Black Crust from Historic Buildings as a Natural Indicator of Air Pollution: A Case Study of the Lipowiec Castle, Babice, Southern Poland

The study is focused on the analysis of black crust and soiling on the building materials of the medieval Lipowiec Castle in southern Poland. The castle was constructed using local, partly dolomitic limestones and dolomites, supplemented with other limestones and bricks, during 20th-century renovations of the castle ruins. The crust and soiling components, secondary mineral phases, and particulate matter of anthropogenic origin were analysed using Raman micro-spectroscopy (RS) and scanning electron microscopy coupled with energy-dispersive spectrometry (SEM-EDS). The crust, mostly composed of gypsum and other sulphate phases, was found to contain carbonaceous matter, spherical Si-Al glass particles, and iron oxides, with admixtures of other elements, including heavy metals, as well as irregularly shaped particles containing various metals. These components reflect the air pollution in the region, related to the combustion of solid fuels in both industrial power plants and local domestic furnaces, Zn-Pb ore mining (operational until 2021), and smelting in the neighbouring industrial centre. Despite its location in a rural area, the castle has been exposed to pollution for an extended period due to its proximity to large industrial centres. Therefore, the crust analysed may serve as an environmental indicator of the nature of the air pollution in the region.