DAMAGE PROCESSES ON STONES IN URBAN ENVIRONMENT: FIELD EXPOSURE TESTS AND LABORATORY ANALYSES CONTRIBUTING TO POLLUTION IMPACT EVALUATION

Air pollution constantly threatens the conservation of carbonate stone monuments and built heritage mainly in urban areas. Even if different studies focused on the effect of pollution on stone materials, by analysing samples collected from historic buildings, performing tests in simulation chamber and/or in field and monitoring air quality (gases and aerosol) of the environment surrounding specific cultural heritage, lack of knowledge still remains in the quantitative correlation between the concentration of particular atmospheric pollutants and their damage induced to stone. Furthermore, the possible repercussions on built heritage of the current atmosphere in Western Europe, poorer than in the past of SO2 but richer of NOx and organic compounds, merit consideration. In this regard, the Institute of Atmospheric Sciences and Climate of the National Research Council of Italy (ISAC-CNR) with the Department of Physics and Earth Sciences of the University of Ferrara performed field exposure tests of stone model samples and passive filters for 24 months in Italian cities characterised by different environmental conditions (i.e. Bologna, Ferrara and Florence) associated with particulate matter monitoring campaigns as a non-invasive methodological approach for studying the impact of urban pollution on carbonate stones. Marble (Carrara Marble) and limestone (Verona Red Marble) were selected as model samples as they were widely used as construction and ornamental elements in historic Italian architecture and for their physico-chemical features. Galvanized metallic racks were prepared to host samples with different exposure orientations (i.e. horizontal, oblique and vertical) in order to identify how positioning may reflect on deposition and removal of pollutants. Polished stone samples were exposed outdoor, partially sheltered from the rain wash-out, in areas strongly affected by pollution due to vehicular traffic. At defined time intervals, several analytical techniques (Colorimetric analysis, IC, EA-IRMS, ESEM-EDX, ICP-MS) were used for characterising the state of degradation of the exposed stone specimens while aerosol monitoring campaigns allowed to compare the atmospheric components (in terms of soluble and carbon fractions) with those actually accumulate on samples surface and passive filters. The results demonstrate an increasing trend of soiling over time in all sites, more evident in horizontal and oblique marble samples. In particular, blackening and yellowing processes of stone surface were identified in relation with deposition of elemental carbon (EC) and accumulation of organic carbon (OC) and sulphate, respectively. The adopted methodological approach provided information about the real deposition of soluble and carbon fractions per surface unit over time as well as the development of methodology for carbon speciation by thermally-based separation allowed to measure C fractions in damage layers without any chemical attack. Moreover, the high concentration of heavy metals on stone deposit, the prevalence of OC over EC both in atmosphere and in deposit of stone samples and passive filters as well as soluble ions (mainly Cl- and SO42- in deposit and NO3-, SO42- and NH4+ in atmospheric PM) confirm as vehicular traffic has directly (combustion of fossil fuels) or indirectly (re-suspended dust and de-icing salts) affected the composition of the deposited particulate matter.L’inquinamento atmosferico rappresenta uno dei principali fattori di degrado di monumenti e beni architettonici costituiti da rocce carbonatiche, soprattutto in ambiente urbano. Sebbene diversi studi abbiano analizzato gli effetti dell’inquinamento sui materiali lapidei attraverso lo studio di campioni prelevati da edifici storici, test di simulazione in camera climatica e/o in campo e monitoraggio della qualità dell’aria (gas e aerosol) relativa all’ambiente circostante un specifico bene culturale, esistono tuttavia delle lacune riguardo la correlazione quantitativa tra la concentrazione degli inquinanti atmosferici e il danno che possono provocare al substrato lapideo. Vanno inoltre anche considerate le ripercussioni della composizione atmosferica attuale, impoverita di SO2 ma arricchita di NOx e composti organici rispetto al passato. A tal proposito, l’Istituto di Scienze dell’Atmosfera e del Clima del Consiglio Nazionale delle Ricerche (ISAC-CNR) in collaborazione con il Dipartimento di Fisica e Scienze della Terra dell’Università di Ferrara hanno condotto dei test di esposizione in campo di provini lapidei e filtri passivi per 24 mesi in città italiane contraddistinte da situazioni ambientali differenti (Bologna, Ferrara e Firenze) insieme a delle campagne di monitoraggio del particolato atmosferico come approccio non-invasivo per studiare l’impatto dell’inquinamento urbano su rocce carbonatiche. Sono stati scelti come campioni un marmo (Marmo di Carrara) e un calcare (Rosso Ammonitico Veronese) per le loro caratteristiche fisico-chimiche e la loro diffusione come materiali da costruzione e decorazione nell’architettura storica italiana. Gli espositori in metallo galvanizzato sono stati preparati per ospitare i campioni con diversa orientazione (orizzontale, obliqua e verticale) in modo da identificare quanto la posizione possa influire sulla deposizione e rimozione degli inquinanti. I campioni lapidei sono stati levigati ed esposti all’aperto in maniera parzialmente protetta delle precipitazioni in aree affette da intenso traffico veicolare. A intervalli di tempo prestabiliti, sono state utilizzate diverse tecniche analitiche (analisi colorimetriche, IC, EA-IRMS, ESEM-EDX, ICP-MS) per valutare lo stato di degrado dei campioni lapidei esposti mentre le campagne di monitoraggio del particolato atmosferico hanno permesso di confrontare i componenti atmosferici (in termini di ioni solubili e frazioni del carbonio) con quelli che si sono effettivamente depositati sulle superfici lapidee e sui filtri passivi. I risultati dimostrano un trend di soiling crescente nel tempo in tutti i siti, più evidente sui campioni di marmo orizzontali e obliqui. In particolare, sono stati riscontrati un annerimento e un ingiallimento della superficie lapidea in relazione all’accumulo rispettivamente di carbonio elementare (EC) e di carbonio organico (OC) e solfati. L’approccio metodologico scelto ha fornito informazioni relative alla reale deposizione delle frazioni solubili e carboniose per unità di superficie nel tempo così come lo sviluppo della metodologia per la speciazione del carbonio attraverso separazione termica ha consentito di misurare le frazioni di C sulle superfici di degrado senza ricorrere a nessun attacco chimico. Inoltre, l’elevata concentrazione di metalli pesanti nel deposito dei provini lapidei, la prevalenza di OC su EC sia in atmosfera che sul deposito dei campioni lapidei e dei filtri passivi e anche gli ioni solubili (soprattutto Cl- e SO42- sul deposito e NO3-, SO42- e NH4+ nel PM atmosferico) hanno confermato come il traffico veicolare possa influenzare la composizione del particolato atmosferico depositato

FIELD EXPOSURE TESTS TO EVALUATE THE EFFICIENCY OF NANO-STRUCTURED CONSOLIDANTS ON CARRARA MARBLE

In a context of changing environment, the preservation of outdoor built heritage is increasingly threatening. Furthermore the application of conservative products not always achieved the expected results as well as preliminary tests aimed at evaluating the performance of new products often proved to be inappropriate. In such situation, the paper reports the outcomes of the innovative methodology adopted to assess the efficiency and durability of nano-based consolidating products utilized for the conservation of carbonate artworks, carrying out field exposure tests on Carrara Marble model samples in different sites. Surface properties, superficial cohesion, distribution, penetration of the conservative products and their interactions with substrates and environmental conditions were examined and compared with the features of undamaged samples and of those artificially damaged

Damage processes on stones in urban environment: field exposure tests and laboratory analyses contributing to pollution impact evaluation

Stone conservation of historical built heritage in polluted atmosphere is an outstanding topic. In particular, the deposition, accumulation and interaction with the substrate of complex mixture of pollutant particles and gases can cause the formation of damage layers and, in consequence, entail chemical modification, physicomechanical damages as well as aesthetic change of stone. Furthermore, environmental policies have recently restricted the concentration of atmospheric sulphur dioxide, considered as the most detrimental pollutant for carbonate materials, while an increase of nitrogen compounds, ozone and organic compounds due to higher vehicular traffic may lead to a chromatic variation of the damage layer and a probably growth in biological degradation. Until now, the impact of pollution on cultural heritage was studied by analysing samples collected from historic buildings or performing tests in simulation chamber and/or in field, but gaps still remain in developing damage and dose-response functions useful for the long-term management of cultural heritage sites and in measuring the deposition fluxes on materials. The Institute of Atmospheric Sciences and Climate, ISAC-CNR (Bologna), in collaboration with the Department of Physics and Earth Sciences of the University of Ferrara, started in November 2015 a research work aimed at assessing the effect of urban atmospheric pollution on mainly carbonate sedimentary and metamorphic stones by performing field exposure tests in Italian cities characterised by different environmental conditions. The methodological approach selected for setting up the field tests and study the impact of pollution is presented. As a first step the selection of the proper stone substrates, time and sites for the exposure and placement of the samples is carrying out. Specifically, the choice of the appropriate litotypes is factoring in marble and limestone widely employed in historic Italian architecture and characterised by an almost totally carbonate composition. Preference for samples exposure will be given to sites located outdoor, partially sheltered from the rain wash-out, in areas strongly affected by pollution due to vehicular traffic. The exposed samples will undergo mineralogical, petrographic and geochemical analyses (such as Optical Microscopy, Inductively Coupled Plasma Mass Spectrometry, Ion Chromatography analysis and Thermal-chemical methodology proposed by Ghedini et al., (2006) using a CHNSO combustion analyser), carried out in predefined time intervals, to characterise the deterioration products coming from the interaction between pollutants and stone substrate in terms of typology, origin and damage caused to stone. Moreover, the integration with colorimetric analysis will hopefully allow to identify a correlation between the deposited soluble and carbon fractions and changes of colorimetric parameters, for setting up damage functions. Finally, environmental monitoring of atmospheric particulate matter will be organised in order to acquire useful information from the comparison between the concentrations of pollutants deposited on stone substrate with those present in the atmospher

Durability assessment to environmental impact of nano-structured consolidants on Carrara marble by field exposure tests

The EU policy of reducing the emissions of combustion generated pollutants entails climate induced deterioration to become more important. Moreover, products applied to preserve outdoor built heritage and their preliminary performance tests often turn out to be improper. In such context, the paper reports the outcomes of the methodology adopted to assess the durability and efficiency of nano-based consolidating products utilized for the conservation of carbonate artworks, performing field exposure tests on Carrara marble model samples in different sites in the framework of the EC Project NANOMATCH. Surface properties and cohesion, extent and penetration of the conservative products and their interactions with marble substrates and environmental conditions are here examined after outdoor exposure for eleven months in four different European cities and compared with the features of undamaged and of untreated damaged specimens undergoing the same exposure settings

Efficiency evaluation of nano-structured consolidants on Carrara marble by field exposure tests

In the context of a changing environment, the preservation of outdoor built heritage is increasingly threatened. Furthermore the application of conservation products does not always achieve the expected results. Furthermore, preliminary tests aimed at evaluating the performance of new products often show them to be inappropriate. In such situations, the paper reports the outcomes of an innovative methodology adopted to assess the efficiency and durability of nano-based consolidating products utilized for the conservation of carbonate artworks, carrying out field exposure tests on Carrara Marble model samples in different sites. Surface properties, superficial cohesion, distribution and penetration of the conservation products and their interactions with substrates and environmental conditions were examined and compared with the features of undamaged samples and of artificially damaged samples

Air pollution impact on stones in urban environment : a multidisciplinary approach

Air pollution is the major responsible for the formation of damage layers on stone monuments and historic buildings in urban areas (Bonazza and Sabbioni, 2016). Among widely used building materials, marble and limestone were selected in previous studies on pollution impact, thanks to their chemical homogeneity (mainly comincia posed by calcium carbonate) and low porosity. The effects of pollution have been heretofore assessed 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. Moreover, the possible effects on built heritage of the current atmosphere poorer than in the past of SO2 but richer of NOx and organic compounds (mainly released by vehicular traffic) should be considered. 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 studying the impact of urban pollution on carbonate stones. The methodological approach selected for this investigation as well as first available results are here discussed. Marble (Carrara Marble) and limestone (Red Verona Marble) were selected as model samples as they were widely used as construction and ornamental elements in historic Italian architecture. 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 prepared to host samples with different exposure orientations: horizontal, oblique (tilted with 45\ub0 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 (Ghedini et al., 2006)) at predefined time intervals to characterise 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. Data of environmental monitoring campaigns as well as results of analyses carried out after the first year of exposure will be also reported

Air pollution impact on carbonate building stones in Italian urban sites⋆

In spite of the widely recognized negative effect of air pollution on stone used in historic building heritage located in urban areas and the numerous studies internationally developed on this topic, gaps still remain in measuring deposition fluxes on architectural surfaces and developing proper tools for short- and long-term management of cultural heritage in polluted areas in a changing environment. Two-years long 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 investigating the impact of urban pollution on carbonate stones (marble and limestone). Several analytical techniques (both physical and chemical) are used for characterising the state of degradation of the exposed stone specimens while aerosol monitoring campaigns allow to compare the atmospheric components with those actually accumulate on samples surface. After a description of the methodological approach of this study and a general environmental characterisation of each selected site, results of aerosol monitoring campaigns (including bioaerosol) and colorimetric analyses performed during the whole period of exposure in Bologna are here presented and discussed

Air pollution impact on carbonate building stones in Italian urban sites

In spite of the widely recognized negative effect of air pollution on stone used in historic building heritage located in urban areas and the numerous studies internationally developed on this topic, gaps still remain in measuring deposition fluxes on architectural surfaces and developing proper tools for short- and long-term management of cultural heritage in polluted areas in a changing environment. Two-years long 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 investigating the impact of urban pollution on carbonate stones (marble and limestone). Several analytical techniques (both physical and chemical) are used for characterising the state of degradation of the exposed stone specimens while aerosol monitoring campaigns allow to compare the atmospheric components with those actually accumulate on samples surface. After a description of the methodological approach of this study and a general environmental characterisation of each selected site, results of aerosol monitoring campaigns (including bioaerosol) and colorimetric analyses performed during the whole period of exposure in Bologna are here presented and discussed