HITRAN Compilation Research Articles

The HITRAN2020 molecular spectroscopic database

The HITRAN database is a compilation of molecular spectroscopic parameters. It was established in the early 1970s and is used by various computer codes to predict and simulate the transmission and emission of light in gaseous media (with an emphasis on terrestrial and planetary atmospheres). The HITRAN compilation is composed of five major components: the line-by-line spectroscopic parameters required for high-resolution radiative-transfer codes, experimental infrared absorption cross-sections (for molecules where it is not yet feasible for representation in a line-by-line form), collision-induced absorption data, aerosol indices of refraction, and general tables (including partition sums) that apply globally to the data. This paper describes the contents of the 2020 quadrennial edition of HITRAN. The HITRAN2020 edition takes advantage of recent experimental and theoretical data that were meticulously validated, in particular, against laboratory and atmospheric spectra. The new edition replaces the previous HITRAN edition of 2016 (including its updates during the intervening years).All five components of HITRAN have undergone major updates. In particular, the extent of the updates in the HITRAN2020 edition range from updating a few lines of specific molecules to complete replacements of the lists, and also the introduction of additional isotopologues and new (to HITRAN) molecules: SO, CH3F, GeH4, CS2, CH3I and NF3. Many new vibrational bands were added, extending the spectral coverage and completeness of the line lists. Also, the accuracy of the parameters for major atmospheric absorbers has been increased substantially, often featuring sub-percent uncertainties. Broadening parameters associated with the ambient pressure of water vapor were introduced to HITRAN for the first time and are now available for several molecules.The HITRAN2020 edition continues to take advantage of the relational structure and efficient interface available at www.hitran.org and the HITRAN Application Programming Interface (HAPI). The functionality of both tools has been extended for the new edition.

Reference spectroscopic data for hydrogen halides, Part II: The line lists

Accurate spectroscopic parameters for the hydrogen halides, namely HF, HCl, HBr, and HI, together with their deuterated isotopologues, are crucial for the quantitative study of terrestrial and planetary atmospheres, astrophysical objects, and chemical lasers. A thorough evaluation of all the hydrogen halide line parameters in previous HITRAN editions has been carried out. A new set of line lists was generated for the HITRAN2012 edition using methods described here. In total, 131,798 entries were generated for numerous pure-rotational and ro-vibrational transitions (fundamental, overtone, and hot bands) for hydrogen halides and their deuterated species in a standard HITRAN 160-character format. Data for the deuterated isotopologues have been entered into HITRAN for the first time. The calculations employ the recently developed semi-empirical dipole moment functions [Li G, et al. J Quant Spectrosc Radiat Transfer 2013;121:78–90] and very accurate analytical potential energy functions and associated functions characterizing Born–Oppenheimer breakdown effects. Line-shape parameters have also been updated using the most recent available experimental and theoretical studies. Comparison with the previous HITRAN compilation has shown significant improvements.

New section of the HITRAN database: Collision-induced absorption (CIA)

This paper describes the addition of Collision-Induced Absorption (CIA) into the HITRAN compilation. The data from different experimental and theoretical sources have been cast into a consistent format and formalism. The implementation of these new spectral data into the HITRAN database is invaluable for modeling and interpreting spectra of telluric and other planetary atmospheres as well as stellar atmospheres. In this implementation for HITRAN, CIAs of N2, H2, O2, CO2, and CH4 due to various collisionally interacting atoms or molecules are presented. Some CIA spectra are given over an extended range of frequencies, including several H2 overtone bands that are dipole-forbidden in the non-interacting molecules. Temperatures from tens to thousands of Kelvin are considered, as required, for example, in astrophysical analyses of objects, including cool white dwarfs, brown dwarfs, M dwarfs, cool main sequence stars, solar and extra-solar planets, and the formation of so-called first stars.

The HITRAN 2008 molecular spectroscopic database

This paper describes the status of the 2008 edition of the HITRAN molecular spectroscopic database. The new edition is the first official public release since the 2004 edition, although a number of crucial updates had been made available online since 2004. The HITRAN compilation consists of several components that serve as input for radiative-transfer calculation codes: individual line parameters for the microwave through visible spectra of molecules in the gas phase; absorption cross-sections for molecules having dense spectral features, i.e. spectra in which the individual lines are not resolved; individual line parameters and absorption cross-sections for bands in the ultraviolet; refractive indices of aerosols, tables and files of general properties associated with the database; and database management software. The line-by-line portion of the database contains spectroscopic parameters for 42 molecules including many of their isotopologues.

Current updates of the water-vapor line list in HITRAN: A new “Diet” for air-broadened half-widths

The current edition of the HITRAN compilation employed a sophisticated algorithm for combining measurements available for the air-broadened half-widths of water-vapor absorption lines with theoretical values. Nevertheless, some of the values in the HITRAN database were found to be far from ideal, due to large dispersions that still exist in the experimental or theoretical methods. Therefore, new criteria were developed for introducing the best available air-broadened half-widths into HITRAN, based on physical principles and statistics. This update concerns the three most abundant isotopologues of water, with the values for H 2 17O and H 2 18O being the ones from analogous transitions of the principal isotopologues. The new parameters have been tested in different remote-sensing applications and improved constituent profiles were obtained. In total, air-broadened half-width values were updated for 11,787 transitions of water vapor in the HITRAN database (6789 for H 2 16O, 2906 for H 2 17O, and 2092 for H 2 18O). Some additional updates to the water-vapor line list are also presented. The resultant file (01_hit06.par) was uploaded to the HITRAN website ( http://www.cfa.harvard.edu/hitran/) in September 2006.

The effect of the half-width of the 22-GHz water vapor line on retrievals of temperature and water vapor profiles with a 12-channel microwave radiometer

We show that observed biases in retrievals of temperature and water vapor profiles from a 12-channel microwave radiometer arise from systematic differences between the observed and model-calculated brightness temperatures at five measurement frequencies between 22 and 30 GHz. Replacing the value for the air-broadened half-width of the 22-GHz water vapor line used in the Rosenkranz absorption model with the 5% smaller half-width from the HITRAN compilation largely eliminated the systematic differences in brightness temperatures. An a priori statistical retrieval based on the revised model demonstrated significant improvements in the accuracy and vertical resolution of the retrieved temperature and water vapor profiles. Additional improvements were demonstrated by combining the MWRP retrievals with those from the GOES-8 sounder and by incorporating brightness temperature measurements at off-zenith angles in the retrievals.

The HITRAN 2004 molecular spectroscopic database

This paper describes the status of the 2004 edition of the HITRAN molecular spectroscopic database. The HITRAN compilation consists of several components that serve as input for radiative transfer calculation codes: individual line parameters for the microwave through visible spectra of molecules in the gas phase; absorption cross-sections for molecules having dense spectral features, i.e., spectra in which the individual lines are unresolvable; individual line parameters and absorption cross-sections for bands in the ultra-violet; refractive indices of aerosols; tables and files of general properties associated with the database; and database management software. The line-by-line portion of the database contains spectroscopic parameters for 39 molecules including many of their isotopologues. The format of the section of the database on individual line parameters of HITRAN has undergone the most extensive enhancement in almost two decades. It now lists the Einstein A -coefficients, statistical weights of the upper and lower levels of the transitions, a better system for the representation of quantum identifications, and enhanced referencing and uncertainty codes. In addition, there is a provision for making corrections to the broadening of line transitions due to line mixing.

High spectral resolution solar absorption measurements of ethylene [formula omitted] in a forest fire smoke plume using HITRAN parameters: Tropospheric vertical profile retrieval

The tropospheric mixing ratio profile of ethylene ( C 2 H 4 ) has been retrieved from a high spectral resolution ground-based infrared solar absorption spectrum. The spectrum was recorded during intense fires in New South Wales, Australia on January 1, 2002, and was analyzed with the C 2 H 4 spectral parameters added to the 2000 HITRAN compilation. Absorption by C 2 H 4 in the smoke-affected spectrum extends over a broad spectral range in a region with observable rotational fine structure. The fine structure occurs in addition to the 949.5 cm - 1 ν 7 band Q branch that is traditionally used to quantify C 2 H 4 amounts from infrared atmospheric measurements assuming room temperature laboratory absorption coefficients. The measured spectrum is fitted to near the noise level with a retrieved vertical column of ( 3.8 ± 0.2 ) × 10 17 molecules per square centimeter. The retrieved vertical C 2 H 4 profile increases with altitude near the surface reaching a maximum of 37 parts per billion ( 10 - 9 ) near 1 km, decreasing above.

The HITRAN molecular spectroscopic database: edition of 2000 including updates through 2001

This paper describes the status circa 2001, of the HITRAN compilation that comprises the public edition available through 2001. The HITRAN compilation consists of several components useful for radiative transfer calculation codes: high-resolution spectroscopic parameters of molecules in the gas phase, absorption cross-sections for molecules with very dense spectral features, aerosol refractive indices, ultraviolet line-by-line parameters and absorption cross-sections, and associated database management software. The line-by-line portion of the database contains spectroscopic parameters for 38 molecules and their isotopologues and isotopomers suitable for calculating atmospheric transmission and radiance properties. Many more molecular species are presented in the infrared cross-section data than in the previous edition, especially the chlorofluorocarbons and their replacement gases. There is now sufficient representation so that quasi-quantitative simulations can be obtained with the standard radiance codes. In addition to the description and justification of new or modified data that have been incorporated since the last edition of HITRAN (1996), future modifications are indicated for cases considered to have a significant impact on remote-sensing experiments.

Linestrengths of nitric acid from 850 to [formula omitted

Several thousand line positions and strengths of HNO 3 in the 850– 920 cm −1 region were retrieved from spectra at low sample pressures at 299 K and high spectral resolution ( 0.0027 cm −1 ) using the McMath–Pierce Fourier transform spectrometer (FTS) at the National Solar Observatory located at Kitt Peak, AZ. Of these, 733 linestrengths of the ν 5 band and 402 lines of the 2 ν 9 band were measured with precisions of 10% or better. In addition, over 800 features with no assignments and 8–15% uncertainties in the linestrengths were obtained. The measured linestrengths of ν 5 and 2 ν 9 were compared to prior measurements and to the values given in the 2000 HITRAN compilation. The average ratios of HITRAN/present was found to be 1.14±0.06, but the relative band intensities of the fundamental and overtone were in agreement with the calculated values. The intensities of strong absorptions in the Q branch of the ν 5+ ν 9− ν 9 band (between 885.418 and 885.437 cm −1 ) were within 4% of the 2000 HITRAN values, although there was an offset in the positions. The analysis of these data was greatly hindered by the high density of transitions and the lack of knowledge about other hot bands in the region.

Determination of Self-, Air-, and Oxygen-Broadening Coefficients of Pure Rotational Absorption Lines of Ozone and of Their Temperature Dependencies

Room temperature measurements of self-, air-, and oxygen-broadening coefficients are reported for 101 pure rotational absorption lines for 16O3 covering a range of 7≤J″≤34 and 3≤K−1″≤11 in the spectral region 50 to 90 cm−. In addition, the temperature dependence of the coefficients has been determined for most of these lines. A total of 14 high-resolution Fourier transform far-IR spectra (0.004 cm− resolution) of ozone/air/dioxygen mixtures were recorded at various temperatures (212, 252, and 296 K). The broadening coefficients and corresponding temperature exponents were deduced by analyzing all of the 14 spectra simultaneously for each absorption line using a nonlinear least-squares fitting technique. Several sources of systematic errors were taken into account: the values of the partial pressures of the species involved, the value of the total optical path length, the sample temperature, thermal emission from sources other than the spectrometer source (e.g., sample emission), the effect of convolution with the instrument function, and intensity contributions from weak and neighbouring absorption lines. The variation of the determined broadening coefficients and temperature exponents with the rotational quantum numbers J″ and K−1″ has been examined. Furthermore the determined pressure-broadening parameters have been compared to the data reported in the 2000 edition of the HITRAN compilation.

SPECTROSCOPIC PARAMETERS FOR OZONE AND ITS ISOTOPES: CURRENT STATUS, PROSPECTS FOR IMPROVEMENT, AND THE IDENTIFICATION OF 16O 16O 17O AND 16O 17O 16O LINES IN INFRARED GROUND-BASED AND STRATOSPHERIC SOLAR ABSORPTION SPECTRA

We describe the updates to the spectroscopic parameters of ozone and its isotopes in the 1996 HITRAN compilation. Recent published studies not included in HITRAN are also summarized. Finally, we report the identification of infrared lines of the ν 3 bands of 16O 16O 17O and 16O 17O 16O in high-resolution solar spectra recorded by stratospheric balloon-borne and ground-based Fourier transform spectrometers.

Temperature Dependence of Air-Broadening and Shift Coefficients of O3Lines in the ν1Band

High-resolution Fourier transform absorption spectra of ozone broadened by dry air have been recorded at a number of temperatures from −63°C to 29°C. Using a multispectrum nonlinear least-squares procedure, we fit 29 of these spectra simultaneously to determine the air-broadening and shift coefficients and their temperature dependences for 450 lines in the 9-μm region; most of these belong to the ν1band. Partial air-broadening results were obtained for 104 additional lines, and room-temperature self-broadening coefficients were also determined for most of the 554 lines measured. These results cover a wide range of rotational quantum numbers, particularly in theRbranch, withJ″ ≤ 55 andKa″≤ 12. The variation of the retrieved broadening and shift parameters with the rotational quantum numbers has been examined; particularly interesting behavior of the broadening coefficients is noted as the value ofKa″approaches that ofJ″. The broadening and shift coefficients compare well with previous room-temperature measurements in the ν1and other bands. The temperature-dependence results are also consistent (within the stated uncertainties) with the few previous measurements of the temperature dependence of air- and N2-broadening coefficients in other O3bands, but disagree with the mean value given in the HITRAN compilation.

Validation of ozone profile retrievals from infrared ground‐based solar spectra

A direct validation of ozone profile retrievals from IR ground‐based high resolution solar spectra has been performed. The spectra were recorded at 0.0035 to 0.01 cm−1 resolution on 11 days between February and October 1994 at the Network for the Detection of Stratospheric Change station in Lauder, New Zealand (45.04°S, 169.68°E, 0.37 km altitude) and analyzed for the O3 profile with a line‐by‐line forward model and semiempirical application of the optimal estimation inversion technique of Rodgers. The line parameters on the 1992 HITRAN compilation were assumed in the analysis. Retrieved ozone columns in three atmospheric layers (0.37–12 km, 12–20 km, and 20–100 km) have been compared with correlative ozonesondes, microwave and Dobson spectrometer data from the same site. IR total and O3 columns above 20 km agree with Dobson and microwave measurements to better than 2%. For the layers 0.37–12 km and 12–20 km the differences between IR and integrated ozonesondes are −7±5% and 2±4%, respectively. Special exercises have been performed to show the applicability of the retrieval method to spectra with a resolution ∼0.02 cm−1 and better.

Comparison of infrared and Dobson total ozone columns measured from Lauder, New Zealand

Ozone total columns have been derived from 13 spectral intervals in 5 infrared bands and compared with values deduced from correlative measurements with a Dobson spectrophotometer. The observations were recorded on 10 days in 1994 at the Network for the Detection of Stratospheric Change station in Lauder, New Zealand. The infrared total columns were derived from spectral fittings of unblended, temperature‐insensitive ozone lines in high resolution solar absorption spectra. The line parameters on the 1992 HITRAN compilation were assumed with the O3 H2O relative volume mixing ratio and temperature profiles specified from correlative balloon ozonesonde, microwave O3, and radiosonde measurements. The retrieved IR/Dobson total column ratios ranged from 0.96 to 1.02 with the lower wavenumber bands yielding lower ratios. The results do not support the revised O3 intensity scale currently used to process O3 infrared measurements from 2 instruments on the Upper Atmosphere Research Satellite.

Indices of refraction for the hitran compilation

Indices of refraction of sulfuric acid solutions, water, and ice, which will become part of the HITRAN database, are discussed. Representative calculations are presented for the sulfate aerosol, to illustrate the broadband spectral features of i.r. aerosol extinction spectra. Values of the sulfuric acid mass density are used in an application of the Lorentz-Lorenz equation, which is used to estimate the sensitivity of extinction coefficients to temperature dependent refractive indices.

The HITRAN molecular database: Editions of 1991 and 1992

We describe in this paper the modifications, improvements, and enhancements to the HITRAN molecular absorption database that have occurred in the two editions of 1991 and 1992. The current database includes line parameters for 31 species and their isotopomers that are significant for terrestrial atmospheric studies. This line-by-line portion of HITRAN presently contains about 709,000 transitions between 0 and 23,000 cm -1 and contains three molecules not present in earlier versions: COF 2, SF 6, and H 2S. The HITRAN compilation has substantially more information on chlorofluorocarbons and other molecular species that exhibit dense spectra which are not amenable to line-by-line representation. The user access of the database has been advanced, and new media forms are now available for use on personal computers.

Infrared nitrogen dioxide: Line parameters in the HITRAN database

The authors present a discussion on the available data for nitrogen dioxide in the HITRAN database. The first part of the paper presents the 14N 16O 2 line positions and intensities which have been updated in the 1992 HITRAN compilation. The new data cover the pure rotation spectrum and the v 2 band (around 13.3 μm) and are based on new experimental and theoretical results. The second part of the discussion deals with the available data which need to be improved or updated, and this concerns mainly the v 3 band (around 6.2 μm). This spectral range corresponds to the strongest i.r. band of nitrogen dioxide and is frequently used for remote sensing of 14N 16O 2 from balloons or satellites.

Diode laser measurements of temperature-dependent line parameters for water vapor near 820 nm

Air- and self-broadening coefficients and relative line strenghts for 8–10 low-J lines in the (2 1 1) vibrational band of water vapor have been accurately measured over the T = 330–540 K range using an 817–824 nm GaAlAs diode laser. The technique of wavelength modulation with third-harmonic line locking and second-harmonic detection was used to derive the line parameters with accuracies of several percent from measurements with absorptivities as low as 2 x 10 -3. The linewidths and temperature coefficients are in good agreement with theoretical calculations and with recent measurements in the (2 2 1) and (3 0 1) bands. Absolute line strenghts have been derived from measurements on two of the lines and are found to be 21 ±4% higher than the values listed in the 1991 HITRAN compilation.

Stratospheric HNO3 measurements from 0.002‐cm−1 resolution solar occultation spectra and improved spectroscopic line parameters in the 5.8‐μm region

Measurements of stratospheric HNO3 are presented based on new very high resolution (0.002‐cm−1 full width at half maximum (FWHM)) solar occultation spectra recorded at 32°N latitude with a balloon‐borne interferometer in the region of the HNO3 v2 band at 5.8 μm and improved spectroscopic line parameters generated for this HNO3 band and the interfering bands of O3 and H2O. The line parameters for HNO3, computed from the spectroscopic constants reported by Maki, are a significant improvement in that the calculated positions are more accurate than previous data and the line list now includes higher J and Ka transitions needed to account for weaker HNO3 absorption features observable in the stratospheric spectra. Verifications of the new line parameters based on the stratospheric spectra and a 0.002‐cm−1 resolution HNO3 laboratory spectrum are presented along with comparisons generated with the parameters from the 1986 HITRAN compilation. Significant improvements are apparent for all the updated bands. Finally, the stratospheric HNO3 profile retrieved from the stratospheric solar spectra using a nonlinear least squares fitting algorithm and the new line parameters is reported and compared with previously reported measurements.