The chemistry of high reactive species and their role on the oxidative capacity at polar regions

• Main Author: Barbero, Albane
• Other Authors: Institut des Géosciences de l’Environnement (IGE), Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes (UGA)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP ), Université Grenoble Alpes (UGA), Université Grenoble Alpes 2020-., Joël Savarino, Roberto Grilli
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: HAL CCSD 2021
• Subjects: Atmosphere; Halogenated compounds; Oxidants; Snow; Nitrogen compounds; Oxydative capacity; Photochemestry; Polar regions; Régions polaires; Photochimie; Capacité oxydante; Atmosphère; Composés halogènes; Oxydants; Neige; Composés azotés; [SDU.STU]Sciences of the Universe [physics]/Earth Sciences; Antarctic; The Antarctic; Antarc*; Antarctica; polar night
• Online Access: https://tel.archives-ouvertes.fr/tel-03329000; https://tel.archives-ouvertes.fr/tel-03329000/document; https://tel.archives-ouvertes.fr/tel-03329000/file/BARBERO_2021_archivage.pdf

Over the last two decades, the paradigm of snow as an inert material has been challenged by the discovery of substantial chemical activity within the snowpack and, in particular, its elevated nitrogen oxides content. When sunlight resumes at the end of the polar night, it triggers photochemistry within the porous snowpack. The highly reactive products of this photochemistry can be exchanged between snow and atmosphere, and these exchanges will redistribute the species governing the oxidizing capacity of the atmosphere.Many studies that sought to better understand these polar processes have shown that: i) highly reactive species (such as NO_x, OH, HO_2, RO_2, and XO) play a key role in such a remote environment, controlling the oxidative capacity and the atmospheric chemistry and ii) snow emissions also locally control the oxidative capacity. Indeed, gaseous nitrogen species, especially nitrogen oxides NO_x (NO_x equiv NO + NO_2), emitted from the photolysis of nitrate contained in the snowpack, lead to a strong production of O_3 and OH radicals in the atmosphere. Unfortunately, these mechanisms are still poorly understood due to the lack of information on the behavior of nitrate in snow and the absence of direct measurements of NO_2 at the snow-atmosphere interface.First, we applied a NO_x measurement technique based on incoherent broadband cavity enhanced absorption spectroscopy (IBBCEAS) that is different from those previously used in Antarctica. This technique allows direct measurement of NO_2 and NO_x, and thus it reduces concentration level uncertainties. We developed, tested, and validated two robust instruments, for NO_2 and NO_x detection, respectively, that reached detection limits around 30 times 10^{-12} mol mol^{-1} (3sigma) and we deployed these instruments in the Antarctic field at Dome C.Two hypotheses explain the behavior of nitrate in the snowpack facing the absorption of a photon. The first one, commonly accepted, assumes the existence of two nitrate fractions: one subject to photolysis and the ...