Tomographic MAX-DOAS observations of sun illuminated targets: a new technique providing well defined absorption paths in the boundary layer

A novel experimental procedure to measure the surface-near distribution of atmospheric trace gases using passive Multi-Axis-Differential Absorption Optical Spectroscopy (MAX-DOAS) is proposed. The idea consists of pointing the receiving telescope of the spectrometer to non-reflecting surfaces or to ‘bright’ targets placed at known distances from the measuring device, which are illuminated by sunlight. We show that the partial trace gas absorptions between the top of the atmosphere and the target can be easily removed from the measured total absorption. Thus it is possible to derive the average concentration of trace gases like e.g. NO2, HCHO, SO2, H2O, Glyoxal, BrO and others along the line of sight between the instrument and the target like for the well-known long-path DOAS observations (but with much less expense). If tomographic arrangements are used, even two- or three-dimensional trace gas distributions can be retrieved. The basic assumptions of the proposed method are confirmed by test measurements across the city of Heidelberg

Mass Mixing, the Fourth Generation, and the Kinematic Higgs Mechanism

We describe how to construct chiral fermion mass terms using Dirac-Kahler (DK) spinors. Classical massive DK spinors are shown to be equivalent to four generations of Dirac spinors with equal mass coupled to a background U(2,2) gauge field. Quantization breaks U(2,2) to U(2)xU(2), lifts mass spectrum degeneracy, and generates a non-trivial mass mixing matrix.Comment: 12 pages. No figures. Phys Lett B version. Minor typos fixe

The Spectrum of the 4-Generation Dirac-Kaehler Extension of the SM

We compute the mass spectrum of the fermionic sector of the Dirac-Kaehler extension of the SM (DK-SM) by showing that there exists a Bogoliubov transformation that transforms the DK-SM into a flavor U(4) extension of the SM (SM-4) with a particular choice of masses and mixing textures. Mass relations of the model allow determination of masses of the 4th generation. Tree level prediction for the mass of the 4th charged lepton is 370 GeV. The model selects the normal hierarchy for neutrino masses and reproduces naturally the near tri-bimaximal and quark mixing textures. The electron neutrino and the 4th neutrino masses are related via a see-saw-like mechanism.Comment: 14 pages. Phys Lett B versio

Towards imaging of atmospheric trace gases using Fabry–Pérot interferometer correlation spectroscopy in the UV and visible spectral range

Many processes in the lower atmosphere including transport, turbulent mixing and chemical conversions happen on timescales of the order of seconds (e.g. at point sources). Remote sensing of atmospheric trace gases in the UV and visible spectral range (UV–Vis) commonly uses dispersive spectroscopy (e.g. differential optical absorption spectroscopy, DOAS). The recorded spectra allow for the direct identification, separation and quantification of narrow-band absorption of trace gases. However, these techniques are typically limited to a single viewing direction and limited by the light throughput of the spectrometer set-up. While two-dimensional imaging is possible by spatial scanning, the temporal resolution remains poor (often several minutes per image). Therefore, processes on timescales of seconds cannot be directly resolved by state-of-the-art dispersive methods. We investigate the application of Fabry–Pérot interferometers (FPIs) for the optical remote sensing of atmospheric trace gases in the UV–Vis spectral range. By choosing a FPI transmission spectrum, which is optimised to correlate with narrow-band (ideally periodic) absorption structures of the target trace gas, column densities of the trace gas can be determined with a sensitivity and selectivity comparable to dispersive spectroscopy, using only a small number of spectral channels (FPI tuning settings). Different from dispersive optical elements, the FPI can be implemented in full-frame imaging set-ups (cameras), which can reach high spatio-temporal resolution. In principle, FPI correlation spectroscopy can be applied for any trace gas with distinct absorption structures in the UV–Vis range. We present calculations for the application of FPI correlation spectroscopy to SO2, BrO and NO2 for exemplary measurement scenarios. In addition to high sensitivity and selectivity we find that the spatio temporal resolution of FPI correlation spectroscopy can be more than 2 orders of magnitude higher than state-of-the-art DOAS measurements. As proof of concept we built a 1-pixel prototype implementing the technique for SO2 in the UV. Good agreement with our calculations and conventional measurement techniques is demonstrated and no cross sensitivities to other trace gases are observed.</p

Quantification of the depletion of ozone in the plume of Mount Etna

Volcanoes are an important source of inorganic halogen species into the atmosphere. Chemical processing of these species generates oxidised, highly reactive, halogen species which catalyse considerable O3 destruction within volcanic plumes. A campaign of ground-based in situ O3, SO2 and meteorology measurements was undertaken at the summit of Mount Etna volcano in July/August 2012. At the same time, spectroscopic measurements were made of BrO and SO2 columns in the plume downwind. Depletions of ozone were seen at all in-plume measurement locations, with average O3 depletions ranging from 11–35 nmol mol 1 (15–45 %). Atmospheric processing times of the plume were estimated to be between 1 and 4 min. A 1-D numerical model of early plume evolution was also used. It was found that in the early plume O3 was destroyed at an approximately constant rate relative to an inert plume tracer. This is ascribed to reactive halogen chemistry, and the data suggests the majority of the reactive halogen that destroys O3 in the early plume is generated within the crater, including a substantial proportion generated in a high-temperature “effective source region” immediately after emission. The model could approximately reproduce the main measured features of the ozone chemistry. Model results show a strong dependence of the near-vent bromine chemistry on the presence or absence of volcanic NOx emissions and suggest that near-vent ozone measurements can be used as a qualitative indicator of NOx emission

The flight of Arcadia: spatial CO2/SO2 variations in a cross section above the Nord East crater of Etna volcano

The CO2/SO2 ratio in volcanic plumes of open conduit volcanoes can provide useful information about the magma depth inside a conduit and the possible occurrence of an eruptive event. Moreover, the same CO2 measurement when combined with a SO2 flux measurement, commonly carried out at many volcanoes nowadays, is used to contribute to an improved estimate of global volcanic CO2 budget. Today worldwide at 13 volcanoes automated in-situ instruments (known as Multi-GAS stations) are applied to continuously determine CO2/SO2 ratios and to use this signal as additional parameter for volcanic monitoring. Usually these instruments carry out measurements of half an hour 4 – 6 times/day and thus provide continuous CO2/SO2 values and their variability. The stations are located at crater rims in a position that according to the prevailing winds is invested by the plume. Obviously, although the stations are carefully positioned, it is inevitable that other sources than the plume itself, e.g. soil degassing and surrounding fumaroles, contribute and will be measured as well, covering the ‘real’ values. Between July and September 2014 experiments were carried out on the North East crater (NEC) of Mount Etna, installing a self-made cable car that crossed the crater from one side to the other. The basket, called “Arcadia”, was equipped with an automated standard Multi-GAS station and a GPS, which acquired at high frequency (0.5 Hz) the following parameters : CO2, SO2, H2S, Rh, T, P and geo-coordinates. The choice of NEC of the volcano Etna was based on its accessibility, the relative small diameter (about 230 m) and the presence of a relatively constant and rather concentrated plume. Actually, NEC belongs also to the monitoring network EtnaPlume (managed by the INGV of Palermo). The aim of these experiments was to observe variations of each parameter, in particular the fluctuation of the CO2/SO2 ratio within the plume, moving from the edge to the center of the crater. The gained results give a first possibility to understand if common measurements carried out at the edge of a crater are subject to overor underestimation and about the order of derivations caused by other sources than the plume. A preliminary analysis results in a lower CO2/SO2 ratio in the central part of the crater versus the more peripheral one. The deviation between the average CO2/SO2 ratio and the center of the plume ranges from a minimum of 58% up to a maximum of 74%. An increased CO2/SO2 emission could be caused by the influence of soil and/or fumarolic degassing at the crater rim. This interpretation leads us to the conclusion that measurements by fixed installed stations might overestimate the CO2/SO2 ratio compared to values originating from the “pure” plume. Further on, it means that variations of up to 74%(in our experiment) don’t necessarily correlate with volcanic activity changes

Continuous SO2 flux measurements for Vulcano Island, Italy

The La Fossa cone of Vulcano Island (Aeolian Archipelago, Italy) is a closed conduit volcano. Today, Vulcano Island is characterized by sulfataric activity, with a large fumarolic field that is mainly located in the summit area. A scanning differential optical absorption spectroscopy instrument designed by the Optical Sensing Group of Chalmers University of Technology in Göteborg, Sweden, was installed in the framework of the European project "Network for Observation of Volcanic and Atmospheric Change", in March 2008. This study presents the first dataset of SO2 plume fluxes recorded for a closed volcanic system. Between 2008 and 2010, the SO2 fluxes recorded showed average values of 12 t.d—1 during the normal sulfataric activity of Vulcano Island, with one exceptional event of strong degassing that occurred between September and December, 2009, when the SO2 emissions reached up to 100 t.d—1

On the link between Earth tides and volcanic degassing

Long-term measurements of volcanic gas emissions conducted during the last decade suggest that under certain conditions the magnitude or chemical composition of volcanic emissions exhibits periodic variations with a period of about 2 weeks. A possible cause of such a periodicity can be attributed to the Earth tidal potential. The phenomenology of such a link has been debated for long, but no quantitative model has yet been proposed. The aim of this paper is to elucidate whether a causal link between tidal forcing and variations in volcanic degassing can be traced analytically. We model the response of a simplified magmatic system to the local tidal gravity variations and derive a periodical vertical magma displacement in the conduit with an amplitude of 0.1–1&thinsp;m, depending on the geometry and physical state of the magmatic system. We find that while the tide-induced vertical magma displacement presumably has no significant direct effect on the volatile solubility, the differential magma flow across the radial conduit profile may result in a significant increase in the bubble coalescence rate at a depth of several kilometres by up to several multiples of 10&thinsp;%. Because bubble coalescence facilitates separation of gas from magma and thus enhances volatile degassing, we argue that the derived tidal variation may propagate to a manifestation of varying volcanic degassing behaviour. The presented model provides a first basic framework which establishes an analytical understanding of the link between the Earth tides and volcanic degassing.</p

Reply to comment from Liotta and Rizzo on “Evolution of CO2 , SO2 , HCl and HNO3 in the volcanic plumes from Etna” by Voigt et al. [Geophys. Res. Lett.; 41, doi:10.1002/2013GL058974]

Editor’s Note: The following comment and reply arise from an article published in Geophysical Research Letters by Voigt et al. (2014). The article addresses a volcanology topic, and the commenters take issue with some conclusions and offer an analysis of their own. Voigt and co-authors have responded. Why is this comment-and-reply being published in the Bulletin? It is because Geophysical Research Letters is one of a number of journals that do not offer any published forum for discussion of the papers they publish. This is a matter of editorial policy and a decision for each journal. The Bulletin of Volcanology does provide a forum for discussion of articles published. When contacted by Marcello Liotta with the request that the Bulletin consider hosting a discussion of the Voigt et al. volcanology article in GRL, I agreed to do so if the GRL authors were willing to engage with the comment. Voigt and co-authors were willing to do so and have been allowed a small amount of additional space to summarize for Bulletin readers the key points of the GRL paper under discussion before responding directly to the comment from Liotta and Rizzo. I hope that Bulletin readers find the discussion and reply of interest