338 research outputs found
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 âbrightâ 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 FabryâPĂ©rot 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 (UVâVis) 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 FabryâPĂ©rot interferometers (FPIs) for
the optical remote sensing of atmospheric trace gases in the UVâVis 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 UVâVis 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 11â35 nmol mol 1 (15â45 %). 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
âeffective source regionâ 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 â 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 ârealâ 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 âArcadiaâ, 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 âpureâ plume. Further on, it means that variations of up to 74%(in our experiment) donât necessarily correlate with volcanic activity changes
New insight into halogen release from experimental studies on BrO/Br ratios in volcanic plumes
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.dâ1 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.dâ1
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 0.1â1 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 %. 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 âEvolution of CO2 , SO2 , HCl and HNO3 in the volcanic plumes from Etnaâ by Voigt et al. [Geophys. Res. Lett.; 41, doi:10.1002/2013GL058974]
Editorâs 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
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