In order to use black crusts as archives of ancient air pollution, it is necessary to understand how they form and identify their growth direction. Two main processes have been proposed in the literature: outward progression by the diffusion and reaction of Ca2+ with SO42- in the water film at the outer surface, and/or inward progression by pseudomorphosis, whereby calcite is replaced by gypsum. To clarify these mechanisms, simulation chamber experiments were designed to evaluate the growth rate of gypsum on pristine limestone slabs, and then to alter old black crusts using 34S-marked SO2 and O3 at 100 % relative humidity (RH). NanoSIMS imaging revealed areas enriched in 34S on the outer surface, suggesting an outward growth of gypsum in these experimental conditions. The extrapolation of these results to field observations is discussed. However, they are key to interpreting the pollution recorded in monument black crusts.

This paper reviews results published by the International Co-operative Programme on Effects on Materials including Historic and Cultural Monuments (ICP Materials) with emphasis on those obtained after the turn of the century. Data from ICP Materials come from two main sources. The first is through exposures of materials and collection of environmental data in a network of atmospheric exposure test sites mainly distributed across Europe. Corrosion of carbon steel has continued to decrease during the period 2000–2020 but corrosion of zinc only up until 2014, and the trend in zinc corrosion is only visible when examining four-year data. Surface recession of limestone as well as soiling of modern glass show no decreasing trend during 2000–2020. The second is through case studies performed at heritage sites across Europe. Risk analysis of corrosion and soiling for twenty-six sites indicate that currently soiling is a more significant maintenance trigger than corrosion. Costs for maintaining heritage sites are substantial and costs attributable to air pollution is estimated from 40% to as much as 80% of the total cost. Future directions of the program are work on effects of particulate matter, improving the scientific basis for the work, and making the monitoring data publicly available.

Fire is a major hazard for built heritage. The fire at Notre-Dame on April 15, 2019 completely destroyed the woodframe and the lead roof (about 285 tons) almost entirely melted due to high temperatures. A part of the molten lead escaped into the atmosphere in the form of aerosols while the majority remains within cathedral enclosure in the form of deposits, metallic remains, spatters etc. In particular unusual yellowish deposits of lead-rich particles were observed and collected inside the monument (in the nave, near the organ and in St-Eloi Chapel). These were then thoroughly characterized to identify the neoformed lead compounds. Both bulk and local analyses were carried out to obtain particle morphology and size distribution, chemistry and mineralogy of the deposits, from macro to nanoscale. We found that the fire-related deposits all contain high amount of lead (10 to 44 %) mainly in the form of monoxides (litharge and massicot) with other lead-bearing phases (Ca-plumbate, metallic lead, lead sulfates and carbonates, plattnerite) in smaller amount. These lead phases are concentrated in heterogeneous microspheres, at the periphery of terrigenous minerals (calcite, quartz, feldspars) or mixed with anhydrite minerals. The size distribution shows that the fire produced giant particles (> 100 μm in diameter) similar to those found near the fallout from industrial emissions. This study provides a better understanding of the lead contamination pathways following the Notre-Dame cathedral fire and new insights into the reactivity of lead during a fire.

The Mn-bearing medieval stained-glass windows are affected by a browning phenomenon that could have a microbiological origin. This study investigates the direct and indirect impact of a model Mn-oxidizing and siderophore productive bacterial strain (Pseudomonas putida) on the alteration of medieval glass. For that, five model glasses with variable contents of Mn and Fe were altered during 1 week at 25degree celsius and pH 6.5 either in the presence of the siderophore desferrioxamine B (DFOB) at 50 mM or with the bacterial strain P. putida with or without external sources of iron. DFOB was shown to accelerate the dissolution of the Mn- and Fe -bearing glasses. By contrast, the presence of bacteria, had no apparent effect on glass dissolution, but led to the formation of a biofilm that was enriched in some elements of the glass, especially Si. The results also underlined the key -role of P of the glass as a nutrient for bacterial growth. Brown Mn oxides phases were only formed either when bacteria were incubated with Mn- and P -bearing glasses and after the production of the siderophore pyoverdine. Conversely, no browning was observed for the glass containing MnO and FeO with bacteria, which highlights that the absence of Fe plays a triggering role in the formation of manganese oxides.

Biological activity, climate and pollution are responsible for the degradation of building stones, especially limestone, which is widely used in the Paris region. In order to determine the respective contribution of physicochemical and biological processes to the degradation of limestone, limestone specimens from the Père-Lachaise cemetery (Paris, France) were exposed for five years under different conditions: sheltered from or exposed to rain and in horizontal or vertical position. After exposure, the collected samples were characterized by light and electron microscopy, X-Ray diffraction and ion chromatography after elution. The results showed an intense biocolonization of the samples exposed to rain, while the sheltered samples were more affected by the pollution (soiling). The characterization of the bacterial and fungal communities using Next Generation Sequencing Illumina 16S for bacteria and ITS for fungi highlighted that five main bacterial phyla were identified: Actinobacteriota, Bacteroidota, Cyanobacteria, Proteobacteria and Deinococcota (major genera Flavobacterium, Methylobacterium-Methylobacter, Sphingomonas, Roseomonas and Nocardiodes). Among the fungi, the phylum Ascomycota was predominant with the genera Cladosporium, Ramularia, Aureobasidium and Lecania. However, the alteration of the limestone is difficult to quantify at this stage. Potassium nitrate of rain origin has been found in the sheltered area, but no gypsum. Therefore, the biocolonization is a fast phenomenon on the stone and the physico-chemical processes derived from it, caused by climate and pollution, are slower. This is in agreement with the long-term observations made on old and unrestored graves of the cemetery described in the literature.

Stained glass windows are a precious heritage to pass on to future generations. However, medieval stained glass windows are particularly altered due to their chemical composition and the effects of climatic (mainly water and temperature), environmental (pollution) and biological factors. In this review, we present the alteration patterns observed on ancient Si-K-Ca stained glass windows. To better understand their formation mechanisms and determine the alteration rates, different exposure campaigns to the current atmosphere in a position sheltered from rain or not and laboratory experiments in aqueous medium or in gaseous phase have been conducted. Either model glass or ancient stained glass windows were studied. Isotopic tracers (D, 18 O, 29 Si) have been used as they constitute a powerful tool to elucidate the involved processes and to measure their kinetics. Thanks to all of these data, an alteration scenario of medieval stained glass alteration is proposed. Besides, the extrapolation of kinetic data based on several hypotheses over seven centuries gives very consistent results compared to the ancient stained glass samples.

In order to explore the role of bacteria in the alteration of stained glass windows, and especially on the browning phenomenon, it is necessary to have an overview of the microbial inhabitants likely to be found on this kind of material. In this study, biological samples were collected on stained glass of different colours, both on site and stored in a conservation workshop. Cultivable bacterial communities were identified by 16S rDNA sequencing. Similarity values ranged from 99 to 100% to known bacteria. Sequence analysis showed different bacterial communities depending on the sampling site. The more represented genera were Arthrobacter, Micrococcus, Paenibacillus and Bacillus. Some of the identified bacteria are known for their weathering potential.

Limestone buildings in urban areas are weathered due to climatic factors, to pollution but also to biological activity. Many studies have focused on microbially-mediated precipitation of calcite but few on their influence on limestone dissolution rates. In this study, a cultivable approach for studying bacterial dissolution of limestone is proposed. The results show, for the first time, that limestone has selected a specific structure in the bacterial communities and that each bacterial class has its own metabolism inducing a different efficiency on the alteration of limestone grains. Cultivable bacterial and fungal strains in our study permit to considerably increase (by 100 to 1,000,000 times) the chemical weathering rates compared to laboratory or field experiments. Individually, the results bring information on the ability to alter limestone by dissolution. Moreover, taken together, a functional ecological adaptation of bacterial and fungal classes to the alteration of the limestone monument has been highlighted. In order to release calcium into solution, these strains slightly acidify the medium and produce low molecular mass organic acids during experiments, especially lactic and oxalic acids.

<p>Since the Industrial revolution and due to increasing anthropogenic emissions, the composition of the atmosphere has been modified, leading to climate change and pollution. The impacts of pollution were depicted through paintings and writing from the beginning of the 19<sup>th</sup> century, but pollution measurements are relatively recent. In order to obtain ancient air pollution data, proxies in urban area need to be found.</p> <p>Black crusts formed on limestone and marble monuments in urban area seem to be a good candidate as local proxy. Mainly composed of gypsum (CaSO<sub>4</sub>.2H<sub>2</sub>O), they are a chemical alteration pattern resulting from the reaction of the dissolution of the calcite (CaCO<sub>3</sub>) of the stone and of sulfation by sulphur dioxide (SO<sub>2</sub>) from the atmosphere. Particulate matter accumulates in the newly formed gypsum layer in sheltered area from the rain, thus giving the black crust a passive sampler potential.</p> <p>To use black crusts as past air pollution archives, samples were collected at Père Lachaise cemetery (Paris) on ancient, dated (1820-1887) and unrestored limestone or marble tombs. Different types of analyses were performed to study sample morphology (by Optical Microscope), particulate matter (by Scanning Electron Microscopy) and chemical composition (especially major elements and trace metals by ICP-AES, LA-ICP-MS). Results underline two important features to use black crusts as past air pollution archives. First, the low variability of chemical composition of black crusts from Père Lachaise cemetery highlights that the black crusts are representative of the site and register the background pollution. Then, the morphology (laminar vs. dendritic) of black crusts is a key parameter to sample black crusts as the stratigraphy is much better preserved in laminar black crusts.</p>

Buildings and monuments are often colonized by microorganisms that can result in colour change and aesthetical and physico-chemical damages. This bio-colonization is dependent of the material and on the environment. In order to better understand and correlate the microbial development at the surface of buildings with meteorological parameters, concentration of green algae and cyanobacteria have been measured using an in situ instrument on the wall of a private habitation in the Parisian region during two periods: spring and fall-winter. Different locations were also chosen to assess the influence of the position (horizontal or vertical) and of the situation (shaded vs. sunny microclimate). The results show that the microorganism development rapidly responds to rainfall events but the response is more intense in winter as temperature is lower and relative humidity (RH) higher. Cyanobacteria are less sensitive to this seasonal effect as they are more resistant to desiccation than green algae. Based on all the data, different dose-response functions have been established to correlate RH, rain and temperature to the green algae concentration. The influence of the microclimate is considered via specific fitting parameters. This approach has to be extended to new campaign measurements but could be very useful to anticipate the effect of climate change.

Most stained-glass windows installed during the Middle Ages have deteriorated over time due to climate and pollution. To reconstruct their alteration history over the centuries, evaluate the current environmental risk, and predict their alteration in the future, two modelling methodologies have been used. First, based on the short-term exposure of medieval-type glass in different sites, dose–response functions (DRFs) were established. These DRFs correlate relevant environmental factors (temperature, rain quantity, rain pH, relative humidity, and SO2 concentration) with the response of the material in terms of alteration layer thickness. The second methodology consists of laboratory experiments that aim at parametrising kinetic laws as a function of specific parameters (temperature, rain pH, and relative humidity). These kinetic laws can be extrapolated over long periods, contrary to DRFs. In this study, we compared both methodologies to simulate the alteration of a model stained glass at different European sites or over different time periods. The results highlighted that the kinetic laws were able to closely represent the data, except for the polluted sites where the alteration was underestimated. This indicated that the dependence of the alteration rate on the pollutant concentrations should be included to improve the model.

A large number of stained glass windows were installed from the 13th century. During the Middle-Ages, most of glass pieces have a Si-K-Ca composition with a relatively low SiO2 content, but high content of K2O and CaO. This chemical composition means that medieval stained glass deteriorates during environmental exposure, from climate and environmental pollution. These alterations are manifested in the form of an alteration layer and secondary phases (mainly gypsum or syngenite). The alteration layer is generally depleted in K and Ca, but rich in Si, Al and Fe. Its thickness varies up to 300 µm after 6 or 7 centuries of alteration. In order to reconstruct the alteration history and predict the deterioration of stained glass windows in the future, it is necessary to determine alteration rates as a function of the climate and environmental parameters.Several methodologies can be used to achieve this. First, short-term exposures or laboratory experiments can assess the first stages of the alteration and short-term kinetics. From these results, dose-response functions (DRF) were established for sheltered and unsheltered rain conditions. They correlate relevant environmental factors (temperature, rain quantity, rain pH, relative humidity, SO2 concentration) with the response of the materials in terms of alteration layer thickness. The second methodology consists in laboratory experiments that aim at parametrizing kinetic laws as a function of specific parameters (temperature, pH of rain, and relative humidity). These kinetic parameters do not directly consider pollution, but they can be extrapolated over long periods and can be inputs to geochemical models. In this study, we have compared both methodologies to simulate the alteration of a model stained glass at different European sites (using data from the ICP-Materials program). Both models give good results, but the geochemical model tends to underestimate the alteration at polluted sites. This indicates that the pollution via the concentration in SO2 for example should be included to improve the model.

This work aims to investigate the role played by a model Mn-oxidizing bacterial strain and its exudates on the alteration of Mn-bearing potash-lime silicate glasses representative of medieval stained glass windows. Two model glasses, with or without manganese, were prepared and used for abiotic and Pseudomonas putida inoculated dissolution experiments. Results show that the presence of P. putida slows down the dissolution kinetics while changing the dissolution stoichiometry. In biotic experiments, the acidification of the solution at the beginning of the experiment favors the release of K. After a few days, a drop in Mn and P in solution is observed, retained by bacterial cells. Reciprocally, the amount of glass influences bacterial behavior. The more glass, the faster the bacterial population increases in size and produces siderophore. In the presence of the Mn-bearing glass, siderophore production is followed by the formation of brown phases, identified as Mn oxides.

Since the Industrial revolution, emissions of pollutant (gas, aerosols) due to human activities increased and modified the composition of the atmosphere, causing air pollution and climate change. However, pollution measurements are relatively recent. In order to know past air pollution and assess its impact on monuments, proxies need to be found and studied. One of these potential local proxies is black crusts that are a chemical alteration pattern mainly found on limestone or marble monuments. They are forming a dark mineralogical layer composed of gypsum (CaSO4.2H2O) that results from the sulfation reaction between the calcite (CaCO3) of the stone and the sulphur dioxide (SO2) from the atmosphere. As gypsum is easily soluble, this pattern particularly affects sheltered area from the rain where particulate matter is trapped and accumulates. Therefore, black crusts act as passive sampler and could be used as an archive of air pollution. To validate black crusts nomination as a new proxy and to find the best pollution marker, samples were collected at Père Lachaise cemetery on ancient tombs (dated from the 1820’s). A specific protocol was applied to separate strata from each other. Then, multiple analyses were realised using SEM-EDS, ICP-AES, and ICP-MS. The results show a different particulate content as a function of the depth, with different contributions of fly-ash typical of coal and oil combustion. This is confirmed by the chemical analyses as the trace metal concentrations are in agreement with the pollution sources. This study demonstrates that laminar black crusts have an internal stratigraphy that can be crucial to reconstruct past air pollution and provides precious data on pollution sources.

France's monumental heritage has been the subject of little theoretical research in the face of global climate change, although many applied studies have concerned its adaptation and resilience, especially at the local level. Furthermore, this heritage includes more than 44,000 monuments and classified sites, 48 of which being inscribed on the UNESCO List and therefore deserves to be taken into account in the context of the current climate unbalance. The complexity lies in the diversity of materials making up the monuments (stones, glass, metals, wood...) and of phenomena that affect them (as well as other constructions). In order to assess the impact of these increasing slow or extreme events already at work, the tools and methodologies range from the description and inventory of the effects, their measurement, mapping and projection into the future using models such as dose-response functions (DRF) with input data from climate models and scenarios. Ancient data can also be used to complement the correlation between climate and heritage, such as dendroclimatology studies of the wood in monuments. Results from research carried out in France will be presented concerning stone facades, ancient stained glass windows, metals, degradation of walls by salts and dendroclimatology. Further research should focus on the consequences on the monumental heritage of rising marine waters, river and urban flood and low waters, freeze-thaw, the stability of monuments on clay soils and the indoor climate of monuments and their carbon footprint. In conclusion, much remains to be done in France: (1) complete the inventory and description of the phenomena, their impacts and their location at the national, regional, urban and monumental scales, (2) quantify these impacts in the future via empirical or geochemical models based on climate models outputs.