Evaluation of black crust formation and soiling process on historical buildings from the Bilbao metropolitan area (north of Spain) using SEM-EDS and Raman microscopy

The tangible impacts of air pollution on built heritage during COVID-19 period on the Historical Peninsula of Istanbul, Turkey

The degree of corrosion of the built cultural heritage site is examined considering the changes in air pollution trends during the COVID-19 pandemic, with the Historical Peninsula of Istanbul as a case study area. Key findings indicate that restricted mobility during stringent lockdown measures contributed to a noticeable reduction in PM10, SO2, NO2, and O3. This causes a temporary decrease in the surface recession rates and corrosion depths of the materials. The maximum reduction in surface recession rate for Portland limestone and White Mansfield dolomitic sandstone reaches to 7.2% and 7.5%, respectively while for cast bronze and zinc, this ratio continues to 17.1% for cast bronze and 4.8% for zinc. Except for the Sultanahmet Urban Archaeological Site, carbon steel and copper exhibit modest variances in corrosion depth, remaining below 2%. Despite the reduction during the pandemic period, Portland limestone surface recession rate and the corrosion depth values of copper, and zinc have already surpassed the 2050 thresholds, indicating that the materials are already experiencing severe damage. This implies that the Istanbul Historical Peninsula necessitates comprehensive conservation strategy plans considering the potential for increased urban and traffic mobility rather than temporary solutions.

Chemical and toxicological studies on black crust formed over historical monuments as a probable health hazard

Studies to date have mostly investigated environmental factors responsible for deterioration of historical monuments. Black crusts formed on historical monuments are considered as factor for deterioration of structures or as an indicator of environmental status of the surrounding area. Black crust formed on historical monuments has never been investigated as a health hazard. Herein, for the first time, we performed in vitro and in vivo toxicology studies of black crust formed on three culturally-rich historical monuments (Rang Ghar, Kareng Ghar, and Talatal Ghar) of the Indian subcontinent to test their toxicological effect. Black crust suspension in ultrapure water was found not to be considerably toxic to the cells upon direct short-term exposure. However, the sub-acute nasal exposure of the black crust suspension in Swiss albino mice produced lung-specific pathologies and mortality. Additionally, structural formation of the black crust along with the speciation of potentially hazardous elements (PHEs), polyaromatic hydrocarbon (PAHs), and other metals were investigated. Overall, these results indicate the potential of black crust deposited on historical monuments as health hazard owing to the atmospheric pollution of the surroundings. However, it may be noted that black crust and its components have very low possibility of health implication unless they are disturbed without proper care.

Characterization of fresh PM deposits on calcareous stone surfaces: Seasonality, source apportionment and soiling potential

Particulate matter (PM) pollution is one of the major threats to cultural heritage outdoors. It has been recently implied that organic aerosols will prevail over inorganic carbon particulates in the future, changing the main mechanisms of damage caused by poor air quality to calcareous heritage in particular. We studied fresh particulate deposits on marble and limestone surfaces exposed to urban air in sheltered and unsheltered configurations. Due to different air pollution sources in different seasons, the amount and composition of surface deposits varied throughout the year. The main and most constant contributor to PM_2.5 (particles smaller than 2.5 μm) were primary traffic emissions (30 %), followed by secondary formation of acidic inorganic aerosols, such as sulphate in summer and nitrate in winter (33 % altogether), and seasonal biomass-burning emissions (14 %). Although biomass burning is the major source of primary organic aerosols including the light-absorbing fraction that prevailed over black carbon (BC) in colder months (up to 60 % carbonaceous aerosol mass), we show that surface darkening causing the soiling effect is still governed by the minor BC fraction of atmospheric aerosols, which remained below 20 % of the carbonaceous aerosol mass throughout the year. This, however, can change in remote environments affected by biomass-burning emissions, such as winter resorts, or by rigorous BC mitigation measures in the future. In the short run, sheltered positions were less affected by different removal processes, but we show that surface deposits are not simply additive when considering longer periods of time. This must be taken into account when extrapolating surface accumulation to longer time scales.

Impact of air pollution on outdoor cultural heritage objects and decoding the role of particulate matter: a critical review

Atmospheric gases and particulate matter (PM) in contact with the material's surface lead to chemical and physical changes, which in most cases cause degradation of the cultural heritage material. Atmospheric damage and soiling are recognized as two pivotal forms of deterioration of cultural heritage materials caused by air pollution. However, the atmospheric damage effect of PM is rather complicated; its variable composition accelerates the deterioration process. Considering this, one of the important contributions of this work is to review the existing knowledge on PM influence on atmospheric damage, further recognize, and critically evaluate the main gaps in current understanding. The second phenomenon related to cultural heritage material and PM pollution is soiling. Even if soiling was recognized long ago, its definition and knowledge have not changed much for several decades. In the past, it was believed that black carbon (BC) was the primary soiling agent and that the change of the lightness could effectively measure the soiling. With the change of pollution situation, the lightness measurements do not represent the degree of soiling correctly. The additional contribution of this work is thus, the critical evaluation of soiling measurements, and accordingly, due to the change of pollution situation, redefinition of soiling is proposed. Even though numerous studies have treated soiling and atmospheric damage separately, there is an overlap between these two processes. No systematic studies exist on the synergy between soiling and atmospheric damage caused by atmospheric PM.

Chemical Characterization of Particulate Matter in the Renaissance City of Ferrara

Atmospheric aerosols are today a key issue in air pollution, mostly related to public health. Two test areas in Ferrara, one in the city center (urban location) and one in the industrial area (industrial location), were studied in June–July 2016 using the SEM technique to identify the environmental impact of some potential pollutant sources. Collection was performed using adhesive tapes applied on the surface of road signs, which allows to select particulate matter moving on air with diffusion movement and to exclude the particles usually deposed by the gravitational process. Dimensional characterization has shown that, usually, smaller particles tend to aggregate themselves in bigger polycrystalline particles with the geometric diameter of up to 10 μm. Micro-analytical data have revealed a wide heterogeneous range of compositions: more abundant silicate followed by carbonate, chlorine, sulphate, carbon, and organic. This preliminary study has highlighted that the Renaissance city of Ferrara is affected by an environmental problem linked to the presence of particulate matter induced by industrial activities, as is the case with some of the most polluted cities in the world. The observations and analytical data pointed out the need for further investigation to better define the features of the fine particulate matter. This will be useful to preserve the cultural heritage of this Medieval-Renaissance city.

Stone-built heritage as a proxy archive for long-term historical air quality: A study of weathering crusts on three generations of stone sculptures on Broad Street, Oxford

Black crusts on historic buildings are mainly known for their aesthetic and deteriorative impacts, yet they also can advance air pollution research. Past air pollutants accumulate in distinct layers of weathering crusts. Recent studies have used these crusts to reconstruct pollution to improve our understanding of its effects on stone-built heritage. However, the majority of the studies provide only coarse resolution reconstruction of pollution, able to distinguish between 'inner = old' and 'outer = modern' crust layers. In contrast, very few studies have linked distinct periods of exposure to pollution variations in the composition of these crusts. Here we address this research gap by developing a finer-scale resolution pollution record. Our study explored the unique configuration of limestone sculptures in central Oxford, which have been exposed over the last 350 years to three different periods of atmospheric pollution; the early Industrial Revolution, the Victorian period and the 20th century. When the first two generations of sculptures were moved to less polluted areas, their 'pollution clocks' were stopped. Here we discuss the potential of investigating the 'pollution clock' recorded in the geochemical makeup of each sculpture generation's weathering crust layers. We found the analysed crusts record clear changes related to the evolution of modes of transport and industrial and technological development in Oxford. Higher levels of Arsenic (As), Selenium (Se) are linked to pollution from coal burning during Victorian times and Lead (Pb) indicated leaded petrol use in modern times. Our work shows that stone-built heritage with a known history of air pollution exposure allows improving the pollution reconstruction resolution of these weathering crusts. The results provide the basis for calibrating long-term geochemical archives. This approach may be used to reconstruct past air quality and has the potential to inform stone weathering research and conservation, in addition to improving the reconstruction of historical pollution.

The influence of marine environment on the conservation state of Built Heritage: An overview study

Marine aerosol is a chemical complex system formed by inorganic salts and organic matter, together with airborne particulate matter from the surrounding environment. The primary particles transported in the marine aerosol can experiment different chemical reactions in the atmosphere, promoting the so-called Secondary Marine Aerosol particles. These kinds of particles (nitrates, sulfates, chlorides etc.), together with the natural crustal or mineral particles and the metallic airborne particulate matter emitted by anthropogenic sources (road traffic, industry, etc.) form clusters which then can be deposited on building materials from a specific construction following dry deposition processes. Apart from that, the acid aerosols (e.g. CO₂, SO₂, NO_X, etc.) present in urban-industrial environments, coming also from anthropogenic sources, can be deposited in the buildings following dry or a wet deposition mechanisms. The interactions of these natural and anthropogenic stressors with building materials can promote different kind of pathologies. In this overview, the negative influence of different marine environments (direct or diffuse influence), with or without the influence of an urban-industrial area (direct or diffuse), on the conservation state of historical constructions including a wide variety of building materials (sandstones, limestones, artificial stones, bricks, plasters, cementitious materials, etc.) is presented.

Decay processes in buildings close to the sea induced by marine aerosol: Salt depositions inside construction materials

Buildings close to the sea experience different kinds of decay processes related with the influence of marine aerosol. This sea spray is a chemically complex system formed by inorganic salts (sulfates, nitrates and mainly chlorides) and organic matter, together even with airborne particulate matter from the surrounding environment. Buildings close to the sea, erected using different materials such as bricks, plasters, limestones and sandstones, can experience many kinds of chemical reactions promoted by the impact of this sea spray, which favour the formation of salt crystallizations. In this work, a study of salts crystallizing in different kinds of building materials of a construction close to the Bay of Biscay (Villa Belza, Biarritz, France) has been studied in order to evaluate the state of conservation of the materials under study. The construction materials affected by salts were analyzed by means of X-ray Diffraction (XRD) and μ-Raman spectroscopy (μ-RS) for molecular analyses, Energy dispersive X-ray Fluorescence spectrometry (μ-ED-XRF) for elemental analyses and soluble salts tests by means of ion chromatography. These analyses revealed different levels of chlorides, nitrates and sulfates. Moreover, using this methodology, some specific chemical reactions that take place in the Villa Belza were understood. This knowledge can help to lay the foundations for possible future restoration works.

Evaluation of the role of biocolonizations in the conservation state of Machu Picchu (Peru): The Sacred Rock

Machu Picchu Inca sanctuary (Cusco Region, Peru) was constructed on a granitic plateau, better known as Vilcabamba batholith. One of the most important carved granitic rocks from this archaeological site is the Sacred Rock, used by Inca citizens for religious rituals. Due to the location and climatic conditions, different rocks from this archaeological site are affected by biocolonizations. Concretely, the Sacred Rock shows flaking and delamination problems. In this work, a non-destructive multi analytical methodology has been applied to determine the possible role of the biodeteriogens, forming the biological patina on the Sacred Rock, in the previously mentioned conservation problems. Before characterizing the biological patina, a mineralogical characterization of the granitic substrate was conducted using X-ray Diffraction, Raman microscopy (RM) and micro energy dispersive X-ray fluorescence spectrometry. For the identification of the main biodeteriogens in the biofilm, Phase Contrast Microscopy was used. RM also allowed to determine the distribution (imaging) and the penetration (depth profiling) of the biogenic pigments present in the biopatina. Thanks to this study, it was possible to asses that some colonizers are growing on inner areas of the rock, reinforcing their possible assistance in the delamination. Moreover, the in-depth distribution of a wide variety of carotenoids in the patinas allowed to approach the penetration ability of the main biodeteriogens and the diffusion of these biogenic pigments to the inner areas of the rocky substrate.

Micro-Raman and SEM-EDS analyses to evaluate the nature of salt clusters present in secondary marine aerosol

Marine aerosol is a complex inorganic and organic chemistry system which contains several salts, mainly forming different type of salt clusters. Different meteorological parameters have a key role in the formation of these aggregates. The relative humidity (%RH), temperature, CO, SO₂ and NO_x levels and even the O₃ levels can promote different chemical reactions giving rise to salt clusters with different morphology and sizes. Sulfates, nitrates and chlorides and even mixed chlorosulfates or nitrosulfates are the final compounds which can be found in environments with a direct influence of marine aerosol. In order to collect and analyze these types of compounds, the use of adequate samplers is crucial. In this work, salt clusters were collected thanks to the use of a self-made passive sampler (SMPS) installed in a 20th century historic building (Punta Begoña Galleries, Getxo, Basque Country, Spain) which is surrounded by a beach and a sportive port. These salt clusters were finally analyzed directly by micro-Raman spectroscopy and Scanning Electron microscopy coupled to Energy Dispersive X-ray spectrometry (SEM-EDS).