The effects of air pollution on cultural Heritage : the case study of Santa Maria delle Grazie al Naviglio Grande (Milan)

Atmospheric pollution causes monuments surface degradation in urban environments. Among the degradation processes the formation of black crusts (BCs) is one of the most dangerous phenomenon. During this process, aerosol particulate matter (PM) can be embedded into gypsum, one of the main crusts constituents, providing the characteristic black colour. EC (elemental carbon) and OC (organic carbon) are the responsible for the yellowing and blackening processes occurring on the surfaces and their quantification in the crusts can provide information on the contribution of atmospheric pollution sources to the degradation products formation. This research study is focused on the characterization of BCs collected from the Church of Santa Maria delle Grazie al Naviglio Grande in Milan, from the point of view of the effects of atmospheric pollution on cultural heritage. The analysed samples consist of mortars and bricks partially degraded and covered with black crusts. Appling different analytical techniques, such as FTIR/ATR, CHN, TGA and IC, the crusts composition has been investigated focusing on the quantification of the carbonaceous fraction. This integrated approach has allowed to identify the sources of pollution responsible for the decay of the different building materials of the church.