Atmospheric Trace Molecule Spectroscopy Research Articles

Stratospheric observations of CH3D and HDO from ATMOS infrared solar spectra: Enrichments of deuterium in methane and implications for HD

Stratospheric mixing ratios of CF3D from 100 mb to 17 mb (≈ 15 to 28 km) and HDO from 100 mb to 10 mb (≈ 15 to 32 km) have been inferred from high resolution solar occultation infrared spectra from the Atmospheric Trace MOlecule Spectroscopy (ATMOS) Fourier‐transform interferometer. The spectra, taken on board the Space Shuttle during the Spacelab 3 and ATLAS‐1, ‐2, and ‐3 missions, extend in latitude from 70°S to 65°N. We find CH3D entering the stratosphere at an average mixing ratio of (9.9±0.8) × 10−10 with a D/H ratio in methane (7.1±7.4)% less than that in Standard Mean Ocean Water (SMOW) (1σ combined precision and systematic error). In the mid to lower stratosphere, the average lifetime of CH3D is found to be (1.19±0.02) times that of CH4, resulting in an increasing D/H ratio in methane as air “ages” and the methane mixing ratio decreases. We find an average of (1.0±0.1) molecules of stratospheric HDO are produced for each CH3D destroyed (1σ combined precision and systematic error), indicating that the rate of HDO production is approximately equal to the rate of CH3D destruction. Assuming negligible amounts of deuterium in species other than HDO, CH3D and HD, this limits the possible change in the stratospheric HD mixing ratio below about 10 mb to be ±0.1 molecules HD created per molecule CH3D destroyed.

Trends of OCS, HCN, SF6, CHClF2 (HCFC‐22) in the lower stratosphere from 1985 and 1994 Atmospheric Trace Molecule Spectroscopy Experiment measurements near 30°N latitude

Volume mixing ratio (VMR) profiles of OCS, HCN, SF6, and CHClF2 (HCFC‐22) have been measured near 30°N latitude by the Atmospheric Trace Molecule Spectroscopy Fourier transform spectrometer during shuttle flights on 29 April–6 May 1985 and 3–2 November 1994. The change in the concentration of each molecule in the lower stratosphere has been derived for this 9 1/2‐year period by comparing measurements between potential temperatures of 395 to 800 K (∼17 to 30 km altitude) relative to simultaneously measured values of the long‐lived tracer N2O. Exponential rates of increase inferred for 1985–to–1994 from these comparisons are (0.1 ± 0.4)% yr−1 for OCS, (1.0±1.0)% yr−1 for HCN, (8.0±0.7)% yr−1 for SF6, and (8.0±1.0)% yr−1 for CHClF2 (HCFC‐22), 1 sigma. The lack of an appreciable trend for OCS suggests the background (i.e., nonvolcanic) source of stratospheric aerosol was the same during the two periods. These results are compared with trends reported in the literature.

1995 Atmospheric Trace Molecule Spectroscopy (ATMOS) linelist

The Atmospheric Trace Molecule Spectroscopy (ATMOS) experiment uses a Fourier-transform spectrometer on board the Space Shuttle to record infrared solar occultation spectra of the atmosphere at 0.01-cm(-1) resolution. The current version of the molecular spectroscopic database used for the analysis of the data obtained during three Space Shuttle missions between 1992 and 1994 is described. It is an extension of the effort first described by Brown et al. [Appl. Opt. 26, 5154 (1987)] to maintain an up-to-date database for the ATMOS experiment. The three-part ATMOS compilation contains line parameters of 49 molecular species between 0 and 10000 cm(-1). The main list, with nearly 700,000 entries, is an updated version of the HITRAN 1992 database. The second compilation contains supplemental line parameters, and the third set consists of absorption cross sections to represent the unresolvable features of heavy molecules. The differences between the ATMOS database and other public compilations are discussed.

Remote sensing of the Earth’s atmosphere from space with high-resolution Fourier-transform spectroscopy: development and methodology of data processing for the Atmospheric Trace Molecule Spectroscopy experiment

The methodology of spectroscopic remote sensing with high-resolution Fourier-transform spectra obtained from low Earth orbit by the Atmospheric Trace Molecule Spectroscopy (ATMOS) experiment is discussed. During the course of the Atmospheric Laboratory for Applications and Science (ATLAS) shuttle missions (1992-1994) a flexible, yet reproducible, retrieval strategy was developed that culminated in the near-real-time processing of telemetry data into vertical profiles of atmospheric composition during the ATLAS-3 mission. The development, evolution, robustness, and validation of the measurements are presented and assessed with a summary comparison of trace-gas observations within the Antarctic polar vortex in November 1994.

Pressure sounding of the middle atmosphere from ATMOS solar occultation measurements of atmospheric CO_2 absorption lines

A method for retrieving the atmospheric pressure corresponding to the tangent point of an infrared spectrum recorded in the solar occultation mode is described and applied to measurements made by the Atmospheric Trace Molecule Spectroscopy (ATMOS) Fourier-transform spectrometer. Tangent pressure values are inferred from measurements of isolated CO(2) lines with temperature-insensitive strengths by measuring the slant-column CO(2) amount and by adjusting the viewing geometry until the calculated column matches the observed column. Tangent pressures are determined with a spectroscopic precision of l%-3%, corresponding to a tangent-point height precision of 70-210 m. The total uncertainty is limited primarily by the quality of the spectra and ranges between 4% and 6% (280-420 m) for spectra with signal-to-noise ratios of 300:1 and between 4% and 10% for spectra with signal-to-noise ratios of 100:1. The retrieval of atmospheric pressure increases the accuracy of the retrieved-gas concentrations by minimizing the effect of systematic errors introduced by climatological pressure data, ephemeris parameters, and the uncertainties in instrumental pointing.

Observations of the infrared solar spectrum from space by the ATMOS experiment

The final flight of the Atmospheric Trace Molecule Spectroscopy experiment as part of the Atmospheric Laboratory for Applications and Science (ATLAS-3) Space Shuttle mission in 1994 provided a new opportunity to measure broadband (625-4800 cm(-1), 2.1-16 µm) infrared solar spectra at anunapodized resolution of 0.01 cm(-1) from space. The majority of the observations were obtained as exoatmospheric, near Sun center, absorption spectra, which were later ratioed to grazing atmospheric measurements to compute the atmospheric transmission of the Earth's atmosphere and analyzed for vertical profiles of minor and trace gases. Relative to the SPACELAB-3 mission that produced 4800 high Sun spectra (which were averaged into four grand average spectra), the ATLAS-3 mission produced some 40,000 high Sun spectra (which have been similarly averaged) with an improvement in signal-to-noise ratio of a factor of 3-4 in the spectral region between 1000 and 4800 cm(-1). A brief description of the spectral calibration and spectral quality is given as well as the location of electronic archives of these spectra.

ATMOS observations of nitric oxide in the mesosphere and lower thermosphere

The nitric oxide density in the Earth's atmosphere between 50 and 130 km was measured by the ATMOS (Atmospheric Trace Molecule Spectroscopy) experiment onboard the Spacelab 3 mission on April 30, 1985 and May 1, 1985. Three observations were made at geographic latitudes of 35°N, 34°N, and 29°N which correspond to geomagnetic latitudes of 26°N, 44°N, and 39°N. The ATMOS measurements of nitric oxide in the thermosphere were compared to SME measurements made during the same time period. The two techniques agree within the geophysical variability of thermospheric nitric oxide. The observations show that during a geomagnetic storm there is a strong latitudinal gradient in the nitric oxide density in the lower thermosphere. Comparison of the observations with a one‐dimensional time‐dependent model shows that at midlatitudes, nitric oxide is transported downward from the thermosphere into the mesosphere as low as 70 km but not downward into the stratosphere.

Validation of nitric oxide and nitrogen dioxide measurements made by the Halogen Occultation Experiment for UARS platform

The Halogen Occultation Experiment (HALOE) experiment on Upper Atmosphere Research Satellite (UARS) performs solar occultation (sunrise and sunset) measurements to infer the composition and structure of the stratosphere and mesosphere. Two of the HALOE channels, centered at 5.26 μm and 6.25 μm, are designed to infer concentrations of nitric oxide and nitrogen dioxide respectively. The NO measurements extend from the lower stratosphere up to 130 km, while the NO2 results typically range from the lower stratosphere to 50 km and higher near the winter terminator. Comparison with results from various instruments are presented, including satellite‐, balloon‐, and ground‐based measurements. Both NO and NO2 can show large percentage errors in the presence of heavy aerosol concentrations, confined to below 25 km and before 1993. The NO2 measurements show mean differences with correlative measurements of about 10 to 15% over the middle stratosphere. The NO2 precision is about 7.5 × 10−13 atm, degrading to 2 × 10−12 atm in the lower stratosphere. The NO differences are similar in the middle stratosphere but sometimes show a low bias (as much as 35%) between 30 and 60 km with some correlative measurements. NO precision when expressed in units of density is nearly constant at 1 × 10−12 atmospheres, or approximately 0.1 ppbv at 10.0 mb or 1.0 ppbv at 1.0 mb, and so forth when expressed in mixing ratio. Above 65 km, agreement in the mean with Atmospheric Trace Molecule Spectroscopy (ATMOS) NO results is very good, typically ±15%. Model comparisons are also presented, showing good agreement with both expected morphology and diurnal behavior for both NO2 and NO.

Comparison of CLAES preliminary N2O5 data with correlative data and a model

The cryogenic limb etalon array spectrometer (CLAES) aboard the Upper Atmosphere Research Satellite (UARS) has made near‐global measurements of N2O5. Data for 388 days have been processed to version 7 (V7) for the period from January 9, 1992, to April 25, 1993. Results from UARS instruments, including CLAES and the improved stratospheric and mesospheric sounder (ISAMS) provide the first near‐global N2O5 measurements. Retrieval below 3.16 mbar is adversely affected by aerosols and above 1.47 mbar by lack of signal and possible instrument effects, so data usage is recommended for just the three “UARS pressure surfaces” 3.16, 2.15, and 1.47 mbar. A comparison of the diurnal data variation with the model suggests there are offsets in the data that are to first order diurnally independent. These offsets are tabulated to facilitate subtraction, which is recommended for most data applications. Candidate mechanisms for the offsets are discussed. Comparisons of CLAES data with the offsets subtracted, with profiles obtained by the shuttle‐deployed Atmospheric Trace Molecule Spectroscopy (ATMOS) experiment and concurrent ISAMS profiles, and with a profile obtained by the balloon‐borne NASA Jet Propulsion Laboratory (JPL) MARK IV instrument, show poorest agreement in equatorial regions at 3.15 mbar where CLAES values are larger by about 30 to 40%. At higher altitudes and latitudes the comparison improves and tends toward consistency with systematic error estimates that are based on instrument and retrieval process characterization and range from 14% at 3.16 mbar to 21% at 1.47 mbar. A similar estimate of random CLAES error ranges from 7% at 3.16 mbar to 26% at 1.47 mbar. By comparison, the average values of the error estimates generated by the production processing algorithm at 3.16 and 1.47 mbar are 8 and 36%, respectively, and the average values derived from the observed data variability are 19 and 24%. Confidence is enhanced by the good global scale agreement and correlation of CLAES and ISAMS during an N2O5 enhancement event in early–mid‐January 1992 polar winter, in which values >5.5 parts per billion at 3.16 mbar by volume are observed. A description of artifacts that may occur at 3.16 mbar and much less frequently at 2.15 mbar, during this and other enhancement conditions, and the demonstrated approach to eliminate these in future versions, is given in the text.

Validation studies using multiwavelength Cryogenic Limb Array Etalon Spectrometer (CLAES) observations of stratospheric aerosol

Validation studies of multiwavelength Cryogenic Limb Array Etalon Spectrometer (CLAES) observations of stratospheric aerosol are discussed. An error analysis of the CLAES aerosol extinction data is presented. Aerosol extinction precision values are estimated at latitudes and times at which consecutive Upper Atmosphere Research Satellite (UARS) orbits overlap. Comparisons of CLAES aerosol data with theoretical Mie calculations, based upon in situ particle size measurements at Laramie, Wyoming, are presented. CLAES aerosol data are also compared to scaled aerosol extinction measured by the Stratospheric Aerosol and Gas Experiment (SAGE II) and Atmospheric Trace Molecule Spectroscopy (ATMOS) experiments. Observed and calculated extinction spectra, from CLAES, Improved Stratospheric and Mesospheric Sounder (ISAMS), and Halogen Occultation Experiment (HALOE) data, are compared. CLAES extinction data have precisions between 10 and 25%, instrumental biases near 30%, and accuracies between 33 and 43%.

Proposed reference model for middle atmosphere water vapor

Several new and significant satellite data sets on middle atmosphere water vapor have been produced recently. They include data from the Stratospheric Aerosol and Gas Experiment II (SAGE II) and the Nimbus-7 Stratospheric and Mesospheric Sounder (SAMS) experiment. The SAGE II data provide an estimate of interannual variability of water vapor in the stratosphere. The SAMS data are appropriate for the upper stratosphere and lower mesosphere. We combine these two data sets with those from the Nimbus-7 Limb Infrared Monitor of the Stratosphere (LIMS) experiment to update the COSPAR interim reference model for water vapor. Water vapor profiles from the Spacelab 3 Atmospheric Trace Molecule Spectroscopy (ATMOS) experiment, ground-based microwave, and in situ balloon and air-craft measurements have been used to check the quality of the satellite data sets. The updated reference model is given as a function of latitude and pressure altitude and now covers all four seasons. Tabulations are included for these seasonal water vapor mixing ratios (in ppmv) and their estimated errors (in percent).

Presence of terrestrial atmospheric gas absorption bands in standard extraterrestrial solar irradiance curves in the near-infrared spectral region

The solar irradiance curves compiled by Wehrli [Physikalisch-Meteorologisches Observatorium Publ. 615 (World Radiation Center, Davosdorf, Switzerland, 1985)] and by Neckel and Labs [Sol. Phys. 90, 205 (1984)] are widely used. These curves were obtained based on measurements of solar radiation from the ground and from aircraft platforms. Contaminations in these curves by atmospheric gaseous absorptions were inevitable. A technique for deriving the transmittance spectrum of the Sun's atmosphere from high-resolution (0.01 cm(-1)) solar occultation spectra measured above the Earth's atmosphere by the use of atmospheric trace molecule spectroscopy (ATMOS) aboard the space shuttle is described. The comparisons of the derived ATMOS solar transmittance spectrum with the two solar irradiance curves show that he curve derived by Wehrli contains many absorption features in the 2.0-2.5-µm region that are not of solar origin, whereas the curve obtained by Neckel and Labs is completely devoid of weak solar absorption features that should be there. An Earth atmospheric oxygen band at 1.268 µm and a water-vapor band near 0.94 µm are likely present in the curve obtained by Wehrli. It is shown that the solar irradiance measurement errors in some narrow spectral intervals can be as large as 20%. An improved solar irradiance spectrum is formed by the incorporation of the solar transmittance spectrum derived from the ATMOS data into the solar irradiance spectrum from Neckel and Labs. The availability of a new solar spectrum from 50 to 50 000 cm(-1) from the U.S. Air Force Phillips Laboratory is also discussed.

ATMOS/ATLAS 1 measurements of thermospheric and mesospheric nitric oxide

The atmospheric trace molecule spectroscopy (ATMOS) instrument obtained solar occultation spectra of the terrestrial atmosphere during the Atmospheric Laboratory for Applications and Science (ATLAS 1) mission of March 26–April 4, 1992. During this time, Ap varied between 11 and 18 while the F10.7 index was near 192. The analyses of the 5.3‐μm spectral data to derive nitric oxide densities in the lower thermosphere and mesosphere are described here. The results show that a peak NO density of 1.0×108 cm−3 occurs at 105±2.5 km for the latitude range 38°N–58°S. The density values are higher than previously reported using UV measurements. These measurements worsen the discrepancy with photochemical models at low latitudes where models already underpredict nitric oxide.

April 1993 Arctic profiles of stratospheric HCl, ClONO2, and CCl2F2 from atmospheric trace molecule spectroscopy/ATLAS 2 infrared solar occultation spectra

Partitioning among the major components of the stratospheric odd chlorine family inside and outside of the remanent Arctic vortex has been studied on the basis of infrared solar occultation measurements obtained by the atmospheric trace molecule spectroscopy (ATMOS) Fourier transform spectrometer during the ATLAS 2 shuttle mission (April 8–17, 1993). Profiles of hydrogen chloride (HCl) and simultaneous profiles of chlorine nitrate (ClONO2) and CFC‐12 (CCl2F2) are reported for examples of in‐vortex and out‐of‐vortex conditions. Increased ClONO2 volume‐mixing ratios (VMRs) are measured in the vortex below 20 mbar (∼25 km altitude) with a peak ClONO2 VMR of 2.05±0.45 ppbv (10−9 per volume) at 56 mbar (∼19 km altitude). The reported error correspond to 1σ uncertainties. Simultaneous CCl2F2 and N2O measurements, combined with published empirical relations, indicate that only 0.34±0.15 ppbv, about 10% of total chlorine, was bound in organic species at the ClONO2 VMR peak in the vortex. A colocated vortex profile of HCl, referenced to simultaneous N2O VMR measurements, has been used to derive a HCl mixing ratio of 1.21±0.12 ppbv corresponding to the ClONO2 VMR peak. The internal consistency of the ATMOS measurements is demonstrated by the agreement between the total chlorine mixing ratio of 3.60±0.72 ppbv derived at the ClONO2 VMR peak in the vortex and HCl measurements of 3.37±0.37 and 3.76±0.41 ppbv at 0.56 mbar, where HCl is the only significant chlorine‐bearing molecule. Outside the vortex the mixing ratio of HCl exceeds the mixing ratio of ClONO2 throughout the stratosphere.

H2SO4 photolysis: A source of sulfur dioxide in the upper stratosphere

Numerous absorption lines of stratospheric sulfur dioxide (SO2) have been identified in solar occultation spectra recorded by the Atmospheric Trace Molecule Spectroscopy (ATMOS) Fourier transform spectrometer during the Atmospheric Laboratory for Applications and Science (ATLAS)‐1 shuttle mission (March 24‐April 2, 1992). Based on their analysis, a volume mixing ratio profile of SO2 increasing from (13 ± 4) p.p.t.v. (parts per 10−12 by volume) at 16 mbar (∼ 28 km) to 455 ± 90 p.p.t.v. at 0.63 mbar (∼ 52 km) has been measured with no significant profile differences between 20°N and 60°S latitude. The increase in the SO2 mixing ratios with altitude indicates the presence of a source of SO2 in the upper stratosphere. Profiles retrieved from ATMOS spectra recorded during shuttle flights in April‐May 1985 and April 1993 show similar vertical distributions but lower concentrations. Two‐dimensional model calculations with SO2 assumed as the end product of H2SO4 photolysis produce SO2 profiles consistent with the ATMOS measurements to within about a factor of 2.

Stratospheric and mesospheric pressure‐temperature profiles from rotational analysis of CO2 lines in atmospheric trace molecule spectroscopy/ATLAS 1 infrared solar occultation spectra

A simple, classical, and expedient method for the retrieval of atmospheric pressure‐temperature profiles has been applied to the high‐resolution infrared solar absorption spectra obtained with the atmospheric trace molecule spectroscopy (ATMOS) instrument. The basis for this method is a rotational analysis of retrieved apparent abundances from CO2 rovibrational absorption lines, employing existing constituent concentration retrieval software used in the analysis of data returned by ATMOS. Pressure‐temperature profiles derived from spectra acquired during the ATLAS 1 space shuttle mission of March–April 1992 are quantitatively evaluated and compared with climatological and meteorological data as a means of assessing the validity of this approach.

Increase in levels of stratospheric chlorine and fluorine loading between 1985 and 1992

Mixing ratios of 3.44 ppbv (parts per billion by volume) and 1.23 ppbv for HCl and HF above 50 km, surrogates for total chlorine and fluorine, have been measured by the Atmospheric Trace Molecule Spectroscopy (ATMOS) experiment on a March 1992 flight of the Space Shuttle. Compared to the measured values obtained on a 1985 flight, these correspond to a 37% and 62% increase for HCl and HF, respectively. The derived trend in HCl (∼0.13 ppbv per year) is in good agreement with the model‐predicted increase in chlorine loading of 0.13 ppbv per year [Prather and Watson, 1990], and with the measured trends in HCl total column abundance from reported ground‐based observations. The main source of this change can be attributed to the release of man‐made chlorofluorocarbons (CFCs) and hydrochloro‐fluorocarbons (HCFCs). This new value for HCl represents an upper limit to the inorganic chlorine concentration in the stratosphere available for participation in photochemical processes which destroy ozone.

Practical example of the correction of Fourier-transform spectra for detector nonlinearity

HgCdTe photoconductive detectors can display a nonlinear response when illuminated. In interferometric applications, this behavior must be accounted for in the data transformation process to avoid errors in the measurement of the spectral distribution of the incident radiation. A model for the distortion of the interferogram is proposed and applied to solar observations made by the Atmospheric Trace Molecule Spectroscopy (ATMOS) Fourier-transform spectrometer during orbital sunrise and sunset from the Space Shuttle. Empirical estimation of the dc current level is necessary for this instrument, and satisfactory nonlinearity correction is obtained for several of the primary ATMOS optical filters. For ATMOS broadband optical filters that cover more than one half the alias bandwidth, the model is inadequate because of the presence of antialiasing electronic filters within the instrument, and it is necessary to resort to estimation and subtraction of the residual baseline offset. In either case the remaining base line offsets are typically smaller than 1%, which is satisfactory, although offset remains a significant systematic source of error in the estimation of the abundance of telluric and solar constituents from the spectra.

Profiles of stratospheric chlorine nitrate (ClONO2) from atmospheric trace molecule spectroscopy/ATLAS 1 infrared solar occultation spectra

Stratospheric volume mixing ratio profiles of chlorine nitrate (ClONO2) have been retrieved from 0.01‐cm−1 resolution infrared solar occultation spectra recorded at latitudes between 14°N and 54°S by the atmospheric trace molecule spectroscopy Fourier transform spectrometer during the ATLAS 1 shuttle mission (March 24 to April 2, 1992). The results were obtained from nonlinear least squares fittings of the ClONO2 ν4 band Q branch at 780.21 cm−1 with improved spectroscopic parameters generated on the basis of recent laboratory work. The individual profiles, which have an accuracy of about ±20%, are compared with previous observations and model calculations.

Mid-infrared extinction by sulfate aerosols from the Mt Pinatubo eruption

Quantitative measurements of the wavelength dependence of aerosol extinction in the 750–3400 cm -1 spectral region have been derived from 0.01 cm -1 resolution stratospheric solar occultation spectra recorded by the ATMOS (Atmospheric Trace Molecule Spectroscopy) Fourier transform spectrometer about 9 1 2 months after the Mt Pinatubo volcanic eruption. Strong, broad aerosol features have been identified near 900, 1060, 1720, and 2900 cm -1 below a tangent height of ~30 km. Aerosol extinction measurements derived from ~0.05 cm -1 wide microwindows nearly free of telluric line absorption in the ATMOS spectra are compared with transmission calculations derived from aerosol size distribution profiles retrieved from correlative SAGE (Stratospheric Aerosol and Gas Experiment) II visible and near i.r. extinction measurements, seasonal and zonally averaged H 2SO 4 aerosol weight percentage profiles, and published sulfuric acid optical constants derived from room temperature laboratory measurements. The calculated shapes and positions of the aerosol features are generally consistent with the observations, thereby confirming that the aerosols are predominantly concentrated H 2SO 4-H 2O droplets, but there are significant differences between the measured and calculated wavelength dependences of the aerosol extinction. We attribute these differences as primarily the result of errors in the calculated low temperature H 2SO 4-H 2O optical constants. Errors in both the published room temperature optical constants and the limitations of the Lorentz-Lorenz relation are likely to be important.