Air Quality Monitoring for Preventive Conservation of the Built Heritage Deteriorated by Salt Crystallization

• Published in: Geosciences (Basel) 2022-09, Vol.12 (9), p.325
• Main Authors: Benavente, David, Pla, Concepción, Gil-Oncina, Sara, Ruiz, Maria Candela, Blanco-Quintero, Idael Francisco, Huesca-Tortosa, Jose Antonio, Spairani-Berrio, Yolanda, Sanchez-Moral, Sergio
• Format: Article
• Language: English
• Subjects: Air; Air monitoring; Air quality; Aquifers; Biocalcarenite; Buildings; Carbon dioxide; Chemical precipitation; Chlorides; Clay; Conservation; Coronaviruses; Crystallization; Damage; Dissolution; Dissolving; Dynamics; Earth science; Environmental aspects; Environmental monitoring; geochemical modelling; geogenic radon potential; Geology; Groundwater; Halite; Historic buildings; Humidity; Indoor air; Indoor air pollution; Indoor air quality; Indoor environments; Memorials & monuments; Microstructure; Nitrates; Periodicities; Porous media; Protection and preservation; Radon; Radon isotopes; Relative humidity; Rising damp; Rock-salt; Salt content; salt weathering; Salts; Saturation; Severe acute respiratory syndrome coronavirus 2; Stone; Stone buildings; Sulfates; Sylvite; Temperature; Temperature variations; Ventilation; Wavelet analysis; wavelets
• ISSN: 2076-3263; 2076-3263
• DOI: 10.3390/geosciences12090325

The Santo Domingo Diocesan School (Orihuela, SE Spain) is a singular case study that relates air quality monitoring and stone conservation. The monument suffers severe damage due to salt crystallization by rising damp, which is related to the indoor environment dynamics, high groundwater salt content, and microstructure, the building’s porous stone (biocalcarenite). Results revealed that 222Rn concentration in indoor air is low due to the building’s high ventilation rate, despite the medium-low geogenic radon potential in the area. Wavelets analysis showed that ventilation is caused by outdoor and indoor temperature variations and directly affects the 222Rn and CO2 dynamics inside the church. CO2, as well as relative humidity (RH), presented periodicities with intermediate frequencies (5–8 days) related to visits. These RH and temperature (T) variations intensified the salt damage by increasing the frequency of dissolution-crystallization cycles. The mineralogical characterization and geochemical calculations concluded that chlorides (halite and sylvite), sulfates (thenardite, epsomite, hexahydrite and aphthitalite) and nitrates (niter) present from dissolution forms to whiskers and hopper-type morphologies. This indicates high saturation values and, therefore, higher crystallization pressure values within the porous media of the biocalcarenite. On the contrary, the near-equilibrium crystal shape and incongruent precipitation reaction for humberstonite suggest a lower alteration for this salt on the building stone.