Projectile-charge-changing cross sections for electron capture by H+ and H collisions with O atoms and electron loss by H collisions with O atoms have been determined. The H+ and H energies ranged from 2.0 down to 0.125 keV. The cross-beam technique involved measuring the cross-section ratios for reactions with O-atom targets to those for O-2 targets. The O-atom-target cross sections were then obtained by normalizing these ratios to previously measured O-2-target cross sections. The experimental apparatus employed is described, and the measured results are compared with other available data.

For the direct measurement of neutral gas in the heliosphere, e.g. interstellar neutral gas, a sensitive neutral particle imaging detector is needed in the energy range of 10 eV 1000 eV. For successful detection, the neutral particles have to be ionized rst, which will be accomplished via surface ionization. This method is currently successfully employed by the LENA instrument on the IMAGE mission. We present a laboratory prototype of an improved version for a neutral particle mass spectrometer and will discuss its instrument characteristics. Performance is evaluated with emphasis on the neutral to negative ions conversion for H and O and the collection of these ions by the mass spectrometer. Measurements of the detection e ciency of the prototype for primary neutral hydrogen and oxygen atoms are presented. Several conversion surfaces were investigated and all are potential candidates for a neutral particle imaging instrument of the next generation.

High-resolution ground-based infrared solar spectra are routinely recorded at the Network for the Detection of Stratospheric Change (NDSC) stations. These data sets play a key role in providing a long-term record of atmospheric composition and their links to climate change. The analysis of observed infrared spectra involves comparison to a computer-modeled atmosphere where knowledge of the air mass distribution is an essential component. This note summarises improvements made to an existing and widely used computer code (FSCATM) to perform refractive ray-tracing and calculation of the air mass distribution. Changes were made towards higher vertical resolution in the troposphere and increased numerical precision. The revised FSCATM improves the analysis of infrared spectra mostly through the more accurate representation of the temperature profile. Air mass differences with respect to earlier versions are documented and are typically <0.7%, exceptions being extreme cases of inversion layers. The current version provides ray tracing and air mass calculations for any terrestrial observation site. The output files are reported in a format compatible with the SFIT and SFIT2 retrieval algorithms, which are widely used for NDSC infrared atmospheric studies. The improved computer code, documentation, reference profiles, and test cases are available electronically.

Nitric acid plays an important role in processes leading to stratospheric ozone loss in polar regions. Spectroscopic absorption measurements of nitric acid have been made during the sunlit part of the Antarctic year at Arrival Heights (78°S, 167°E) since the late 1980s. This paper presents the first extension of these nitric acid measurements through the winter, using the Moon as a light source. Both solar and lunar measurements for the years 1998–2003 are presented. For the lunar measurements, additional corrections owing to emission of the atmosphere and the instrument must be made. The measurements show that the column amount of nitric acid within the polar vortex continues to increase after polar sunset reaching values of ∼2.5 × 1016 molecules cm−2 ∼1 month after sunset. When temperatures become low enough for the condensation of water and nitric acid molecules, polar stratospheric clouds form, and rapid depletion of the gaseous nitric acid column is observed. The measurements have captured this event particularly well in 2002. At the time of the polar sunrise the column amounts of nitric acid are extremely depleted and are as low as 0.5 × 1016 molecules cm−2. During the spring period the site can sample air from both inside and outside the polar vortex. Inside the vortex the observed gradual recovery of HNO3 in the spring and summer months is consistent with predictions of denitrification occurring during the Antarctic winter. For measurements outside the vortex, higher HNO3 columns are observed.

The CO2 triad of bands in the 9300–9700cm−1 region have been observed in near infrared 0.05cm−1 resolution ground-based solar absorption spectra. This interval is a portion of spectra taken in the 9000–12,000cm−1 region, at large solar zenith angles. Considering the available line positions and pressure line shifts for CO2, H2O and O2 in this region as of 2000, it was concluded that these observations show significant inconsistencies among the line positions of the species as listed in the atmospheric spectroscopy databases. The spectra allow a better definition of the O2 (0–1) X3Σg−−a1Δg band, with the discrete (0–1) transitions observable in the 9300–9450cm−1, superimposed on a collision-induced continuum covering the 9200–9700cm−1 region. This continuum, as well as the (0–0) continuum in the 7900cm−1 region, have been previously studied only from atmospheric spectra with much lower spectral resolution. The discrete O2 (1–0) transitions of the X3Σg−−b1Σg+ atmospheric B-band are observed in the 11,500–11,600cm−1 region, but no evidence is found for an underlying continuum. A recent laboratory study of the 2ν1+3ν312CO2 triad significantly improves the consistency between the O2, H2O and CO2 lines in the atmospheric spectra.

Experimental results of atom-surface scattering are presented for variable energy (25–200 eV) collisions of hydrogen with a polycrystalline copper surface. Negative ion measurements are made for proton and hydrogen-atom beams impacting the surface. Energy and angular distributions of the resulting H− ions are analyzed for an 18° angle of incidence. Charge state effects become apparent in the H− ion energy spectra at incident energies less than ∼70 eV. Measurements show that H− ions resulting from incident hydrogen atoms are approximately 3 eV less energetic than those from protons with the same kinetic energy. Energy losses can be accounted for by the inclusion of charge state dependent thresholds in a linear function of incident energy.

A heliostat has been designed and built for use in optical remote sensing of the atmosphere. The heliostat uses two flat mirrors to track the sun and direct the sunlight to optical instruments. A stepper motor driven horizontal turntable is used to track the sun in azimuth and support an elevation assembly and a mechanical tower. The stepper motor driven elevation assembly drives an acquisition mirror that tracks the sun in elevation. This mirror directs the solar beam to a secondary mirror fixed on the mechanical tower. The secondary mirror then directs the solar beam along the axis of the tracker for use in measurements.A sensitive, high resolution CCD camera, receives a small part of the solar beam to analyze for fine servo-control. Ground based tests have demonstrated this instrument's tracking capability for the sun, the moon, stars and for long pathlength sources. Presently, this system is coupled with a high-resolution Brucker 120M spectrometer used to obtain solar absorption spectra.The heliostat directs the solar radiation along the spectrometer optical axis. The pointing precision was measured to be better than 0.5 arcsec. A description of the heliostat is presented, as well as the results of ground tests.

Long‐term time series of hydrogen chloride (HCl) and chlorine nitrate (ClONO 2 ) total column abundances has been retrieved from high spectral resolution ground‐based solar absorption spectra recorded with infrared Fourier transform spectrometers at nine NDSC (Network for the Detection of Stratospheric Change) sites in both Northern and Southern Hemispheres. The data sets span up to 24 years and most extend until the end of 2001. The time series of Cl y (defined here as the sum of the HCl and ClONO 2 columns) from the three locations with the longest time‐span records show rapid increases until the early 1990s superimposed on marked day‐to‐day, seasonal and inter‐annual variability. Subsequently, the buildup in Cl y slows and reaches a broad plateau after 1996, also characterized by variability. A similar time evolution is also found in the total chlorine concentration at 55 km altitude derived from Halogen Occultation Experiment (HALOE) global observations since 1991. The stabilization of inorganic chlorine observed in both the total columns and at 55 km altitude indicates that the near‐global 1993 organic chlorine (CCl y ) peak at the Earth's surface has now propagated over a broad altitude range in the upper atmosphere, though the time lag is difficult to quantify precisely from the current data sets, due to variability. We compare the three longest measured time series with two‐dimensional model calculations extending from 1977 to 2010, based on a halocarbon scenario that assumes past measured trends and a realistic extrapolation into the future. The model predicts broad Cl y maxima consistent with the long‐term observations, followed by a slow Cl y decline reaching 12–14% relative to the peak by 2010. The data reported here confirm the effectiveness of the Montreal Protocol and its Amendments and Adjustments in progressively phasing out the major man‐related perturbations of the stratospheric ozone layer, in particular, the anthropogenic chlorine‐bearing source gases.

Infrared solar spectra recorded with the Fourier transform spectrometer in the McMath solar telescope complex on Kitt Peak (31.9°N latitude, 111.6°W, 2.09km altitude), southwest of Tucson, Arizona, have been analyzed to retrieve average SF6 tropospheric mixing ratios over a two-decade time span. The analysis is based primarily on spectral fits to absorption by the intense, unresolved ν3 band Q branch at 947.9cm−1. A best fit to measurements recorded with SF6 near typical background concentrations yields a SF6 increase in the average tropospheric mixing ratio from 1.13pptv (10−12 per unit volume) in March 1982 to 3.77pptv in March 2002. The long-term increase by a factor of 3.34 over the time span is consistent with the rapid growth of surface mixing ratios measured in situ at Northern Hemisphere remote stations, though the infrared measurements show a large scatter. Average tropospheric mixing ratio enhancements above background by 2–3 orders of magnitude have been identified in spectra recorded on 5 days between November 1988 and April 1997. These spectra were individually analyzed in an attempt to detect the strongest 8–12μm band of SF5CF3, a molecule recently identified with an atmospheric growth that has closely paralleled the rise in SF6 during the past three decades. Absorption by the strongest SF5CF3 band was predicted to be above the noise level in the Kitt Peak spectrum with the highest average mean tropospheric SF6 mixing ratio, assuming the reported atmospheric SF5CF3/SF6 ratio and a room temperature absorption cross sections reported for the SF5CF3 903-cm−1 band. An upper limit of 8×1015 moleculescm−2 for the SF5CF3 total column was estimated for this case. We hypothesize that the highly elevated SF6 levels above Kitt Peak resulted from a local release experiment rather than production via electrochemical fluoridation of intermediate products, the proposed source of atmospheric SF5CF3. The absence of the SF5CF3 feature in the spectra with elevated SF6 is consistent with the absence of SF5CF3 reported in a pure SF6 sample.

In this article we review ozone spectroscopy from the microwave to the ultraviolet since the release of the 1996 HITRAN database. Uncertainties, deficiencies, areas of potential improvement, and anticipated new spectral line parameters datasets are highlighted.

Long-term time series of hydrogen chloride (HCl) and chlorine nitrate (ClONO2) total column abundances has been retrieved from high spectral resolution ground-based solar absorption spectra recorded with infrared Fourier transform spectrometers at nine NDSC (Network for the Detection of Stratospheric Change) sites in both Northern and Southern Hemispheres. The data sets span up to 24 years and most extend until the end of 2001. The time series of Cl-y (defined here as the sum of the HCl and ClONO2 columns) from the three locations with the longest time-span records show rapid increases until the early 1990s superimposed on marked day-to-day, seasonal and inter-annual variability. Subsequently, the buildup in Cl-y slows and reaches a broad plateau after 1996, also characterized by variability. A similar time evolution is also found in the total chlorine concentration at 55 km altitude derived from Halogen Occultation Experiment (HALOE) global observations since 1991. The stabilization of inorganic chlorine observed in both the total columns and at 55 km altitude indicates that the near-global 1993 organic chlorine (CCly) peak at the Earth's surface has now propagated over a broad altitude range in the upper atmosphere, though the time lag is difficult to quantify precisely from the current data sets, due to variability. We compare the three longest measured time series with two-dimensional model calculations extending from 1977 to 2010, based on a halocarbon scenario that assumes past measured trends and a realistic extrapolation into the future. The model predicts broad Cl-y maxima consistent with the long-term observations, followed by a slow Cl-y decline reaching 12-14% relative to the peak by 2010. The data reported here confirm the effectiveness of the Montreal Protocol and its Amendments and Adjustments in progressively phasing out the major man-related perturbations of the stratospheric ozone layer, in particular, the anthropogenic chlorine-bearing source gases.

The CO2 triad of bands in the 9300–9700cm−1 region have been observed in near infrared 0.05cm−1 resolution ground-based solar absorption spectra. This interval is a portion of spectra taken in the 9000–12,000cm−1 region, at large solar zenith angles. Considering the available line positions and pressure line shifts for CO2, H2O and O2 in this region as of 2000, it was concluded that these observations show significant inconsistencies among the line positions of the species as listed in the atmospheric spectroscopy databases. The spectra allow a better definition of the O2 (0–1) X3Σg−−a1Δg band, with the discrete (0–1) transitions observable in the 9300–9450cm−1, superimposed on a collision-induced continuum covering the 9200–9700cm−1 region. This continuum, as well as the (0–0) continuum in the 7900cm−1 region, have been previously studied only from atmospheric spectra with much lower spectral resolution. The discrete O2 (1–0) transitions of the X3Σg−−b1Σg+ atmospheric B-band are observed in the 11,500–11,600cm−1 region, but no evidence is found for an underlying continuum. A recent laboratory study of the 2ν1+3ν312CO2 triad significantly improves the consistency between the O2, H2O and CO2 lines in the atmospheric spectra.

Get PDF Email Share Share with Facebook Tweet This Post on reddit Share with LinkedIn Add to CiteULike Add to Mendeley Add to BibSonomy Get Citation Copy Citation Text E. Neefs, F. Scolas, M. De Mazière, B. Barret, T. Stephen, and T. Hawat, "The BARCOS system for automatic and remote control of a Bruker FTS for solar absorption measurements from ground," in Fourier Transform Spectroscopy, A. Sawchuk, ed., Vol. 84 of OSA Trends in Optics and Photonics (Optica Publishing Group, 2003), paper FMD25. Export Citation BibTex Endnote (RIS) HTML Plain Text Citation alert Save article

The absolute solar transmittance interferometer measures absolute solar radiance at the Earth's surface. The instrument is based on a Fourier-transform spectrometer that utilizes a liquid-nitrogen-cooled InSb detector and appropriate optical bandpass filters. The recorded solar spectra are calibrated against National Institute of Standards and Technology traceable lamps and a blackbody source. The spectral range addressed by this instrument is from 1950 to 10100 cm(-1) at a resolution of 2 cm(-1). The optical design of the instrument and the experimental methods are discussed. A discussion of the uncertainties involving the instrument and the calibration sources is presented. Initial measurements from several sites are compared with atmospheric model calculations.

Isotopic ozone lines of 16O16O17O and 16O17O16O in the 5μm region are identified for the first time in balloon-borne high-resolution (0.003cm−1) solar absorption spectra. A few of these lines also are observed in ground-based spectra. These lines need to be included in analysis of atmospheric absorption spectra, in addition to the recently identified 16O16O18O,16O18O16O and 16O12C34S lines in this region.