Christian Servais

Observed trends in total vertical column abundances of atmospheric gases from IR solar spectra recorded at the Jungfraujoch

Since 1984, about 15000 high quality infrared solar spectra have beenrecorded with state-of-the-art grating and Fourier transform spectrometersat the International Scientific Station of the Jungfraujoch, Switzerland.Nonlinear least squares spectral curve fitting of selected microwindowscontaining isolated and well characterized lines of 20 telluric gases haveallowed to retrieve their total vertical column abundances above thestation, leading to observational data bases essential to derive long- andshort-term changes experienced by these species during the last 12 years. Inthis paper, we focus on atmospheric gases of particular interest within thecontext of the EUROTRAC/TOR (Tropospheric Ozone Research) project; secularevolution as well as seasonal cycles of the minor constituentsCH4, CO and of the trace gasesC2H6, OCS, C2H2, HCNand H2CO are reported and discussed. The long-livedN2O is included as a tracer of the dynamic activity of theatmosphere.

Recent Northern Hemisphere stratospheric HCl increase due to atmospheric circulation changes

The abundance of chlorine in the Earth’s atmosphere increased considerably during the 1970s to 1990s, following large emissions of anthropogenic long-lived chlorine-containing source gases, notably the chlorofluorocarbons. The chemical inertness of chlorofluorocarbons allows their transport and mixing throughout the troposphere on a global scale, before they reach the stratosphere where they release chlorine atoms that cause ozone depletion. The large ozone loss over Antarctica was the key observation that stimulated the definition and signing in 1987 of the Montreal Protocol, an international treaty establishing a schedule to reduce the production of the major chlorine- and bromine-containing halocarbons. Owing to its implementation, the near-surface total chlorine concentration showed a maximum in 1993, followed by a decrease of half a per cent to one per cent per year, in line with expectations. Remote-sensing data have revealed a peak in stratospheric chlorine after 1996, then a decrease of close to one per cent per year, in agreement with the surface observations of the chlorine source gases and model calculations. Here we present ground-based and satellite data that show a recent and significant increase, at the 2σ level, in hydrogen chloride (HCl), the main stratospheric chlorine reservoir, starting around 2007 in the lower stratosphere of the Northern Hemisphere, in contrast with the ongoing monotonic decrease of near-surface source gases. Using model simulations, we attribute this trend anomaly to a slowdown in the Northern Hemisphere atmospheric circulation, occurring over several consecutive years, transporting more aged air to the lower stratosphere, and characterized by a larger relative conversion of source gases to HCl. This short-term dynamical variability will also affect other stratospheric tracers and needs to be accounted for when studying the evolution of the stratospheric ozone layer.

The dissociative electroionization of ammonia and ammonia-d3. I. The NH+ and NH2+ dissociation channels

Abstract The dissociative electroionization of NH3 (ND3), in the NH2+ (ND2+) dissociation channels, is investigated in the 15–50 eV electron energy range. The translational energy distributions of ND2+ (NH2+) exhibit several components, whereas NH+only shows a continuous, broad distribution. For both ions a kinetic energy versus appearance energy diagram is obtained and discussed. The predissociation of the Jahn-Teller split NH3+ (A, 2E) state produces both ions at their lowest threshold. At higher energies, dissociative autoionization (in the 22 eV region), dissociative ionization through the NH3+ (B 2A1 state in (the 24–30 eV region) as well as dissociation by Coulomb repulsion of doubly ionized states (in the 35–50 eV region) produce NH2+ (ND2+) and NH+ with large amounts of translational energy. Some arguments are brought forward to indicate that the former value of the NH2-H dissociation energy is overestimated.

Evolution of a dozen non-CO2 greenhouse gases above central Europe since the mid-1980s

Abstract High-resolution infrared solar observations have been conducted consistently since the mid-1980s at the International Scientific Station of the Jungfraujoch, Switzerland, by the GIRPAS-ULg team (Groupe Infra-Rouge de Physique Atmosphérique et Solaire-University of Liège), and by colleagues from the Belgian Institute for Space Aeronomy and from the Royal Observatory of Belgium, Brussels. These observations were performed with state-of-the-art Fourier transform infrared (FTIR) spectrometers, revealing specific absorption features of over 20 atmospheric gases in the middle-infrared. Related spectrometric analyses have allowed the derivation of their burdens, seasonal and inter-annual variability, as well as their long-term evolution. In addition to updates of long-term changes for CCl2F2, CHClF2, CH4, N2O, SF6, CO, C2H6 and C2H2 already dealt with at previous Non-CO2 Greenhouse Gases (NCGG) symposia, this paper further reports temporal evolutions observed during the past two decades for a series of other source gases, namely OCS, HCN, CCl3F and CCl4, which also have direct or indirect effects on the radiation balance of the troposphere and on the stratospheric ozone layer.

Vertical column abundances of COF2 above the Jungfraujoch Station, derived from ground-based infrared solar observations

Total vertical column abundances of carbonyl fluoride (COF2) have been derived from observations made at the International Scientific Station of the Jungfraujoch (ISSJ; altitude 3.58 km, latitude 46.5°N, longitude 8.0°E), Switzerland. A systematic analysis of two microwindows containing lines of the ν1 band was performed, based on a large set of high resolution infrared solar absorption spectra recorded with Fourier transform spectrometers, from 1985 to 1995. Examination of the whole available database indicates a significant increase of the burden of COF2 during the 1988–1995 period. The average exponential rate and the average linear rate referenced to 1992, calculated from daily mean measurements, are both equal to (4.0 ± 0.5)% yr-1 (one σ error). The results are also evaluated and discussed within the context of seasonal variability and correlation between carbonyl fluoride and hydrogen fluoride (HF) columns above the ISSJ.

The appearance energy of C2H+ from C2H2 revisited. A photoion-photoelectron coincidence spectroscopic determination

Abstract The dissociative ionization of C 2 H 2 in a C 2 H + -producing channel has been reconsidered. The photoion-photoelectron coincidence (PIPECO) technique has been used. The C 2 H + /e − coincidence rate curve has been recorded between 16.2 and 21.2 eV. The lowest appearance energy determined for C 2 H + is 17.35 ± 0.04 eV. A second appearance energy is measured at 18.40 ± 0.04 eV. At both energies ethynyl ions are produced through a predissociation mechanism at the expense of the C 2 H 2 + (A 2 A g ) state at 17.35 eV and C 2 H 2 + (B 2 Σ u + at 18.40 eV. These results are in good agreement with the most recent TPIPECO experiments and dissociative electroionization results. This comparison leads to the exclusion of any contribution of autoionization phenomena to the C 2 H + ion production between 16.2 and 21.2 eV. Investigations of C 2 H + through the ion pair formation channel (and the dissociative electron attachment producing C 2 H − and H − ) in C 2 H 2 are reported and its contribution to C 2 H + ion production below 17.3 eV must be discarded.

How complex can be the Unimolecular Decomposition of a simple Molecule? The case of Acetylene. An Electron Impact and PIPECO Investigation.

The dissociative ionization of C2H2, C2D2 and C2HD is presented in this work. Excepting the H2 + ion formation, all dissociation channels are thoroughly investigated by electron impact. The translational energy distribution as a function of the impinging electron energy and the appearance energy as a function of the translational energy are measured for all fragment ions. KE versus AE diagrams are obtained and the isotope effect is examined. All observed thresholds are analyzed in detail and dissociation mechanisms are proposed. For the C2H + ion, the PIPECO technique has also been used. From these discussions the H-C2H, HC≡CH and H-C2 binding energy values are proposed, i.e. 5.33±0.23eV, 9.83±0.10eV and 5.44±0.40 eV respectively. The fragmentation paths leading to C, CH2 + and C2 + are discussed in terms of dissociation mechanisms involving the transient vinylidene structure of the molecular ion as an intermediate. Keyword: Acetylene / Dissociation / Electroionization / Photoionization / Coincidence / Kinetic energy Die dissoziative Ionisation von C2H2, C2D2 und C2HD wird in dieser Arbeit vorgestellt. Sâmtliche der dissoziativen Zerfallskanale, bis auf die H2 -Bildung, wurden mit Hilfe der Elektronenstoβionisation untersucht. Fur sâmtliche Fragmentionen wurde die Verteilung der Translationsenergie als Funktion der Energie der auftreffenden Elektronen sowie die Auftrittspotentiale als Funktion der Translationsenergie gemessen. KE-AEDiagramme werden ermittelt sowie Isotopeneffekte bestimmt. Die experimentellen Schwellenenergien werden im Detail analysiert, so daβ sich Dissoziationsmechanismen ableiten lassen. Zur Bestimmung der Eigenschaften des C2H -Ions wurde die PEPICO-Technik verwendet. Aus den experimentellen Resultaten lassen sich die Bindungsenergien von H-C2H, HC≡CH und H-C2 ableiten, die 5,33±0,23 eV, 9,83±0,10 eV, 5,44±0,40 eV betragen. Die Bildung von C, CH2 + sowie C2 + wird mit Hilfe eines Dissoziationsmechanismus diskutiert, der eine transiente Vinyliden-Struktur des intermediaren Molekulions beinhaltet.

An FPGA-based data acquisition and processing system for the MATMOS FTIR instrument

The MATMOS Fourier Transform Infrared (FTIR) spectrometer is a concept instrument designed to measure the Mars atmospheric composition using solar occultation from orbit. MATMOS requires high sampling rate (up to 300 kHz), high dynamic range (up to 22 bits) data acquisition to record time-domain interferograms which get converted to spectra on-board the spacecraft. Our previous work presented a system that utilized the Xilinx Virtex-4FX hybrid-FPGA to process raw interferogram data in a mixed HW/SWenvironment. We are now expanding the role of the FPGA to the analog data acquisition domain by interfacing it to high bandwidth, high data rate analog-to-digital converters. The quality of the collected data is verified by recording ground-based solar spectra with the existing JPL MkIV interferometer using the new acquisition system in parallel with the standard MkIV electronics. Processing time is reduced by upgrading to the Xilinx Virtex-5FXT FPGA.

A versatile low-cost automation system for an electro-ionization experiment

Abstract A cheap complete automation system designed for an electro-ionization experiment is described. This system is based on a Sinclair ZX Spectrum computer and a modular architecture. The control program and general building blocks diagrams are discussed and give a general idea of how to build modules or procedures adapted to different applications.

Long-term evolution of the loading of CH4, N2O, CO, CCl2F2, CHClF2 and SF6 above Central Europe during the last 15 years

Long-term monitoring activities of some 20 atmospheric constituents are continuing at the International Scientific Station of the Jungfraujoch, Switzerland, based on remote infra-red solar observations with high spectral resolution Fourier transform spectrometers. As a contribution to non-CO2 greenhouse gas investigations, we report the trends observed in the vertical column abundances measured regularly since the mid-1980s for CH4, N2O, CO, CC12F2, CHC1F2 and SF6. With the exception of CO, all species show positive rates of change in their near past atmospheric loading, those of CH4, N2O and CC12F2 having slowed significantly during the more recent years. The derived rates of change will be compared to findings resulting from ground-level in situ investigations at latitudes similar to that of the Jungfraujoch, and be interpreted in terms of resulting global loading changes.