Microanalysis of museum aerosols to elucidate the soiling of paintings: Case of the Correr Museum, Venice, Italy

The results of the characterization of individual airborne particles collected during two separate sampling campaigns at the Correr Museum, situated at the San Marco Square in Venice, Italy, are reported. The chemical composition and associated diameter of individual aerosol particles in the size range of 0.2-20 mu m were determined by electron probe X-ray microanalysis and scanning electron microscopy with energy dispersive X-ray measurement (SEM-EDX). Multivariate techniques were used for the reduction of the data set. Based on hierarchical cluster analysis results, the majority of samples from both campaigns appeared to be composed of six to eight different particle types from which the Ca-rich particles together with the aluminosilicates and organic material can be identified as the most important ones. The correlation between the abundance of the particle types and their diameters as well as between the sampling periods was investigated. Factor analysis revealed similar results. To provide a better view on the nature, composition, and possible sources of the indoor aerosol particles, the indoor and outdoor aerosol compositions of three sampling periods were compared, and additionally two possible indoor particle sources were investigated. The results indicated the existence of a Ca-rich indoor particle source, probably the deterioration of the interior plaster walls. The homogeneity study of giant aerosol particles >8 mu m, using the X-ray mapping facilities on the SEM-EDX instrument under optimal conditions, revealed that these particles are heterogeneous and mainly consist of Ca and Si. The other particle types were identified as small aluminosilicate and CaSO4 particles or very small Fe-rich particles, and they seemed to be adsorbed at the surface of the Ca-Si-rich particles. Preliminary results of scanning transmission electron microscopy and scanning proton microprobe measurements on submicrometer indoor aerosol particles and giant indoor Ca-rich aerosol particles, respectively, are discussed as well.