Multi-scale characterization of lead-rich deposited particles originating from the fire of Notre-Dame de Paris.

Fire is a major hazard for built heritage. The fire at Notre-Dame on April 15, 2019 completely destroyed the woodframe and the lead roof (about 285 tons) almost entirely melted due to high temperatures. A part of the molten lead escaped into the atmosphere in the form of aerosols while the majority remains within cathedral enclosure in the form of deposits, metallic remains, spatters etc. In particular unusual yellowish deposits of lead-rich particles were observed and collected inside the monument (in the nave, near the organ and in St-Eloi Chapel). These were then thoroughly characterized to identify the neoformed lead compounds. Both bulk and local analyses were carried out to obtain particle morphology and size distribution, chemistry and mineralogy of the deposits, from macro to nanoscale. We found that the fire-related deposits all contain high amount of lead (10 to 44 %) mainly in the form of monoxides (litharge and massicot) with other lead-bearing phases (Ca-plumbate, metallic lead, lead sulfates and carbonates, plattnerite) in smaller amount. These lead phases are concentrated in heterogeneous microspheres, at the periphery of terrigenous minerals (calcite, quartz, feldspars) or mixed with anhydrite minerals. The size distribution shows that the fire produced giant particles (> 100 μm in diameter) similar to those found near the fallout from industrial emissions. This study provides a better understanding of the lead contamination pathways following the Notre-Dame cathedral fire and new insights into the reactivity of lead during a fire.