Quantification of the depletion of ozone in the plume of Mount Etna

Volcanoes are an important source of inorganic halogen species into the atmosphere. Chemical processing of these species generates oxidised, highly reactive, halogen species which catalyse considerable O₃ destruction within volcanic plumes. A campaign of ground-based in situ O₃, SO₂ and meteorology measurements was undertaken at the summit of Mount Etna volcano in July/August 2012. At the same time, spectroscopic measurements were made of BrO and SO₂ columns in the plume downwind. <br><br> Depletions of ozone were seen at all in-plume measurement locations, with average O₃ depletions ranging from 11–35 nmol mol⁻¹ (15–45%). Atmospheric processing times of the plume were estimated to be between 1 and 4 min. A 1-D numerical model of early plume evolution was also used. It was found that in the early plume O₃ was destroyed at an approximately constant rate relative to an inert plume tracer. This is ascribed to reactive halogen chemistry, and the data suggests the majority of the reactive halogen that destroys O₃ in the early plume is generated within the crater, including a substantial proportion generated in a high-temperature "effective source region" immediately after emission. The model could approximately reproduce the main measured features of the ozone chemistry. Model results show a strong dependence of the near-vent bromine chemistry on the presence or absence of volcanic NO_x emissions and suggest that near-vent ozone measurements can be used as a qualitative indicator of NO_x emission

Which processes drive observed variations of HCHO columns over India?

We interpret HCHO column variations observed by the Ozone Monitoring Instrument (OMI), aboard the NASA Aura satellite, over India during 2014 using the GEOS-Chem atmospheric chemistry and transport model. We use a nested version of the model with a horizontal resolution of approximately 25 km. HCHO columns are related to local emissions of volatile organic compounds (VOCs) with a spatial smearing that increases with the VOC lifetime. Over India, HCHO has biogenic, pyrogenic, and anthropogenic VOC sources. Using a 0-D photochemistry model, we find that isoprene has the largest molar yield of HCHO which is typically realized within a few hours. We also find that forested regions that neighbour major urban conurbations are exposed to high levels of nitrogen oxides. This results in depleted hydroxyl radical concentrations and a delay in the production of HCHO from isoprene oxidation. We find that propene is the only anthropogenic VOC emitted in major Indian cities that produces HCHO at a comparable (but slower) rate to isoprene. The GEOS-Chem model reproduces the broad-scale annual mean HCHO column distribution observed by OMI (<i>r</i> = 0.6), which is dominated by a distinctive meridional gradient in the northern half of the country, and by localized regions of high columns that coincide with forests. Major discrepancies are noted over the Indo-Gangetic Plain (IGP) and Delhi. We find that the model has more skill at reproducing observations during winter (JF) and pre-monsoon (MAM) months with Pearson correlations <i>r</i> &gt; 0.5 but with a positive model bias of  <mo form="infix">≃</mo> 1×10¹⁵ molec cm⁻². During the monsoon season (JJAS) we reproduce only a diffuse version of the observed meridional gradient (<i>r</i> = 0.4). We find that on a continental scale most of the HCHO column seasonal cycle is explained by monthly variations in surface temperature (<i>r</i> = 0.9), suggesting a role for biogenic VOCs, in agreement with the 0-D and GEOS-Chem model calculations. We also find that the seasonal cycle during 2014 is not significantly different from the 2008 to 2015 mean seasonal variation. There are two main loci for biomass burning (the states of Punjab and Haryana, and northeastern India), which we find makes a significant contribution (up to 1×10¹⁵ molec cm⁻²) to observed HCHO columns only during March and April over northeastern India. The slow production of HCHO from propene oxidation results in a smeared hotspot over Delhi that we resolve only on an annual mean timescale by using a temporal oversampling method. Using a linear regression model to relate GEOS-Chem isoprene emissions to HCHO columns we infer seasonal isoprene emissions over two key forest regions from the OMI HCHO column data. We find that the a posteriori emissions are typically lower than the a priori emissions, with a much stronger reduction of emissions during the monsoon season. We find that this reduction in emissions during monsoon months coincides with a large drop in satellite observations of leaf phenology that recovers in post monsoon months. This may signal a forest-scale response to monsoon conditions

Modelling the atmospheric chemistry of volcanic plumes

Abstract Volcanoes are the principal way by which volatiles are transferred from the solid Earth to the atmosphere-hydrosphere system. Once released into the atmosphere, volcanic emissions rapidly undergo a complex series of chemical reactions. This thesis seeks to further the understanding of such processes by both observation and numerical modelling. I have adapted WRF-Chem to model passive degassing from Mount Etna, the chemistry of its plume, and its influence on the wider atmosphere. This investigation considers model plumes from the point of emission up to a day’s travel from the vent and is able to reproduce observed phenomena of BrO formation and O3 depletion within volcanic plumes. The model plume influences several atmospheric chemistry systems, including reactive nitrogen and organic chemistry. Plume chemistry is driven by sunlight, and I examine how the modelled phenomena identified in this investigation vary with the diurnal cycle. In the modelled plume all of the bromine is involved in O3-destructive cycling. When HBr is exhausted, volcanic HCl sustains the cycling. The rate-limiting factor of this cycling, and therefore the rate of O3 destruction, is sunlight. I find qualitative differences between the chemistry of low and high intensity plumes, with the bromine chemistry in the latter case being limited by O3 depletion. This modelling investigation is complemented by an observational study of O3 in a young Etnean plume from which I estimate the rate of in-plume O3 destruction within seconds to minutes after emission. These investigations demonstrate that volcanic plumes can be included in complex, 3D atmospheric chemistry models, and that the output from these can be used to observe and quantify influences of volcanic plumes on the wider atmosphere

Sources of Influence on Perceptions of South Korean Youths about Unification of North and South Korea

The purpose of this research is to explore what information sources are influencing the perception of south Korean youths about unification between North and South Korea. The Research Examined the sources and the tone of message which the youths receive from non-school sources such as family, peers, teachers, religious institutions and media. The research methodology combined a survey with interviews. Questionnaires were collected from a total of 273 students in 3 high schools located in metropolitan ares of Seoul in South Korea. Interviews with a student and a unification education lecturer who is a North Korean defector were also conducted. SPSS was used to analyze questionnaires with descriptive analysis, correlation, and multiple regression. Interviews were analyzed for emerging themes. The findings showed that the media and teachers were the primary sources of information about unification. In terms of feeling about messages, students feel that their peers provide mostly negative messages whereas their teachers and religious institutions are more positive. Both media and family were judged to provide about equally negative and positive messages. The students feel that the overall tone of messages from all sources is about equally balanced between positive and negative messages. Lastly, 56% of students have negative feelings about North Korea and unification, which reflects the messages from peer groups. Teachers\u27 positive messages are not very related to students\u27 perception s on unification and North Korea. Among media, movies are a strong influential source in the formation of perceptions toward North Korea. All the information sources such as family, teachers, peers and media equally affect students\u27 feelings about North Korea and unification. Media that students heavily rely on for information are not the exclusive factor contributing to the most personal feelings. My findings suggest that high school students need unification education in formal school curriculum since teachers\u27 messages are not through official curriculum but through informal communications. Without formal education about unification, students tend to rely on other information sources. Also, to positively influence the narrative of unification, unification education needs to expand to adults through civic education. This research supports the necessity of unification education for South Korean youths and adults as a way of achieving unification

Gas emission strength and evolution of the molar ratio of BrO/SO2 in the plume of Nyiragongo in comparison to Etna

Airborne and ground-based differential optical absorption spectroscopy observations have been carried out at the volcano Nyiragongo (Democratic Republic of Congo) to measure SO2 and bromine monoxide (BrO) in the plume in March 2004 and June 2007, respectively. Additionally filter pack and multicomponent gas analyzer system (Multi-GAS) measurements were carried out in June 2007. Our measurements provide valuable information on the chemical composition of the volcanic plume emitted from the lava lake of Nyiragongo. The main interest of this study has been to investigate for the first time the bromine emission flux of Nyiragongo (a rift volcano) and the BrO formation in its volcanic plume. Measurement data and results from a numerical model of the evolution of BrO in Nyiragongo volcanic plume are compared with earlier studies of the volcanic plume of Etna (Italy). Even though the bromine flux from Nyiragongo (2.6t/d) is slightly greater than that from Etna (1.9t/d), the BrO/SO2 ratio (maximum 7x10(-5)) is smaller than in the plume of Etna (maximum 2.1x10(-4)). A one-dimensional photochemical model to investigate halogen chemistry in the volcanic plumes of Etna and Nyiragongo was initialized using data from Multi-GAS and filter pack measurements. Model runs showed that the differences in the composition of volcanic volatiles led to a smaller fraction of total bromine being present as BrO in the Nyiragongo plume and to a smaller BrO/SO2 ratio

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

Acknowledgements. As well as the financial support noted below, the authors would like to acknowledge the following. Computer modelling benefited from access to IDRIS HPC resources (GENCI allocation A007017141) and the IPSL mesoscale computing cen- tre (CICLAD: Calcul Intensif pour le CLimat, l’Atmosphère et la Dynamique). Aircraft measurements were carried out within the Global Mercury Observation System project (GMOS; http://www. gmos.eu, last access: 12 August 2021), and we acknowledge the contribution of the GMOS teams of CNR IIA, Italy, and Helmholtz- Zentrum Geesthacht, Germany. GMOS was financially supported by the European Union within the seventh framework programme (FP-7; project ENV.2010.4.1.3-2). The authors would like to thank Louis Marelle and Jennie Thomas for their assistance with the model development. The model presented in this paper is a devel- opment of work undertaken as part of Luke Surl’s PhD, which was funded by the UK’s Natural Environment Research Council and su- pervised by Deanna Donohoue and Roland von Glasow. The authors would like to thank the two anonymous referees for suggesting var- ious improvements to this paper. Financial support. This paper is a result of a project that has re- ceived funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement no. 800062 as well as ANR Projet de Recherche Collaborative VOLC-HAL-CLIM (Volcanic Halogens: from Deep Earth to Atmospheric Impacts), ANR-18-CE01-0018.Peer reviewedPublisher PD

Investigating the Role of Non-Covalent Interactions in Conformation and Assembly of Triazine-Based Sequence-Defined Polymers

Grate and co-workers at Pacific Northwest National Laboratory recently developed high information content triazine-based sequence-defined polymers that are robust by not having hydrolyzable bonds and can encode structure and functionality by having various side chains. Through molecular dynamics (MD) simulations, the triazine polymers have been shown to form particular sequential stacks, have stable backbone-backbone interactions through hydrogen bonding and $\pi$-$\pi$ interactions, and conserve their \emph{cis/trans} conformations throughout the simulation. However, we do not know the effects of having different side chains and backbone structures on the entire conformation and whether the \emph{cis} or \emph{trans} conformation is more stable for the triazine polymers. For this reason, we investigate the role of non-covalent interactions for different side chains and backbone structures on the conformation and assembly of triazine polymers in MD simulations. Since there is a high energy barrier associated to the \emph{cis}-\emph{trans} isomerization, we use replica exchange molecular dynamics (REMD) to sample various conformations of triazine hexamers. To obtain rates and intermediate conformations, we use the recently developed concurrent adaptive sampling (CAS) algorithm for dimer of triazine trimers. We found that the hydrogen bonding ability of the backbone structure is critical for the triazine polymers to self-assemble into nanorod-like structures, rather than that of the side chains, which can help researchers design more robust materials

Ancestral evolution of oxidase activity in a class of (S)-nicotine and (S)-6-hydroxynicotine degrading flavoenzymes

Reduced flavin cofactors have the innate ability to reduce molecular oxygen to hydrogen peroxide. Flavoprotein oxidases turbocharge the reaction of their flavin cofactor with oxygen whereas flavoprotein dehydrogenases generally suppress it, yet our understanding of how these two enzyme classes control this reactivity remains incomplete. Here we used ancestral sequence reconstruction and biochemical characterization to retrace the evolution of oxidase activity in a lineage of nicotine/6-hydroxynicotine degrading enzymes of the flavoprotein amine oxidase superfamily. Our data suggest that the most ancient ancestor that gave rise to this lineage was a dehydrogenase, and that oxidase activity emerged later from within this group of dehydrogenases. We have identified the key amino acid replacements responsible for this emergence of oxidase activity, which, remarkably, span the entire protein structure. Molecular dynamics simulations indicate that this constellation of substitutions decreases the global dynamics of the protein in the evolution of oxidase function. This coincides with a dramatic restriction in the movement of a lysine residue in the active site, which more optimally positions it in front of the flavin to promote the reaction with O2. Our results demonstrate that sites distant from the flavin microenvironment can help control flavin-oxygen reactivity in flavoenzymes by modulating the conformational space and dynamics of the protein and catalytic residues in the active site