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

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.

Two Independent Light Dilution Corrections for the SO2 Camera Retrieve Comparable Emission Rates at Masaya Volcano, Nicaragua

SO2 cameras are able to measure rapid changes in volcanic emission rate but require accurate calibrations and corrections to convert optical depth images into slant column densities. We conducted a test at Masaya volcano of two SO2 camera calibration approaches, calibration cells and co-located spectrometer, and corrected both calibrations for light dilution, a process caused by light scattering between the plume and camera. We demonstrate an advancement on the image-based correction that allows the retrieval of the scattering efficiency across a 2D area of an SO2 camera image. When appropriately corrected for the dilution, we show that our two calibration approaches produce final calculated emission rates that agree with simultaneously measured traverse flux data and each other but highlight that the observed distribution of gas within the image is different. We demonstrate that traverses and SO2 camera techniques, when used together, generate better plume speed estimates for traverses and improved knowledge of wind direction for the camera, producing more reliable emission rates. We suggest combining traverses and the SO2 camera should be adopted where possible.

SO₂ and BrO emissions of Masaya volcano from 2014–2020

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.

DIVERSIDAD DE MURCIÉLAGOS Y USO DE HÁBITAT EN EL PARQUE NACIONAL VOLCÁN MASAYA, EN EL PACÍFICO DE NICARAGUA

ResumenDurante 2014 estudiamos la diversidad de murciélagos del Parque Nacional Volcán Masaya a través de capturas en diferentes tipos de cobertura arbórea; también caracterizamos la comunidad de murciélagos insectívoros que habita el tubo de lava llamado Tzinacanoste, determinando patrones de desplazamiento de una de las especies. El ensamble taxonómico de murciélagos en el parque se determinó y describió analizando su potencial de conservación y la importancia que representa (por sus servicios ambientales) para las zonas de producción sostenible alrededor del volcán Masaya. En total se identificaron 29 especies (26.3% del total de especies identificadas en Nicaragua) pertenecientes a 5 familias. En el bosque cerrado se encontró la mayor riqueza con 18 especies, de las cuales, un tercio de éstas fueron exclusivas de este tipo de bosque; a diferencia del área abierta de uso público, que presentó valores mínimos de riqueza con cuatro especies. Destacan cuatro especies con fines de conservación e investigación, tres de la familia Phyllostomidae (subfamilia Phyllostominae), Micronycteris microtis, Micronycteris schmidtorum y Lophostoma brasiliense y una especie de Mormoopidae, Mormoops megalophylla, cuya subespecie M. megalophylla megalophylla, presenta su límite sur de distribución mundial en este parque. También es importante considerar en los planes de conservación a las cuatro especies asociadas al bosque seco (Balantiopteryx plicata, Pteronotus davyi, Glossophaga leachii y Carollia subrufa), que en el país se distribuyen básicamente en la región Pacífica. Los resultados demuestran la importancia del Parque Nacional Volcán Masaya como un área importante para la conservación y la investigación de los murciélagos.Palabras clave: Bosque seco, conservación, especies, gremio trófico, servicio ambiental.AbstractDuring 2014 we studied the diversity of bats in the Masaya Volcano National Park through captures in different types of tree cover; we also characterize the community of insectivorous bats that inhabits the lava tube locally called Tzinacanoste, determining displacement patterns for one of the species. The taxonomic assembly of bats in the park was determined and described, analyzing its conservation potential and the importance it represents (for its environmental services) for the sustainable production areas around the Masaya volcano. In total 29 species were identified (26.3% of the total species identified in Nicaragua) belonging to 5 families. The closed forest presented the highest species richness with 18, and a third of these were exclusive to this type of forest; unlike the open area for public use, which presented minimum values with four species. Four species are of conservation and research interest, three of the family Phyllostomidae (subfamily Phyllostominae), Micronycteris microtis, Micronycteris schmidtorum and Lophostoma brasiliense, and a species of Mormoopidae: Mormoops megalophylla, whose subspecies M. megalophylla megalophylla, presents the southern limit of world distribution in this park. It is also important to consider in the conservation plans the four species associated with the dry forest, which in the country are basically distributed in the Pacific region: Balantiopteryx plicata, Pteronotus davyi, Glossophaga leachii and Carollia subrufa. The results demonstrate the importance of the Masaya Volcano National Park as an important area for the conservation and research of bats.Key words: Conservation, dry forest, environmental service, species, trophic guild.