EGUsphere EGUsphere EGUsphere EGUsphere Copernicus Publications Göttingen, Germany 10.5194/egusphere-2026-3918 Harmonizing measurements of oxidative potential of PM: an interlaboratory comparison of the ascorbic acid assay Marsal Anouk https://orcid.org/0000-0003-0898-1467 1 Cavalli Fabrizia 2 Di Antonio Elise 1 Houdier Stephan 1 Dominutti Pamela 1 Darfeuil Sophie https://orcid.org/0000-0003-3307-2548 1 Jaffrezo Jean-Luc 1 Sauvage Stéphane 1 Putaud Jean-Philippe 2 Mudway Ian S. 3 Nenes Athanasios https://orcid.org/0000-0003-3873-9970 4 5 Bougiatioti Aikaterini 6 Mihalopoulos Nikolaos 6 7 Prévôt André S. H. 8 Paraskevopoulou Despina https://orcid.org/0000-0002-8482-4925 6 Kušan Ana Cvitešić 9 Frka Sanja https://orcid.org/0000-0002-9018-6165 9 Kroflič Ana 10 41 Delić Ajda 10 40 Tariba Lovaković Blanka https://orcid.org/0000-0001-5908-506X 11 Jurič Andreja 11 Molina Carolina 4 Contini Daniele https://orcid.org/0000-0003-4454-0642 12 Guascito Maria Rachele https://orcid.org/0000-0002-3399-4983 12 39 Lintz Mathilde 13 Rousset Davy 13 Herrmann Hartmut https://orcid.org/0000-0001-7044-2101 14 Souza Eduardo J. d. S. 14 Ledoux Frédéric https://orcid.org/0000-0001-6475-1450 15 Fadel Marc https://orcid.org/0000-0003-3129-3873 15 Yu Haoran 16 Yu Jianzhen https://orcid.org/0000-0002-6165-6500 17 Baeza Romero Maria Teresa https://orcid.org/0000-0001-6891-4982 18 Cerrato-Alvarez Maria 18 42 van Os Marloes F. 19 Delaval Mathilde N. 20 Mena Cabrera Yamaris Mercedes 20 Trieu Nicole https://orcid.org/0009-0000-8896-1882 21 Evans Greg https://orcid.org/0000-0002-9641-4499 21 Galindo Nuria 22 Gómez-Sanchez Noelia https://orcid.org/0000-0001-9282-1858 22 Hlaváčková Hana 23 Mikuška Pavel 23 Kadam Shrutika 24 Shahpoury Pourya 24 López-Mahía Purificación 25 Moreda-Piñeiro Jorge https://orcid.org/0000-0001-6101-1879 25 Cheung Rico K. Y. 26 Kalberer Markus https://orcid.org/0000-0001-8885-6556 26 Introna Micol https://orcid.org/0000-0002-5564-1994 27 Steimer Sarah S. https://orcid.org/0000-0002-1955-9467 27 28 Lin Zhuoying 29 Paulson Suzanne E. 29 Iram Saima 30 Stevanovic Svetlana https://orcid.org/0000-0002-9472-0169 30 Audoux Thomas https://orcid.org/0000-0001-9682-2698 31 Alleman Laurent Y. 31 Liu Jianing 32 Fang Ting https://orcid.org/0000-0002-4845-2749 32 33 Subramanian P. S. Ganesh 34 Verma Vishal 34 Petäjä Tuukka https://orcid.org/0000-0002-1881-9044 35 Querol Xavier https://orcid.org/0000-0002-6549-9899 36 Hoek Gerard 37 Harrison Roy M. https://orcid.org/0000-0002-2684-5226 38 Uzu Gaëlle https://orcid.org/0000-0002-7720-0233 1 University Grenoble Alpes, CNRS, INRAE, IRD, Grenoble INP, IGE (UMR 5001), 38000 Grenoble, France European Commission, Joint Research Centre (JRC), Ispra, Italy MRC Centre for Environment and Health, Environmental Research Group, Imperial College London, 86 Wood Lane, London, W12 0BZ, UK Center for the Study of Air Quality and Climate Change, Institute of Chemical Engineering Sciences, Foundation for Research and Technology Hellas, Patras, 26504, Greece Laboratory of Atmospheric Processes and their Impacts, Institute of Environmental Engineering, École Polytechnique Fédérale de Lausanne, 1015 Lausanne, Switzerland Institute for Environmental Research and Sustainable Development, National Observatory of Athens, Lofos Koufou, P. Penteli, Athens, 15236, Greece Environmental Chemical Processes Laboratory, Department of Chemistry, University of Crete, Heraklion, 71003, Greece Laboratory of Atmospheric Chemistry, Paul Scherrer Institute, 5232 Villigen PSI, Switzerland Division for Marine and Environmental Research, Ruđer Bošković Institute, 10000, Zagreb, Croatia Department of Catalysis and Chemical Reaction Engineering, National Institute of Chemistry, 1000 Ljubljana, Slovenia Division of Toxicology, Institute for Medical Research and Occupational Health, 10000 Zagreb, Croatia Institute of Atmospheric Sciences and Climate, ISAC-CNR, Str. Prv. Lecce-Monteroni km 1.2, 73100 Lecce, Italy Department of Pollutant Metrology, Institut National de Recherche et de Sécurité (INRS), 54500 Vandœuvre-lès-Nancy, France Atmospheric Chemistry Department (ACD), Leibniz Institute for Tropospheric Research (TROPOS), Permoserstraße 15, 04318 Leipzig, Germany Unité de Chimie Environnementale et Interactions sur le vivant (UCEIV), UR4492, Université du Littoral Côte d’Opale, 59140, Dunkerque, France Department of Civil and Environmental Engineering, University of Alberta, Edmonton, Canada The Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong Escuela de Ingeniería Industrial y Aeroespacial de Toledo, Universidad de Castilla-la-Mancha, Toledo 45004, Spain Netherlands Organization for Applied Scientific Research (TNO), Princetonlaan 8, 3584 CB Utrecht, Netherlands Comprehensive Molecular Analytics (CMA), Helmholtz Zentrum München, Neuherberg, Germany Southern Ontario Centre for Atmospheric Aerosol Research, University of Toronto, Toronto, M5S 3E5, Canada Atmospheric Pollution Laboratory (LCA), Department of Applied Physics, Miguel Hernández University, Avda. de la Universidad S/N, Elche 03202, Spain Department of Environmental Analytical Chemistry, Institute of Analytical Chemistry, Czech Academy of Sciences, Veveří 97, 60200 Brno, Czech Republic Environmental and Life Sciences, Trent University, Peterborough, Canada University of A Coruña. Grupo Química Analítica Aplicada (QANAP), University Institute of Research in Environmental Studies (IUMA), Center for Technological Innovation in Construction and Civil Engineering Environmental Studies (IUMA), Center for Technological Innovation in Construction and Civil Engineering Spain Department of Environmental Sciences, University of Basel, 4056 Basel, Switzerland Department of Environmental Science, Stockholm University, Stockholm, 11418, Sweden Bolin Centre for Climate Research, Stockholm, 11418, Sweden Department of Atmospheric and Oceanic Sciences, University of California Los Angeles, Los Angeles, CA 90095, United States School of Engineering, Deakin University, Geelong, 3216 Victoria, Australia IMT Nord Europe, Institut Mines-Télécom, Univ. Lille, Centre for Energy and Environment, 59000 Lille, France Thrust of Sustainable Energy and Environment, The Hong Kong University of Science and Technology (Guangzhou), Guangzhou, 511400, China Thrust of Earth, Ocean, and Atmospheric Sciences, The Hong Kong University of Science and Technology (Guangzhou), Guangzhou, 511400, China Department of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign, 205 North Mathews Avenue, Urbana, IL 61801, United States Institute for Atmospheric and Earth System Research, Faculty of Science, University of Helsinki, Helsinki 00014, Finland Institute of Environmental Assessment and Water Research (IDAEA-CSIC), 08034 Barcelona, Spain Institute for Risk Assessment Sciences, Utrecht University, Utrecht, 3584CM, the Netherlands Division of Environmental Health and Risk Management, School of Geography, Earth and Environmental Sciences, Edgbaston, Birmingham, B15 2TT, UK University of Salento, Department of Biological and Environmental Sciences and Technologies, Via per Arnesano, 73100 Lecce, Italy University of Maribor, Faculty of Chemistry and Chemical Technology, Smetanova ulica 17, 2000 Maribor, Slovenia School of Environmental Sciences, University of Nova Gorica, 5271 Vipava, Slovenia now at: Department of Analytical Chemistry, Physical Chemistry and Chemical Engineering, University of Alcala, 28871, Alcalá de Henares (Madrid), Spain 30 07 2026 2026 1 28 Copyright: © 2026 Anouk Marsal et al. 2026 This work is licensed under the Creative Commons Attribution 4.0 International License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/4.0/ This article is available from https://egusphere.copernicus.org/preprints/2026/egusphere-2026-3918/ The full text article is available as a PDF file from https://egusphere.copernicus.org/preprints/2026/egusphere-2026-3918/egusphere-2026-3918.pdf

Oxidative potential (OP) of atmospheric particulate matter (PM) is a metric of increasing scientific interest because it potentially links chemical particle properties to particle health effects. OP has been recently introduced as a recommended monitoring metric in the European Air Quality Directive. However, inconsistent protocols in the existing literature make it difficult to compare results across studies. Following a 2023 inter-laboratory comparison that focused on PM OP measured using the dithiothreitol (DTT) assay, this paper presents the findings and lessons learnt from a second inter-laboratory study focused on the ascorbic acid assay (OP-AA). In this study, twenty-six laboratories worldwide quantified OP of four PM filter samples and of one chemical compound to evaluate the entire analytical chain, including the extraction step, using a simplified OP-AA protocol. While most laboratories produced repeatable internal results when applying the simplified protocol, significant discrepancies between participants highlight the need for each laboratory to carefully evaluate deviations from the simplified OP-AA protocol. Over half of the 26 participants achieved satisfactory results, suggesting that the protocol is suitable for large-scale implementation. Beyond assessing performance, this work investigates technical, analytical, and mathematical refinements to measurement protocols. Building on the first DTT assay study, this second inter-laboratory comparison represents a significant step toward harmonizing OP assays, and provides specific recommendations to ensure consistent future measurements, ready to be applied in the new air quality directive EU 2024/2881.

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