Blackening as major atmospheric pollution effect on monuments

The effects of air pollution on monuments and historical buildings have been studied over the last decades. The burning of fossil fuels produces gases, smoke and particulate carbonaceous matter that deposit on building surfaces and react with the underlying calcareous materials to form a damage layer. Carbonaceous particles have a catalytic effect on CaSO4·2H2O formation and the ensuing surface blackening on building exteriors. Considering the trends of major air pollutants, e.g. SO2, NOx and particulate, the increase in particle concentrations in urban area is threatening and will threaten the protection of cultural heritage in the future. For this reason, particular attention has been focused in recent years on the impact of carbonaceous particles on surfaces of artistic interest, with the aim of assessing their contribution in terms of carbon quantification. Venice is presented as case of study and, in particular, the Corner Palace on the Canal Grande. The carbon fractions were discriminated and measured following a chemical-thermal methodology specifically developed for damage layer specimens. The resulting data show that the evaluation of pollution impact requires the quantification of the carbonaceous particles which are responsible of black crust formation and, particularly, elemental carbon, as tracer of anthropogenic deposition.