Chemical-Thermal quantitative methodology for carbon speciation in damage layers on building surfaces

The issue of environment protection, including the
conservation of the monumental heritage worldwide, is
related to atmospheric pollution, and its future therefore
depends on air pollutant reduction. Carbonaceous particles
emitted by combustion processes are the main factors
responsible for the blackening of buildings. The identification
and evaluation of the carbon species constituting the
noncarbonate fraction of total carbon in damage layers,
particularly in urban areas, are required in order to investigate
atmospheric deposition on building surfaces. Since
noncarbonate carbon contains organic and elemental
carbon originating from various human activities, its
measurement and speciation are crucial to the protection
and conservation of monuments and ancient masonry,
playing an important role both in the proposal of mitigation
strategies and in the definition of conservation treatments.
The availability of a correct, accurate, and reproducible
analytical method for a complete carbon balance is essential
in studying the effects of atmospheric pollutants on the
environment, including those affecting cultural heritage. A
chemical-thermal methodology was set up, and its
sensitivity, accuracy, repeatability, and reproducibility
were tested on appropriate standard samples of composition
similar to the black crusts on stones and mortars. The
results indicate that the technique satisfactorily distinguishes
among carbon species, particularly those of anthropogenic
origin, allowing a reliable evaluation of their quantities
in damage layers. In view of the difficulties encountered
in applying the thermo-optical methods adopted for the
measurement of carbon filters, the proposed methodology
contributes to filling the current gap in suitable and
reliable analytical procedures in the field of cultural heritage protection.