Atmospheric biological particles, including pollen and other plant-derived materials, constitute a substantial fraction of coarse particulate matter, particularly during flowering seasons. Olive trees represent one of the most widespread crops in southern Europe, and olive oil is a major economic resource for the region. Approximately 95% of global olive cultivation is concentrated in the Mediterranean basin (Sofiev et al., 2017). Pollen production from an area with complete olive coverage can reach up to 10¹⁰ pollen grains m⁻² season⁻¹, with an average grain diameter of 20.1 ± 4.0 μm. Olive pollen is considered among the most allergenic tree pollens in Europe, inducing respiratory symptoms such as rhinitis and asthma in humans (Liccardi et al., 1996), while also acting as a significant atmospheric source of organic matter and nutrients to terrestrial and aquatic ecosystems (Rösel et al., 2012; Violaki et al., 2021).In this study, a series of chamber experiments was conducted to investigate the response of olive pollen to atmospheric stressors, with a particular focus on NOx pollution. Olive pollen (Olea europaea L.) was collected between 5 and 7 May 2024 from Puglia, southern Italy (https://www.bonapol.com/). Prior to chamber exposure, comprehensive lipidomic, biological, and chemical characterizations were performed, including analyses of metals, major ions, and carbon content.A robust analytical workflow for pollen lipidomics was developed and applied before and after chamber aging. Using LC-Q-TOF/MS with ESI in both positive and negative ionization modes, approximately 480 lipid species spanning 41 lipid classes were identified. Phosphatidylcholines (PC) were the dominant class (66%), followed by diacylglyceryl carboxyhydroxymethylcholine (DGCC, 19%), and ether monogalactosyldiacylglycerols (MGDG, 8%). A significant decrease in major membrane lipids (PC, PG, SM, DGDG, and MGDG) was observed after aging, indicating lipid degradation processes. In contrast, oxidized lipid species, including oxidized triacylglycerols (OxTG), oxidized phosphatidylcholines (OxPC), and ether-linked lipids, showed a pronounced increase, highlighting oxidative transformations induced by atmospheric aging. Overall, these results highlight the sensitivity of lipids in pollen grains to atmospheric aging and emphasize the importance of considering oxidative processing when assessing the chemical evolution of primary biological aerosol particles.
References
Liccardi et al., Int Arch Allergy Immunol. Nov;111(3):210-7, 1996.Rösel, et al., Aquatic Sciences, 74, 87–99, 2012.Sofiev, et al., Atmos. Chem. Phys., 17, 12341–12360, 2017.Violaki, et al., npj Clim Atmos Sci 4, 63, 2021.
