Where: t = exposure time (years). T = air temperature (annual average in °C). [SO2] = SO2 concentration (annual average in mg/m3). Rain[H+] = multiplication of the concentration of protons in precipitation (measured in mg/l) by the amount of precipitation (measured in mm/year). The relation between pH and [H+] is: [H+] = 1007.97. 10− pH.

Bleibleh, S. & Awad, J. Preserving cultural heritage: shifting paradigms in the face of war, occupation, and identity. J. Cult. Herit. 44, 196–203 (2020).

Despite the listed limits, there are observations of daily PM10 levels exceeding the limit of 120 micrograms per cubic meter (µg/m3) on several days, indicating temporary spikes in PM10 levels. Additionally, one monitoring station in the Mahatta area exceeded the annual average limit of 70 micrograms per cubic meter, suggesting a persistent criticism in this location17. The main reason for PM10 exceedances were sandstorms, traffic emissions, and industrial17. Exceedances in NO2 levels were observed primarily in terms of hourly averages, particularly in two stations: Mahatta area in Amman and the King Abdullah Sports City area in Irbid. Daily averages of NO2 exceed the Jordanian standard’s limit of 80 ppb in the Mahatta area and Tabarbour stations in Amman17. This report highlighted the corrosive effects of SO₂, NOx, O3, HNO3, particulate matter and acid precipitation in combination with climatic parameters. Sandstone and limestone are particularly subject to deterioration due to the presence of SO2 and this deterioration is particularly evident in the presence of NO2 or O318,19. NOx compounds contribute to the degradation of limestone, through the acidification of rain20. A combined effect of SO2 and O3 has been demonstrated in laboratory exposures on calcareous stone materials21,22. Due to the difficulty to define the “critical” level of deterioration, to estimate it, it is necessary to define the deterioration rate that is defined as the levels for which the deterioration is considered “acceptable” or “tolerable”. In particular, for cultural heritage “tolerable” definition is used23. As for ecosystems, the critical load/level approach is used, but must be modified according to the level of deterioration of the material as even the lowest concentration of pollutants causes an increase in the deterioration rate21.

Ambient Air Quality Monitoring. Report (Amman-Irbid-Zarqa). https://www.moenv.gov.jo/ebv4.0/root_storage/en/eb_list_page/2021_ambient_air_quality_monitoring_report.pdf (2019).

Hechler, J. J., Boulanger, J. & Noel, D. Microclimates and corrosion on the exterior of a building. Historic Struct. Contemp. Atmos. 1991, 20–25 (1991).

Despite the well-documented challenges faced by Jordan’s cultural heritage sites, there remains a significant gap in the quantitative assessment of environmental factors, particularly air pollution, on the degradation of Jordan’s sandstone and limestone structures. Previous research has focused primarily on the impact of tourism, development, and regional instability, but has not systematically evaluated the long-term effects of air pollution in a local context. Globally, studies have shown the harmful effects of pollutants like SO₂, NO₂, and particulate matter on cultural heritage materials; however, these assessments have largely been conducted in Europe and North America, with little emphasis on regions like the Middle East, where cultural heritage is equally, if not more, vulnerable. Therefore, this study fills an important gap by offering the first risk assessment of air pollution impacts on cultural heritage in Jordan. Moreover, while climate change is increasingly recognized as a threat to heritage conservation, there is a lack of localized studies that analyze future risks under specific climate change scenarios. This study is particularly relevant in Jordan, where extreme weather events, rising temperatures, and shifting wind patterns can exacerbate the damage caused by air pollution. By considering future climate projections (SSP5-8.5 scenario), this study aims to provide a forward-looking analysis that can inform preventive conservation strategies.

Doytchinov, S., Screpanti, A. & Leggeri, G. Combined stock at risk and mapping for Italy at the national level. In Report No. 63: Combined Stock at Risk and Mapping for Italy at the National Level (ENEA, 2010).

This study examines the impact of air pollution on Jordan’s cultural heritage sites, focusing on key pollutants (SO2, HNO3, O3, PM10) and climate conditions. Using 2019 data and future projections for 2040–2059 and 2080–2099, the research reveals significant material corrosion in urban areas like Amman and Irbid, driven by pollutants such as SO₂ and PM10. Random Forest Analysis identifies these pollutants as primary contributors to material degradation. Future scenarios indicate corrosion rates exceeding safe limits across Jordan, underscoring the need for proactive conservation strategies. This work highlights the critical role of air quality management in protecting cultural heritage, especially under climate change pressures, and provides guidance for national policy development.

Here, ‘n’ takes values of either 2.5 or 2, representing the corrosion level deemed acceptable for cultural heritage28. ‘Kb’ is the background corrosion rate which considers the fact that the impacts of climate change are related to the geographical location13 and cannot be controlled. It corresponds to the baseline corrosion rates for different materials, considering the acceptable corrosion rate to estimate the exceedances (See Table 1), where the corrosion rate exceeds the acceptable threshold.

Jaradat, Q. et al. Chemical composition of urban wet deposition in Amman, Jordan. Water Air Soil. Pollut. 112, 55–65 (1999).

Jordan Ministry of Municipal, Rural affairs and the Environment. National Environment Strategy for Jordan. Gland: IUCN–The World Conservation Union, Jordan Department of Libraries, Documentation and National Archives deposit number (1991).

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The decision to use dose-response functions and tolerable corrosion rates stems from the need to quantify the impact of air pollutants and climate conditions on the deterioration of cultural heritage materials in Jordan. These functions provide a well-established, scientifically validated approach to assess how environmental factors, such as sulfur dioxide (SO₂), particulate matter (PM10), and climate change, contribute to the corrosion of materials like sandstone and limestone, which are commonly used in Jordan’s monuments. This approach, widely applied in the International Co-operative Programme on Effects on Materials (ICP Materials)26, allows for a rigorous, quantitative evaluation of the current and future risks posed by pollution. Dose-response functions have been successfully used in similar contexts, particularly in Europe, to estimate corrosion rates. By applying these models to Jordan, we can not only compare results with international studies but also adapt them to local climatic conditions, addressing a research gap specific to the Middle East.

Shah, V., Jacob, D. J., Moch, J. M., Wang, X. & Zhai, S. Global modeling of cloud water acidity, precipitation acidity, and acid inputs to ecosystems. Atmos. Chem. Phys. 20, 12223–12245 (2020).

The Random Forests Analysis (RFA) is realized following the method outlined in20. Predictors are chosen based on previous studies20,29. The analysis aimed to understand how pollutants (such as SO2, NO2, HNO3, O3, PM10, and pH) and environmental factors (Temperature, Precipitation, Humidity) influence the corrosion of material surfaces, as described in34. All statistical analyses were carried out using STATISTICA 7.0 software developed by StatSoft Inc. in Tulsa, OK, USA.

Air pollution plays a pivotal role in the degradation of buildings, structures, and cultural heritage objects10,35,36. Investigating the corrosive impacts of SO2, HNO3, O3, PM10, and acid rain, in conjunction with meteorological and climatic factors, is of high relevance to assess the risk for materials and cultural heritage. This study is crucial because the restoration costs for cultural heritage are substantial and often inestimable, which is why it is important to underscore the prevention of the damage. One of the significant challenges related to the deterioration of limestone involves the development of black crusts. These crusts form due to the interaction between limestone, sulphur dioxide (SO2), and particulate matter (PM10) present in urban air37,38. Additionally, it’s worth noting the significance of rain acidity (pH) in the chemical process that leads to the erosion of the limestone surface39,40.

Sorrentino, B., Screpanti, A. & De Marco, A. Corrosion on cultural heritage buildings in Jordan in current situation and in future climate scenarios. Sci Rep 14, 25373 (2024). https://doi.org/10.1038/s41598-024-77195-y

Ferm, M., Watt, J., O’Hanlon, S., De Santis, F. & Varotsos, C. Deposition measurement of particulate matter in connection with corrosion studies. Anal. Bioanal. Chem. 384, 1320–1330 (2006).

The “acceptable” corrosion rate was determined according with UNECE Task Force on ICP Materials methodology33. The corrosion level is defined by the equation:

To assess the effects of climate change on materials is important to emphasize that this study provides a groundbreaking opportunity to measure, for the very first time, both the geographical extent and the severity of the damage caused by the 2019 heatwave41 on different materials. This study evaluates the corrosion levels of limestone and sandstone, in Jordan for the year 2019 and in two future time frames, based on scenario SSP5-8.5. The level of corrosion (9.5 μm/year on average) obtained in Jordan are comparable with the corrosion level observed in Europe20,29 in previous studies. Previous European research, such as the study conducted in20, also emphasized the crucial role of PM10 in limestone corrosion, a pattern that our study confirms for Jordan. The winds in Jordan, particularly from desert regions, carry large quantities of particulate matter, further contributing to material degradation. The finding that PM10 is a key pollutant affecting corrosion aligns with similar observations in Mediterranean regions where arid conditions and airborne particulates exacerbate corrosion20.

The use of Geographic Information Systems (GIS) tools increases the validity of this study because they are valuable tools that also allow assessing the impact of air pollution and environmental factors on cultural heritage sites. GIS allows for the mapping and spatial analysis of large datasets, which is essential in identifying areas where cultural heritage sites are most at risk from pollution and climate change. By integrating pollution data, climate models, and geographic location of heritage sites, GIS can highlight risk zones, predict future scenarios, and aid in planning conservation efforts. GIS enables a more comprehensive risk assessment, offering insights into how specific heritage sites, especially those built with sandstone and limestone, may be affected by pollution and environmental changes. Moreover, using GIS in the study supports a data-driven preventive approach, which is critical for the sustainable management and conservation of Jordan’s cultural heritage in the face of ongoing climate change. Indeed around 85% of overseas tourists come to Jordan for culture and heritage destinations29. In the upcoming three years, Jordan plans to allocate substantial financial resources towards the conservation and preservation of its cultural and heritage sites. This initiative entails significant enhancements and upgrades to 15 key attractions between 2022 and 2024, aiming to safeguard these invaluable treasures for future generations.

Rh = relative humidity (annual average in %). [O3] = concentration, (annual average in mg/m3). Rh60 = Rh – 60 when Rh > 60, 0 otherwise. PM10 = PM10 concentration (annual average in mg/m3). [HNO3] = HNO3 concentration (annual average in mg/m3) obtained with the relation: HNO3 = 516 e− 3400/(T+273) ([NO2] [O3] Rh)0.5. Rain[H+] = multiplication of the concentration of protons in precipitation (measured in mg/l) by the amount of precipitation (measured in mm/year).

Another aspect to consider is that cultural heritage tourism is a major driver of Jordan’s economy45 and any degradation in the condition of these iconic sites will likely result in a reduction in visitor numbers, a diminished global reputation and a direct hit to the sector of tourism44. The costs of restoring cultural heritage sites are often inestimable, and prolonged closures during restoration periods can severely impact local tourism-dependent economies46. Considering this, it becomes crucial to emphasize preventative conservation over expensive and time-consuming restoration efforts. Implementing air quality monitoring measures and structural interventions could extend the lifespan of heritage materials, minimizing the need for extensive restorations in the future. Proactive, preventive conservation strategies are not only about protecting historical artifacts and structures but are also economically sound. This study underscores the importance of developing policies that integrate air pollution control with conservation efforts, not only to safeguard Jordan’s cultural heritage but also to ensure the long-term sustainability of tourism revenues. Investing in such preventive measures could ultimately prove to be more cost-effective than large-scale restoration projects that may become necessary if these sites are allowed to degrade unchecked. A cost-benefit analysis would likely reveal that early intervention—through pollution control and heritage preservation initiatives—would yield significant economic savings in the long term. Future research should explore the potential influence of CO₂ levels and localized extreme weather on corrosion rates to provide a more comprehensive risk assessment. This study offers valuable insights for protecting cultural heritage in Jordan and other Middle Eastern countries from the adverse effects of air pollution and climate change. By integrating global pollutant control measures and localized climate adaptation strategies, it is possible to mitigate the impact of environmental stressors on the degradation of culturally significant materials.

SO2—three 1-hour average concentrations greater than 300 ppb over 12-month period; 24-hour average Jordanian Standard for ambient air quality of 140 ppb and yearly average of 40 ppb.

Black, E. The impact of climate change on daily precipitation statistics in Jordan and Israel. Atmos. Sci. Lett. (2009).

Air pollution is an important factor in the deterioration of many materials therefore, buildings as well as cultural heritage objects exposed to the atmosphere, deteriorate more quickly due to pollution8,9,10,11,12. The damage due to the deterioration of cultural heritage has both economic and social impacts, but also the loss of unique aspects of cultural heritage. The main deterioration is due to corrosion reactions involving irreversible processes, which proceeds even in the absence of pollutants13. In Jordan air pollution reach very high levels in the bigger cities like Amman, where high levels of particulate matter with a diameter of 10 microns or less (PM10) are prevalent, leading to formation of regional dust and local abrasion3,14. Since the wind direction in the city is mostly from the west, pollution levels in the centre of Amman are higher as they include air pollution emitted from the various activities in the cities, such as industry, domestic heating and motor vehicles15. Limits for air pollutants set in Jordan16 are the following:

Vagnon, F. et al. Effects of thermal treatment on physical and mechanical properties of Valdieri Marble—NW Italy. Int. J. Rock. Mech. Min. Sci. 116, 75–86 (2019).

PM10—annual average of 70 µg/m3 and daily average (24 h) of 120 µg/m3, which should not be exceeded for more than three times in a 12-month period.

Allen, G. C., El-Turki, A., Hallam, K., McLaughlin, D. & Stacey, M. Role of NO₂ and SO₂ in degradation of limestone. Br. Corros. J. 35, 35–38 (2000).

Ruffolo, S. A. et al. An analysis of the black crusts from the Seville Cathedral: a challenge to deepen the understanding of the relationships among microstructure, microchemical features and pollution sources. Sci. Total Environ. 502, 157–166 (2015).

Random Forests Analysis (# of trees = 100 and R² = 0.97) for limestone (SO2 dominated (B), multi-pollutant (C)) and sandstone (A) in the year 2019 (black bars) and for future time frames (2040–2059 grey bars and 2080–2099 white bars).

Mehta, P. Science behind acid rain: analysis of its impacts and advantages on life and heritage structures. South. Asian J. Tour Herit. 3(2), 124–132 (2010).

Spezzano, P. Mapping the susceptibility of UNESCO World Cultural Heritage sites in Europe to ambient (outdoor) air pollution. Sci. Total Environ. 754, 142345 (2021).

Tzanis, C. et al. Nitric acid and particulate matter measurements at Athens, Greece, in connection with corrosion studies. Atmos. Chem. Phys. 9(21), 8309–8316 (2009).

Kucera, V. & Fitz, S. Direct and indirect air pollution effects on materials including cultural monuments. Water Air Soil. Pollut. 85, 153–165 (1995).

Beatrice Sorrentino: Writing, Data collection, Data analysis; Alessandra de Marco: editing and Supervision, reviewing; Augusto Screpanti: Data analysis, reviewing.

In consideration of this, quantify, for the first time in one country outside Europe, potential impacts of air pollution and climate change on sandstone and limestone at national scale and define the potential risk areas for cultural heritages, is largely relevant. Furthermore, the manuscript aims are to make assess the impacts of the climate change scenario. The scenario selected SSP5-8.5 was analysed in the two timeframe 2040–2059 and 2080–2099. The study of the scenarios is useful as it can be considered from a preventive perspective for conservation program. So, this work aims to be the first risk-assessment for the air pollution impacts on Cultural Heritage in Jordan, evaluating the surface recession for the year 2019 and future scenarios, for sandstone and limestone, the most common materials for Jordan’s artworks (see Fig. 1), looking at the future changes due to climate modification. The importance of this analysis is also linked to the high value of tourism in Jordan.

Jordan is a repository of cultural heritage that has endured the ages. The nation’s geographical positioning has rendered it a crossroads for civilizations, fostering the convergence of diverse cultural influences. Amidst this historical richness, however, pressing challenges that impact the state of Jordan’s monuments and cultural heritage are hidden1. The cultural heritage of Jordan is threatened by various challenges and factors that can compromise its preservation and conservation. The lack of sustainable development plans can jeopardize the integrity of these sites2,3. Another menace is the unregulated tourism: while tourism can bring economic benefits, high tourist inflow without proper management protocols can cause physical damage to structures and the surrounding environment2. Environmental changes such as climate change and adverse environmental conditions can damage monuments and artworks4. Floods, erosion, and physical deterioration can occur due to these changes. During periods of geopolitical instability, sites can be intentionally damaged or destroyed5,6. The lack of financial and technical resources leads to a shortage of adequate funding that can hinder conservation and restoration programs. The shortage of specialized technical skills can limit the ability to effectively preserve sites6. Furthermore, air pollution, the use of chemicals, and lack of regular maintenance can cause damage to the surfaces of monuments and artworks7. To address these threats and protect Jordan’s cultural heritage, an integrated approach involving the government, local communities, international organizations, and experts in the field is essential.

Climate change play an important contribution to the deterioration of Cultural Heritage24; facades can deteriorate due to thermal stress caused by temperature change (diurnal, seasonal, extreme events), wind can cause erosion, surface deterioration and structural damage25.

The Multi Pollutant (MP) Situation formula used to calculate the corrosion rate of limestone, or recession (R in µm/y) was:

Hussein, T. et al. Particulate matter concentrations in a Middle Eastern city: an insight to sand and dust storm episodes. Aerosol Air Qual. Res. 20, 2780–2792 (2020).

This manuscript for the first time presents an analysis of the corrosion levels found in Jordan due to air pollution and meteorological conditions using two different approaches (Single and Multi-Pollutant analysis) developed and used currently in Europe for materials risk-assessment23.

For both materials corrosion rate depends on various factors, including the surrounding environment, material composition, and the presence of corrosive agents such as humidity, salt, and atmospheric pollution. In the case of Jordan, there are several reasons why the corrosion rate might increase when moving westward, towards the sea and Amman. The proximity to the Dead Sea could be a source of humid air rich in salts. Humidity and the presence of salts in the air can accelerate the corrosion process, as salt promotes the formation of corrosive deposits on material surfaces. As one moves westward in Jordan, a more humid climate might be encountered, which can raise the corrosion rate. Humidity in the air creates a favourable environment for corrosion, especially when exposed metals are present.

Kucera, V. Chapter 4: mapping of effects on materials. In Manual on Methodologies and Criteria for Modelling and Mapping Critical Loads and Levels and air Pollution Effects, Risks and Trends. UNECE Convention on Long-range Transboundary Air Pollution (CLRTAP), Geneva (ed. Kucera, V.) IV-1e IV-10 (2004).

Kucera, V. et al. The UN/ECE ICP materials multi-pollutant exposure on effects on materials including historic and cultural monuments. In Acid Rain Conference (2007).

Di Turo, F. et al. Impacts of air pollution on cultural heritage corrosion at European level: what has been achieved and what are the future scenarios. Environ. Pollut. 218, 586–594 (2016).

de la Fuente, D., Vega, J. M., Viejo, F., Díaz, I. & Morcillo, M. Mapping air pollution effects on atmospheric degradation of cultural heritage. J. Cult. Herit. 14(2), 138–145 (2013).

Broomandi, P. et al. Impacts of ambient air pollution on UNESCO World Cultural Heritage sites in Eastern Asia: dose-response calculations for material corrosions. Urban Clim. 46, 2212–0955 (2022).

Ozga, I. et al. Assessment of air pollutants sources in the deposit on monuments by multivariate analysis. Sci. Total Environ. 490, 776–784 (2014).

The dose-response functions and the concept of tolerable corrosion rates are particularly useful tools for identifying high-risk areas and establishing acceptable thresholds of deterioration. This provides a decision-making framework for heritage conservation professionals, helping them prioritize interventions on structures that are at risk of accelerated degradation in the future.

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Figure 3 shows predictor importance of each climatic or environmental stressor for the two materials: sandstone and limestone in all the configurations chosen for the previous analysis. It can be observed that both for sandstone and limestone in the single pollutant analysis, SO2 is the predominant factor affecting the corrosion rate. During the year 2019 also temperature and precipitation affected corrosion for both materials, underlining the combined effect of climatic factors and pollutants. It is clear from the Fig. 3 that PM10 is the most important parameter affecting limestone corrosion in case of Multi Pollutant analysis, both for control than for future scenarios, while in the other case for limestone the main factor influencing surface recession is SO2. Climatic parameters like Rh60, pH and H+, do not show level of significant importance affecting corrosion for limestone and sandstone. Temperature (T) shows 0.40 and 0.37 values of influence for limestone for the Multi Pollutant analysis in the time period 2 and 1 respectively. O3 in the Multi Pollutant analysis has an important influence on the corrosion rate of limestone in the time period 2, where reach a value of 0.73, instead remain equal to 0.3 both for current situation and time-period (1) This indicates a growing concern over the role of ozone in future material corrosion, especially under higher temperature scenarios. HNO3 has a value of 0.58 for limestone in the year 2019 and time period 1 in the Multi Pollutant analysis and a value of 0.3 for time period (2) From the random forest analysis, it is also clear that precipitation in the multi pollutant analysis plays an important role in influencing the level of corrosion, in fact for all the three time frames it reaches a level of 0.8. This highlights the significance of rainfall in affecting corrosion rates, particularly for sandstone and limestone, further emphasizing the complex interaction between climatic and pollutant stressors.

Jordan’s meteorological data were obtained from Copernicus Climate Data Store ERA530 which is the fifth generation ECMWF reanalysis, with a horizontal resolution of 0.25° × 0.25°. Data were collected as annual means, T2 reanalysis is the temperature of air at 2 m above the surface of land, sea, or inland waters. T2 is calculated by interpolating between the lowest model level and the Earth’s surface, taking account of the atmospheric conditions. The ERA5 meteorological data were used to calculate the corrosion rates for sandstone and limestone under current climatic conditions, as well as to understand the baseline environmental stresses. For future climate scenario analysis, the meteorological data were also sourced from Copernicus Climate Data Store30. The future scenarios were based on the Shared Socioeconomic Pathway SSP5-8.5 projections, with a focus on the time periods 2040–2059 and 2080–2099. These scenarios were used to assess the potential impacts of climate change on the corrosion rates of materials, especially under more extreme temperature and precipitation conditions. The air pollutant data for the year 2019 were sourced from EAC4 (ECMWF Atmospheric Composition Reanalysis 4)30. EAC4 is the latest iteration of ECMWF’s global reanalysis of atmospheric composition, offering a detailed depiction of air pollutant concentrations worldwide. This dataset provides high-resolution (0.75° × 0.75°) global data on air pollutant concentrations, including sulphur dioxide (SO2), nitrogen dioxide (NO2), ozone (O2), and particulate matter (PM10), which are known contributors to the deterioration of cultural heritage materials. These pollutant concentrations were used to model the corrosion rates of sandstone and limestone, factoring in the specific pollutants that are prevalent in Jordan. The EAC4 dataset was also crucial in identifying pollution hotspots around major heritage sites, such as those near urban and industrial areas. For rain pH is used a constant pH value of 6.24 for the entire Jordan region. This value was chosen based on existing literature and averaged across the study area to account for the potential influence of acid rain on material degradation31. The pH value was integrated into the corrosion models, particularly for its role in exacerbating chemical reactions that lead to material degradation in the presence of pollutants like SO₂ and NO₂. Data on the location of archaeological site in Jordan were obtained by United Nations Educational, Scientific and Cultural Organization (UNESCO)25. This dataset includes geographic coordinates and classification of sites, such as World Heritage Sites, that are of high cultural and historical value. These location data were incorporated into the GIS model to spatially correlate pollution levels and climatic factors with specific heritage sites, allowing for targeted analysis of high-risk areas. All spatial representation and interpolation of data were performed using the open-source Geographic Information System (GIS) software, QGIS 3.28. The kriging interpolation method, as described by21, was employed to generate spatial distributions of air pollution and climate data across Jordan. This allowed for the identification of regions with the highest corrosion risks to cultural heritage materials. The precipitation and temperature data for the development of the scenarios were downloaded from the Climate Change Knowledge Portal (CCKP)32, with a horizontal resolution of 1° × 1°. These climate variables were essential for modelling future corrosion risks, as both temperature and precipitation influence the rate of chemical weathering and physical degradation of heritage materials.

Al-Saad, S. The conflicts between sustainable tourism and urban development in the Jerash archaeological site (Gerasa), Jordan (2016).

NO2—three 1-hour average concentrations greater than 210 ppb over 12-month period; 24-hour average Jordanian Standard for ambient air quality of 80 ppb and yearly average of 50 ppb.

Esteban-Cantillo, O. J., Menendez, B. & Quesada, B. Climate change and air pollution impacts on cultural heritage building materials in Europe and Mexico. Sci. Total Environ. 921, 0048–9697 (2024).

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Dose–response functions were obtained from Mapping Of Effects On Materials manual23. These functions derived from the ICP Materials exposure program depict how climate conditions and air pollutants influence the degradation of structural materials. In simpler terms, they illustrate how environmental factors like weather and airborne pollutants contribute to the deterioration of building materials. The corrosion rate or surface recession (R in µm/year) of sandstone was determined using the equation primarily influenced by sulphur dioxide (SO2) concentration:

Recession in Jordan for limestone: SO2 dominated (A) and multi pollutant (C) in the year 2019, scenario 1 (2040–2059) (D and F) scenario 2 (2080–2099) in (G and I) and sandstone: SO2 dominated (B) in the year 2019, scenario 1 (2040–2059) (E) scenario 2 (2080–2099) in (H).

Figure 2 show risk assessment for limestone recession in current years (A) and in the future scenario (D, G). The results indicate a significant increase in recession values moving westward, with the western regions of Jordan showing the highest risk. As visible from the figures all the Jordan’s UNESCO sites fall in the exceeding area in the current years. In this case the percentage value exceeding the tolerable corrosion level for n = 2 is 100% and for n = 2.5 is 63.2%. This suggests a widespread and severe impact of air pollutants on Jordan’s limestone-based cultural heritage in the current climate. Figure 2B, E and H shows recession values and extension of risk areas for sandstone. The areas in dark orange exceeded acceptable rate of corrosion and an increase of recession could be observed moving to the West. All the Jordan’s UNESCO sites are in areas where higher recession values occur. In fact, percentage value exceeding the tolerable corrosion level have been calculated for sandstone for both value n = 2 and 2.5 and results respectively 100% and 91.8% in the current years. Both limestone and sandstone follow similar recession trends, confirming the vulnerability of Jordan’s cultural heritage materials to environmental stressors. The trend for both sandstone and limestone is similar. In Fig. 2C, F and I the risk assessment for limestone recession is calculated with the Multi Pollutant Situation formula for the three different time frames, and we observed that the values of the recession are high, towards the more densely populated cities, the sea and the desert to the east side. In this case the percentage value exceeding the tolerable corrosion level is 4.1% for n = 2 and 2% for n = 2.5. This suggests that while specific pollutants, such as SO2 and particulate matter, contribute heavily to corrosion in some areas, the overall risk is more localized compared to single-pollutant analyses.

Italian National Agency for New Technologies, Energy and Sustainable Economic Development, (ENEA), Via Anguillarese 301, Rome, 00123, Italy

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The findings of this study emphasize the necessity of monitoring both meteorological conditions and air pollutant concentrations in understudied regions such as Jordan, to develop effective strategies for mitigating corrosion risks. Comparing the results of this research to previous studies conducted in Europe20,29 and Eastern Asia44 underlines the shared environmental challenges faced by Mediterranean and Middle Eastern countries, particularly in preserving cultural heritage.

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Recognizing the challenge of air pollution in affecting building materials, the United Nations Economic Commission for Europe (UNECE) ratified the Convention on Long-Range Transboundary Air Pollution (CLRTAP). Started in 1985, the study investigating the impact of air pollution on materials was instrumental, culminating in the Multi-Asses project’s integration of Cultural Heritage materials within the broader International Co-operative Programme on Effects on Materials, including Historic and Cultural Monuments (ICP Materials)26. Leveraging insights from the CULT-STRAT project27, dose-response functions emerged as a valuable tool to assess the cumulative effects of pollutants and meteorological conditions on materials28.

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Densely populated areas like Amman tend to have higher levels of atmospheric pollution due to industrial activity, vehicular traffic, and other emission sources17. Atmospheric pollution can contribute to increase the corrosion rate. The corrosion rate can increase also when moving eastward because the presence of sand and dust: wind can transport sand and dust across the desert and deposit them on the surfaces of stone materials. These abrasive particles can damage the surface, gradually removing the outer layer and increasing susceptibility to corrosion. Also, extreme climate variations can contribute to increase the corrosion rate, desert regions often experience extreme climate variations between day and night, with daytime temperatures reaching high levels and nighttime temperatures dropping significantly. These variations can induce thermal stress on stone materials, leading to the formation of cracks and subsequent corrosion42. In future scenario we find a decreasing trend for the corrosion levels both for sandstone and limestone, in fact even though there is an increase in temperature, it is expected a noticeable decrease in rainfall in Jordan. Indeed, significant reduction in boreal winter precipitation in Jordan is predicted by the end of the 21st century. This decline is attributed to a reduction in the occurrence and duration of rainy events, resulting in fewer days with rainfall43.

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Two different future time frames (2040–2059, 2080–2099) for the SSP5-8.5 scenario have been used for corrosion level assessment for sandstone and limestone. For the 2040–2059 period, the variations taken into consideration are 6 mm less rainfall and an increase of 2.2 °C for temperature. For the 2080–2099 period, 15 mm less rainfall and a 5.1 °C increase in temperature were applied. The obtained maps (Fig. 2D–I) show a reduction in corrosion levels, because, despite the temperature increase, there is still a significant decrease in rainfall. The total area exceeding “tolerable” limit, has been calculated for limestone and sandstone which is the same for both time periods: 45,884 km2 and 59,723 km2, which corresponds to a 51.4% and 66.9% respectively of the total country area. In Fig. 2F and I are shown the two time frames (2040–2059 and 2080–2099) obtained with the Multi Pollutant analysis for limestone, highlighting that there is no area exceeding in the future. In the period 2080–2099, however, two red areas can be observed, which reach the “tolerable” level of corrosion, set to 6.4 μm/year, highlighting that while future climatic conditions may reduce overall corrosion rates, localized risks still persist.

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