Chemical processes of alteration on the surface of building stones by antropogenic contamination

Hot fumes and smokes from a forge located in the Royal Palace of Madrid modify the microenvironment in some restricted areas, and therefore the concentration of atmospheric components adsorbed by building materials (nanoenvironment). In a first stage, water vapour with CO2 is adsorbed, which descomposes the calcic plagioclases (anortite) of the granitic material, originating calcium carbonates that impregnate all the minerals, even those formed by the disolution of the upper limestone. Calcium carbonates also impregnate the blued grille. In the granitic rock, the iron from the forge acts as a catalyst of the SO2 and O2, by chemisorption (chemical sorption), and the SO3 formed allows the transformation into gypsum of the carbonates. In relation to the grille, the process can be considered as similar, the fissures of the EPAVONADO favouring the access of water, which oxidizes the iron of the grille. The obtained goethite, when increases its volume, breaks the blue finishing, comes out to the exterior and acts as a SO2-catalyst. The resulting sulphuric acid transforms the carbonates-from the plagioclases alteration or from the carbonatic impregnation of the grille- into gysum.