Fine particulate matter (PM) poses a major threat to public health, with organic aerosol (OA) being a key component. Major OA sources, hydrocarbon-like OA (HOA), biomass burning OA (BBOA), and oxygenated OA (OOA), have distinct health and environmental impacts. However, OA source apportionment via positive matrix factorization (PMF) applied to aerosol mass spectrometry (AMS) or aerosol chemical speciation monitoring (ACSM) data is costly and limited to a few supersites, leaving over 80% of OA data uncategorized in global monitoring networks. To address this gap, we trained machine learning models to predict HOA, BBOA, and OOA using limited OA source apportionment data and widely available organic carbon (OC) measurements across Europe (2010-2019). Our best performing model expanded the OA source data set 4-fold, yielding 85 000 daily apportionment values across 180 sites. Results show that HOA and BBOA peak in winter, particularly in urban areas, while OOA, consistently the dominant fraction, is more regionally distributed with less seasonal variability. This study provides a significantly expanded OA source data set, enabling better identification of pollution hotspots and supporting high-resolution exposure assessments.

Aerosol Physics Laboratory Tampere University 33100 Tampere Finland

Agence Nationale pour la Gestion des Déchets Radioactifs RD960 55290 Bure France

Air Quality and Climate Department Estonian Environmental Research Centre Marja 4D 10617 Tallinn Estonia

Aix Marseille University CNRS LCE 13003 Marseille France

Arpae Emilia Romagna Centro Tematico Regionale Qualità dell'Aria 40139 Bologna Italy

Atmospheric Composition Research Finnish Meteorological Institute 00560 Helsinki Finland

Bolin Centre for Climate Research Stockholm University 114 18 Stockholm Sweden

Center for Atmospheric Research University of Nova Gorica SI 5000 Nova Gorica Slovenia

Center for Research in Sustainable Chemistry Associate Unit CSIC University of Huelva Atmospheric Pollution Campus El Carmen s n 21071 Huelva Spain

Climate and Atmosphere Research Center The Cyprus Institute 2121 Nicosia Cyprus

College of Environmental Sciences and Engineering Peking University Beijing 100084 China

Datalystica Limited 5234 Villigen Switzerland

Department of Applied Physics Universidad de Granada Av de la Fuente Nueva 18071 Granada Spain

Department of Climate Air and Sustainability TNO 3584 CB Utrecht Netherlands

Department of Environment and Planning Centre for Environmental and Marine Studies University of Aveiro 3810 193 Aveiro Portugal

Department of Environmental Science Stockholm University 114 18 Stockholm Sweden

Department of Environmental Sciences Aarhus University DK 4000 Aarhus Denmark

Department of Intelligent Systems KTH Royal Institute of Technology 11428 Stockholm Sweden

Department of Physics University of Genoa and INFN Genoa 16146 Liguria Italy

Empa Swiss Federal Laboratories for Materials Science and Technology 8600 Dübendorf Switzerland

Environmental Protection Agency of Lombardy 20124 Milan Italy

Environmental Radioactivity and Aerosol Technology for Atmospheric and Climate Impact Lab INRaSTES NCSR Demokritos 15310 Athens Greece

European Commission Joint Research Centre 21027 Ispra Italy

Faculty of Physics and Applied Computer Science AGH University of Krakow 30 059 Krakow Poland

German Meteorological Service 82383 Hohenpeissenberg Germany

Global Institute for Urban and Regional Sustainability School of Ecological and Environmental Sciences East China Normal University Shanghai 200231 China

HPRU in Environmental Exposures and Health Imperial College London 86 Wood Lane London W12 0BZ United Kingdom

IMT Nord Europe Institut Mines Télécom Université de Lille Centre for Energy and Environment 59000 Lille France

Institut National de l'Environnement Industriel et des Risques 60550 Verneuil en Halatte France

Institut Scientifique de Service Public 4000 Liège Belgium

Institute for Atmospheric and Earth System Research Physics Faculty of Science University of Helsinki 00014 Helsinki Finland

Institute for Environmental Research and Sustainable Development National Observatory of Athens 15236 Athens Greece

Institute of Chemical Process Fundamentals Czech Academy of Sciences 165 00 Prague 6 Czech Republic

Institute of Chemistry Eötvös Loránd University 1053 Budapest Hungary

Institute of Environmental Assessment and Water Research 08034 Barcelona Spain

Institute of Physics University of Tartu 50411 Tartu Estonia

Italian National Research Council Institute of Atmospheric Sciences and Climate 40129 Bologna Italy

Italian National Research Council Institute of Polar Sciences 20125 Milan Italy

Laboratoire de Météorologie Physique Université Clermont Auvergne CNRS 63170 Aubière France

Laboratoire des Sciences du Climat et de l'Environnement 91190 Gif sur Yvette France

Leibniz Institute for Tropospheric Research 04318 Leipzig Germany

MRC Centre for Environment and Health Environmental Research Group Imperial College London 86 Wood Lane London W12 0BZ United Kingdom

National Institute for Nuclear Physics Florence Section Via Sansone 1 50019 Sesto Fiorentino Florence Italy

National Institute of Research and Development for Optoelectronics 077125 Magurele Romania

NILU 2007 Kjeller Norway

PSI Center for Energy and Environmental Sciences 5232 Villigen Switzerland

School of Earth and Atmospheric Sciences Queensland University of Technology Gardens Point Brisbane Queensland 4000 Australia

School of Natural Sciences Physics Centre for Climate and Air Pollution Studies Ryan Institute University of Galway Galway H91 CF50 Ireland

SRI Center for Physical Sciences and Technology 10257 Vilnius Lithuania

State Key Laboratory of Loess Sciences Center for Excellence in Quaternary Science and Global Change Institute of Earth Environment Chinese Academy of Sciences Xi'an 710061 China

Swiss Data Science Center EPFL and ETH Zürich 8092 Zürich Switzerland

Swiss Tropical and Public Health Institute Kreuzstraße 2 4123 Allschwil Switzerland

Umweltbundesamt 06844 Dessau Roßlau Germany

University Grenoble Alpes CNRS IRD INP G INRAE IGE 38000 Grenoble France

University of Basel 4001 Basel Switzerland

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