Abstract
Organic aerosol particles (OA) can absorb solar radiation with varying efficiencies depending on their chemical composition and physical properties. This light-absorbing fraction of OA, commonly referred to as brown carbon (BrC), is difficult to accurately represent in climate models due to the inherent diversity of its optical properties. This variability arises from differences in emission sources and atmospheric processing, as well as from variations in experimental design and the analytical methods used to quantify BrC absorption. As a result, the climate effect of BrC remains uncertain. Here, we studied the light absorption properties of surface ambient OA using measurements from 17 sites across Europe. Combining multi-wavelength absorption measurements from filter-based photometers with OA mass concentrations and source apportionment derived from ACSM/AMS data, we derive empirical estimates of the OA mass absorption cross section (MACOA), its wavelength dependence (AAEOA), the OA density (⍴OA), and the MAC associated with different primary and secondary OA sources. We further develop parameterizations that relate MACOA, AAEOA and ⍴OA to the ambient black carbon-to-organic aerosol ratio (eBC/OA) and propose a corresponding parameterization for the imaginary refractive index (kOA). Given the widespread availability of eBC and OA measurements in global monitoring networks, the framework presented here provides a practical approach for estimating the absorptive properties of surface OA particles under real-world conditions.
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Supplementary data to this article can be found online at https://doi.org/10.5281/zenodo.17649258.
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Acknowledgements
This work was supported by the Spanish Ministry of Economy, Industry and Competitiveness and I + D + I “Retos Colaboración” funds under the CAIAC project (PID2019−108990PB−100), by the EU HORIZON-EUROPE project FOCI under grant agreement n° 101056783, by the Horizon 2020 RI-URBANS project (contract 101036245). IDAEA acknowledges support by the Generalitat de Catalunya, (DTER, DGQA and AGAUR 2021 SGR47) and the European Commission via ACTRIS-IMP (project 871115). We acknowledge support of the COST Action CA16109 COLOSSAL. G.M. and A.G. acknowledges support from the Slovenian Research Agency program P1-0385 “Remote sensing of atmospheric properties” and projects V1-2373, L1-4386, L2-4485. J.Y.D., M.V., and I.S. are supported by the European Union’s Horizon Europe research and innovation program under the Marie Skłodowska-Curie Postdoctoral Fellowship Programme, SMASH is co-funded by the Republic of Slovenia and the European Union from the European Regional Development Fund under the grant agreement No. 101081355. Finnish Meteorological gratefully acknowledges funding from Academy of Finland via the project Black and Brown Carbon in the Atmosphere and the Cryosphere (BBrCAC) (decision nr. 341271). University of Helsinki acknowledges support of Research Council of Finland via Atmosphere and Climate Competence Center (337549, 357902, 359340), INAR RI (345510, 358647, 367739). Irish datasets were supported by the EPA-Ireland (AEROSOURCE), the Department of Environment, Climate and Communications and Taighde Éireann—Research Ireland under Grant number [22/FFP-A/10611]. INOE acknowledges support of Core Program within the Romanian National Research Development and Innovation Plan 2022-2027, carried out with the support of MCID, project no. PN 23 05. Multi-wavelength absorption data for Birkenes Observatory is obtained as part of the Norwegian national monitoring programme119 and is funded by the Norwegian Environment Agency (Contract No. 21087006). ATOLL measurements have been supported by the Labex CaPPA project, which is funded by the French National Research Agency (ANR) through the PIA (Programme d’Investissement d’Avenir) under contract ANR-11-LABX-0005-01; the CLIMIBIO and ECRIN projects, all financed by the Regional Council “Hauts-de-France” and the European Regional Development Fund (ERDF); and the French Ministry of Environment through the CARA program of the Laboratoire Central de Surveillance de la Qualité de l’Air (LCSQA). Institute of Chemical Process Fundamentals (CAS) and Global Change Research Institute (CAS) acknowledge support of the Ministry of Education, Youth and Sports of the Czech Republic within the Large Research Infrastructure Support Project, ACTRIS—Participation of the Czech Republic (ACTRIS-CZ LM2023030).
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J.R. led data curation, formal analysis, investigation, visualization, and wrote the original draft. J.Y.D. and M.P. contributed to conceptualization, methodology, and validation. M.P. also contributed to resources, supervision, and funding acquisition, and co-wrote the original draft. J.Y.D. contributed to supervision. Data curation was performed by J.R., G.I.C., G.M., M.G.B., W.A., M.A., J.B., S.B., B.T.B., A.C.A., B.C., K.R.D., J.F.d.B., E.D., K.E., M.E., O.F., H.F., M.I.G., A.G., R.H., L.H., C.H., A.H., M.I., H.K., G.K., E.L., C.L., R.L., K.L., M.M., H.E.M., M.I.M., N.Ma., S.M., N.Mi., M.C.M., J.V.N., J.O., N.P., J.E.P., S.M.P., P.P., A.S.H.P., V.R., M.R., M.R., J.S., I.S., E.T., K.T., H.T., A.T., J.V., M.V., P.V., S.V., K.E.Y., N.Z., O.Z., A.A., T.P., and X.Q. Methodology development involved J.Y.D., M.G.B., and M.P. Validation was carried out by J.Y.D. and M.P. Funding acquisition was obtained by D.N., J.O., A.A., T.P., X.Q., and M.P. Writing—review and editing was performed by all authors.
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A.G., M.I. and M.R. are employed by the manufacturer of the instruments used in this study. The other authors have no competing interests.
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Rovira, J., Yus-Díez, J., Chen, G.I. et al. Constraining the intensive absorption properties of ambient organic aerosol particles based on pan-European observations. npj Clim Atmos Sci (2026). https://doi.org/10.1038/s41612-026-01405-9
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DOI: https://doi.org/10.1038/s41612-026-01405-9
