Deposition of airborne organic pollutants on historic buildings

The black crusts coating the surfaces of building materials located in urban (polluted) environments contain all kinds of organic compounds present in aerosols and particulate matter. Wet and dry deposition processes combined with gypsum crystal growth result in dirty, grey-to-black crust formation, in which aerosols, spores, pollen, dust and every class of particulate matter are entrapped in the mineral matrix. Analysis of the organic compounds extracted from black crusts demonstrate them to be mainly composed of molecular markers that are characteristic of petroleum derivatives. The composition of each crust is governed by the composition of the particular airborne pollutants in the area.