Passive infrared (FTIR) and correlation spectrometer (COSPEC) measurements were conducted at Popocatépetl volcano during February 10 to 26, 1998 from sites 4 to 17 km distant from the summit. Volcano behavior was relatively quiet and SO2 flux averaged 1670±1420 t/day (51 measurements), relatively small for Popocatépetl. Concurrent HCl/SO2 and HF/SO2 ratios were 0.17±0.01 and 0.031±0.003, respectively, about the same as ratios measured from 1994 to 1997. The amount of CO2 in the volcanic plume was quantified using FASCODE in which atmospheric CO2 is numerically subtracted from the total infrared spectrum to obtain the residual magmatic CO2. Surprisingly, CO2/SO2 mass ratios rose dramatically to values as high as 140, about 30 times higher than typical values of 2 to 8 measured from 1994 to 1996. These excursions in high CO2/SO2 ratios were short-lived, lasting no longer than about 0.5 to 3.0 h but CO2 flux occasionally exceeded 100,000 t/day. We estimate that the average CO2/SO2 ratio for the period was about 23, yielding an average CO2 flux of roughly 38,000 t/day. Chemical and petrographic analyses of lava and pumice erupted during explosions on June 30, 1997 and January 1, 1998 show conclusively that Popocatépetl produces mixed products formed by injection of mafic magma into a more silicic chamber at temperatures and pressures of roughly 1040°C and 5 kbar. In addition, Popocatépetl eruptive products include xenoliths of metamorphosed carbonate rocks containing wollastonite and other calc-silicate minerals indicating reaction of magma with Cretaceous limestone underlying the volcano. Using a normal CO2/SO2 ratio of 4 for reference, we calculate an average excess CO2 production of 32,000 t/day for 17 days. This would require assimilation of only 5×10−4 km3 of limestone, an amount easily accessible in the 3-km-thick Cretaceous section beneath the volcano. We also examine two scenarios in which excess CO2 is produced by degassing of subjacent basalt magma, but these explanations seem less plausible to us. Because many other volcanoes are underlain by carbonate sequences, short-duration bursts of CO2 flux, and increased CO2/SO2 ratio, might be observed at other sites, if simultaneous, real-time measurements of major gas species are made.

Gaseous volcanic emissions provide important insights on volcanic processes and may aid in predicting eruptive activity, but traditional in situ measurements are prohibitively dangerous at many volcanoes. Here we describe techniques for remotely measuring volcanic gas composition, at ranges up to tens of kilometers, using ground-based passive infrared spectroscopy. The principles of passive infrared spectroscopic remote sensing are discussed, and the effects of thermal contrast on the detectability of gases in various viewing geometries are quantitatively examined. This examination reveals that, for ground-based measurements, a sky background usually provides the best results. Our initial remote sensing campaign (April-May, 1996) at the White Island and Ruapehu volcanoes in New Zealand, combining passive Fourier transform infrared (FTIR) spectroscopy with traditional COSPEC and direct sampling measurements, confirmed this and demonstrated spectroscopic detection of SO2, H2O and HCl at ranges of up to 6 km, with good agreement between FTIR-derived and direct sampling based gas ratios. In measurement campaigns at Mexico's Popocatepetl volcano (February 1997 and February 1998), we monitored variations of SO2, SiF4, HCl, and HF, and extended the range of sky-background passive infrared techniques to over 17 km. In the highest temporal resolution study to date of short-term compositional variations associated with an explosive eruption (25-26 February 1997), we observed a steady increase in SiF4/SO2 over several days preceding the eruption, followed by a tenfold decrease in this ratio over a few hours immediately afterwards, a signature suggesting an adiabatic expansion prior to and during a gas-driven explosion. We examine the ultimate range limits of ground-based passive FTIR spectroscopy and possible future extensions to imaging and airborne instruments.

Get PDF Email Share Share with Facebook Share on X Post on reddit Share with LinkedIn Add to Mendeley Add to BibSonomy Share with WeChat Get Citation Copy Citation Text S. P. Love, F. Goff, D. Counce, S. C. Schmidt, C. Siebe, and H. Delgado, "Remote Monitoring of Volcanic Gases using Passive Fourier Transform Spectroscopy," in Fourier Transform Spectroscopy: New Methods and Applications, OSA Technical Digest (Optica Publishing Group, 1999), paper FWC3. Export Citation BibTex Endnote (RIS) HTML Plain Text Citation alert Save article

We have obtained vibrational spectra of molecular materials at simultaneous high pressure and high temperature using the combined techniques of shock wave compression and coherent Raman spectroscopy. The high pressure/high temperature states produced and investigated are similar to those found in the interior of planets and in detonating high explosives. The molecular structures of simple molecular fluids and fluid mixtures, such as of diatomic and triatomic molecules, are inferred from the spectral parameters - Raman frequencies, linewidths, and peak Raman susceptibilities - of the transitions, which are extracted from the spectral data using a standard semi-classical treatment.For a simple diatomic molecule such as N-2, CO or O-2, the measured vibrational frequencies increase with increasing shock pressure. In N-2, above 17 GPa single-shock pressure the vibrational frequency ceases to rise further and appears to begin to decrease. Observation of a further decrease at higher pressures is prevented by the onset of optical opacity. CO and O-2 become optically opaque at pressures insufficient to observe a similar maximum. The vibrational frequencies of CO and N-2 exhibit distinctly different shock pressure dependencies. The data show a factor of 5 smaller vibrational frequency versus pressure slope in CO as in N-2. Under shock compression, mixtures of CO and N-2 show a highly non linear dependence of their vibrational frequencies with mixture mole fraction, while at ambient pressure this dependence is linear.We have also estimated vibrational relaxation times for these simple molecules under shock-compression, using a simple population filling argument for the longitudinal relaxation time (T-1), and from the measured linewidth for the transverse relaxation time (T-2). T-2 shows a strong temperature dependence but little density (pressure) dependence. The intensities of the vibrational hot bands were those expected from a Boltzmann vibrational population distribution, and they were used to estimate vibrational temperatures. These temperatures have been also used to refine the equations of state for nitrogen and argon as well as to understand the effects of non-ideal mixing at these extreme conditions.

Vibrational spectra of liquid nitrogen, carbon monoxide, oxygen, and their mixtures, shock compressed to several high-pressure/ high-temperature states were obtained using single-pulsed multiplex coherent anti-Stokes Raman scattering (CARS).

Spectroscopic measurements of OH-radical and O-atom concentrations are analyzed for high-intensity turbulent combustion of methane/air in a modified Longwell jet-stirred reactor at conditions P=0.92 atm, ΦFA=0.57 to 1,33, andm0307/V=1.89×10−2 to 4.03 ×10−2 g/cm3-s. Absolute OH concentrations were determined from the measured integrated absorption of resolved spectral lines in the OH2π-2+ (0,0) band. Atomic oxygen was inferred from chemiluminescence measured at 3500due to the radiative recombination CO+O→CO2+hv. Thermocouple temperatures varied from 1440 to 1910°K, with the OH rotational temperature being greater by ca. 7%. Hydroxyl radical concentrations versus equivalence ratio exhibited an apparent maximum near ΦFA≅0.85, and increased with increasingm0307/V. Partial equilibrium between OJ and O-atom was also observed in the vicinity of ΦFA≅0.85. The peak O-atom concentration occurred at FA≅0.8. Form0307/V=1.89×10−2 g/cm3-s, the peak values for OH and O-atom were 2700 and 720 ppm (molar), respectively. Calculations of NOx formation, using the PSR model with the measurements of OH and O-atom concentrations and rotational temperature as input, fell below measurements of NOx determined by gas sampling.

The enlargement of the E.E.C. and the consequential proliferation of preferential agreements with a growing number of developing and West European countries is expected to lead to increased intra‐area trade in a number of temperate zone and tropical products to the detriment of third country suppliers. This possibility is bound to accentuate incipient and prospective imbalances in commodity markets as well as the division and distrust regarding trade policies among developed countries and between developed and developing countries.Since the Community of Ten will constitute the leading world trade power, it has a major role to play in resolving the current commodity, trade and monetary disequilibria. Solutions to these problems are complex, but must be innovative, and are certain to affect everyone in the world. Possible actions that might be taken include: (1) international co‐ordination of agricultural policies; (2) formulation of new guidelines and construction of negotiating mechanisms for the removal of nontariff distortions; (3) conclusion of international commodity agreements; (4) improving conditions of developing countries with regard to trade, financial and monetary matters; and (5) formation of free trade associations or common markets among developing countries.RésuméCOMMUNAUTÉ EUROPÉENNE ÉLARGIE ET CHOIX DE POLITIQUES COMMERCIALES AGRICOLES POUR LES PAYS TIERSL'on s'attend à ce que l'élargissement de la C.E.E. et la multiplication des accords préférentiels qui en résultera avec un nombre croissant de pays en développement et de l'Europe occidentale conduisent à l'intensification du commerce intrarégional dans un certain nombre de zones témpéres et de produits tropicaux au détriment des fournisseurs du tiers monde. Cette possibilité risque d'accentuer les déséquilibres naissants et en perspective dans les marchés des produits ainsi que la division et la méfiance en matière de politiques commerciales entre pays développés et entre pays développés et pays en développement.Dés lors que la Communauté des Dix va constituer la puissance commerciale mondiale dominante, elle a un rôle capital à jouer dans la solution à apporter aux déséquilibres actuels sur le plan des produits, du commerce et de la monnaie. Les solutions à ces problèmes sont complexes, mais elles doivent être novatrices et sont certaines d'affecter tout le monde dans tous les pays. Les mesures d'action possibles qui pourraient être adoptées comprennent: (1) la coordination internationale des politiques agricoles, (2) la formulation de nouvelles lignes directrices d'orientation et l'elaboration de mécanismes négociateurs pour faire disparaître les vices non tarifaires, (3) la conclusion d'accords internationaux de produits, (4) l'amélioration des conditions des pays en développement au regard des questions commerciales, financières et monétaires et (5) la formation d“associations de libre échange ou de marchés communs entre les pays en développement.ZusammenfassungEINE ERWEITERTE EUROPÄISCHE GEMEINSCHAFT UND AUSWAHLMÖGLICHKEITEN AN AGRARHANDELSPOLITIK FÜR LÄNDER DER 3. WELTDie Erweiterung der Europäischen Wirtschaftsgemeinschaft und die sich daraus ergebende starke Zunahme an Vorzugsüberein‐kommen mit einer zunehmenden Anzahl von Entwicklungs‐ und westeuropäischen Ländern wird erwartungsgemäss zu einem Zuwachs an innergebietlichem Handel bei einer Anzahl von Produkten aus Zonen mit gemässigtem und tropischem Klima führen, zum Nachteil von Lieferantdenländern der 3. Welt. Diese Möglichkeit wird unweigerlich anfängliche und für die Zukunft voraussehbare Gleichgewichtsstörungen innerhalb von Warenmärkten sowie Uneinigkeit und Misstrauen im Hinblick auf Richtungen der Handelspolitik der entwickelten Länder untereinander und zwischen entwickelten und Entwicklungsländern stärker hervorheben.Da die Gemeinschaft der Zehn die führende Welthandelsmacht darstellen wird, spielt sie notwendig eine Hauptrolle bei dem Ausgleich des gestörten Gleichgewichts, wie es gegenwärtig auf den Gebieten von Waren, Handel und Währung herrscht. Läsungen zu diesen Problemen sind kompliziert, aber müssen Neuerungen bringen und betreffen mit Sicherheit jederman in der ganzen Welt. Zu den möglichen Schritten, die unternommen werden können, zählen: (1) die Internationale Koordinierung der verschiedenen Formen von Agrarpolitik; (2) die Formulierung neuer Richtlinien und die Bildung von Verhandlungsapparaten zur Beseitigung von Tarifverzerrungen; (3) der Abschluss von intemationalen Warenab‐kommen; (4) die Verbesserungen der Bedingungen in Entwicklungs‐ländern in Bezug auf Handel, Finanz‐ und Währungsangelegen‐heiten; und (5) die Bildung von freien Handelsverbänden oder gemeinsamen Märkten (Wirtschaftsgemeinschaften) der Entwick‐lungsländer untereinander.