An extraction method for nitrogen isotope measurement of ammonium in a low-concentration environment

• Published in: Atmospheric Measurement Techniques
• Main Authors: Lamothe, Alexis, Savarino, Joel, Ginot, Patrick, Soussaintjean, Lison, Gautier, Elsa, Akers, Pete, D, Caillon, Nicolas, Erbland, Joseph
• 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), Climate and Environmental Physics Bern (CEP), Physikalisches Institut Bern, Universität Bern / University of Bern (UNIBE)-Universität Bern / University of Bern (UNIBE), Trinity College Dublin, Grenoble University Foundation (FUGA), Ice Memory foundation
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2023
• Subjects: Stable isotope; Ammonia; Ice core; Solid phase extraction; [CHIM.ANAL]Chemical Sciences/Analytical chemistry; [SDU.STU.GL]Sciences of the Universe [physics]/Earth Sciences/Glaciology; Mont Blanc; ice core
• Online Access: https://hal.science/hal-04310338; https://hal.science/hal-04310338/document; https://hal.science/hal-04310338/file/Lamothe%20et%20al.%20-%202023%20-%20An%20extraction%20method%20for%20nitrogen%20isotope%20measurem.pdf; https://doi.org/10.5194/amt-16-4015-2023

International audience Abstract. Ammonia (NH3) participates in the nucleation and growth of aerosols and thus plays a major role in atmospheric transparency, pollution, health, and climate-related issues. Understanding its emission sources through nitrogen stable isotopes is therefore a major focus of current work to mitigate the adverse effects of aerosol formation. Since ice cores can preserve the past chemical composition of the atmosphere for centuries, they are a top tool of choice for understanding past NH3 emissions through ammonium (NH4+), the form of NH3 archived in ice. However, the remote or high-altitude sites where glaciers and ice sheets are typically localized have relatively low fluxes of atmospheric NH4+ deposition, which makes ice core samples very sensitive to laboratory NH3 contamination. As a result, accurate techniques for identifying and tracking NH3 emissions through concentration and isotopic measurements are highly sought to constrain uncertainties in NH3 emission inventories and atmospheric reactivity unknowns. Here, we describe a solid-phase extraction method for NH4+ samples of low concentration that limits external contamination and produces precise isotopic results. By limiting NH3atm exposure with a scavenging fume hood and concentrating the targeted NH4+ through ion exchange resin, we successfully achieve isotopic analysis of 50 nmol NH4+ samples with a 0.6 ‰ standard deviation. This extraction method is applied to an alpine glacier ice core from Col du Dôme, Mont Blanc, where we successfully demonstrate the analytical approach through the analysis of two replicate 8 m water equivalent ice cores representing 4 years of accumulation with a reproducibility of ±2.1 ‰. Applying this methodology to other ice cores in alpine and polar environments will open new opportunities for understanding past changes in NH3 emissions and atmospheric chemistry.