Report No 83: Call for Data “Inventory and condition of stock of materials at UNESCO world cultural heritage sites”. Part II – Risk assessment September 2018 PREPARED BY THE SUB-CENTRE FOR STOCK OF MATERIALS AT RISK AND CULTURAL HERITAGE Italian National Agency for New Technologies, Energy and Sustainable Economic Development (ENEA), Rome, Italy CONVENTION ON LONG-RANGE TRANSBOUNDARY AIR POLLUTION INTERNATIONAL CO-OPERATIVE PROGRAMME ON EFFECTS ON MATERIALS, INCLUDING HISTORIC AND CULTURAL MONUMENTS (ICP Materials) Report No 83 Call for Data “Inventory and condition of stock of materials at UNESCO world cultural heritage sites” Part II – Risk assessment Pasquale Spezzano1, Johan Tidblad2, Mirna Bojić3, Zrinka Radunić3, Vanja Kovačić3, Sonja Vidić4, Nina Zovko5, Stefan Brüggerhoff6, Markus Faller7, Ulrik Hans7, Terje Grøntoft8, Jessica Andersson2 1ENEA, Italy 2Swerea KIMAB AB, Sweden 3Ministry of Culture, Croatia 4Meteorological and Hydrological Service, Croatia 5Croatian Agency for Environment and Nature 6Deutsches Bergbau – Museum Bochum, Germany 7Swiss Federal Laboratories for Materials Testing and Research (EMPA), Switzerland 8Norwegian Institute for Air Research (NILU), Norway ENEA, Rome, Italy September 2018 http://www.enea.it/ Contents 1. Introduction ........................................................................................................................................ 4 2. Cultural objects .................................................................................................................................. 5 3. Assessment of air pollution risks for corrosion of materials ........................................................... 21 3.1 Limestone ................................................................................................................................... 21 3.2 Sandstone ................................................................................................................................... 27 3.3 Copper ........................................................................................................................................ 30 3.4 Bronze ........................................................................................................................................ 33 4. Assessment of air pollution risks for soiling of materials ................................................................ 38 4.1 Limestone ................................................................................................................................... 38 4.2 Glass........................................................................................................................................... 40 5. Discussion of air pollution risks to materials .................................................................................. 45 6. Comparison of predicted degradation rates: local data vs. EMEP model data. ............................. 48 7. Conclusions ...................................................................................................................................... 55 8. References ........................................................................................................................................ 56 3 1. Introduction The International Co-operative Programme on Effects on Materials, including Historic and Cultural Monuments (ICP Materials) was launched in 1985 within the scope and the activities of the Convention on Long-range Transboundary Air Pollution. The aim of the Programme is to fill some of the major gaps in scientific knowledge in the area of materials corrosion influenced by atmospheric pollutants by performing a quantitative evaluation of multi-pollutant effects on atmospheric corrosion on both technically important materials and materials used in historic and cultural monuments. Many of the materials used in the construction of historic and cultural monuments are very sensitive to air pollution resulting in corrosion and soiling of the materials that were used to create the artefacts. The Programme, through the Sub-Centre for stock of materials at risk and cultural heritage, agreed to launch a Call for Data on “Inventory and condition of stock of materials at UNESCO world cultural heritage sites”. UNESCO sites are considered of outstanding universal value and are therefore ideal for illustration and dissemination of effects of air pollution on materials. The Call was approved at the 1st joint session of the Steering Body to the EMEP and the Working Group on Effects (Geneva, 14-18th September 2015) and then launched in October 2015. Documents provided by the Call included the Call text, the reporting template, an explanatory note with guidance on the use of the reporting template, and a brochure on a pilot study “Inventory and condition of stock of materials at risk at five UNESCO world cultural heritage sites”, exemplifying the approach. In addition, a page dedicated to the Call for Data was added to the ICP Materials website (http://www.corr-institute.se/icp-materials), where all documents and some examples of the reporting template were available for downloading. The call was closed in June 2017. Six Parties to the Convention; Croatia, Germany, Italy, Norway, Sweden and Switzerland, provided qualitative and quantitative data on both historic/cultural monuments and on concentrations of main air pollutants and meteo-climatic parameters measured at monitoring stations close to the selected UNESCO world cultural heritage sites. Taken together, the twenty-one cultural heritage objects included in the call have a total external surface area of about 430,000 m2 and cover a wide range of materials (natural stone, artificial stone, copper, bronze, glass and others) as well as a wide range of environmental conditions. Detailed information on monuments/sites and their selection can be found in a thematic report, ICP Materials Report No 80: Call for Data “Inventory and condition of stock of materials at UNESCO World Cultural Heritage sites”. Part I - Status Report, released in September 2017. The purpose of this report (Part II) is to assess the potential risk of damage due to air pollution on the materials of which these twenty-one cultural objects are made by using dose-response functions established by ICP Materials. The degradation rates predicted on the basis of these functions and using the environmental parameters collected during the Call for data, calculated for the materials constituting the twenty-one cultural objects, were compared with the target (tolerable corrosion rate) suggested by ICP Materials for protecting cultural heritage monuments for 2050. This comparison was then used to assess the relative risks due to air pollution for different pollutants and different materials. Future reports planned to be launched are Part III on Economic Evaluation and Part IV on the relationship between the environment and the artefact. 4 2. Cultural objects The list of the twenty-one cultural objects considered in the call for data is shown in Table 1. The beauty and uniqueness of these monuments can be appreciated from the Figures 1-21. Table 2 summarizes the occurrence of the different materials in these monuments of outstanding universal value. A more detailed description of the materials can be found in the previous ICP Materials report (ICP Materials, 2017). Taken together, the twenty-one cultural heritage objects have a total external surface area of about 430,000 m2. Not surprisingly, a high percentage of the external surfaces of this sample of built heritage, about 60%, consists of natural stone, mainly several varieties of sandstone and limestone but also talc-schist, tufa, slate (mainly for roofing) and other ornamental stone varieties, which reflect the geo-diversity and the availability of stone resources in a determined region or territory. The different stone materials that are found in built heritage are an important element in the cultural heritage of people. The exterior of the considered monuments is often finely decorated and adorned by statues, bas-reliefs, columns, capitals, etc. Carved stone is very delicate and more vulnerable to damage than bulk masonry. Artificial stone materials such as ceramic (bricks, “terracotta” tiles), plasters, mortars, and cement- based concrete also have a large presence in the exteriors of the monuments covered by the study (about 17% of the total external surface). Artificial stone materials have different characteristics with respect to natural stones. Sometimes, roofs of buildings are covered with waterproof materials based on asphalt, bitumen or tar (about 2.5% of the total external surface of the monuments considered in the present study). In some cases a certain fraction (a little less than 2%) of the outer surfaces of the monuments is painted. Most of the decorations and paintings are inside the buildings and therefore not directly exposed to outdoor concentrations of atmospheric pollutants and other external deteriorating parameters (wind, rain, salt crystallization, presence of lichens or moss, cycles of wetting and drying, etc.). Regarding the use of metals, copper and bronze are widely present in the monuments considered. In addition, decorative objects of historic and artistic interest may include other metals such as iron and lead. Copper is a constituent element of the roof in eight cultural buildings and accounts for about 3% of the total outer surface. Bronze is mainly present in belfries in the form of bells. However, it was