On bromine, nitrogen oxides and ozone depletion in the tropospheric plume of Erebus volcano (Antarctica)

• Published in: Atmospheric Environment
• Main Authors: Boichu, Marie, Oppenheimer, Clive, Roberts, Tjarda J., Tsanev, V.I., Kyle, Philip R.
• Other Authors: University of Cambridge UK (CAM), Department of Geography Cambridge, UK, Institut des Sciences de la Terre d'Orléans (ISTO), Université de Tours-Institut national des sciences de l'Univers (INSU - CNRS)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS), Norwegian Polar Institute, New Mexico Institute of Mining and Technology New Mexico Tech (NMT), NSF Office of Polar Programs grants ANT-0538414 and ANT-0838817 and the United States Antarctic Program.
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2011
• Subjects: Volcanic plume; Antarctic troposphere; Reactive bromine chemistry; Reactive nitrogen chemistry; Ozone depletion; Phonolitic magma; [SDU.STU.VO]Sciences of the Universe [physics]/Earth Sciences/Volcanology; [SDE.MCG]Environmental Sciences/Global Changes; Antarctic; Lava Lake; Antarc*; Antarctica
• Online Access: https://hal-insu.archives-ouvertes.fr/insu-00587549; https://hal-insu.archives-ouvertes.fr/insu-00587549/document; https://hal-insu.archives-ouvertes.fr/insu-00587549/file/boichu-AtmosphericEnvironment-2011.pdf; https://doi.org/10.1016/j.atmosenv.2011.03.027

International audience Since the discovery of bromine oxide (BrO) in volcanic emissions, there has been speculation concerning its role in chemical evolution and notably ozone depletion in volcanic plumes. We report the first measurements using Differential Optical Absorption Spectroscopy (DOAS) of BrO in the tropospheric plume of the persistently degassing Erebus volcano (Antarctica). These are the first observations pertaining to emissions from an alkaline phonolitic magma. The observed BrO/SO2 ratio of 2.5 x 10-4 is similar to that measured at andesitic arc volcanoes. The high abundance of BrO is consistent with high abundances of F and Cl relative to sulfur in the Erebus plume. Our estimations of HBr flux and BrO production rate suggest that reactive bromine chemistry can explain a 35% loss of tropospheric O3 observed in the Erebus plume at approximately 30 km from source (Oppenheimer et al., 2010). Erebus also has a permanent lava lake, which could result in generation of NOx by thermal fixation of atmospheric N2 at the hot lava surface. Any NOx emission could play a potent role in reactive bromine chemistry. However, the presence of NO2 could not be detected in the plume, about 400 m above the lake, in our DOAS observations of 2005. Nor could we reproduce spectroscopic retrievals that reportedly identified NO2 in DOAS observations from 2003 made of the Erebus plume (Oppenheimer et al., 2005). Based on the NO2 detection limit of our analysis, we can state an upper limit of the NO2/SO2 ratio of ≤ 0.012, an order of magnitude lower than previously reported. Our new result supports a rapid oxidation of NOx in the young plume and is more consistent with measurements of NOy species measured using an instrumented aircraft flying in the plume. Model simulations, tuned for Erebus, were performed to reproduce the BrO/SO2 observed in the young plume and to investigate the impact of NOx emissions at source on the subsequent formation of BrO in the plume. They support our hypothesis of rapid conversion of NOx to NOy ...