SO 2 and BrO emissions of Masaya volcano from 2014 to 2020
TL;DR: In this article, the authors presented a continuous time series of SO2 emission fluxes and BrO/ SO2 molar ratios in the gas plume of Masaya from March 2014 to March 2020.
Abstract: . Masaya volcano (Nicaragua, 12.0° N, 86.2° W, 635 m a.s.l.) is one of the few volcanoes hosting a lava lake, today. We present continuous time series of SO2 emission fluxes and BrO / SO2 molar ratios in the gas plume of Masaya from March 2014 to March 2020. This study has two foci: (1) discussing the state of the art of long-term SO2 emission flux monitoring on the example of Masaya and (2) the provision and discussion of a continuous dataset on volcanic gas data unique in its temporal coverage, which poses a major extension of the empirical data base for studies on the volcanologic as well as atmospheric bromine chemistry. Our SO2 emission flux retrieval is based on a comprehensive investigation of various aspects of the spectroscopic retrievals, the wind conditions, and the plume height. Our retrieved SO2 emission fluxes are on average a factor of 1.4 larger than former estimates based on the same data. We furthermore observed a correlation between the SO2 emission fluxes and the wind speed when several of our retrieval extensions are not applied. We make plausible that such a correlation is not expected and present a partial correction of this artefact via applying dynamic estimates for the plume height as a function of the wind speed (resulting in a vanishing correlation for wind speeds larger than 10 m/s). Our empirical data set covers the three time periods (1) before the lava lake elevation, (2) period of high lava lake activity (December 2015–May 2018), (3) after the period of high lava lake activity. For these three time periods, we report average SO2 emission fluxes of 1000 ± 200 t d−1, 1000 ± 300 t d−1, and 700 ± 200 t d−1 and average BrO / SO2 molar ratios of (2.9 ± 1.5) × 10−5, (4.8 ± 1 : 9) ×10−5, and (5.5 ± 2–6) × 10−5. These variations indicate that the two gas proxies provide complementary information: the BrO / SO2 molar ratios were susceptible in particular for the transition between the two former periods while the SO2 emission fluxes were in particular susceptible for the transition between the two latter time periods. We observed an extremely significant annual cyclicity for the BrO / SO2 molar ratios (amplitudes between 1–4–2–6 × 10−5) with a weak semi-annual modulation. We suggest that this cyclicity might be a manifestation of meteorological cycles. We found an anti-correlation between the BrO / SO2 molar ratios and the atmospheric water concentration (correlation coefficient of −47 %) but in contrast to that neither a correlation with the ozone mixing ratio (+21 %) nor systematic dependencies between the BrO / SO2 molar ratios and the atmospheric plume age for an age range of 2–20 min after the release from the volcanic edifice. The two latter observations indicate an early stop of the autocatalytic partial transformation of bromide Br− solved in aerosol particles to atmospheric BrO. Further patterns in the BrO / SO2 time series were (1) a step increase by 0.7 × 10−5 in late 2015, (2) a linear trend of 1.2 × 10−5 per year from December 2015 to March 2018, and (3) a linear trend of −0.8 × 10−5 per year from June 2018 to March 2020. The step increase in 2015 coincided with the 55 elevation of the lava lake and was thus most likely caused by a change in the magmatic system. The linear trend between late 2015 and early 2018 may indicate the evolution of the magmatic gas phase during the ascent of juvenile gas-rich magma whereas the linear trend from June 2018 on may indicate a decreasing bromine abundance in the magma.
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01 Jan 2011
TL;DR: In this paper, the authors used the ground-based remote sensing technique MAX-DOAS (Multi-Axis Differential Optical Absorption Spectroscopy) to measure sulphur dioxide, halogen oxides and nitrogen oxide at the rim of Nyiragongo volcano.
Abstract: In June 2007 and July 2010 spectroscopic measurements and chemical in-situ studies were carried out at Nyiragongo
volcano located 15 km north of the city Goma, North Kivu region (DRC), both at the crater rim and within the crater itself, next to the lava lake. Nyiragongo volcano belongs to the Virunga volcanic chain and it is associated with the Western branch of the Great Rift Valley. The volcanism at Nyiragongo is caused by the rifting of the Earth’s crust where two parts of the African plates are breaking apart. Niyragongo crater contains the biggest lava lake on Earth and it is considered one of the most active volcanoes in the world.
The ground-based remote sensing technique MAX-DOAS (Multi-Axis Differential Optical Absorption Spectroscopy)
using scattered sunlight has been applied during both field trips at the crater rim of the volcano to
measure sulphur dioxide, halogen oxides and nitrogen oxide. Additionally filter pack and spectroscopic in-situ carbon dioxide measurements were carried out, as well as SO2 flux measurements by a scanning DOAS instrument
from the NOVAC project at the flank of the volcano.
Nyiragongo is the first rift volcano where halogen oxides have been observed in the plume.
Observations indicate that the gas composition of Nyiragongo might change with a changing lava lake level in
short and long-term time scales. Before and during an overflow of the lava lake the molar ratios of BrO/SO2 were
decreasing in 2007 and 2010 from about 3.10-5 to about 0 (below the detection limit). Such a decreasing trend
was also observed before and during the eruption of Mt. Etna 2006 and 2008.
In a larger timescale between 2007 and 2010 the molar ratios of S/Cl and CO2/SO2 generally decreased from 6.7 -
16.5 to 0.7 – 2.1, from 5 -10 to 1 - 5, respectively. The lower S/Cl and CO2/SO2 could lead to the conclusion that
the magma reservoir below Niyragongo has had no new input from a deeper source.
The chemical composition as well as its temporal variability within the volcanic plume from the lava lake will be discussed, as well as its implication on the understanding of the dynamics of the plumbing system of this volcano.
16 citations
01 Apr 2016
TL;DR: In this article, the authors used a modelled FRS (based on a high-resolution solar atlas) for the extraction of volcanic sulfur dioxide (SO2) emissions.
Abstract: Abstract. Scanning spectrometer networks using scattered solar radiation in the ultraviolet spectral region have become an increasingly important tool for monitoring volcanic sulfur dioxide (SO2) emissions. Often measured spectra are evaluated using the differential optical absorption spectroscopy (DOAS) technique. In order to obtain absolute column densities (CDs), the DOAS evaluation requires a Fraunhofer reference spectrum (FRS) that is free of absorption structures of the trace gas of interest. For measurements at volcanoes such a FRS can be readily obtained if the scan (i.e. series of measurements at different elevation angles) includes viewing directions where the plume is not seen. In this case, it is possible to use these viewing directions (e.g. zenith) as FRS. Possible contaminations of the FRS by the plume can then be corrected by calculating and subtracting an SO2 offset (e.g. the lowest SO2 CD) from all viewing directions of the respective scan. This procedure is followed in the standard evaluations of data from the Network for Observation of Volcanic and Atmospheric Change (NOVAC). While this procedure is very efficient in removing Fraunhofer structures and instrumental effects it has the disadvantage that one can never be sure that there is no SO2 from the plume in the FRS. Therefore, using a modelled FRS (based on a high-resolution solar atlas) has a great advantage. We followed this approach and investigated an SO2 retrieval algorithm using a modelled FRS. In this paper, we present results from two volcanoes that are monitored by NOVAC stations and which frequently emit large volcanic plumes: Nevado del Ruiz (Colombia) recorded between January 2010 and June 2012 and from Tungurahua (Ecuador) recorded between January 2009 and December 2011. Instrumental effects were identified with help of a principal component analysis (PCA) of the residual structures of the DOAS evaluation. The SO2 retrieval performed extraordinarily well with an SO2 DOAS retrieval error of 1 − 2 × 1016 [molecules cm−2]. Compared to a standard evaluation, we found systematic differences of the differential slant column density (dSCD) of only up to ≈ 15 % when looking at the variation of the SO2 within one scan. The major advantage of our new retrieval is that it yields absolute SO2 CDs and that it does not require complicated instrumental calibration in the field (e.g. by employing calibration cells or broadband light sources), since the method exploits the information available in the measurements. We compared our method to an evaluation that is similar to the NOVAC approach, where a spectrum that is recorded directly before the scan is used as an FRS and an SO2 CD offset is subtracted from all retrieved dSCD in the scan to correct for possible SO2 contamination of the FRS. The investigation showed that 21.4 % of the scans (containing significant amounts of SO2) at Nevado del Ruiz and 7 % of the scans at Tungurahua showed much larger SO2 CDs when evaluated using modelled FRS (more than a factor of 2). For standard evaluations the overall distribution of the SO2 CDs in a scan can in some cases indicate whether the plume affects all viewing directions and thus these scans need to be discarded for NOVAC emission rate evaluation. However, there are other cases where this is not possible and thus the reported SO2 emission rates would be underestimated. The new method can be used to identify these cases and thus it can considerably improve SO2 emission budgets.
12 citations
TL;DR: In this paper, the authors used nested grids to model the plume close to the volcano at 1 km and found that ozone loss rate was 1.3 × 10 −5 molecules of O 3 per second per molecule of SO2.
Abstract: Volcanoes emit halogens into the atmosphere that undergo chemical cycling in plumes and cause destruction of ozone. The impacts of volcanic halogens are inherently difficult to measure at volcanoes, and the complexity of the chemistry, coupled with the mixing and dispersion of the plume, makes the system challenging to model numerically. We present aircraft observations of the Mount Etna plume in the summer of 2012, when the volcano was passively degassing. Measurements of SO 2-an indicator of plume intensity-and ozone were made in the plume a few 10s of km from the source, revealing a strong negative correlation between ozone and SO 2 levels. From these observations we estimate a mean in-plume ozone loss rate of 1.3 × 10 −5 molecules of O 3 per second per molecule of SO2. This value is similar to observation-derived estimates reported very close to the Mount Etna vents, indicating continual ozone loss in the plume up to at least 10's km downwind. The chemically reactive plume is simulated using a new numerical 3D model "WRF-Chem Volcano" (WCV), a version of WRF-Chem we have modified to incorporate volcanic emissions (including HBr and HCl) and multi-phase halogen chemistry. We used nested grids to model the plume close to the volcano at 1 km. The focus is on the early evolution of passively degassing plumes aged less than one hour and up to 10's km downwind. The model reproduces the so-called 'bromine explosion': the daytime bromine activation process by which HBr in the plume is converted to other more reactive forms that continuously cycle in the plume. These forms include the radical BrO, a species whose ratio with SO 2 is commonly measured in volcanic plumes as an indicator of halogen ozone-destroying chemistry. We track the modelled partitioning of bromine between its forms. The model yields in-plume BrO/SO 2 ratios (around 10 −4 mol/mol) similar to those observed previously in Etna plumes. The modelled BrO/SO 2 is lower in plumes which are more dilute (e.g. at greater windspeed). It is also slightly lower in plumes in the middle of the day compared than in the morning and evening, due to BrO's reaction with diurnally varying HO 2. Sensitivity simulations confirm the importance of near-vent products from high temperature chemistry, notably bromine radicals, in initiating the ambient temperature plume halogen cycling. Note also that heterogeneous reactions that activate bromine also activate a small fraction of the emitted chlorine; the resulting production of chlorine radical Cl causes a strong reduction in the methane lifetime and increasing formation of HCHO in the plume.
7 citations
Cites background from "SO 2 and BrO emissions of Masaya vo..."
...…the bromine-to-sulfur ratio and volcanic activity have been found in long-term observations (e.g. Bobrowski and Giuffrida, 2012; Dinger et al., 2018; Warnach et al., 2019; Dinger et al., 2021), suggesting that this ratio could potentially be used for monitoring and forecasting of volcanic activity....
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...The observations of Dinger et al. (2021) show that this quantity can vary with meteorological conditions....
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TL;DR: In this article, the authors investigate the effects of the 3D structure of volcanic plumes on the retrieval results of satellite and ground-based UV-Vis observations, using Monte Carlo radiative transfer simulations.
Abstract: Abstract. We investigate effects of the three-dimensional (3D) structure of volcanic plumes on the retrieval results of satellite and ground-based UV–Vis observations. For the analysis of such measurements, 1D
scenarios are usually assumed (the atmospheric properties only depend on altitude). While 1D assumptions are well suited for the analysis of many atmospheric
phenomena, they are usually less appropriate for narrow trace gas plumes.
For UV–Vis satellite instruments with large ground pixel sizes like the Global Ozone Monitoring Experiment-2 (GOME-2), the SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY (SCIAMACHY) or the Ozone Monitoring Instrument (OMI), 3D effects are of minor importance, but usually these observations are not sensitive to small volcanic plumes. In contrast,
observations of the TROPOspheric Monitoring Instrument (TROPOMI) on board Sentinel-5P have a much smaller ground pixel size (3.5 × 5.5 km2). Thus, on the one hand, TROPOMI can detect much smaller plumes than previous instruments. On the other hand, 3D effects become more important, because the TROPOMI ground pixel size is
smaller than the height of the troposphere and also smaller than horizontal
atmospheric photon path lengths in the UV–Vis spectral range. In this study we investigate the following 3D effects using Monte Carlo radiative transfer simulations: (1) the light-mixing effect caused by horizontal photon paths, (2) the saturation effect for strong SO2
absorption, (3) geometric effects related to slant illumination and viewing
angles and (4) plume side-effects related to slant illumination angles and photons reaching the sensor from the sides of volcanic plumes. The first two effects especially can lead to a strong and systematic underestimation of the true trace gas content if 1D retrievals are applied (more than 50 % for the light-mixing effect and up to 100 % for the saturation effect). Besides the atmospheric radiative transfer, the saturation effect also
affects the spectral retrievals. Geometric effects have a weaker influence
on the quantitative analyses but can lead to a spatial smearing of elevated plumes or even to virtual double plumes. Plume side-effects are small for short wavelengths but can become large for longer wavelengths (up to
100 % for slant viewing and illumination angles). For ground-based observations, most of the above-mentioned 3D effects are not important because of the narrow field of view (FOV) and the closer distance between the instrument and the volcanic plume. However, the light-mixing effect shows a similar strong dependence on the horizontal plume extension as for satellite observations and should be taken into account for the analysis of ground-based observations.
2 citations
TL;DR: In this paper , the authors investigate the effects of the 3D structure of volcanic plumes on the retrieval results of satellite and ground-based UV-vis observations, using Monte-Carlo radiative transfer simulations.
Abstract: . We investigate effects of the 3-dimensional (3D) structure of volcanic plumes on the retrieval results of satellite and ground based UV-vis observations. For the analysis of such measurements usually 1D scenarios are assumed (the atmospheric properties only depend on altitude). While 1D assumptions are well suited for the analysis of many atmospheric 15 phenomena, they are usually less appropriate for narrow trace gas plumes. For UV/vis satellite instruments with large ground pixel sizes like GOME-2, SCIAMACHY, or OMI, 3D effects are of minor importance, but usually these observations are not sensitive to small volcanic plumes. In contrast, observations of TROPOMI aboard Sentinel-5P have a much smaller ground pixel size (3.5 x 5.5 km²). Thus on the one hand, TROPOMI can detect much smaller plumes than previous instruments. On the other hand 3D effects become more important, because the TROPOMI ground pixel size is smaller than the height of the 20 troposphere and also smaller than horizontal atmospheric photon path lengths in the UV/vis spectral range. In this study we investigate the following 3D-effects using Monte-Carlo radiative transfer simulations: 1. the light mixing effect caused by horizontal photon paths, 2. the saturation effect for strong SO 2 absorption, 3. geometric effects related to slant illumination and viewing angles, and 4. Plume side effects related to slant illumination angles and photons reaching the sensor from the sides of volcanic plumes. Especially the first two effects can lead to a strong and systematic underestimation 25 if 1D retrievals are applied (more than 50% for the light mixing effect, and up to 100% for the saturation effect). Besides the atmospheric radiative transfer, the saturation effect also affects the the spectral retrievals. Geometric effects have a weaker influence on the quantitative analyses, but can lead to a spatial smearing of elevated plumes or even to virtual double plumes. Plume side effects are small for short wavelengths, but can become large for longer wavelengths (up to 100% for slant viewing and illumination angles). For ground based observations, most of the above mentioned 3D effects are not important, 30 because of the narrow FOV and the closer distance between the instrument and the volcanic plume. However, the light mixing effect shows a similar strong dependence on the horizontal plume extension as for satellite observations and should be taken into account for the analysis of ground based observations. 1990; Lyapustin and Kaufman, 2001). Such retrievals are based on radiance measurements, and the effect of horizontal light paths can strongly affect the measurements in the presence of strong spatial radiance contrasts, e.g. caused by sea-land boundaries or cloud edges. In such cases, horizontal light paths cause an increase (decrease) of the radiance 295 above the dark (bright) scene and thus systematically affects the aerosol retrieval. This effect (for absolute radiance measurements) was referred to as adjacency effect (Richter, 1990). a vertically oriented plume might contribute to the observed trace gas absorption. 2) horizontal plumes: for larger eruptions often elongated plumes are found, which are dominated by horizontal transport. Both scenarios should be simulated and eventually a direct connection between the observed trace gas SCDs and the emission flux from the volcano should be 665 established. Such simulations will be carried out in a follow-up study. c) How important are 3D effects for other confined trace gas plumes? Confined trace gas plumes also occur for other localised emission sources, in particular power plants. For measurements of the SO 2 emissions from power plants (in the UV spectral range), a similar strong underestimation will occur (up to more than 50%) as for the volcanic plumes. As shown in this study, for NO 2 observations in the blue spectral range the light mixing effect is much smaller than for the UV spectral 670 range. But these results were obtained for a pure Rayleigh atmosphere outside the plume. Since power plant emissions usually occur in polluted regions with high aerosol concentrations, aerosol scattering will enhance the diffuse atmospheric radiation compared to a pure Rayleigh atmosphere, which will possibly increase the light mixing. Also 3D effects for realistic power plant plumes will be addressed in a forthcoming study.
2 citations
References
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01 Jan 2008
686 citations
"SO 2 and BrO emissions of Masaya vo..." refers methods in this paper
...Furthermore, all spectra recorded at zenith angles ε larger than |ε|> 76◦ were rejected in order to avoid large light paths or spectroscopic200 For every scan passing the filters, SO2 DOAS fits were applied on each of the passing spectra where the initial zenith spectrum of the respective scan was used as reference spectrum (the DOAS fit scenarios are summarised in Table 3)....
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...Kleinbek, T.: Retrieval of SO2 and BrO slant column densities from Network for Observation of Volcanic and Atmospheric Change data with the software HeiDOAS, Bachelor Thesis, Ruperto Carola University of Heidelberg, Germany, 2020....
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...Such retrievals have been developed, e.g. for satellite data (Sun et al., 2017), and are for example available in the QDOAS software package (http://uv-vis.aeronomie.be/software/QDOAS/)....
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...Other obvious candidates are chlorine and fluorine compounds.65 Remote sensing techniques allow a retrieval of hydrogen chloride (HCl) and hydrogen fluorine (HF) via Fourier Transform InfraRed (FTIR) spectroscopy (e.g. Mori and Notsu, 1997; Mori et al., 2002), and chlorine dioxide (OClO) via UV-DOAS (e.g. Bobrowski et al., 2007; Donovan et al., 2014; Gliß et al., 2015; Kern and Lyons, 2018)....
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...We retrieved a unique fixed first principal component for the total 6 years time series and added it as a pseudo-absorbers to the DOAS fit....
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TL;DR: In this article, the authors measured the NO2 absorption cross-section from 42 000 to 10 000 cm−1 (238-1000 nm) with a Fourier transform spectrometer (at the resolution of 2 cm− 1, 0.01 nm at 240 nm to 0.2 nm at 1000 nm).
Abstract: The NO2 absorption cross-section has been measured from 42 000 to 10 000 cm−1 (238–1000 nm) with a Fourier transform spectrometer (at the resolution of 2 cm−1, 0.01 nm at 240 nm to 0.2 nm at 1000 nm) and a 5 m temperature controlled multiple reflection cell. The uncertainty on the cross-section is estimated to be less than 3% below 40 000 cm−1 (λ > 250 nm) at 294 K, 3% below 30 000 cm−1 (λ > 333 nm) at 220 K, but reaches 10% for higher wavenumbers. Temperature and pressure effects have been observed. Comparison with data from the literature generally shows a good agreement for wavenumbers between 37 500 and 20 000 cm−1 (267–500 nm). Outside these limits, the difference can reach several percent.
684 citations
"SO 2 and BrO emissions of Masaya vo..." refers background in this paper
...…SO2 Vandaele et al. (2009), @298 K (same) O3 Burrows et al. (1999), @221 K (same) BrO Fleischmann et al. (2004), @298 K O4 Hermans et al. (2003) NO2 Vandaele et al. (1998), @294 K CH2O Meller and Moortgat (2000), @298 K Ring spectrum (Grainer and Ring, 1962) calculated from the particular…...
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TL;DR: In this paper, the Global Ozone Monitoring Experiment (GOME) Flight-Model (FM) satellite spectrometer was used to measure the absorption cross sections of O3 in the 231-794nm range.
Abstract: Absorption cross sections of O3 in the 231–794 nm range have been measured at temperatures between 202 and 293 K using the Global Ozone Monitoring Experiment (GOME) Flight-Model (FM) satellite spectrometer. The GOME FM spectra have a spectral resolution of about 0.2 nm below 400 nm and of about 0.3 nm above 400 nm, and were recorded covering simultaneously the Hartley, Huggins, and Chappuis bands centered around 255, 340, and 610 nm, respectively. The variation of the O3 absorption cross sections was investigated over the entire spectral range 231–794 nm. The new cross sections are important as reference data for atmospheric remote-sensing of O3 and other trace gases.
476 citations
01 Jan 1996
TL;DR: The composition of gases released from volcanoes is a function of deep processes, such as vapor-melt separation during the generation and rise of the magmas, and shallow processes, active within the volcanic structures themselves as discussed by the authors.
Abstract: The composition of gases released from volcanoes is a function of deep processes, such as vapor-melt separation during the generation and rise of the magmas, and shallow processes, active within the volcanic structures themselves. Of the three major types of volcanic systems, those associated with andesitic magmatism are the most suitable to the application of geochemical surveillance and monitoring techniques. Volatile contents of andesitic magmas, largely representing fluids released from the subducted slab, are likely to be high enough to allow a separate, volatile-rich phase to be present during all stages of magma generation and migration. In spite of highly variable solubilities in magmatic melts, the proportions of volatiles present in the vapors discharged from volcanic fumaroles resemble closely those acquired at depth suggesting that the vapor-melt systems have attained steady-state and that the overall process active during the rise of the volatiles is effectively nonfractionating.
424 citations
"SO 2 and BrO emissions of Masaya vo..." refers background in this paper
...…followed in abundance by carbon dioxide (CO2) and sulphur dioxide (SO2), as well as by a large number of trace gases such as halogen compounds (Giggenbach, 1996; Aiuppa, 2009; Oppenheimer et al., 2014; Bobrowski and Platt, 2015).35 Monitoring magnitude or chemical composition of volcanic gas…...
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...1 Introduction Volcanic gas emissions consist predominantly of water (H2O), followed in abundance by carbon dioxide (CO2) and sulphur dioxide (SO2), as well as by a large number of trace gases such as halogen compounds (Giggenbach, 1996; Aiuppa, 2009; Oppenheimer et al., 2014; Bobrowski and Platt, 2015)....
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TL;DR: In this article, the authors measured the absorption cross sections of formaldehyde (HCHO) with a spectral resolution of 0.025 nm in the wavelength range 225-375 nm at 298 K using a diode array detector.
Abstract: UV absorption cross sections of formaldehyde (HCHO) have been measured with a spectral resolution of 0.025 nm in the wavelength range 225–375 nm at 298 K using a diode array detector. At selected temperatures ranging from 223 to 323 K, measurements have been conducted to obtain temperature gradients in the wavelength range 250–356 nm. Error limits for the reported absorption cross sections are ±5% but at least ±3×10−22 cm2 molecule−1. For the temperature gradients, uncertainties are <8%. Spectra and temperature gradients are compared with earlier measurements.
405 citations
"SO 2 and BrO emissions of Masaya vo..." refers background in this paper
...SO2 fit BrO fit Fit range 314.8–326.8 nm 330.6–352.75 nm (Pseudo-)Absorption cross sections: SO2 Vandaele et al. (2009), @298 K (same) O3 Burrows et al. (1999), @221 K (same) BrO Fleischmann et al. (2004), @298 K O4 Hermans et al. (2003) NO2 Vandaele et al. (1998), @294 K CH2O Meller and Moortgat (2000), @298 K Ring spectrum (Grainer and Ring, 1962) calculated from the particular reference spectrum Ring spectrum multiplied with the wavelength4 (see Wagner et al., 2009) Further DOAS fit parameters: Polynomial of order n= 3 in the optical depth space Stray light polynomial of order n= 0 in the intensity space Reference spectrum (+ 2 Ring spectra): ashift ∈ ±0.2 nm and asqueeze ∈ 1± 0.02 Absorption cross sections (linked together): ashift ∈ ±0.2 nm and asqueeze ∈ 1± 0.02 Choice of the wavelength range in the SO2 DOAS fit The choice of the wavelength range (and in particular its lower limit) used in the SO2 DOAS fit can cause major deviations in the210 spectroscopic results....
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...…(same) O3 Burrows et al. (1999), @221 K (same) BrO Fleischmann et al. (2004), @298 K O4 Hermans et al. (2003) NO2 Vandaele et al. (1998), @294 K CH2O Meller and Moortgat (2000), @298 K Ring spectrum (Grainer and Ring, 1962) calculated from the particular reference spectrum Ring spectrum…...
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