Optical properties from extinction cross-section of single pollen particles under laboratory-controlled relative humidity Valenzuela, Antonio García-Izquierdo, F.J. Sánchez-Jiménez, G. Bazo, E. Guerrero- Rascado, Juan Luis Cariñanos, Paloma Alados-Arboledas, Lucas Olmo-Reyes, Francisco J. Single aerosol particle Optical properties Hygroscopicity Radiative effects This work was supported by the Spanish Ministry of Science and Innovation through projects ELPIS (PID2020-12001-5RB-I00), by the Junta de Andalucía Excellence project ADAPNE (P20-00136), AEROPRE (P-18-RT-3820), FEDER Una manera de hacer Europa, EQC2019-006423-P, INTEGRATYON (PID2020-117825 GB-C21 and PID2020-117825 GB-C22), the European Union's Horizon 2020 research and innovation program through project ACTRIS. IMP (grant agreement No 871115), and ATMO-ACCESS (grant agreement No 101008004), and ACTRIS-España (RED2022-134824-E), FEDER/Junta de Andalucía-Consejería de Transformación Económica, Industria, Conocimiento y Universidades project DEM3TRIOS (A-RNM-430-UGR20) and by University of Granada Plan Propio through Excellence Research Unit Earth Science and Singular Laboratory AGORA (LS2022-1) programs and project Pre-GREENMITIGATION (PP2022.PP.34). A growing body of research suggests that pollen suspended in the atmosphere have a major environmental and climatic impact. However, our current knowledge of pollen is rather limited with respect to its extinction capacity, its optical properties and how these vary with atmospheric water content. Understanding their water absorption capacity can improve our understanding of their radiative effects and, thus, improve climate models. In this work, an electrodynamic Paul trap was coupled to a cavity ring down spectroscopy (CRDS) to directly measure the ring down time () of four individual types of pollen particles: Olea, Fraxinus, Populus and Salix exposed to changing relative humidity (RH). Resonant structures in values between ∼90 and 45 % RH indicated that pollen was wettable at high RHs. was used to calculate light extinction cross-section at 532 nm as a function of RH. Optical growth factor () was evaluated as the ratio between and From , the semi-empirical single hygroscopicity parameter () was found to be 0.038–0.058 for the four pollen types. Under controllable treatment of the water content and an adequate selection of complex refractive index , CRDS- data was fitted to theoretical from Mie theory. The reasonable agreement achieved allowed for gaining knowledge about the and how particle size shrugged during dehydration. As a result, a climate-lowering effect of Olea pollen particles, which contain a fraction of scattered aerosol, should be considered in the models. 2023-12-14T11:54:25Z 2023-12-14T11:54:25Z 2023 journal article Published version: Valenzuela A, García-Izquierdo FJ, Sánchez-Jiménez G, Bazo E, Guerrero- Rascado JL, Cariñanos P, Alados-Arboledas L, Olmo-Reyes FJ, Optical properties from extinction cross-section of single pollen particles under laboratory-controlled relative humidity, Journal of Aerosol Science (2024), doi: https://doi.org/10.1016/j.jaerosci.2023.106311 https://hdl.handle.net/10481/86207 10.1016/j.jaerosci.2023.106311 eng info:eu-repo/grantAgreement/EC/H2020/871115 http://creativecommons.org/licenses/by-nc-nd/3.0/ open access Creative Commons Attribution-NonCommercial-NoDerivs 3.0 License Elsevier