if we are able to measure the Stokes parameters Q, U and V with accuracy comparable to that of the intensity, the information contained in the measurements, and therefore the inversion, will improve. Furthermore, we find that the measurement of the full Stokes vector from the ground-based instrument will especially enhance the retrieval of tropospheric ozone. Utilizing concepts from information theory, our arguments are confirmed by increases in the degrees of freedom and the Shannon information content in the simulated measurements.     

High-resolution Russian–German beamline at BESSY

The superior performance of the high-resolution Russian–German bending-magnet beamline at BESSY is demonstrated by measuring photon flux and photoionization spectra in the spectral region of the 2,-1₃ resonance of doubly-excited He as well as at the 1s absorption thresholds of gas-phase N₂, O₂, and Ne. It is shown that even after 6 years of successful operation, the beamline remains to provide a solid basis for a further development of the Russian–German scientific cooperation in the field of applications of synchrotron radiation.     

Synthesis and characterization of spinel LiMn<Subscript>2</Subscript>O<Subscript>4</Subscript> nanoparticles prepared by high-energy milling and hydrothermal method

Spinel LiMn₂O₄ has been known to be a technologically important, environmental-friendly, and low-cost cathode material used in Li-based rechargeable batteries, and it is also widely available. Nanoparticle spinel LiMn₂O₄ has been synthesized by the top-down, high-energy milling, and hydrothermal methods. SEM images, X-ray diffraction patterns, and neutron high-resolution powder diffraction patterns have confirmed the nanocrystalline nature of the spinel LiMn₂O₄ samples. Raman and Fourier transform infrared (FTIR) measurements show typical absorption and vibration spectra typical for the spinel LiMn₂O₄ showing the formation of various metallic bonds in the sample. The strongest Raman and FTIR signals come from the higher frequency region, with weaker signals appearing in the lower frequency range.     

X-ray and UV photoelectron spectra of the metal sesquioxides

He(I,II) and MgKα valence region photoelectron spectra of polycrystalline Ti₂O₃, V₂O₃, Cr₂O₃, Mn₂O₃, Fe₂O₃ and Rh₂O₃ have been recorded. The method of sample preparation employed gave rise to UV-PE spectra which are significantly different from those previously reported. While clear changes are observed in the spectra accompanying the semiconductor-to-metal transition of V₂O₃ at 150 K, there is no apparent modification of the Ti₂O₃ spectra accompanying its second order transition at 500 K. The remaining first row transition metal sesquioxides exhibit spectra indicative of localised 3d electrons.     

Ozone profiles and total column amounts derived at Izaña, Tenerife Island, from FTIR solar absorption spectra, and its validation by an intercomparison to ECC-sonde and Brewer spectrometer measurements

Since February 1999 high-resolution Fourier transform infrared (FTIR) solar absorption spectra are recorded at the Izaña Observatory (, 2370 m a.s.l.), which forms part of the network for detection of stratospheric change (NDSC). The vertical distribution of the ozone amount was deduced from the spectra by using the retrieval code PROFFIT. Two microwindows at 782.5 and are used whereby an individually and regularly determined instrumental line shape (ILS) was applied. A detailed error analysis of the ozone retrieval is performed, i.e. the height-dependent impact of all important error sources on the retrieved profiles is estimated. The retrieved total column amounts and profiles as well as their estimated error budgets are verified by comparisons with column amounts and profiles derived from Brewer spectrometer and ECC-sonde measurements performed simultaneously at the same location. Whereas the mean difference of 1.9% of the FTIR total column amounts and the Brewer data lies within the precision of the instruments, systematic differences of up to 9% between FTIR and ECC-sonde profile are observed above . The assumed precisions of the experiments are consistent with the experimental results, which demonstrates the excellent characterization of the FTIR data. The analysis of systematic errors allows to conclude that the systematic differences are mainly due to the sonde data since the systematic errors in the FTIR profile can only explain a small part of them.     

Cancer targeting potential of bioinspired chain like magnetite (Fe3O4) nanostructures

Iron is significant, earth abundant and inexpensive materials in everyday use. Non toxicity and clean manufacturing process is still a challenging role in scientific world. The chain like Fe₃O₄ nanostructures were synthesized using the mixtures such as iron nitrate and Rambutan. Magnetite Fe₃O₄ was verified using X-ray powder diffraction (XRD). Metal oxide (Fe–O) and A_1g and E_g phonon modes are substantiated employing Fourier-transform infrared spectroscopy (FTIR) and Raman spectra. A product chemical state was investigated by high resolution X-ray photoelectron spectroscopy (XPS) spectra. Chain like morphology and polycrystalline nature is attributed by transmission electron microscopy (TEM) analysis. Weight loss activity was revealed through thermogravimetric analysis (TGA) analysis. In application studies, higher concentration of Fe₃O₄ nanostructures was more effective than the low concentration. Moreover, cytotoxicity effects and cell viability on human cancer cell lines were observed and tested for cancer treatment.     

Spectral least squares quantification of several atmospheric gases from high resolution infrared solar spectra obtained at the South Pole

Spectral least squares fitting has been used to analyze high resolution (0.02 cm^-1) i.r. solar spectra obtained at the South Pole in 1980. The spectral regions analyzed allow the simultaneous quantification of CO₂, H₂O, N₂O, CH₄, and O₃. Information is obtained on the column amount and on the vertical distribution.