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Resumen:
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Air pollution usually derives in the development of black crusts on the surface of cultural heritage materials. A methodological approach for the morphological, mineralogical and chemical characterization of black crusts developed on limestone on historic buildings of Cairo, Milano, Budapest and Madrid, besides suspended and settling particulate matter, has been carried out. By means of traditional techniques, such as POM, XRD, SEM-EDS and FT-IR, combined with innovative application of laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), a complete characterization in terms of trace elements distribution (including heavy metals) from the black crusts and host limestone has been achieved. Some studied areas display high levels of pollutants and important concentration of heavy metals (Cd, Cu, Pb, Ni, Zn) in the suspended dust (El-Bady, 2014). Within laminar and dendritic black crusts high concentration of gypsum was recorded with increased amount of different elements and metals (Si, Al, Ti, Fe) especially derived from atmospheric inputs and, in particular, by anthropogenic pollution; in dust samples siliceous fly-ash particles are more common than carbonaceous ones and mineral fragments representing windblown particles were also detected (Perez-Monserrat et al., 2011; Török et al., 2011). Heavy metals content (Pb, Zn) are higher in black crust than in substrate, suggesting that polluted atmosphere has a great influence on their formation. Moreover, some specific heavy metals tend to migrate from the crust to the unaltered stone, becoming catalysts for new crust (Barca et al., 2014; La Russa et al., 2014). Black crusts composition entails markers to evaluate the major combustion sources responsible for stone decay and the changes on the used fuels over time. As trace element concentration is directly related with environmental conditions, the study of black crusts can be a marker for human health.
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