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Article ; Online: An algorithm for correction of atmospheric scattering dilution effects in volcanic gas emission measurements using skylight differential optical absorption spectroscopy

B. Galle / S. Arellano / M. Johansson / C. Kern / M. A. Pfeffer

Frontiers in Earth Science, Vol

2023 Volume 11

Abstract: Differential Optical Absorption Spectroscopy (DOAS) is commonly used to measure gas emissions from volcanoes. DOAS instruments measure the absorption of solar ultraviolet (UV) radiation scattered in the atmosphere by sulfur dioxide (SO2) and other trace ... ...

Abstract	Differential Optical Absorption Spectroscopy (DOAS) is commonly used to measure gas emissions from volcanoes. DOAS instruments measure the absorption of solar ultraviolet (UV) radiation scattered in the atmosphere by sulfur dioxide (SO2) and other trace gases contained in volcanic plumes. The standard spectral retrieval methods assume that all measured light comes from behind the plume and has passed through the plume along a straight line. However, a fraction of the light that reaches the instrument may have been scattered beneath the plume and thus has passed around it. Since this component does not contain the absorption signatures of gases in the plume, it effectively “dilutes” the measurements and causes underestimation of the gas abundance in the plume. This dilution effect is small for clean-air conditions and short distances between instrument and plume. However, plume measurements made at long distance and/or in conditions with significant atmospheric aerosol, haze, or clouds may be severely affected. Thus, light dilution is regarded as a major error source in DOAS measurements of volcanic degassing. Several attempts have been made to model the phenomena and the physical mechanisms are today relatively well understood. However, these models require knowledge of the local atmospheric aerosol composition and distribution, parameters that are almost always unknown. Thus, a practical algorithm to quantitatively correct for the dilution effect is still lacking. Here, we propose such an algorithm focused specifically on SO2 measurements. The method relies on the fact that light absorption becomes non-linear for high SO2 loads, and that strong and weak SO2 absorption bands are unequally affected by the diluting signal. These differences can be used to identify when dilution is occurring. Moreover, if we assume that the spectral radiance of the diluting light is identical to the spectrum of light measured away from the plume, a measured clean air spectrum can be used to represent the dilution component. A ...
Keywords	DOAS ; scattering ; volcanic gas ; sulfur dioxide ; emission monitoring ; Science ; Q
Subject code	535
Language	English
Publishing date	2023-07-01T00:00:00Z
Publisher	Frontiers Media S.A.
Document type	Article ; Online
Database	BASE - Bielefeld Academic Search Engine (life sciences selection)

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Article ; Online: A rapid deployment instrument network for temporarily monitoring volcanic SO 2 emissions – a study case from Telica volcano

V. Conde / D. Nilsson / B. Galle / R. Cartagena / A. Muñoz

Geoscientific Instrumentation, Methods and Data Systems Discussions, Vol 4, Iss 1, Pp 191-

2014 Volume 211

Abstract: Volcanic gas emissions play a crucial role in describing geophysical processes; hence measurements of magmatic gases such as SO 2 can be used as tracers prior and during volcanic crises. Different measurement techniques based on optical spectroscopy have ...

Abstract	Volcanic gas emissions play a crucial role in describing geophysical processes; hence measurements of magmatic gases such as SO 2 can be used as tracers prior and during volcanic crises. Different measurement techniques based on optical spectroscopy have provided valuable information when assessing volcanic crises. This paper describes the design and implementation of a network of spectroscopic instruments based on Differential Optical Absorption Spectroscopy (DOAS) for remote sensing of volcanic SO 2 emissions, which is robust, portable and can be deployed in relative short time. The setup allows the processing of raw data in situ even in remote areas with limited accessibility, and delivers pre-processed data to end-users in near real time even during periods of volcanic crisis, via a satellite link. In addition, the hardware can be used to conduct short term studies of volcanic plumes in remotes areas. The network was tested at Telica, an active volcano located in western Nicaragua, producing what is so far the largest data set of continuous SO 2 flux measurements at this volcano.
Keywords	Science ; Q ; Geology ; QE1-996.5
Subject code	550
Language	English
Publishing date	2014-04-01T00:00:00Z
Publisher	Copernicus Publications
Document type	Article ; Online
Database	BASE - Bielefeld Academic Search Engine (life sciences selection)

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Article ; Online: A rapid deployment instrument network for temporarily monitoring volcanic SO 2 emissions – a case study from Telica volcano

V. Conde / D. Nilsson / B. Galle / R. Cartagena / A. Muñoz

Geoscientific Instrumentation, Methods and Data Systems, Vol 3, Iss 2, Pp 127-

2014 Volume 134

Abstract: Volcanic gas emissions play a crucial role in describing geophysical processes; hence, measurements of magmatic gases such as SO 2 can be used as tracers prior to and during volcanic crises. Different measurement techniques based on optical spectroscopy ... ...

Abstract	Volcanic gas emissions play a crucial role in describing geophysical processes; hence, measurements of magmatic gases such as SO 2 can be used as tracers prior to and during volcanic crises. Different measurement techniques based on optical spectroscopy have provided valuable information when assessing volcanic crises. This paper describes the design and implementation of a network of spectroscopic instruments based on differential optical absorption spectroscopy (DOAS) for remote sensing of volcanic SO 2 emissions, which is robust, portable and can be deployed in relatively short time. The setup allows the processing of raw data in situ even in remote areas with limited accessibility, and delivers pre-processed data to end users in near real time, even during periods of volcanic crisis, via a satellite link. In addition, the hardware can be used to conduct short-term studies of volcanic plumes in remote areas. We describe here tests of the network at Telica, an active volcano located in western Nicaragua, during three different measurement periods, including an eruptive crisis. The tests produced what is so far the largest data set of continuous SO 2 flux measurements at this volcano. The measurements show that, during the period 2010–2013, the flux averages approximately 100 tons per day (t day −1 ).
Keywords	Science ; Q ; Geology ; QE1-996.5 ; Geophysics. Cosmic physics ; QC801-809
Subject code	550
Language	English
Publishing date	2014-08-01T00:00:00Z
Publisher	Copernicus Publications
Document type	Article ; Online
Database	BASE - Bielefeld Academic Search Engine (life sciences selection)

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Article ; Online: BrO/SO 2 molar ratios from scanning DOAS measurements in the NOVAC network

P. Lübcke / N. Bobrowski / S. Arellano / B. Galle / G. Garzón / L. Vogel / U. Platt

Solid Earth, Vol 5, Iss 1, Pp 409-

2014 Volume 424

Abstract: The molar ratio of BrO to SO 2 is, like other halogen/sulfur ratios, a possible precursor for dynamic changes in the shallow part of a volcanic system. While the predictive significance of the BrO/SO 2 ratio has not been well constrained yet, it has the ... ...

Abstract	The molar ratio of BrO to SO 2 is, like other halogen/sulfur ratios, a possible precursor for dynamic changes in the shallow part of a volcanic system. While the predictive significance of the BrO/SO 2 ratio has not been well constrained yet, it has the major advantage that this ratio can be readily measured using the remote-sensing technique differential optical absorption spectroscopy (DOAS) in the UV. While BrO/SO 2 ratios have been measured during several short-term field campaigns, this article presents an algorithm that can be used to obtain long-term time series of BrO/SO 2 ratios from the scanning DOAS instruments of the Network for Observation of Volcanic and Atmospheric Change (NOVAC) or comparable networks. Parameters of the DOAS retrieval of both trace gases are given. The influence of co-adding spectra on the retrieval error and influences of radiative transfer will be investigated. Difficulties in the evaluation of spectroscopic data from monitoring instruments in volcanic environments and possible solutions are discussed. The new algorithm is demonstrated by evaluating data from the NOVAC scanning DOAS systems at Nevado del Ruiz, Colombia, encompassing almost 4 years of measurements between November 2009 and end of June 2013. This data set shows variations of the BrO/SO 2 ratio several weeks prior to the eruption on 30 June 2012.
Keywords	Geology ; QE1-996.5 ; Science ; Q ; Stratigraphy ; QE640-699 ; Petrology ; QE420-499 ; Dynamic and structural geology ; QE500-639.5
Subject code	290
Language	English
Publishing date	2014-06-01T00:00:00Z
Publisher	Copernicus Publications
Document type	Article ; Online
Database	BASE - Bielefeld Academic Search Engine (life sciences selection)

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Article ; Online: Global monitoring of volcanic SO2 degassing with unprecedented resolution from TROPOMI onboard Sentinel-5 Precursor

N. Theys / P. Hedelt / I. De Smedt / C. Lerot / H. Yu / J. Vlietinck / M. Pedergnana / S. Arellano / B. Galle / D. Fernandez / C. J. M. Carlito / C. Barrington / B. Taisne / H. Delgado-Granados / D. Loyola / M. Van Roozendael

Scientific Reports, Vol 9, Iss 1, Pp 1-

2019 Volume 10

Abstract: Abstract Over the last four decades, space-based nadir observations of sulfur dioxide (SO2) proved to be a key data source for assessing the environmental impacts of volcanic emissions, for monitoring volcanic activity and early signs of eruptions, and ... ...

Abstract	Abstract Over the last four decades, space-based nadir observations of sulfur dioxide (SO2) proved to be a key data source for assessing the environmental impacts of volcanic emissions, for monitoring volcanic activity and early signs of eruptions, and ultimately mitigating related hazards on local populations and aviation. Despite its importance, a detailed picture of global SO2 daily degassing is difficult to produce, notably for lower-tropospheric plumes, due largely to the limited spatial resolution and coverage or lack of sensitivity and selectivity to SO2 of current (and previous) nadir sensors. We report here the first volcanic SO2 measurements from the hyperspectral TROPOspheric Monitoring Instrument (TROPOMI) launched in October 2017 onboard the ESA’s Sentinel-5 Precursor platform. Using the operational processing algorithm, we explore the benefit of improved spatial resolution to the monitoring of global volcanic degassing. We find that TROPOMI surpasses any space nadir sensor in its ability to detect weak degassing signals and captures day-to-day changes in SO2 emissions. The detection limit of TROPOMI to SO2 emissions is a factor of 4 better than the heritage Aura/Ozone Monitoring Instrument (OMI). Here we show that TROPOMI SO2 daily observations carry a wealth of information on volcanic activity. Provided with adequate wind speed data, temporally resolved SO2 fluxes can be obtained at hourly time steps or shorter. We anticipate that TROPOMI SO2 data will help to monitor global volcanic daily degassing and better understand volcanic processes and impacts.
Keywords	Medicine ; R ; Science ; Q
Language	English
Publishing date	2019-02-01T00:00:00Z
Publisher	Nature Publishing Group
Document type	Article ; Online
Database	BASE - Bielefeld Academic Search Engine (life sciences selection)

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Article ; Online: Observations of high rates of NO 2 – HONO conversion in the nocturnal atmospheric boundary layer in Kathmandu, Nepal

R. Prinn / A. Panday / B. Galle / E. Hodson / Y. Yu / S. Wang

Atmospheric Chemistry and Physics Discussions, Vol 9, Iss 1, Pp 183-

2009 Volume 223

Abstract: Nitrous acid (HONO) plays a significant role in the atmosphere, especially in the polluted troposphere. Its photolysis after sunrise is an important source of hydroxyl free radicals (OH). Measurements of nitrous acid and other pollutants were carried out ...

Abstract	Nitrous acid (HONO) plays a significant role in the atmosphere, especially in the polluted troposphere. Its photolysis after sunrise is an important source of hydroxyl free radicals (OH). Measurements of nitrous acid and other pollutants were carried out in the Kathmandu urban atmosphere during January–February 2003, contributing to the sparse knowledge of nitrous acid in South Asia. The results showed average nocturnal levels of HONO (1.7±0.8 ppbv), NO 2 (17.9±10.2 ppbv), and PM 10 (0.18± 0.11 mg m −3 ) in urban air in Kathmandu. Surprisingly high ratios of chemically formed secondary [HONO] to [NO 2 ] (up to 30%) were found, which indicates unexpectedly efficient chemical conversion of NO 2 to HONO in Kathmandu. The ratios of [HONO]/[NO 2 ] at nights are much higher than previously reported values from measurements in urban air in Europe, North America and Asia. The influence of aerosol plumes, relative humidity, aerosol surface and ground reactive surface, temperature on NO 2 -HONO chemical conversion were discussed. The high humidity, strong and low inversion layer at night, and serious aerosol pollution burden may explain the particularly efficient conversion of NO 2 to HONO.
Keywords	Environmental sciences ; GE1-350 ; Geography. Anthropology. Recreation ; G ; DOAJ:Environmental Sciences ; DOAJ:Earth and Environmental Sciences
Subject code	333 ; 290
Language	English
Publishing date	2009-01-01T00:00:00Z
Publisher	Copernicus Publications
Document type	Article ; Online
Database	BASE - Bielefeld Academic Search Engine (life sciences selection)

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Article ; Online: Tula industrial complex (Mexico) emissions of SO 2 and NO 2 during the MCMA 2006 field campaign using a Mini-DOAS system

M. Johansson / B. de Foy / H. Wöhrnschimmel / G. Sosa / C. Rivera / B. Galle

Atmospheric Chemistry and Physics Discussions, Vol 9, Iss 1, Pp 5153-

2009 Volume 5176

Abstract: The Mexico City Metropolitan Area (MCMA) has presented severe pollution problems for many years. There are several point and mobile emission sources inside and outside the MCMA which are known to affect air quality in the area. In particular, speculation ...

Abstract	The Mexico City Metropolitan Area (MCMA) has presented severe pollution problems for many years. There are several point and mobile emission sources inside and outside the MCMA which are known to affect air quality in the area. In particular, speculation has risen as to whether the Tula industrial complex, located 60 km northwest of the MCMA has any influence on high SO 2 levels occurring on the northern part of the city, in the winter season mainly. As part of the MILAGRO Field Campaign, from 24 March to 17 April 2006, the total columns of sulfur dioxide (SO 2 ) and nitrogen dioxide (NO 2 ) were measured during plume transects in the neighborhood of the Tula industrial complex using mini-DOAS instruments. Vertical profiles of wind speed and direction obtained from pilot balloons and radiosondes were used to calculate SO 2 and NO 2 fluxes in the plume. According to our measurements, calculated average flux emission for SO 2 and NO 2 were 155±120 and 9±8 ktons per year, respectively. The standard deviation of these estimations is due to actual variations in the observed emissions from the refinery and power plant, as well as to the uncertainty in the wind fields at the exact time of the measurements. These values are in good agreement with available datasets and with simulated plumes.
Keywords	Environmental sciences ; GE1-350 ; Geography. Anthropology. Recreation ; G ; DOAJ:Environmental Sciences ; DOAJ:Earth and Environmental Sciences ; Geophysics. Cosmic physics ; QC801-809
Subject code	333
Language	English
Publishing date	2009-02-01T00:00:00Z
Publisher	Copernicus Publications
Document type	Article ; Online
Database	BASE - Bielefeld Academic Search Engine (life sciences selection)

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Article ; Online: Tula industrial complex (Mexico) emissions of SO 2 and NO 2 during the MCMA 2006 field campaign using a mobile mini-DOAS system

C. Rivera / G. Sosa / H. Wöhrnschimmel / B. de Foy / M. Johansson / B. Galle

Atmospheric Chemistry and Physics, Vol 9, Iss 17, Pp 6351-

2009 Volume 6361

Abstract	The Mexico City Metropolitan Area (MCMA) has presented severe pollution problems for many years. There are several point and mobile emission sources inside and outside the MCMA which are known to affect air quality in the area. In particular, speculation has risen as to whether the Tula industrial complex, located 60 km northwest of the MCMA has any influence on high SO 2 levels occurring on the northern part of the city, in the winter season mainly. As part of the MILAGRO Field Campaign, from 24 March to 17 April 2006, the differential vertical columns of sulfur dioxide (SO 2 ) and nitrogen dioxide (NO 2 ) were measured during plume transects in the neighborhood of the Tula industrial complex using mobile mini-DOAS instruments. Vertical profiles of wind speed and direction obtained from pilot balloons and radiosondes were used to calculate SO 2 and NO 2 emissions. According to our measurements, calculated average emissions of SO 2 and NO 2 during the field campaign were 384±103 and 24±7 tons day −1 , respectively. The standard deviation of these estimations is due to actual variations in the observed emissions from the refinery and power plant, as well as to the uncertainty in the wind fields at the exact time of the measurements. Reported values in recent inventories were found to be in good agreement with calculated emissions during the field campaign. Our measurements were also found to be in good agreement with simulated plumes.
Keywords	Physics ; QC1-999 ; Chemistry ; QD1-999
Subject code	290
Language	English
Publishing date	2009-09-01T00:00:00Z
Publisher	Copernicus Publications
Document type	Article ; Online
Database	BASE - Bielefeld Academic Search Engine (life sciences selection)

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Article ; Online: Observations of high rates of NO 2 -HONO conversion in the nocturnal atmospheric boundary layer in Kathmandu, Nepal

Y. Yu / B. Galle / A. Panday / E. Hodson / R. Prinn / S. Wang

Atmospheric Chemistry and Physics, Vol 9, Iss 17, Pp 6401-

2009 Volume 6415

Abstract	Nitrous acid (HONO) plays a significant role in the atmosphere, especially in the polluted troposphere. Its photolysis after sunrise is an important source of hydroxyl free radicals (OH). Measurements of nitrous acid and other pollutants were carried out in the Kathmandu urban atmosphere during January–February 2003, contributing to the sparse knowledge of nitrous acid in South Asia. The results showed average nocturnal levels of HONO (1.7±0.8 ppbv), NO 2 (17.9±10.2 ppbv), and PM 10 (0.18±0.11 mg m −3 ) in urban air in Kathmandu. Surprisingly high ratios of chemically formed secondary [HONO] to [NO 2 ] (up to 30%) were found, which indicates unexpectedly efficient chemical conversion of NO 2 to HONO in Kathmandu. The ratios of [HONO]/[NO 2 ] at night were found to be much higher than previously reported values from measurements in urban air in Europe, North America and Asia. The influences of aerosol surface, ground reactive surface, and relative humidity on NO 2 -HONO chemical conversion were discussed. The high humidity, strong and low inversion layer at night, and high aerosol pollution burden in Kathmandu may explain the particularly efficient conversion of NO 2 to HONO.
Keywords	Physics ; QC1-999 ; Chemistry ; QD1-999
Subject code	290
Language	English
Publishing date	2009-09-01T00:00:00Z
Publisher	Copernicus Publications
Document type	Article ; Online
Database	BASE - Bielefeld Academic Search Engine (life sciences selection)

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Article ; Online: Mobile mini-DOAS measurement of the outflow of NO 2 and HCHO from Mexico City

L. Molina / B. Galle / Y. Zhang / J. Song / W. Lei / B. de Foy / M. Johansson / C. Rivera

Atmospheric Chemistry and Physics, Vol 9, Iss 15, Pp 5647-

2009 Volume 5653

Abstract: We here present the results from mobile measurements using two ground-based zenith viewing Differential Optical Absorption Spectroscopy (DOAS) instruments. The measurement was performed in a cross-section of the plume from the Mexico City Metropolitan ... ...

Abstract	We here present the results from mobile measurements using two ground-based zenith viewing Differential Optical Absorption Spectroscopy (DOAS) instruments. The measurement was performed in a cross-section of the plume from the Mexico City Metropolitan Area (MCMA) on 10 March 2006 as part of the MILAGRO field campaign. The two instruments operated in the UV and the visible wavelength region respectively and have been used to derive the differential vertical columns of HCHO and NO 2 above the measurement route. This is the first time the mobile mini-DOAS instrument has been able to measure HCHO, one of the chemically most important and interesting gases in the polluted urban atmosphere. Using a mass-averaged wind speed and wind direction from the WRF model the instantaneous flux of HCHO and NO 2 has been calculated from the measurements and the results are compared to the CAMx chemical model. The calculated flux through the measured cross-section was 1.9 (1.5–2.2) kg/s of HCHO and 4.4 (4.0–5.0) kg/s of NO 2 using the UV instrument and 3.66 (3.63–3.73) kg/s of NO 2 using the visible light instrument. The modeled values from CAMx for the outflow of both NO 2 and HCHO, 1.1 and 3.6 kg/s, respectively, show a reasonable agreement with the measurement derived fluxes.
Keywords	Environmental sciences ; GE1-350 ; Geography. Anthropology. Recreation ; G ; DOAJ:Environmental Sciences ; DOAJ:Earth and Environmental Sciences
Subject code	290
Publishing date	2009-08-01T00:00:00Z
Publisher	Copernicus Publications
Document type	Article ; Online
Database	BASE - Bielefeld Academic Search Engine (life sciences selection)

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