Magnetic and chemical air biomonitoring for the preservation of cultural heritage

Air pollution poses a challenging threat to cultural heritage: the deposition of particulate matter (PM) on surfaces leads to soiling, colour alteration, and material degradation. Pollution monitoring is therefore central to preventive conservation; however, traditional PM samplers are not always feasible in museums and archaeological sites for aesthetic and operational reasons. This thesis addresses this problem by adopting a nature-based biomonitoring approach—using lichens and tree leaves—to delineate deposition patterns of PM and potentially toxic elements (PTEs) both inside and outside the study contexts. The three chapters present different applications of magnetic and chemical biomonitoring based on transplants of the lichen Evernia prunastri and leaf sampling from site-specific tree species. In the first case study (Peggy Guggenheim Collection, Venice), located in a peculiar aquatic traffic area, lichens showed no substantial indoor bioaccumulation of PM and PTEs (with a limited exception for Zn); outdoors, magnetic measurement highlighted a moderate bioaccumulation only on lichens, that was not evident for Pittosporum tobira leaves. The second chapter (Colosseum Archaeological Park, Palatine Hill, Rome) examines an archaeological site in an urban setting: lichen transplants and leaves from several plant species indicate that the horizontal distance from the road source drives PM diffusion more strongly than elevation. Leaves intercept both airborne and resuspended fractions, confirming their potential for preventive mitigation, while lichens are specifically suitable for outlining the airborne component of PM. The third chapter (Museo Nacional de Bellas Artes and Museo Histórico Nacional, Buenos Aires) shows, via magnetic properties and elemental analyses, that most outdoor metallic PM derives from brake abrasion; this signal does not translate into measurable indoor bioaccumulation. Under comparable conditions, Jacaranda mimosifolia is more efficient than Fraxinus americana at intercepting PM and PTEs. Overall, the thesis validates an integrated magnetic–chemical biomonitoring approach that identifies vehicle-derived particulate sources, quantifies indoor–outdoor gradients of exposure to PM, and guides vegetation-based mitigation measures to support the preventive conservation of cultural heritage.