BrO/SO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; molar ratios from scanning DOAS measurements in the NOVAC network

Lübcke, Peter; Bobrowski, Nicole; Arellano, Santiago; Galle, Bo; Garzón, Gustavo; Vogel, L.; Platt, U.

doi:10.5194/se-5-409-2014

Cited by 54 publications

(95 citation statements)

References 33 publications

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“…This would lead to an OD of τ = S × σ max = 1.2 for MAX-DOAS measurements with a SCD S H 2 O = 4 × 10 23 molec cm −2 (a typical MAX-DOAS column density for mid-latitude summer conditions) under a telescope elevation angle of 3 • , which is clearly in disagreement with our observations. Also measurements of other tropospheric trace gases such as HCHO (336.5-359 nm) (Pinardi et al, 2013), .75 nm) and SO 2 (314.8-326.8 nm) (Lübcke et al, 2014), which would have also been affected, did not show any unknown differential absorption of this size but did yield residual spectra with at least 2 orders of magnitude smaller amplitudes.…”

Section: Absorption Of Water Vapour In the Uv Wavelength Rangementioning

confidence: 99%

On the relative absorption strengths of water vapour in the blue wavelength range

et al. 2015

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Abstract. In recent updates of the HITRAN water vapour H 2 O spectroscopic compilation covering the blue spectral region (here: 394-480 nm) significant changes for the absorption bands at 416 and 426 nm were reported. In order to investigate the consistency of the different cross-sections calculated from these compilations, H 2 O vapour column density ratios for different spectral intervals were retrieved from long-path and multi-axis differential optical absorption spectroscopy (DOAS) measurements. We observed a significant improvement of the DOAS evaluation when using the updated HITRAN water vapour absorption cross-sections for the calculation of the reference spectra. In particular the magnitudes of the residual spectra as well as the fit errors were reduced.However, we also found that the best match between measurement and model is reached when the absorption crosssection of groups of lines are scaled by factors ranging from 0.5 to 1.9, suggesting that the HITRAN water vapour absorption compilation still needs significant corrections. For this spectral region we present correction factors for HI-TRAN 2009, HITRAN 2012, HITEMP and BT2 derived from field measurements. Additionally, upper limits for water vapour absorption in the UV-A range from 330 to 390 nm are given.

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Section: Absorption Of Water Vapour In the Uv Wavelength Rangementioning

confidence: 99%

On the relative absorption strengths of water vapour in the blue wavelength range

et al. 2015

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“…We evaluated spectra recorded between 1 January 2010 and 30 June 2012 from these two NOVAC stations (see Garzon et al, 2013, andLübcke et al, 2014, for maps of the stations and more information on NO-VAC measurements at Nevado del Ruiz). After evaluating the spectra, we found that the instrument's GPS antennas occasionally reported erroneous times, which led to offsets in the time stamps of spectra of up to 55 min.…”

Section: Resultsmentioning

confidence: 99%

Retrieval of absolute SO<sub>2</sub> column amounts from scattered-light spectra: implications for the evaluation of data from automated DOAS networks

et al. 2016

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Abstract. Scanning spectrometer networks using scattered solar radiation in the ultraviolet spectral region have become an increasingly important tool for monitoring volcanic sulfur dioxide (SO 2 ) 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 SO 2 offset (e.g. the lowest SO 2 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 SO 2 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 SO 2 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 SO 2 retrieval performed extraordinarily well with an SO 2 DOAS retrieval error of 1−2×10 16 [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 SO 2 within one scan. The major advantage of our new retrieval is that it yields absolute SO 2 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 SO 2 CD offset is subtracted from all retrieved dSCD in the scan to correct for possible SO 2 contamination of the FRS. The investigation showed that 21.4 % of the scans (containing significant amounts of SO 2 ) at Nevado del Ruiz and 7 % of the Published by Copernicus Publications on behalf of the European Geosciences Union. 5678 P. Lübcke et al.: DOAS evaluation ...

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“…Accordingly, even under the assumption that the HBr/SO 2 degassing ratio is purely pressure-dependent no quantitative deduction of the pressure change could be made based on BrO/SO 2 molar ratios. Further, it was even not yet possible to derive the sign of this correlation indirectly by empirical studies of BrO/SO 2 molar ratios simultaneously to pressure changes 15 (Bobrowski and Giuffrida (2012), Lübcke et al (2014)) because of the still limited data sets available. In the absence of an explicit interpretation of the BrO/SO 2 molar ratio, at least the reasoning that a change in BrO/SO 2 molar ratios is probably caused by a significant change in magmatic conditions appears to be nevertheless a reasonable hypothesis.…”

Section: Comparison Of Bro/so 2 Time Series With Meteorologymentioning

confidence: 99%

Periodicity in the BrO/SO<sub>2</sub> molar ratios in the volcanic gas plume of Cotopaxi and its correlation with the Earth tides during the eruption in 2015

Dinger¹,

Bobrowski²,

Warnach³

et al. 2017

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Abstract. We evaluated NOVAC (Network for Observation of Volcanic and Atmospheric Change) gas emission data from the 2015 eruption of Cotopaxi volcano (Ecuador) for BrO/SO 2 molar ratios. Statistical analysis of the data revealed a conspicuous periodic pattern with a periodicity of about two weeks in a three month time series. While the time series is too short to rule out a chance recurrence of transient geological or meteorological events as a possible origin for the periodic signal, we nevertheless took this observation as a motivation to examine the influence of natural forcings with periodicities of around two weeks on 5 volcanic gas emissions. One strong aspirant with such a periodicity are the Earth tides, which are thus central in this study. We present the BrO/SO 2 data, analyse the reliability of the periodic signal, discuss a possible meteorological or eruption-induced origin of this signal, and compare the signal with the theoretical ground surface displacement pattern caused by the Earth tides. Central result is the observation of a significant correlation between the BrO/SO 2 molar ratios with the North-South and vertical components of the calculated tide-induced surface displacement with correlation coefficients of 47 % and 36 %, 10 respectively. From all other investigated parameters, only the correlation between the BrO/SO 2 molar ratios and the relative humidity in the local atmosphere resulted in a comparable correlation coefficient of about 33 %.

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BrO/SO<sub>2</sub> molar ratios from scanning DOAS measurements in the NOVAC network

Cited by 54 publications

References 33 publications

On the relative absorption strengths of water vapour in the blue wavelength range

On the relative absorption strengths of water vapour in the blue wavelength range

Retrieval of absolute SO<sub>2</sub> column amounts from scattered-light spectra: implications for the evaluation of data from automated DOAS networks

Periodicity in the BrO/SO<sub>2</sub> molar ratios in the volcanic gas plume of Cotopaxi and its correlation with the Earth tides during the eruption in 2015

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BrO/SO&lt;sub&gt;2&lt;/sub&gt; molar ratios from scanning DOAS measurements in the NOVAC network

Cited by 54 publications

References 33 publications

On the relative absorption strengths of water vapour in the blue wavelength range

On the relative absorption strengths of water vapour in the blue wavelength range

Retrieval of absolute SO&lt;sub&gt;2&lt;/sub&gt; column amounts from scattered-light spectra: implications for the evaluation of data from automated DOAS networks

Periodicity in the BrO/SO&lt;sub&gt;2&lt;/sub&gt; molar ratios in the volcanic gas plume of Cotopaxi and its correlation with the Earth tides during the eruption in 2015

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BrO/SO<sub>2</sub> molar ratios from scanning DOAS measurements in the NOVAC network

Retrieval of absolute SO<sub>2</sub> column amounts from scattered-light spectra: implications for the evaluation of data from automated DOAS networks

Periodicity in the BrO/SO<sub>2</sub> molar ratios in the volcanic gas plume of Cotopaxi and its correlation with the Earth tides during the eruption in 2015