Stone conservation of historic built heritage of urban centres is continuously threatened by high pollution induced by heavy traffic and industrial activities. The deposition, accumulation and interaction with the substrate of complex mixture of pollutant particles and gases can lead to the formation of damage layers, responsible for chemical modification, physic-mechanical damages as well as aesthetic change of stone. The emissions of sulphur dioxide, considered as the most harmful pollutant for carbonate materials, underwent a decrease in the last decades due to environmental regulation but the current increase in vehicular traffic is causing higher concentration of ozone, nitrogen oxides and organic compounds. In this context, heritage materials undergo chromatic variations due to damage layers formation and enhancement of biodegradation. The impact of pollution on built heritage has been heretofore studied by analyzing samples collected from historic buildings or performing tests in simulation chamber and/or in field but gaps still remain in measuring deposition fluxes on materials and developing proper tools for long-term management of cultural heritage. Field exposure tests with model samples are currently under execution in Italian cities characterized by different environmental conditions as a non invasive methodological approach for assessing the effect of urban pollution on carbonate stones. The methodological approach selected for investigating the impact of pollution as well as first available results are here presented. Marble (Carrara Marble) and limestone (Nembro Limestone) widely used as construction and ornamental elements in historic Italian architecture were selected as model samples. They will be exposed at least for 2 years in Bologna, Ferrara, and Florence. Preference for samples exposure were given to sites located outdoor, partially sheltered from the rain wash-out, in areas strongly affected by pollution due to vehicular traffic. Galvanized metallic racks was purposely built to host samples with three different exposure orientations: horizontal, oblique (tilted with 45° slope) and vertical, in order to identify how positioning may reflect on deposition and removal of pollutants. The exposed samples will undergo mineralogical, petrographic and geochemical analyses (Optical Microscopy, Scanning Electron Microscopy coupled with Energy Dispersive X-ray Analysis, Inductively Coupled Plasma Mass Spectrometry, Ion Chromatography analysis and Thermal-chemical methodology using a CHNSO combustion analyzer [1]) at predefined time intervals to characterize the products derived from pollutants-stone interaction in terms of typology, origin and impact on stone. Moreover, the integration with colorimetric analysis will allow to identify a connection between the deposited soluble and carbon fractions and changes of colorimetric parameters, for setting up damage functions. Simultaneously passive sampling of aerosol has been designed by the exposure of filters while seasonal environmental monitoring campaigns of particulate matter will allow to compare the quantity of soluble ions and carbon fractions present into atmosphere with that actually accumulated on samples surface. Additionally, monitoring campaigns of bioaerosol has been planned in Bologna in order to quantify the microbial load (fungi and bacteria) in air. First data of winter and summer environmental monitoring campaigns as well as results of analyses performed after the first year of exposure will be also presented. [1] Ghedini N., Sabbioni C., Bonazza A., Gobbi G., 2006. Chemical-Thermal quantitative methodology for carbon speciation in damage layers on building surfaces. Environmental Science & Technology 40(3): 939-944.
Pollution effects on stones: a multidisciplinary approach
Vidorni G;Sardella A;De Nuntiis P;Bonazza A
2017
Abstract
Stone conservation of historic built heritage of urban centres is continuously threatened by high pollution induced by heavy traffic and industrial activities. The deposition, accumulation and interaction with the substrate of complex mixture of pollutant particles and gases can lead to the formation of damage layers, responsible for chemical modification, physic-mechanical damages as well as aesthetic change of stone. The emissions of sulphur dioxide, considered as the most harmful pollutant for carbonate materials, underwent a decrease in the last decades due to environmental regulation but the current increase in vehicular traffic is causing higher concentration of ozone, nitrogen oxides and organic compounds. In this context, heritage materials undergo chromatic variations due to damage layers formation and enhancement of biodegradation. The impact of pollution on built heritage has been heretofore studied by analyzing samples collected from historic buildings or performing tests in simulation chamber and/or in field but gaps still remain in measuring deposition fluxes on materials and developing proper tools for long-term management of cultural heritage. Field exposure tests with model samples are currently under execution in Italian cities characterized by different environmental conditions as a non invasive methodological approach for assessing the effect of urban pollution on carbonate stones. The methodological approach selected for investigating the impact of pollution as well as first available results are here presented. Marble (Carrara Marble) and limestone (Nembro Limestone) widely used as construction and ornamental elements in historic Italian architecture were selected as model samples. They will be exposed at least for 2 years in Bologna, Ferrara, and Florence. Preference for samples exposure were given to sites located outdoor, partially sheltered from the rain wash-out, in areas strongly affected by pollution due to vehicular traffic. Galvanized metallic racks was purposely built to host samples with three different exposure orientations: horizontal, oblique (tilted with 45° slope) and vertical, in order to identify how positioning may reflect on deposition and removal of pollutants. The exposed samples will undergo mineralogical, petrographic and geochemical analyses (Optical Microscopy, Scanning Electron Microscopy coupled with Energy Dispersive X-ray Analysis, Inductively Coupled Plasma Mass Spectrometry, Ion Chromatography analysis and Thermal-chemical methodology using a CHNSO combustion analyzer [1]) at predefined time intervals to characterize the products derived from pollutants-stone interaction in terms of typology, origin and impact on stone. Moreover, the integration with colorimetric analysis will allow to identify a connection between the deposited soluble and carbon fractions and changes of colorimetric parameters, for setting up damage functions. Simultaneously passive sampling of aerosol has been designed by the exposure of filters while seasonal environmental monitoring campaigns of particulate matter will allow to compare the quantity of soluble ions and carbon fractions present into atmosphere with that actually accumulated on samples surface. Additionally, monitoring campaigns of bioaerosol has been planned in Bologna in order to quantify the microbial load (fungi and bacteria) in air. First data of winter and summer environmental monitoring campaigns as well as results of analyses performed after the first year of exposure will be also presented. [1] Ghedini N., Sabbioni C., Bonazza A., Gobbi G., 2006. Chemical-Thermal quantitative methodology for carbon speciation in damage layers on building surfaces. Environmental Science & Technology 40(3): 939-944.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
