Spectral Absorption Cross-sections Research Articles

Calculation of the absorption coefficient of air at different heights using the HITRAN and ACE-FTS databases

Subject of study. Increasing requirements for the accuracy of modeling the brightness characteristics of the atmosphere at different heights motivate the development of more detailed methods for the calculation of the absorption coefficient of air. Method. Modern databases of satellite sounding of the atmosphere that contain information on the volume fractions of air components at different heights in combination with a database of the parameters of the spectral lines of gases can be used in this task to calculate the spectral absorption coefficient. The possibility of specifying the geographic position of the height profiles of the air components (by specifying latitude and longitude) is an additional advantage of using the databases of satellite sounding. This method enables the differences in air compositions above different regions of the Earth to be considered. These databases usually provide information starting from a certain height; thus, databases of satellite sounding must be combined with the data obtained either from ground-based meteorological stations or using model distributions. The ACE-FTS database was used in this study, and it was combined with the standard atmosphere MODTRAN models at low heights. A filter for the ACE-FTS database was implemented using C++. The HITRAN database was used to calculate absorption coefficients. The ACE-FTS database provides data for 43 components of air, and the HITRAN database contains data for line-by-line calculation for 27 of these components and data on spectral absorption cross-sections for the remaining 16 components. Main results. A program for the calculation of the absorption coefficient of a multicomponent gas mixture was developed using C++. A Voigt profile was used in the line-by-line calculation, the effects of pressure and temperature on the line shift were considered, and line broadening owing to the following processes was considered: self-broadening, broadening resulting from interaction with water and carbon dioxide molecules, and broadening owing to interaction with other components of the air. The software explicitly considers the isotopic composition of molecules, thus enabling the calculation of not only the air mixture but also an arbitrary mixture with specified isotopic composition, information on which is in the HITRAN database. Moreover, the data of the high-temperature version HITEMP are considered. Practical significance. The combination of the ACE-FTS and HITRAN databases enables the calculation of a detailed profile of the spectral absorption coefficient of air for the specified month, temperature at the surface of the Earth, and geographic latitude and longitude, thus increasing the information content of the input data for the calculation of the brightness and transmission of the atmosphere at different heights. The data readout rate (parsing) and calculation speed of the developed program and the program HAPI implemented using Python are compared.

Time-Resolved Laser-Induced Incandescence Measurements on Aerosolized Nickel Nanoparticles.

This work presents the first quantitative analysis of time-resolved laser-induced incandescence (TiRe-LII) measurements on aerosolized nickel nanoparticles in several gases and over a range of laser fluences. A measurement model composed of spectroscopic and heat transfer submodels is used to recover the particle size distribution parameters and the thermal accommodation coefficient (TAC). A qualitative analysis of the results reveals evidence of nonincandescent laser-induced emission temporally aligned with the laser pulse, and more laser energy is absorbed than can be accounted for from the modeled spectral absorption cross section of the nanoparticles. The TiRe-LII inferred particle size parameters were generally consistent with values found from ex situ transmission electron microscopy (TEM) analysis. The TACs for nickel nanoparticles in polyatomic gases were larger than those in monoatomic gases, which may indicate chemisorption.

Theoretical analysis of radiative properties of pronucleus multicellular cyanobacteria

Many species of cyanobacteria are of multicellular filamentous structure with chains of spherical or capsule monomer cells and having morphology of linear or spiral shape. In this paper, we built three models to represent such featured cyanobacteria cells and the effect of cell wall and adjacent monomer cell interaction on the radiative properties of the multicellular microalgae were studied using the discrete dipole approximation in the visible spectral region. The validity of equivalent volume and equivalent surface cylinder models on prediction of the radiative properties of the multicellular microalgae were examined. The extinction cross-section shows an overall decreased trend with wavelength in the spectral range 380 to 750 nm. The featured absorption peaks in the theoretically predicted spectral absorption cross-sections are consistent with experimental observations, which are corresponding to absorption of Chl a, phycocyanin and β-carotenoid. The scattering phase function exhibit strongly forward scattering peak due to the large size parameter of the cyanobacteria cells. The equivalent volume cylinder model generally gives better predictions on the extinction cross-section, absorption cross-section, and asymmetry factor of multicellular filamentous cyanobacteria.

Factors influencing starch accumulation in microalga Chlorella sorokiniana

The spectral absorption cross-section of microalgae is an essential parameter in modeling the microalgae metabolism and growth kinetics as well as in estimating the productivity and efficiency of photobioreactors. This paper presents a simple experimental procedure for retrieving the average spectral absorption cross-section of concentrated microalgal suspensions. The method combines experimental measurements of the normal–hemispherical transmittance and reflectance of the suspensions in conventional cuvettes with an inverse method and analytical expressions obtained from the modified two-flux approximation accounting for absorption and multiple scattering. The method was validated with direct measurements of the scattering phase function and of the absorption and scattering cross-sections of freshwater microalgae Chlorella vulgaris. It was able to retrieve the absorption cross-section with acceptable accuracy. The latter was then used to estimate successfully the fluence rate using a simplified light transfer model, the local rate of photon absorption, and the biomass productivity in flat plate PBRs.

Comparison of Nitric Oxide Concentrations in μs- and ns-Atmospheric Pressure Plasmas by UV Absorption Spectroscopy

In this paper, an absorption spectroscopy measurement method was applied on two atmospheric pressure plasma sources to determine their production of nitric oxide. The concentrations are essential for evaluating the plasma sources based on the principle of the Dielectric Barrier Discharge (DBD) for applications in plasma medicine. The described method is based on a setup with an electrodeless discharge lamp filled with a mixture of oxygen and nitrogen. One of the emitted wavelengths is an important resonance wavelength of nitric oxide (λ = 226.2 nm). By comparing the absorption behaviour at the minimum and maximum of the spectral absorption cross section of nitric oxide around that wavelength, and measuring the change in intensity by the absorbing plasma, the concentration of nitric oxide inside the plasma can be calculated. The produced nitric oxide concentrations depend on the pulse duration and are in the range of 180 ppm to 1400 ppm, so that a distance of about 10cm to the respiratory tract is enough to conform to the VDI Guideline 2310.

Simple method for measuring the spectral absorption cross-section of microalgae

The spectral absorption cross-section of microalgae is an essential parameter in modeling the microalgae metabolism and growth kinetics as well as in estimating the productivity and efficiency of photobioreactors. This paper presents a simple experimental procedure for retrieving the average spectral absorption cross-section of concentrated microalgal suspensions. The method combines experimental measurements of the normal–hemispherical transmittance and reflectance of the suspensions in conventional cuvettes with an inverse method and analytical expressions obtained from the modified two-flux approximation accounting for absorption and multiple scattering. The method was validated with direct measurements of the scattering phase function and of the absorption and scattering cross-sections of freshwater microalgae Chlorella vulgaris. It was able to retrieve the absorption cross-section with acceptable accuracy. The latter was then used to estimate successfully the fluence rate using a simplified light transfer model, the local rate of photon absorption, and the biomass productivity in flat plate PBRs.

Efficient representation of the absorption line blackbody distribution function for H2O, CO2, and CO at variable temperature, mole fraction, and total pressure

The absorption line blackbody distribution function (ALBDF) is the primary tool used in the SLW model for calculating the weights of gray gases. The ALBDF for H2O, CO2, and CO is calculated rigorously using the HITEMP 2010 spectroscopic database. The line-by-line data is the basis for an updated and improved hyperbolic tangent correlation of the ALBDF, valid for temperatures ranging from 400K to 3000K and total pressures ranging from 0.1atm to 50atm. The correlations are first established at atmospheric pressure, and variable total pressure is accounted for as a shift from the atmospheric pressure calculation. Further, the line-by-line ALBDF data have been tabulated to directly represent the ALBDF; the ALBDF has been tabulated for discrete temperatures ranging from 300K to 3000K, mole fractions (where appropriate) from 0 to 1, and total pressures ranging from 0.1atm to 50atm. The data have been made available on the website http://albdf.byu.edu. Improvements made compared to other representations of the ALBDF include more rigorous generation of the detailed spectral absorption cross-section, correlation and tabulation of the ALBDF for CO, expansion to variable total pressure, and a higher temperature ceiling. The accuracy of the hyperbolic tangent correlation is characterized and regimes of relative lower accuracy identified, and it is demonstrated to be sufficiently accurate for engineering applications. The tabulated ALBDF data, which can be used directly in place of the correlation, are shown to be considerably more accurate than the correlation. There is an initial computational cost to read the tabulated data after which interpolation is used to obtain the ALBDF at specified conditions.The updated and expanded ALBDF correlation and the tabulated ALBDF data are used to compute total emissivity and radiative transfer in both homogeneous, isothermal media and non-homogeneous, non-isothermal media and are compared to line-by-line benchmark calculations. The hyperbolic tangent correlation performs very well in these calculations and shows excellent accuracy, while the accuracy of calculations using the tabulated data is considerably better.

High Resolution Spectroscopic Study in the Terahertz

Spectroscopic measurements with a 1 GHz resolution were performed to examine fine spectral absorbance details in the signature of materials in the terahertz domain. The existence of fine spectroscopic details in the terahertz region can contribute to the understanding of chemical structure and its dynamics. Another important application in consequence of such spectroscopic findings is its potential to serve as a technique to discriminate among materials also in a concealed form, using remote sensing techniques. In this paper, we describe a new measurement method to extract the spectral absorption cross-section of materials from the inevitable presence of a standing wave pattern in a standard optical setup, based on frequency multiplication of a monochromatic RF source. This method demonstrates the benefit of tracking the standing wave phase to simultaneously measure both the absorption and spectral refractive index of low absorptive samples, such as polyethylene pellets. The spectral phase shifts are translated to variations in the material index of refraction and compared with that evaluated by the Kramers-Kronig analysis. The absorption cross sections are extracted by fitting the optical density of several different pellets having various concentrations of the materials to the prediction of the Beer-Lambert law. Periodical spectral artifacts resulting from the interference of multiple reflections from sample surfaces are removed by setting the incidence angle to the Brewster angle, in respect to the p-polarization of the source. The spectroscopic study in this paper is limited to the spectral range of 300-650 GHz, where atmospheric transmission allows remote sensing to achieve reasonable ranges.

Influence of Filter Band Function on Retrieval of Aerosol Optical Depth from Sunphotometer Data

Abstract Beer’s attenuation law is the basis for the retrieval of aerosol optical depth (AOD) from sunphotometer data. However, the filter band function causes uncertainty during the retrieval of AOD from sunphotometer data, particularly for channels covering spectral regions of strong gas absorption. In this work, the uncertainty in AOD retrieval due to the filter band function is systematically analyzed by employing fine spectral absorption cross sections obtained from the Molecular Spectroscopy and Chemical Kinetics Group and the line-by-line radiative transfer model (LBLRTM). The uncertainty in AOD retrieval includes the uncertainty due to the wings of the filter band function in the ultraviolet (UV) region and errors in the optical depth calculation for Rayleigh scattering and absorption of O3, NO2, H2O, CH4, and CO2. The results showed that 1) the uncertainty of AOD retrieval by this method, which is called the approximate AOD retrieval method, might become large when the filter band function is not well designed, particularly in the UV region; 2) in the case of a large zenith observation condition, the errors will be nonnegligible if the Rayleigh scattering optical depth is calculated at a central wavelength without including filter band function; 3) the band-weighted absorption coefficients of O3 and NO2 remain nearly constant when the gas amounts change, except in the case of questionably designed band filters; and 4) these weak-absorption optical depths for H2O, CH4, and CO2 cannot be ignored in the 1020- or 1640-nm channels, where an optical depth error of 0.01−0.02 may be introduced.

Temperature- and pressure-dependent midinfrared absorption cross sections of gaseous hydrocarbons

Transmittance spectra of four gaseous hydrocarbons were measured by using a Fourier transform infrared spectrometer. The analyzed substances are propane, n-butane, ethanol, and iso-octane (2,2,4-trimethyl-pentane). Mixtures of hydrocarbons and nitrogen were prepared and analyzed in an optical cell between 298 and 473 K at pressures up to 1800 kPa. Molecule specific absorption cross sections were calculated for different temperatures and pressures that are relevant for technical absorption measurements. Dependences of the spectral absorption cross sections, as well as the integrated absorption cross sections on temperature and pressure, were investigated.

Absorption cross-sections off HFC-23 at atmospheric conditions

Spectral absorption cross-sections, k ν (cm −1 atm −1), were measured in the 8.64 μm band system of HFC-23 using a high-resolution Fourier transform spectrometer. Temperature and total (N 2-broadening) pressure were selected to represent atmospheric layers according to various atmospheric models. The measured absolute intensity (or integrated cross-section) was obtained to be 0.693±0.029×10 −16 cm molecule −1.

A comparison between radiative transfer calculation and pyranometer data gathered at Observatoire de Haute Provence

The energy received on the ground from the sun is calculated using the Tropospheric Ultraviolet Visible (TUV) model of Madronich and Flocke (Handbook of Environmental Chemistry, Boule, P., (Ed.), Springer-Verlag, Heildelberg; pp. 1–26). Additions are made for running the model up to the infrared domain. Moreover, modifications in the algorithms describing several physical processes experienced by the solar radiations and models of the atmosphere properties are replaced by available local data in the area where the calculation is needed. For that, specific aerosols distribution, spectral absorption cross section of water vapour, local albedo season dependent and a recent extraterrestrial solar spectrum from UV to IR obtained from space measurements, are used. At Observatoire de Haute Provence (44°N, 6°E), a set of instruments provide us with information necessary to run the TUV model. Furthermore, the energy including the scattered and direct solar irradiance is measured by pyranometers in two wavelength ranges. To validate the additions made to the model, comparisons in clear sky conditions between the observations and the model output are made. The additions led to increase the accuracy of the model predictions to about 4%. Furthermore, this study shows that pyranometers characterization have to be improved by taking into account the contribution of the scattered light at large solar zenith angle.

Thermal infrared absorption cross-sections of CCl 4 needed for atmospheric remote sensing

Highly accurate spectral absorption cross-sections k ν ( cm 2 molecule −1 ) were measured in the 12.7 μm band of CCl 4 at temperatures between 208 and 296 K and pressures between 10 and 1013 mb with a high-resolution Fourier-transform spectrometer. Our data were obtained at pressures p and temperatures T that characterize the atmospheric layers in the commonly adapted models of the atmosphere. The selected ( p, T) combinations also represent tangent heights in solar-occultation-type remote sensing observations and actual conditions recorded by balloon-borne instruments in the Arctic. The combined absolute intensity (or integrated cross-section) of the bands contributing to the absorption around 12.7 μm is 6.295±0.102×10 −17 cm molecule −1 .

Thermal infrared absorption cross-sections of CF 4 for atmospheric applications

Spectral absorption cross-sections, k ν ( cm 2 molecule −1 ), have been measured in the 7.8 μm band of CF 4 at temperatures between 180 and 296 K and pressures between 10 and 1013 mb (hPa) with a high-resolution Fourier-transform spectrometer. Our data were obtained at pressures and temperatures that parameterize several of the commonly adapted model atmospheres, represent tangent heights in solar-occultation type remote-sensing observations of the atmosphere, and the conditions recorded in atmospheric observations at polar latitudes. The combined absolute intensity of all of the bands contributing to the absorption around 7.8 μm is (1.926±0.012)×10 −16 cm molecule −1 . The spectral absorption cross-section data have been incorporated into the two established and widely used spectroscopic databases.

Thermal infrared cross-sections of C 2F 6 at atmospheric temperatures

Spectral absorption cross-sections, k ν ( cm −1 atm −1 ), have been measured in the 8.0 and 8.95 μm bands of C 2F 6. Temperature and total (N 2-broadening) pressure have been varied to represent the conditions specified in various models of the terrestrial atmosphere so that the absorption cross-sections can be applied directly to the optical remote-sensing of C 2F 6 in the atmosphere. The measured absolute intensities of the 8.0 and the 8.95 μm bands are (1.636±0.003)×10 −16 and ( 0.467±0.0018)×10 −16 cm molecule −1 , respectively.

Absorption cross-sections of HFC-134a in the spectral region between 7 and [formula omitted

Spectral absorption cross-sections k ν ( cm 2 molecule −1) were measured in the 7.07, 8.08, 9.24, 10.3, and 11.9 μm bands of HFC-134a at temperatures between 190 and 296 K and pressures between 10 and 1013 hPa with a high-resolution Fourier-transform spectrometer. Our data were obtained at pressures and temperatures that characterise several of the commonly adapted model atmospheres, represent tangent heights in solar-occultation-type remote-sensing observations of the atmosphere, and the conditions recorded in atmospheric observations at Arctic latitudes. The integrated cross-sections (or integrated intensities) of the absorption bands in the 7.07, 8.08, 9.24, 10.3, and 11.9 μm regions are, in the unit of 10 −17 cm molecule −1 , 0.4674, 9.711, 1.508, 0.8753, and 0.2527, respectively.

Effects of temperature, nitrogen, and light limitation on the optical properties of the marine diatom Thalassiosira pseudonana

A series of laboratory experiments were conducted to examine the optical properties of the marine diatom Thalassiosira pseudonana for a broad range of growth rates (µ from 0.22 to 2 d−1) under temperature‐, nitrogen‐, and light‐limited conditions. The effects of temperature and nitrogen limitation on spectral absorption cross‐sections expressed on a per cell basis, σa(λ), were similar. With the reduction in growth rate, σa at a light wavelength λ = 674 nm showed an equivalent decrease regardless of whether the cells were limited by temperature or nitrogen. The effect of growth irradiance was distinctively different, since σa increased with light limitation. The chlorophyll a (Chl a)—specific absorption coefficient showed the opposite trends than those of σa. These patterns resulted primarily from the acclimative strategies of T. pseudonana involving an increase in Chl a content in response to light limitation and a decrease in Chl a under temperature and nitrogen limitation. The scattering cross‐sections, σb(λ), and carbon‐specific scattering coefficients, b*c(λ), were generally not a strong function of growth rate with the exception of lower values of b*c for light‐limited cells. While T. pseudonana exhibited some changes in cell size, variations in the refractive index had the major influence on cell optical properties. The imaginary part of the refractive index (at λ = 674 nm) showed a strong correlation with intracellular Chl a concentration, and the real part of the refractive index (at λ = 660 nm) was correlated with the intracellular carbon concentration. Our results indicate that integrated studies of the effects of various environmental factors such as light, nutrients, and temperature are needed to adequately describe optical variability in phytoplankton.

Global climatology of abundance and solar absorption of oxygen collision complexes

To improve our understanding of the absorption of solar radiation in the atmosphere we have characterized the spectral absorption, the spatial and temporal abundance, and the radiative forcing of the oxygen collision pairs O2·O2 and O2·N2 (O2·X ≡ O2·O2 + O2·N2). The regional, vertical, seasonal, and annual patterns of O2·X abundance and radiative forcing are obtained from a general circulation model. We estimate the mean absorption by O2·X, heretofore neglected in large scale atmospheric models, is 0.75–1.2 W m−2, or 1–2% of total atmospheric solar absorption. O2·X absorption reduces surface insolation by 0.48–0.78 W m−2 and increases the net radiative flux at the tropopause by 0.32–0.52 W m−2. These ranges bracket the uncertainties due to spectral absorption cross sections, O2·N2 efficiency, O2·X abundance, and cloud distribution. Globally averaged, O2·X enhances absorption equally in clear and in cloudy skies. We create a global climatology of well‐mixed collision complex abundances by scaling O2·X abundance to other complexes such as N2·N2 and O2·Ar. Collision complex abundance depends quadratically on the concentrations of the constituents. This dependence causes a 20% increase in O2·X abundance in the Arctic relative to the Tropics for the same sea level pressure. The variations in zonal mean O2·X abundance due to surface elevation, the annual mean meridional temperature gradient, and to seasonal temperature variations are 40, 15, and 10%, respectively. O2·X heating obeys the weakly absorbing, linear limit so it peaks at the surface in clear skies, but clouds shift this peak up by 200–300 mb on seasonal timescales. Surface albedo and clouds strongly modulate the solar forcing efficiency of O2·X (forcing per unit abundance) by altering the mean photon path length. These factors produce annual mean forcing maxima in the subtropics over bright deserts and regions of marine stratus. Inclusion of O2·X in models is likely to reduce cold biases in the summertime polar atmosphere, where O2·X contributes 2–4% of total solar heating.

Contribution of water vapour dimers to clear sky absorption of solar radiation

Using recently derived-values of the water vapor dimer spectral absorption cross section wecalculate the water vapor dimer contribution to the clear sky absorption of solar radiation. Weconsider the water dimer concentrations deduced from local equilibrium thermodynamics, andwe account for the overlap of water vapor dimer and monomer absorption bands. We estimatethat water vapor dimer contribution to the clear sky broad band column absorption of solarradiation is around 3 and 6 W/m 2 for the cases of midlatitude summer and tropical atmosphere,respectively, at the solar zenith angle of 30°. For the cases of midlatitude winter, the US standardatmosphere and subarctic winter atmosphere, the dimer contribution to the absorption of solarradiation is less than 1 W/m 2 . Due to an uncertainty of the dimer’s concentration within clouds,we are not able to deduce, at this time, the dimer absorption in a cloudy atmosphere. DOI: 10.1034/j.1600-0870.1999.t01-2-00010.x

Transport of broadband radiation through a nonlinear dispersive medium

Analytical and numerical solutions are presented to elucidate the important physical aspects of the incoherent nonlinear interaction and propagation of high-intensity radiation in an absorbing (or amplifying) medium. The properties of radiation-driven one-dimensional density discontinuities or wave fronts are examined for monochromatic and broadband radiation sources, and for a nonlinear absorbing medium characterized by a spectral absorption cross section that is square, Gaussian, or Lorentzian. The effect of the angular distribution of the radiation source is considered in detail. The results of the analysis show that the propagation behavior of the radiation-driven wave front depends strongly on the spectral dependence of the absorption cross section. The wave front propagates with a constant shape and at a constant velocity ${v}_{b}$ only for monochromatic radiation or a square absorption cross section. For a Lorentzian, ${v}_{b}\ensuremath{\sim}{x}^{\frac{1}{2}}$ at large values of the propagation distance $x$. The absorption of intense radiation in a medium generally causes local heating, which can introduce hydrodynamic disturbances that propagate behind, along with, or ahead of the radiation-driven wave front. Conditions are derived for the amount of heat addition that is required to produce these disturbances for a given velocity of the wave front.