Modelling Arctic halogen chemistry and its impacts on ozone and mercury

• Main Author: Ahmed, Shaddy
• 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)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE)-Université Grenoble Alpes (UGA)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP ), Université Grenoble Alpes (UGA), Université Grenoble Alpes 2020-., Aurélien Dommergue, Jennie L. Thomas
• Format: Doctoral or Postdoctoral Thesis
• Language: French
• Published: HAL CCSD 2022
• Subjects: Modelling; Halogens; Arctic; Atmospheric chemistry; Ozone; Mercury; Modélisation; Arctique; Halogènes; Chimie atmosphérique; Mercure; [SDU.STU]Sciences of the Universe [physics]/Earth Sciences; Arctique*; Sea ice; Alaska
• Online Access: https://theses.hal.science/tel-04368946; https://theses.hal.science/tel-04368946/document; https://theses.hal.science/tel-04368946/file/AHMED_2022_archivage.pdf

Halogens are an important component of Arctic atmospheric chemistry, responsible for the depletion of boundary layer ozone and mercury, oxidation of hydrocarbons, and impacts on nitrogen oxide chemistry and oxidative capacity. During spring, reactive halogens are photochemically activated on salty surfaces (e.g. land-based snow, snow on sea ice, aerosols) and released into the atmosphere. However, the interplay between polar chemical emissions, recycling, transport, and chemistry is complex and remains poorly understood. As a result, descriptions of such processes in atmospheric chemistry models are largely simplified or neglected. This thesis presents an investigation of the role of halogens (chlorine and bromine) on springtime Arctic boundary layer chemistry, through the development and use of atmospheric chemistry models.First, a 1-dimensional model (PACT-1D) is used to study molecular halogen emissions from surface snow and the impact on oxidative chemistry within the boundary layer. The model is used to simulate reactive halogen chemistry observed during the spring 2009 OASIS (Ocean-Atmospheric-Sea ice-Snowpack) measurement campaign in Utqiagvik, Alaska. Model results show that chlorine can be confined to a very shallow layer near the surface, resulting in a large chemical reactivity gradient with altitude. Second, the 3-dimensional WRF-Chem model is used to investigate the interaction of halogens with ozone and mercury during Arctic spring. Several major WRF-Chem model developments are made in this work, including the addition of a new mercury chemical description. The model is evaluated with unique data from the central Arctic, obtained during the 2020 MOSAiC (Multidisciplinary drifting Observatory for the Study of Arctic Climate) expedition. Model results show that bromine emissions and recycling from surface snow and sea ice are necessary to capture ozone and mercury depletion events. This work highlights a need for improved model descriptions of surface emissions to accurately represent boundary layer ...