Reaction Rates Control High-Temperature Chemistry of Volcanic Gases in Air

Roberts, Tjarda; Dayma, Guillaume; Oppenheimer, Clive

doi:10.3389/feart.2019.00154

Cited by 33 publications

(62 citation statements)

References 68 publications

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“…Bromine from various sources (e.g., polar regions, salt lakes, and volcanoes) is involved in tropospheric and stratospheric ozone depletion (e.g., Wennberg, 1999;Rose et al, 2006;Simpson et al, 2007). Tropospheric ozone depletion has also been observed in volcanic plumes (e.g., Hobbs et al, 1982;Kelly et al, 2013;Surl et al, 2015;Roberts, 2018), which supports the proposed reaction mechanisms for BrO formation via autocatalytic chain reactions.…”

Section: Introductionsupporting

confidence: 59%

Halogen activation in the plume of Masaya volcano: field observations and box model investigations

et al. 2021

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Abstract. Volcanic emissions are a source of halogens in the atmosphere. Rapid reactions convert the initially emitted hydrogen halides (HCl, HBr, and HI) into reactive species such as BrO, Br2, BrCl, ClO, OClO, and IO. The activation reaction mechanisms in the plume consume ozone (O3), which is entrained by ambient air that is mixed into the plume. In this study, we present observations of the oxidation of bromine, chlorine, and iodine during the first 11 min following emission, examining the plume from Santiago crater of the Masaya volcano in Nicaragua. Two field campaigns were conducted: one in July 2016 and one in September 2016. The sum of the reactive species of each halogen was determined by gas diffusion denuder sampling followed by gas chromatography–mass spectrometry (GC-MS) analysis, whereas the total halogens and sulfur concentrations were obtained by alkaline trap sampling with subsequent ion chromatography (IC) and inductively coupled plasma mass spectrometry (ICP-MS) measurements. Both ground and airborne sampling with an unoccupied aerial vehicle (carrying a denuder sampler in combination with an electrochemical SO2 sensor) were conducted at varying distances from the crater rim. The in situ measurements were accompanied by remote sensing observations (differential optical absorption spectroscopy; DOAS). The reactive fraction of bromine increased from 0.20 ± 0.13 at the crater rim to 0.76 ± 0.26 at 2.8 km downwind, whereas chlorine showed an increase in the reactive fraction from (2.7 ± 0.7) × 10−4 to (11 ± 3) × 10−4 in the first 750 m. Additionally, a reactive iodine fraction of 0.3 at the crater rim and 0.9 at 2.8 km downwind was measured. No significant change in BrO / SO2 molar ratios was observed with the estimated age of the observed plume ranging from 1.4 to 11.1 min. This study presents a large complementary data set of different halogen compounds at Masaya volcano that allowed for the quantification of reactive bromine in the plume of Masaya volcano at different plume ages. With the observed field data, a chemistry box model (Chemistry As A Boxmodel Application Module Efficiently Calculating the Chemistry of the Atmosphere; CAABA/MECCA) allowed us to reproduce the observed trend in the ratio of the reactive bromine to total bromine ratio. An observed contribution of BrO to the reactive bromine fraction of about 10 % was reproduced in the first few minutes of the model run.

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Section: Introductionsupporting

confidence: 59%

Halogen activation in the plume of Masaya volcano: field observations and box model investigations

et al. 2021

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“…Roberts et al (2014) alluded the need for an alternative explanation for NOX at volcanoes, where it has been observed. In a recent study Roberts et al (2019) presented a time-resolved chemical kinetics model for the high temperature near source chemistry of volcanic emissions that is an improvement to the HSC model. In contrast to HSC Roberts et al (2019) reproduced reduced gas species and high temperature formation of HO2, OH, and H2O2, but do not include NOX chemistry yet.…”

Section: Bromine Chemistrymentioning

confidence: 99%

“…In a recent study Roberts et al (2019) presented a time-resolved chemical kinetics model for the high temperature near source chemistry of volcanic emissions that is an improvement to the HSC model. In contrast to HSC Roberts et al (2019) reproduced reduced gas species and high temperature formation of HO2, OH, and H2O2, but do not include NOX chemistry yet. Therefore, two scenarios with magmatic and atmospheric HXOY/NOX composition are investigated as extremes, representing the HSC output and the atmospheric background composition, respectively.…”

Section: Bromine Chemistrymentioning

confidence: 99%

Halogen activation in the plume of Masaya volcano: field observations and box model investigations

Rüdiger

Gutmann

Bobrowski

et al. 2020

Preprint

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Abstract. Volcanic emissions are a source of halogens to the atmosphere. Rapid reactions convert the initially emitted hydrogen halides (HCl, HBr, HI) into reactive species e.g. BrO, Br2, BrCl, ClO, OClO and IO. The activation reaction mechanisms in the plume consume ozone (O3), which is entrained by in-mixed ambient air. In this study, we present observations of the oxidation of bromine, chlorine and iodine during the first 11 minutes after emission, investigating the plume of Santiago Crater of Masaya volcano in Nicaragua. Two field campaigns were conducted, in July 2016 and September 2016. The sum of the reactive species of the respective halogens were determined by gas diffusion denuder sampling followed by GC-MS analysis, while the total amounts of halogens and sulfur amounts were obtained by alkaline trap sampling with subsequent IC and ICP-MS measurements. Both ground and airborne sampling with an unmanned aerial vehicle (including a denuder sampler in combination with an electrochemical SO2 sensor) was performed at different distances from the crater rim. The in-situ measurements were accompanied by remote sensing observations (DOAS). For bromine, the reactive fraction increased from 0.20 ± 0.13 at the crater rim to 0.76 ± 0.26 at 2.8 km downwind, while chlorine showed an increase of the reactive fraction from (2.7 ± 0.7) × 10−4 to (11 ± 3) × 10−4 in the first 750 m. Additionally, a reactive iodine fraction of 0.3 at the crater rim and 0.9 at 2.8 km was measured. No significant increase in BrO / SO2 molar ratios was observed with the estimated age of the observed plume ranging from 1.4 min to 11.1 min. This study presents a comprehensive gas diffusion denuder data set on reactive halogen species and compares BrO / SO2 ratios with the sum of all reactive Br species. With the observed field data, a chemistry box model (CAABA/MECCA) enabled the reproduction of the observed progression of the reactive bromine to total bromine ratio. An observed contribution of BrO to the reactive bromine fraction of about 10 % was reproduced in the first minutes of the model run. The model results emphasize the importance of ozone entrainment into the plume for the reproduction of the measured reactive bromine formation and the dependence on the availability of HXOY and NOX.

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“…This bromine partitioning follows previous thermodynamic modeling estimates (Roberts et al, 2014). Emissions of volcanic HO x are highly uncertain, there exist order-of-magnitude differences between kinetic and thermodynamic model predictions, and in the speciation between OH and HO 2 (Roberts et al, 2019). Here, we define the volcanic HO x emission by setting a OH/SO 2 molar ratio of 0.001 11 https://doi.org/10.5194/acp-2021-145 Preprint.…”

Section: Model Settingsmentioning

confidence: 67%

Observation and modelling of ozone-destructive halogen chemistry in a passive degassing volcanic plume

Surl¹,

Roberts²,

Bekki³

2021

Preprint

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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 SO2 – 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 SO2 levels. From these observations we estimate a mean in-plume ozone loss rate of 1.3 × 10−5 molecules of O3 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 SO2 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 / SO2 ratios (around 10−4 mol/mol) similar to those observed previously in Etna plumes. The modelled BrO / SO2 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 HO2. 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. Modelled rates of ozone depletion are found to be similar to those derived from aircraft observations. Ozone destruction in the model is controlled by the processes that recycle bromine, with about three-quarters of this recycling occurring via reactions between halogen oxide radicals. Through sensitivity simulations, a relationship between the magnitude of halogen emissions and ozone loss is established. Volcanic halogens cycling impacts profoundly the overall plume chemistry, notably hydrogen oxide radicals (HOx), nitrogen oxides (NOx), sulfur, and mercury chemistry. In the model, it depletes HOx within the plume, increasing the lifetime of SO2 and hence slowing sulfate aerosol formation. Halogen chemistry also promotes the conversion of NOx into nitric acid (HNO3). This, along with the displacement of nitrate out of background aerosols in the plume, results in enhance HNO3 levels and an almost total depletion of NOx in the plume. The halogen-mercury model scheme is simple but includes newly-identified photo-reductions of mercury halides. With this set-up, the mercury oxidation is found to be slow and in near-balance with the photo-reduction in the plume. Overall, the model findings demonstrate that halogen chemistry has to be considered for a complete understanding of sulfur, HOx, reactive nitrogen, and mercury chemistry, and of the formation of sulfate particles in volcanic plumes.

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Reaction Rates Control High-Temperature Chemistry of Volcanic Gases in Air

Cited by 33 publications

References 68 publications

Halogen activation in the plume of Masaya volcano: field observations and box model investigations

Halogen activation in the plume of Masaya volcano: field observations and box model investigations

Halogen activation in the plume of Masaya volcano: field observations and box model investigations

Observation and modelling of ozone-destructive halogen chemistry in a passive degassing volcanic plume

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