Chemical−Thermal Quantitative Methodology for Carbon Speciation in Damage Layers on Building Surfaces

Abstract

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 orderto 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 thatthe 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.

Carbon in Black Crusts from the Tower of London

“…The carbon fractions in the crusts were quantified using a novel analytical procedure (17). The analytical methodology consists of three steps and requires about 1 g of powdered material for a complete analysis.…”

Did Smoke from the Kuwait Oil Well Fires Affect Iranian Archaeological Heritage?

“…Ion chromatographic analyses were performed using a Dionex Chromatograph (4500i model). Subsequently, to discriminate and quantify the carbon species in the damage layers, the powder specimens underwent an analytical methodology specifically set up for carbon measurement (12). In this case, for non carbonate carbon (NCC) quantification, samples were placed in silver capsules, subjected to two repeated steps of acidification with HCl concentrate solution to remove carbonates, and then fully oxidized to quantify the carbon content by flash combustion/gas chromatographic analysis using a commercial carbon-hydrogen-nitrogen-sulfur-oxygen (CHNSO EA 1108 FISONS Instruments) analyzer.…”

“…The NCC fraction is the carbon component that is not linked to the carbonate substrate, but originates from biological weathering (11) and anthropogenic activities (9,12,19). The latter includes the deposition atmospheric particles containing elemental and organic carbon, of primary and secondary origin (20) as well as the decay of past surface treatments (oils, waxes, proteins, etc.)…”

“…The peak at around 350°C under oxygen corresponds to the evolution of a dark (gray) component, attributed to black carbon (also referred to as soot) (20). Thus, in the analysis of black sulfated crusts from urban monuments (12,19), the first peak is certainly related to organic carbon, while the second peak can be attributed to elemental carbon, which is known to be a tracer of particles emitted into the atmosphere by combustion processes (12). However, in biological samples, the refractory biopolymers highly resistant to drastic chemical treatments, upon pyrolysis at 400°C yielded up to 46% of a highly aromatic insoluble residue (22), which could account for the observed peak around 450°C.…”

Nanomatch: A European Project to Develop Consolidants through the Synthesis of New Inorganic Nanomaterials for the Conservation of Built Heritage

“…Moreover, the same factors acting on historic substrates will also be impacting on the treatment used. Organic polymers, for example, have demonstrated to be subject to weathering due to UV/sun radiation, water and salts, which reduce their efficiency and removability (Goudie, 1997;Ghedini, 2006). From this perspective, it is necessary to take these weathering processes into account and not only design new compatible and resistant materials, but also define the most suitable ageing tests.…”