The magnetism of leaves and lichens for monitoring and mitigating the impact of particulate matter in urban and cultural heritage settings.

Particulate matter (PM) can show remarkable magnetic properties arising from magnetite-like ferrimagnetic particles, often associated with heavy metals. In urban areas, motor vehicles represent the main source of magnetic PM, mostly emitted by disk brakes. Rock magnetism can be applied to the biomonitoring of the airborne pollution, using leaves and lichens as efficient bioaccumulators of anthropogenic dust. Here, we will discuss the role of the magnetic biomonitoring methodologies applied to cultural heritage settings, where PM causes, e.g., dark layers, abrasion of materials and artistic loss. Biomonitoring techniques were firstly applied at Villa Farnesina, Rome. Lichen exposure was preceded by the sampling of plant leaves outside the Villa and inside its gardens: trees and shrubs are important for their role in removing air pollutants, providing ecosystem services for the protection of cultural heritage. Further investigations are going on at Parco Archeologico del Colosseo and Terme di Diocleziano in Rome, at Peggy Guggenheim Collection in Venice and at selected National Museums in Buenos Aires, for assessing the impact of PM on various cultural heritage urban contexts.