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City scale assessment model for air pollution effects on the cultural heritage
Atmospheric Environment 45 (2011) 1242e1250
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City scale assessment model for air pollution effects on the cultural heritage D. de la Fuente a, *, J.M. Vega a, F. Viejo b, I. Díaz a, M. Morcillo a a b
National Centre for Metallurgical Research (CENIM/CSIC), Materials Engineering, Degradation and Durability, Avda. Gregorio del Amo 8, 28040-Madrid, Spain School of Chemical Engineering, Industrial University of Santander, Ciudad Universitaria, Carrera 27-Calle 9, Bucaramanga, Santander, Colombia
a r t i c l e i n f o
a b s t r a c t
Article history: Received 7 June 2010 Received in revised form 30 November 2010 Accepted 2 December 2010
Damage caused to objects of cultural heritage is one of the most serious detrimental effects of air pollutants. Within the 6th Framework Programme of the EU, the CULT-STRAT project is an inter-agency, multi-disciplinary project that has integrated research and monitoring information to provide answers to policy and management questions, which relate the effects of air pollutants on heritage and the management options available to mitigate them. The overall aim of the project has been to assess and predict the effects of different pollutants on materials and objects of cultural heritage in a multipollutant scenario and to identify indicators and thresholds levels of pollutants. These have been used for development of management strategies for sustainable maintenance and preventive conservation of European Cultural Heritage and air quality policy from continental to local scale. The present paper reports one of the studies carried out in the CULT-STRAT project at city level and focused on the town of Madrid (Spain). Different maps are shown for the present and possible future scenarios (2010 and 2020): inventory of stock of cultural heritage for each selected material, concentration of selected pollutants (SO2, NO2, O3 and PM10), corrosion (cast bronze) and recession (Portland limestone), exceedance of tolerable degradation thresholds for each material and corrosion-cultural heritage overlapped maps. Ó 2010 Elsevier Ltd. All rights reserved.
Keywords: Cultural heritage Air pollution Corrosivity Mapping
1. Introduction The costs for deterioration and soiling of different materials due to air pollution are huge and the damage to culture targets endangers seriously the rich European cultural heritage. Effective policy making requires environmental impact assessment, cost benefit analysis and risk management. All of these techniques need a sound scientific basis to underpin the assessment and the calculation of the effects of pollution. It is clear that there are two sets of end users that need reliable, up-to-date data on air quality and its effects on heritage e policy makers and local heritage owners or managers. The information that they require, though arising from the same sources (pollution monitoring, damage estimation and impact modelling), clearly needs interpretation at different scales. In this framework, the aim of CULT-STRAT (Cult Strat, 2010) has been to establish a scientific reference for developing strategies for policy and decision makers on European and national levels within the CAFE (Clean Air for Europe, 2010) Program and for decision makers and heritage managers for strategic decisions at a local level. It will do this
* Corresponding author. Tel.: þ34 915538900; fax: þ34 915347425. E-mail address: [email protected] (D. de la Fuente). 1352-2310/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.atmosenv.2010.12.011
through a choice of material indicators and pollution threshold levels based on best available scientific data including deterioration models, spatial distribution and mapping of pollutants and of stock of materials at risk, cost estimates and comparison studies of different conservation approaches. On the other hand, not only air pollution has effects on Cultural Heritage but also climate change has a significant influence. In this way, the Noah’s Ark Project (Sabbioni et al., 2010; Bonazza et al., 2009a,b; Brimblecombe et al., 2006) focused on the effects of climate change on Europe’s built heritage and cultural landscapes at different scenarios, highlighting how some processes of building decay will be accelerated or intensified by climate change, while others will be delayed. The main parameters were grouped as: (1) Temperature derived parameters (range, freeze thaw, thermal shock), (2) Water derived parameters (precipitation, humidity cycles, time of wetwess), (3) Wind derived parameters (wind, wind driven rain, sand and salt), (4) Pollution derived parameters (SO2, NO2, pH, etc.). The impact of climate change on monuments and historic buildings has been addressed for the first time, in terms of modelling and predicting. Within the Cult-Strat project (Watt et al., 2009), strategic actions to reach target values and to minimize corrosion costs have been evaluated. Methodologies for performing stock at risk studies of cultural heritage objects on different geographical scale have been
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developed. Inventories of stock at risk have been performed on European level (UNESCO World Heritage Sites), on country level (Italy, Czech Republic, Norway), on city level (Madrid, Milan), for parts of historical town areas (Paris, Venice, Rome) and for individual historic buildings. Mapping of damage and cost of cultural heritage at different pollution scenarios (past, present and different possible future) have been performed using both measured data and modeled future scenarios. For example, by joining together updated national data sets on pollution and climate for Germany, Czech Republic, Switzerland and Austria, and with the application of the developed doseeresponse functions within previous Projects: UNECE-ICP Materials (ICPMaterials, 2010), MULTI-ASSESS (Multi-Assess, 2010), it became possible to calculate and to produce corrosivity maps for zinc, carbon steel, copper, bronze and Portland limestone for the area covered by the four countries, representative for Central Europe. The models, that were validated and further developed within the project, take into account the present multi-pollutant situation, where apart of SO2 also NO2, O3 and PM10 are considered. They will permit and will be used for the ranking of the effects of different pollutants, which are deposited both by dry and wet deposition. This is especially important when taking into account the significant decreasing trends of SO2 levels but a constant trend or only slight decrease of PM10 and NO2 in many parts of Europe, which can increase the relative importance of these pollution parameters (Kucera et al., 2007; Sokhi and Kitwiroon, 2008). The doseeresponse functions, which describe the deterioration of the individual materials, are used for assessment of threshold levels of pollutants (Tidblad et al., 2001). With the same methodology as for the nationwide mapping, corrosivity maps for some important urban areas (Berlin, Paris, Madrid, Milan and Vienna) were also produced (Watt et al., 2009). Specifically, the present paper reports one of the studies carried out in the CULT-STRAT project at city level focused on the town of Madrid (Spain). This town is an important spotlight of cultural heritage with 260 Immovable Cultural Heritage objects (buildings such as palaces, churches, monasteries, etc.) and more than 1600 Movable Cultural Heritage objects exposed to the atmosphere (fountains, sculptures, etc.) declared of cultural interest by the Local Cultural Heritage Office. The study covers an inventory of Cultural Heritage and different distribution maps for the present and possible future scenarios (2010, 2020, etc.): inventories of stock of cultural heritage at risk for each selected material (cast bronze and Portland limestone), concentrations of selected pollutants (SO2, NO2, O3 and PM10),
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corrosivity and exceedance of tolerable degradation thresholds for each material, and corrosion-cultural heritage overlapped maps. These could be useful for management strategies for sustainable maintenance and preventive conservation of local Cultural Heritage. 2. Materials and methods 2.1. Inventory of cultural heritage For the development of the inventory of Cultural Heritage, all monuments, monumental sites, buildings and sculptures included in the Official Local List of Protected Cultural Heritage and exposed to the atmosphere were considered. This list considers two types of objects: 1. Immovable Cultural Heritage objects (buildings such as museums, churches, etc.). 260 objects are registered 2. Movable Cultural Heritage objects (sculptures, monoliths, fountains, etc) exposed to the atmosphere. Near to 1600 movable objects are registered, included in the Regional Movable Cultural Heritage List and in Madrid Council files, among others Microsoft Access Software was used, recording as main information the following fields: a) Inventory Number, b) Denomination (name of the object), c) Category (church, school, museum, sculpture, memorial stone, monolith, etc.), d) Address, e) X and Y UTM coordinates, f) Materials used in the construction of the building and g) Construction date. In most cases, the materials were very roughly described in the Official List. The missing information was obtained by consulting additional sources (books, guides, etc.). In the case of objects without any description of materials used, in-situ inspection was carried out. 2.2. Pollution database Historical environmental data at different places in Madrid have been collected. In this case, an open access was obtained to the Air Pollutants Database of the Council Service for Environmental
Fig. 1. Network of environmental control stations in Madrid city.
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Table 1 Doseeresponse functions for the multi-pollutant situation, including temperature function, for unsheltered cast bronze and Portland limestone exposed for one year. Units and abbreviations are described in the text. Material Doseeresponse function Temperature function Cast Bronze R ¼ 0.15 þ 0.000985[SO2]Rh60ef(T) þ 0.00465Rain[Hþ] þ 0.00432PM10 f(T) ¼ 0.060(T-11) when T < 11 C, 0.067(T-11) otherwise Portland limestone R ¼ 4.0 þ 0.0059[SO2]Rh60 þ 0.054Rain[Hþ] þ 0.078[HNO3]Rh60 þ 0.0258PM10
Information. Since 1978, this service supports 27 control stations that cover the extension of the town (Fig. 1), and offers daily and monthly average environmental data of air pollutants (SO2, O3, NO2, NOx, particulate matter,.), temperature, rain precipitation, relative humidity, etc. As consequence, maps of air pollutants concentration for different years in Madrid City (1995, 2000 and 2008) with good coverage were obtained. 2.3. Doseeresponse functions A doseeresponse function links the dose of pollution, measured in ambient concentration and/or deposition, to the rate of material corrosion. For unsheltered positions the materials damage is usually discussed in terms of dry and wet deposition. Wet deposition includes transport by means of precipitation and dry deposition transport by any other process (Mikhailov et al., 2004; Tidblad et al., 2002). Dose response functions for corrosion in the new pollution situation in Europe have been developed in the EU project MULTIASSESS (Multi-Assess, 2010) based on data obtained in the ICP Materials multi-pollutant exposure programme (see Table 1) (Kucera, 2004) Corrosion of cast bronze and degradation of Portland limestone is expressed as surface recession (R, mm). These functions include a range of pollution and climate parameters. The pollution parameters are the gases SO2, HNO3, and particulates as PM10, expressed in mg m3. The climatic parameters are temperature (T, C), amount of rain (Rain, mm), relative humidity (RH, %) and acidity in rain (Hþ, mg L1). The effect of relative humidity is introduced through the parameter Rh60, which is equal to (RH-60) when RH > 60, otherwise 0.
In our case, only the dose response functions for cast bronze and Portland limestone were considered and the spatial corrosion distribution maps of both materials in the city for different years were obtained. Only cast bronze and Portland limestone were considered because they are the most representative and the most widely used, metallic and stone material respectively, in the Cultural Heritage of the town. Cast bronze is present as main material in the 26% (422 objects) of the movable objects and Portland limestone is the main material in the 47% (122 objects) and 30% (485 objects) of the immovable and movable objects respectively. 2.4. Mapping Finally, and once obtained all the information needed, GIS (Geographic Information System) maps at different scenarios were developed: pollutants (SO2, O3, NO2, NOx, PM10, etc.), Cultural Heritage distribution (cast bronze and Portland limestone), corrosion (cast bronze and Portland limestone), overlapped corrosionCultural Heritage and tolerable-exceedance maps. In our case, the ArcGis 9.1 software with the Spatial Analyst Extension was used for the preparation of the maps by interpolation i.e. by predicting values for cells in a raster from a limited number of sample data points. The Kriging Interpolation method for representing data (pollutants concentration, corrosion, etc.) in the map was employed, considering a grid cell size of 500 by 500 meters. Specifically, the Ordinary Kriging model, which is the most general and widely used of the Kriging methods and which assumes the constant mean is unknown, was used. The semivariogram model selected was the spherical and the search radius was variable. With a variable search radius, the number of points used in calculating the value of the interpolated cell is specified (12 points in our case), which makes the radius distance vary for each interpolated cell, depending on how far it has to search around each interpolated cell to reach the specified number of input points. Thus, some neighborhoods can be small and others can be large, depending on the density of the measured points near the interpolated cell. 3. Results and discussion 3.1. Cultural heritage maps As an example of the produced maps, the spatial distribution of the Movable Cultural Heritage of Madrid town is shown in Fig. 2
Fig. 2. Spatial distribution map of Cultural Heritage objects (left) and a zoom in of an area at the city centre where buildings are represented in red and other objects as yellow stars (right).
D. de la Fuente et al. / Atmospheric Environment 45 (2011) 1242e1250
(left). As expected, the concentration of artifacts decreases with the distance to the centre. One of the advantages of the use of GIS tools is the possibility of presenting data and associated attributes in a dynamic mode, i.e. it is possible to zoom in a specific area, present only data that match certain criteria in the database, etc. As an example, the Fig. 2 (right) shows the distribution of Cultural Heritage objects in the city centre. 3.2. Pollutants maps As an example of the developed maps with the database of pollution (data obtained from the local network of environmental stations shown in Fig. 1) the distribution maps of SO2, NO2 and PM10 in years 2000 and 2008 are shown in Fig. 3. As can be observed, SO2 concentrations decreased drastically, almost 50%, in most areas of the city and the highest values (city centre) are always lower than 15 mg m3. Anyway, this is still a high value compared to SO2 concentrations in most European cities according to the measured data in 2008 at the 420 traffic sites of the Airbase database of the European Environment Agency (Amsterdam: 2.3 mg m3, Brussels: 3.9 mg m3, Berlin: 2.7 mg m3, London: 3.5e7 mg m3, Dublin: 0.7 mg m3, Lisbon: 1.4 mg m3, etc.) (AIRBASE, 2008). On the other hand, less significant differences have been observed in case of NO2 and PM10. It is worth noting that in this period, PM10 has slightly decreased in most parts of the city but has increased in the nearest areas to the airport and the centre of the city (north-south central axis). 3.3. Corrosion/recession maps By means of the application of the Multi-Assess doseeresponse functions (Table 1) to each cell of the grid (500 500 m), once the environmental parameters needed were obtained from the network of test sites (Fig. 1), and with the help of the Kriging Interpolation method, the corrosion map for cast bronze and surface recession for Portland limestone at different years were obtained. Some examples are shown in Fig. 4, where a significant reduction of both, corrosion and recession, from 1995 to 2008 can
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be observed. As can be seen, the Kriging standard deviation in all cases is always lower than 6% and therefore the errors of the calculated corrosion values could be considered acceptable. 3.4. Overlapped corrosion/cultural heritage maps Finally, the combination of the corrosion (cast bronze) or recession (Portland limestone) maps with the Cultural Heritage database, where information concerning the location and materials used for each object is included, made possible the preparation of different overlapped maps. As examples, annual mass loss of cast bronze-movable cultural heritage made of bronze and recession of Portland limestone-immovable cultural heritage made of this material are shown in Fig. 5 upper and lower respectively. 3.5. Stock at risk When assessing target levels of corrosion for policy purposes the status of the object cannot be a parameter and a uniform approach is needed. If the approach in the UN/ECE Mapping Manual is applied to tolerable levels, the tolerable corrosion rate, first year exposure (Ktol) can be calculated as:
Ktol ¼ nKb
(1)
where n is a factor and Kb is the background corrosion rate, first year exposure for Europe. The tolerable corrosion rate has to be based on experiences from restoration work and can be calculated from two important components: a) the “tolerable corrosion before action”, based on the stage of deterioration when the restoration must start and b) the “tolerable time between maintenance”, based on how often it is acceptable to restore the object. As an example of the compiled experience in the Multi-Assess Project (Multi-Assess, 2010) from the restoration work, the data relevant for old cultural heritage materials are given in Table 2. As can be seen, this tolerable corrosion rates estimated based on maintenance intervals and tolerable corrosion attack before maintenance for cultural heritage
Fig. 3. SO2, NO2 and PM10 levels in 2000 and 2008.
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Fig. 4. Corrosion (left) and recession (right) maps obtained from cast bronze and Portland limestone doseeresponse functions respectively in 1995 (upper) and 2008 (lower).
objects are close to 2.5 times the background corrosion values showed in Table 3, therefore a factor n ¼ 2.5 can be defined for tolerable corrosion rates. In Table 3 the tolerable corrosion rate, first year exposure, for the most common materials are shown for n ¼ 2.5. The tolerable corrosion rates given in Table 3 are those used for further assessment of target levels and is thus considered a conservative lower estimate of the tolerable level. From the tolerable corrosion rate, the corresponding acceptable pollution concentrations can be calculated by using the available doseeresponse equations. On the other hand, based on the tolerable corrosion rates given in Table 3 and the real measured or estimated corrosion rates, it is possible to establish if individual sites have conditions that can be classified as tolerable or exceedance. In the case of bronze in Madrid, as can be observed in Fig. 4 (left), the predicted corrosion levels in 2008 from the doseeresponse function are in the range 0.25e0.33 mm, always lower than the tolerable level (0.6 mm). The same conclusion can be drawn in the case of Portland limestone (Fig. 4, right), where recession levels are in the range 4.5e5.3 mm, once again lower than the tolerable level (8.0 mm). These results show that the risk for the Cultural Heritage in Madrid, from the corrosion point of view is low and of course much lower than in most European cities (London: 0.9 mm and 9 mm for cast bronze and Portland limestone respectively, Lisbon: 0.6 mm and 10.5 mm, Rome: 0.6 mm and 6.5 mm, Moscow: 0.4 mm and 8 mm, Oslo: 0.4 mm and 7.5 mm, Stockholm: 0.5 mm and 7.5 mm, etc.) (ICPMaterials, 2010; Multi-Assess, 2010). As can be observed, the comparison of the predicted corrosion levels from the dosee response function in 2008 (0.25e0.33 mm and 4.5e5.3 mm for cast bronze and Portland limestone respectively) and the actual measured values (0.37 mm and 3.91 mm for cast bronze and Portland limestone respectively) confirms the validity of the function for this region. It is important to note, that the main reason for the low corrosion in Madrid may be is not related to pollution but to the low humidity levels (around 60% of RH). The parameter Rh60 is RH-60
when RH > 60 otherwise is “0”, therefore, as can be observed in both doseeresponse functions (Table 1), when RH 60, the effect of SO2, and also HNO3 in case of Portland limestone, is not taken into account in the functions because when this occurs the parameter RH60 is “0”. Then, the calculated corrosion, and also the real corrosion rate measured in Madrid, is low regardless SO2 and HNO3 concentrations, even when RH is slightly higher than 60% due to the low value of RH-60. This is the reason why in a dry climate more pollution could be tolerated. According to these results, as can be observed in Fig. 5, all Cultural Heritage objects are located in areas where corrosion or recession rates are lower than the maximum tolerable. Anyway, the methodology developed could be useful if apply it to towns, regions or countries in order to quantify the percentage of Cultural Heritage at risk by means of the overlapped (corrosionCultural Heritage) maps and taking into account the established tolerable levels. Additionally, although the corrosion or recession rates are lower than the maximum tolerable values, it does not mean complete absence of degradation. During the in-situ inspections of the monuments carried out in order to prepare the Cultural Heritage database, a general good condition of the materials was observed due to the low corrosion rates but also for the importance of the restoration/maintenance works carried out, especially during the last decades of the 20th Century. In spite of that, some slight problems were also detected and therefore, maintenance is always necessary even at tolerable intervals. Management of heritage at local level is clearly complex and can require both reactive and proactive interventions. Anyway, it is clear that all future conservation and maintenance strategies should take into account the concept of sustainability. In that way, at was stated within the CultStrat project, buildings and monuments should be considered within the context of the overall built heritage and so repair and restoration should be seen as a conservation project within an overall conservation plan which draws on an underlying conservation philosophy. The key considerations for a conservation philosophy can be summarized as:
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Table 3 Tolerable corrosion rate based on background corrosion rates and n ¼ 2.5. Material
Background corrosion
Background corrosion/ recession depth
Factor for acceptable corrosion/ recession
Tolerable corrosion/ recession rate per year
Zinc
3.1 g m2
0.46 mm
2.5
Copper
2.8 g m2
0.34 mm
2.5
2
0.25 mm
2.5
3.2 mm 2.8 mm
2.5 2.5
7.8 g m2 1.1 mm 7.1 g m2 0.8 mm 5.25 g m2 0.6 mm 8.0 mm 7.0 mm
Cast Bronze Portland Limestone White Mansfield dolomitic sandstone
2.1 g m
- Conservation and restoration must have recourse to all the sciences and techniques which can contribute to the study and safeguarding of the architectural heritage. - Restoration and refurbishment should be based on a programme of “minimum intervention” whilst taking into account the need to balance the costs of such work and the disruption of activities on the site. Wherever possible interventions should be reversible, that is that they can reversed at a later date, for example if a better solution becomes available at some future date.
3.6. Tolerable and exceedance maps (n-factor maps)
Fig. 5. Overlapped map: corrosion of cast bronze-movable cultural heritage made of bronze in 2008 (upper) and recession of Portland limestone-immovable cultural heritage made of this material in 2008 (lower).
- An holistic approach: the buildings and their setting needs to be considered as an entity. - The historic environment must allow for new architecture and modern life-styles but with a presumption in favour of preservation.
Table 2 Tolerable corrosion rate based on tolerable corrosion before action and tolerable time between maintenance. Material
Type of surface
Tolerable Tolerable Tolerable corrosion time between corrosion before maintenance rate action
Portland Limestone Ornament, aged 100 mm Ornament, corroded 50 mm
12 years 6 years
8.3 mm y1 8.3 mm y1
Copper monument Ornament, aged 50 mm Ornament, corroded 10 mm
50 years 20 years
1.0 mm y1 0.5 mm y1
Bronze monument Ornament, aged 50 mm Ornament, corroded 10 mm
50 years 15 years
1.0 mm y1 0.7 mm y1
80 mm
50 years
1.6 mm y1
Zinc monument
Evenly corroded
As explained before, although Madrid case is not a good example for quantification of areas where corrosion/recession levels are tolerable or exceeds the maximum tolerable (Ktol ¼ 2.5Kb), i.e. (0.6 mm) in the case of cast bronze and 8.0 mm in the case of Portland limestone, n-factor maps have been also developed (Fig. 6). As can be observed, in 2008 the predicted corrosion of bronze from the doseeresponse function is in the range n ¼ 1.0e1.5 times the background level and the recession of Portland limestone in the range n ¼ 1.0e2.0 times the background level, always lower than the tolerable n ¼ 2.5. However, these maps could be useful if apply it to other towns, regions or countries in order to quantify the percentage of the area where corrosion/ recession exceeds 2.5Kb. 3.7. Future scenarios In order to analyze future scenarios climate and pollution evolution should be taken into account because both parameters have notable influence in the materials degradation, as it is described in the doseeresponse functions. Regarding the effect of climate change, the predictions of the Noah’s Ark project for both, near and far future, are a decrease in annual precipitation in Southern Europe (Sabbioni et al., 2010). Temperature and relative humidity were not specifically mapped but in principle the predictions seems to indicate a slightly increase in case of temperature and a slightly decrease of the relative humidity in Southern Europe. Although the Atlas claims that the models are not necessary true in the case of local sites, because at local scale many other considerations should be taken into account, the most probable situation in Madrid would be a slight increase in case of temperature, a slight decrease of the relative humidity and a slight decrease in precipitation. All those trends would always drive to a lower corrosion rate. Therefore, from the climatic point of view, the worst case future scenario would be to keep constant in
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Fig. 6. n-factor maps for cast bronze (left) and Portland limestone (right).
Fig. 7. Predicted cast bronze corrosion in 2010 and 2020 for different future scenarios.
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Fig. 8. Predicted Portland limestone recession in 2010 and 2020 for different future scenarios.
the predictions both, temperature and relative humidity and consider only the extra beneficial effect of pollution. Therefore, a study consisted in the estimation of the levels of corrosion and recession for cast bronze and Portland limestone in 2010 and 2020 was also carried out considering RH and T always constant and two possible different future scenarios regarding pollution: 1. A neutral trend during the period 2008e2020 (following the same trend than the observed in the period 1995e2008). 2. An optimistic trend during the period 2008e2020 (following a 10% higher reduction of mass loss and recession from 2008 to 2010, and the same reduction from 2010 to 2020). In Figs. 7 and 8 the maps for cast bronze and Portland limestone respectively are shown. As can be observed the annual mass loss and recession could be in 2020 very close to the background values (0.24 mm and 3.2 mm). 4. Conclusions Different maps have been developed: inventory of stock of cultural heritage at risk for each selected material (cast bronze and Portland limestone), selected pollutants (SO2, NO2, O3 and PM10), corrosivity for each material (by the application of doseeresponse functions), corrosion-Cultural Heritage overlapped maps, exceedance maps and future scenarios. The risk for the Cultural Heritage in Madrid, from the corrosion point of view due to pollution, is lower than in most cities of Central and North Europe, being the prediction of cast bronze corrosion and Portland limestone recession always lower than
the previously established tolerable levels for those materials. Nevertheless, maintenance/restoration is always necessary even at tolerable intervals and all future strategies should take into account the concepts of sustainablility and conservation philosophy. Anyway, the model and the methodology developed could be useful if apply it to towns, regions or countries in order to quantify the percentage of Cultural Heritage at risk or to quantify the percentage of the area where corrosion/recession exceeds the tolerable levels (2.5Kb). Acknowledgements The authors of this paper would like to thank the European Community 6th Framework Programme (CULT-STRAT: Specific Targeted Research Project, STREP, SSPI-CT-2004-501609) and the Ministry of Science and Innovation of Spain (MAT2005-23937-E) for the financial support. They thank also the Petrology Research Group of Miner Engineering School of Madrid and the municipal authorities for the help offered during the elaboration of the inventory of Cultural Heritage, as well as, the free access to the pollution and Cultural Heritage databases. References AIRBASE, 2008. Air Quality Data. European Environment Agency. http://www.eea. europa.eu/themes/air/airbase/map-statistics (2010). Bonazza, A., Messina, P., Sabbioni, C., Grossi, C.M., Brimblecombe, P., 2009a. Mapping the impact of climate change on surface recession of carbonate buildings in Europe. Science of the Total Environment 407, 2039e2050. Bonazza, A., Sabbioni, C., Messina, P., Guaraldi, C., De Nuntiis, P., 2009b. Climate change impact: mapping thermal stress on Carrara marble in Europe. Science of the Total Environment 407, 4506e4512.
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Brimblecombe, P., Grossi, C.M., Harris, J., 2006. Climate change critical to cultural heritage. In: Fort, R., et al. (Eds.), Heritage, Weathering and Conservation. Taylor and Francis Group, London, pp. 387e393. Clean air for Europe (CAFE), 2010. http://europa.eu/legislation_summaries/ environment/air_pollution/l28026_en.htm. Cult Strat, 2010. Assessment of air pollution effects on cultural heritage e management strategies, the CULT-STRAT project. http://www.corr-institute.se/ cultstrat/web/page.aspx. ICP-Materials, 2010. International cooperative programme on effects on materials, including historic and cultural monuments, convention on long-range transbondary air pollution (CLRTAP), United Nations Economic Commission for Europe (UN ECE). http://www.corr-institute.se/ICP-Materials/. Kucera, V., 2004. Chapter 4: mapping of effects on materials. In: Kucera, V. (Ed.), Manual on Methodologies and Criteria for Modeling and Mapping Critical Loads and Levels and Air Pollution Effects, Risks and Trends. UNECE convention on Long-Range Transbondary Air Pollution (CLRTAP), Geneva, pp. IV-1eIV-10. Kucera, V., Tidblad, J., Kreislova, K., Knotkova, D., Faller, M., Snethlage, R., Yates, T., Henriksen, J., Schreiner, M., Ferm, M., Lefèvre, R.A., Kobus. J., 2007. The UN/ECE ICP Materials multi-pollutant exposure on effects on materials including historic and cultural monuments. Acid Rain 2005 Conference, Prague, 12e17 June 2007.
Mikhailov, A.A., Tidblad, J., Kucera, V., 2004. The classification system of ISO 9223 standard and the doseeresponse functions assessing the corrosivity of outdoor atmospheres. Protection of Metals 40 (6), 541e550. Multi-Assess, 2010. Model for multi-pollutant impact and assessment of threshold levels for cultural heritage, MULTI-ASSESS project. http://www.corr-institute. se/MULTI-ASSESS/. Sabbioni, C., Brimblecombe, P., Cassar, C. (Eds.), 2010. The Atlas of Climate Change Impact on European Cultural Heritage. Scientific Analysis and Management Strategies. Anthem Press, London, p. 146. Sokhi, R.S., Kitwiroon, N., 2008. Air pollution in urban areas. In: Sokhi, R.S. (Ed.), World Atlas of Atmospheric Pollution. Anthem Press, London, pp. 19e34. Tidblad, J., Kucera, V., Mikhailov, A.A., Henriksen, J., Kreislova, K., Yates, T., Stöckle, B., Schreiner, M., 2001. UN ECE ICP materials: doseeresponse functions on dry and wet acid deposition effects after 8 years of exposure. Water, Air and Soil Pollution 130 (1e4), 1457e1462. Tidblad, J., Kucera, V., Mikhailov, A.A., Kreislova, K., 2002. Improvement of the ISO classification system based on doseeresponse functions describing the corrosivity of outdoor atmospheres. In: Townsend, H.E. (Ed.), Outdoor and Indoor Atmospheric Corrosion. American Society For Testing and Materials (ASTM), West Conshohocken (PA), pp. 73e87. Special Technical Publication ASTM STP 1421. Watt, J., Tidblad, J., Kucera, V., Hamilton, R. (Eds.), 2009. The Effects of Air Pollution on Cultural Heritage. Springer, New York, p. 306.
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City scale assessment model for air pollution effects on the cultural heritage D. de la Fuente a, *, J.M. Vega a, F. Viejo b, I. Díaz a, M. Morcillo a a b
National Centre for Metallurgical Research (CENIM/CSIC), Materials Engineering, Degradation and Durability, Avda. Gregorio del Amo 8, 28040-Madrid, Spain School of Chemical Engineering, Industrial University of Santander, Ciudad Universitaria, Carrera 27-Calle 9, Bucaramanga, Santander, Colombia
a r t i c l e i n f o
a b s t r a c t
Article history: Received 7 June 2010 Received in revised form 30 November 2010 Accepted 2 December 2010
Damage caused to objects of cultural heritage is one of the most serious detrimental effects of air pollutants. Within the 6th Framework Programme of the EU, the CULT-STRAT project is an inter-agency, multi-disciplinary project that has integrated research and monitoring information to provide answers to policy and management questions, which relate the effects of air pollutants on heritage and the management options available to mitigate them. The overall aim of the project has been to assess and predict the effects of different pollutants on materials and objects of cultural heritage in a multipollutant scenario and to identify indicators and thresholds levels of pollutants. These have been used for development of management strategies for sustainable maintenance and preventive conservation of European Cultural Heritage and air quality policy from continental to local scale. The present paper reports one of the studies carried out in the CULT-STRAT project at city level and focused on the town of Madrid (Spain). Different maps are shown for the present and possible future scenarios (2010 and 2020): inventory of stock of cultural heritage for each selected material, concentration of selected pollutants (SO2, NO2, O3 and PM10), corrosion (cast bronze) and recession (Portland limestone), exceedance of tolerable degradation thresholds for each material and corrosion-cultural heritage overlapped maps. Ó 2010 Elsevier Ltd. All rights reserved.
Keywords: Cultural heritage Air pollution Corrosivity Mapping
1. Introduction The costs for deterioration and soiling of different materials due to air pollution are huge and the damage to culture targets endangers seriously the rich European cultural heritage. Effective policy making requires environmental impact assessment, cost benefit analysis and risk management. All of these techniques need a sound scientific basis to underpin the assessment and the calculation of the effects of pollution. It is clear that there are two sets of end users that need reliable, up-to-date data on air quality and its effects on heritage e policy makers and local heritage owners or managers. The information that they require, though arising from the same sources (pollution monitoring, damage estimation and impact modelling), clearly needs interpretation at different scales. In this framework, the aim of CULT-STRAT (Cult Strat, 2010) has been to establish a scientific reference for developing strategies for policy and decision makers on European and national levels within the CAFE (Clean Air for Europe, 2010) Program and for decision makers and heritage managers for strategic decisions at a local level. It will do this
* Corresponding author. Tel.: þ34 915538900; fax: þ34 915347425. E-mail address: [email protected] (D. de la Fuente). 1352-2310/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.atmosenv.2010.12.011
through a choice of material indicators and pollution threshold levels based on best available scientific data including deterioration models, spatial distribution and mapping of pollutants and of stock of materials at risk, cost estimates and comparison studies of different conservation approaches. On the other hand, not only air pollution has effects on Cultural Heritage but also climate change has a significant influence. In this way, the Noah’s Ark Project (Sabbioni et al., 2010; Bonazza et al., 2009a,b; Brimblecombe et al., 2006) focused on the effects of climate change on Europe’s built heritage and cultural landscapes at different scenarios, highlighting how some processes of building decay will be accelerated or intensified by climate change, while others will be delayed. The main parameters were grouped as: (1) Temperature derived parameters (range, freeze thaw, thermal shock), (2) Water derived parameters (precipitation, humidity cycles, time of wetwess), (3) Wind derived parameters (wind, wind driven rain, sand and salt), (4) Pollution derived parameters (SO2, NO2, pH, etc.). The impact of climate change on monuments and historic buildings has been addressed for the first time, in terms of modelling and predicting. Within the Cult-Strat project (Watt et al., 2009), strategic actions to reach target values and to minimize corrosion costs have been evaluated. Methodologies for performing stock at risk studies of cultural heritage objects on different geographical scale have been
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developed. Inventories of stock at risk have been performed on European level (UNESCO World Heritage Sites), on country level (Italy, Czech Republic, Norway), on city level (Madrid, Milan), for parts of historical town areas (Paris, Venice, Rome) and for individual historic buildings. Mapping of damage and cost of cultural heritage at different pollution scenarios (past, present and different possible future) have been performed using both measured data and modeled future scenarios. For example, by joining together updated national data sets on pollution and climate for Germany, Czech Republic, Switzerland and Austria, and with the application of the developed doseeresponse functions within previous Projects: UNECE-ICP Materials (ICPMaterials, 2010), MULTI-ASSESS (Multi-Assess, 2010), it became possible to calculate and to produce corrosivity maps for zinc, carbon steel, copper, bronze and Portland limestone for the area covered by the four countries, representative for Central Europe. The models, that were validated and further developed within the project, take into account the present multi-pollutant situation, where apart of SO2 also NO2, O3 and PM10 are considered. They will permit and will be used for the ranking of the effects of different pollutants, which are deposited both by dry and wet deposition. This is especially important when taking into account the significant decreasing trends of SO2 levels but a constant trend or only slight decrease of PM10 and NO2 in many parts of Europe, which can increase the relative importance of these pollution parameters (Kucera et al., 2007; Sokhi and Kitwiroon, 2008). The doseeresponse functions, which describe the deterioration of the individual materials, are used for assessment of threshold levels of pollutants (Tidblad et al., 2001). With the same methodology as for the nationwide mapping, corrosivity maps for some important urban areas (Berlin, Paris, Madrid, Milan and Vienna) were also produced (Watt et al., 2009). Specifically, the present paper reports one of the studies carried out in the CULT-STRAT project at city level focused on the town of Madrid (Spain). This town is an important spotlight of cultural heritage with 260 Immovable Cultural Heritage objects (buildings such as palaces, churches, monasteries, etc.) and more than 1600 Movable Cultural Heritage objects exposed to the atmosphere (fountains, sculptures, etc.) declared of cultural interest by the Local Cultural Heritage Office. The study covers an inventory of Cultural Heritage and different distribution maps for the present and possible future scenarios (2010, 2020, etc.): inventories of stock of cultural heritage at risk for each selected material (cast bronze and Portland limestone), concentrations of selected pollutants (SO2, NO2, O3 and PM10),
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corrosivity and exceedance of tolerable degradation thresholds for each material, and corrosion-cultural heritage overlapped maps. These could be useful for management strategies for sustainable maintenance and preventive conservation of local Cultural Heritage. 2. Materials and methods 2.1. Inventory of cultural heritage For the development of the inventory of Cultural Heritage, all monuments, monumental sites, buildings and sculptures included in the Official Local List of Protected Cultural Heritage and exposed to the atmosphere were considered. This list considers two types of objects: 1. Immovable Cultural Heritage objects (buildings such as museums, churches, etc.). 260 objects are registered 2. Movable Cultural Heritage objects (sculptures, monoliths, fountains, etc) exposed to the atmosphere. Near to 1600 movable objects are registered, included in the Regional Movable Cultural Heritage List and in Madrid Council files, among others Microsoft Access Software was used, recording as main information the following fields: a) Inventory Number, b) Denomination (name of the object), c) Category (church, school, museum, sculpture, memorial stone, monolith, etc.), d) Address, e) X and Y UTM coordinates, f) Materials used in the construction of the building and g) Construction date. In most cases, the materials were very roughly described in the Official List. The missing information was obtained by consulting additional sources (books, guides, etc.). In the case of objects without any description of materials used, in-situ inspection was carried out. 2.2. Pollution database Historical environmental data at different places in Madrid have been collected. In this case, an open access was obtained to the Air Pollutants Database of the Council Service for Environmental
Fig. 1. Network of environmental control stations in Madrid city.
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Table 1 Doseeresponse functions for the multi-pollutant situation, including temperature function, for unsheltered cast bronze and Portland limestone exposed for one year. Units and abbreviations are described in the text. Material Doseeresponse function Temperature function Cast Bronze R ¼ 0.15 þ 0.000985[SO2]Rh60ef(T) þ 0.00465Rain[Hþ] þ 0.00432PM10 f(T) ¼ 0.060(T-11) when T < 11 C, 0.067(T-11) otherwise Portland limestone R ¼ 4.0 þ 0.0059[SO2]Rh60 þ 0.054Rain[Hþ] þ 0.078[HNO3]Rh60 þ 0.0258PM10
Information. Since 1978, this service supports 27 control stations that cover the extension of the town (Fig. 1), and offers daily and monthly average environmental data of air pollutants (SO2, O3, NO2, NOx, particulate matter,.), temperature, rain precipitation, relative humidity, etc. As consequence, maps of air pollutants concentration for different years in Madrid City (1995, 2000 and 2008) with good coverage were obtained. 2.3. Doseeresponse functions A doseeresponse function links the dose of pollution, measured in ambient concentration and/or deposition, to the rate of material corrosion. For unsheltered positions the materials damage is usually discussed in terms of dry and wet deposition. Wet deposition includes transport by means of precipitation and dry deposition transport by any other process (Mikhailov et al., 2004; Tidblad et al., 2002). Dose response functions for corrosion in the new pollution situation in Europe have been developed in the EU project MULTIASSESS (Multi-Assess, 2010) based on data obtained in the ICP Materials multi-pollutant exposure programme (see Table 1) (Kucera, 2004) Corrosion of cast bronze and degradation of Portland limestone is expressed as surface recession (R, mm). These functions include a range of pollution and climate parameters. The pollution parameters are the gases SO2, HNO3, and particulates as PM10, expressed in mg m3. The climatic parameters are temperature (T, C), amount of rain (Rain, mm), relative humidity (RH, %) and acidity in rain (Hþ, mg L1). The effect of relative humidity is introduced through the parameter Rh60, which is equal to (RH-60) when RH > 60, otherwise 0.
In our case, only the dose response functions for cast bronze and Portland limestone were considered and the spatial corrosion distribution maps of both materials in the city for different years were obtained. Only cast bronze and Portland limestone were considered because they are the most representative and the most widely used, metallic and stone material respectively, in the Cultural Heritage of the town. Cast bronze is present as main material in the 26% (422 objects) of the movable objects and Portland limestone is the main material in the 47% (122 objects) and 30% (485 objects) of the immovable and movable objects respectively. 2.4. Mapping Finally, and once obtained all the information needed, GIS (Geographic Information System) maps at different scenarios were developed: pollutants (SO2, O3, NO2, NOx, PM10, etc.), Cultural Heritage distribution (cast bronze and Portland limestone), corrosion (cast bronze and Portland limestone), overlapped corrosionCultural Heritage and tolerable-exceedance maps. In our case, the ArcGis 9.1 software with the Spatial Analyst Extension was used for the preparation of the maps by interpolation i.e. by predicting values for cells in a raster from a limited number of sample data points. The Kriging Interpolation method for representing data (pollutants concentration, corrosion, etc.) in the map was employed, considering a grid cell size of 500 by 500 meters. Specifically, the Ordinary Kriging model, which is the most general and widely used of the Kriging methods and which assumes the constant mean is unknown, was used. The semivariogram model selected was the spherical and the search radius was variable. With a variable search radius, the number of points used in calculating the value of the interpolated cell is specified (12 points in our case), which makes the radius distance vary for each interpolated cell, depending on how far it has to search around each interpolated cell to reach the specified number of input points. Thus, some neighborhoods can be small and others can be large, depending on the density of the measured points near the interpolated cell. 3. Results and discussion 3.1. Cultural heritage maps As an example of the produced maps, the spatial distribution of the Movable Cultural Heritage of Madrid town is shown in Fig. 2
Fig. 2. Spatial distribution map of Cultural Heritage objects (left) and a zoom in of an area at the city centre where buildings are represented in red and other objects as yellow stars (right).
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(left). As expected, the concentration of artifacts decreases with the distance to the centre. One of the advantages of the use of GIS tools is the possibility of presenting data and associated attributes in a dynamic mode, i.e. it is possible to zoom in a specific area, present only data that match certain criteria in the database, etc. As an example, the Fig. 2 (right) shows the distribution of Cultural Heritage objects in the city centre. 3.2. Pollutants maps As an example of the developed maps with the database of pollution (data obtained from the local network of environmental stations shown in Fig. 1) the distribution maps of SO2, NO2 and PM10 in years 2000 and 2008 are shown in Fig. 3. As can be observed, SO2 concentrations decreased drastically, almost 50%, in most areas of the city and the highest values (city centre) are always lower than 15 mg m3. Anyway, this is still a high value compared to SO2 concentrations in most European cities according to the measured data in 2008 at the 420 traffic sites of the Airbase database of the European Environment Agency (Amsterdam: 2.3 mg m3, Brussels: 3.9 mg m3, Berlin: 2.7 mg m3, London: 3.5e7 mg m3, Dublin: 0.7 mg m3, Lisbon: 1.4 mg m3, etc.) (AIRBASE, 2008). On the other hand, less significant differences have been observed in case of NO2 and PM10. It is worth noting that in this period, PM10 has slightly decreased in most parts of the city but has increased in the nearest areas to the airport and the centre of the city (north-south central axis). 3.3. Corrosion/recession maps By means of the application of the Multi-Assess doseeresponse functions (Table 1) to each cell of the grid (500 500 m), once the environmental parameters needed were obtained from the network of test sites (Fig. 1), and with the help of the Kriging Interpolation method, the corrosion map for cast bronze and surface recession for Portland limestone at different years were obtained. Some examples are shown in Fig. 4, where a significant reduction of both, corrosion and recession, from 1995 to 2008 can
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be observed. As can be seen, the Kriging standard deviation in all cases is always lower than 6% and therefore the errors of the calculated corrosion values could be considered acceptable. 3.4. Overlapped corrosion/cultural heritage maps Finally, the combination of the corrosion (cast bronze) or recession (Portland limestone) maps with the Cultural Heritage database, where information concerning the location and materials used for each object is included, made possible the preparation of different overlapped maps. As examples, annual mass loss of cast bronze-movable cultural heritage made of bronze and recession of Portland limestone-immovable cultural heritage made of this material are shown in Fig. 5 upper and lower respectively. 3.5. Stock at risk When assessing target levels of corrosion for policy purposes the status of the object cannot be a parameter and a uniform approach is needed. If the approach in the UN/ECE Mapping Manual is applied to tolerable levels, the tolerable corrosion rate, first year exposure (Ktol) can be calculated as:
Ktol ¼ nKb
(1)
where n is a factor and Kb is the background corrosion rate, first year exposure for Europe. The tolerable corrosion rate has to be based on experiences from restoration work and can be calculated from two important components: a) the “tolerable corrosion before action”, based on the stage of deterioration when the restoration must start and b) the “tolerable time between maintenance”, based on how often it is acceptable to restore the object. As an example of the compiled experience in the Multi-Assess Project (Multi-Assess, 2010) from the restoration work, the data relevant for old cultural heritage materials are given in Table 2. As can be seen, this tolerable corrosion rates estimated based on maintenance intervals and tolerable corrosion attack before maintenance for cultural heritage
Fig. 3. SO2, NO2 and PM10 levels in 2000 and 2008.
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Fig. 4. Corrosion (left) and recession (right) maps obtained from cast bronze and Portland limestone doseeresponse functions respectively in 1995 (upper) and 2008 (lower).
objects are close to 2.5 times the background corrosion values showed in Table 3, therefore a factor n ¼ 2.5 can be defined for tolerable corrosion rates. In Table 3 the tolerable corrosion rate, first year exposure, for the most common materials are shown for n ¼ 2.5. The tolerable corrosion rates given in Table 3 are those used for further assessment of target levels and is thus considered a conservative lower estimate of the tolerable level. From the tolerable corrosion rate, the corresponding acceptable pollution concentrations can be calculated by using the available doseeresponse equations. On the other hand, based on the tolerable corrosion rates given in Table 3 and the real measured or estimated corrosion rates, it is possible to establish if individual sites have conditions that can be classified as tolerable or exceedance. In the case of bronze in Madrid, as can be observed in Fig. 4 (left), the predicted corrosion levels in 2008 from the doseeresponse function are in the range 0.25e0.33 mm, always lower than the tolerable level (0.6 mm). The same conclusion can be drawn in the case of Portland limestone (Fig. 4, right), where recession levels are in the range 4.5e5.3 mm, once again lower than the tolerable level (8.0 mm). These results show that the risk for the Cultural Heritage in Madrid, from the corrosion point of view is low and of course much lower than in most European cities (London: 0.9 mm and 9 mm for cast bronze and Portland limestone respectively, Lisbon: 0.6 mm and 10.5 mm, Rome: 0.6 mm and 6.5 mm, Moscow: 0.4 mm and 8 mm, Oslo: 0.4 mm and 7.5 mm, Stockholm: 0.5 mm and 7.5 mm, etc.) (ICPMaterials, 2010; Multi-Assess, 2010). As can be observed, the comparison of the predicted corrosion levels from the dosee response function in 2008 (0.25e0.33 mm and 4.5e5.3 mm for cast bronze and Portland limestone respectively) and the actual measured values (0.37 mm and 3.91 mm for cast bronze and Portland limestone respectively) confirms the validity of the function for this region. It is important to note, that the main reason for the low corrosion in Madrid may be is not related to pollution but to the low humidity levels (around 60% of RH). The parameter Rh60 is RH-60
when RH > 60 otherwise is “0”, therefore, as can be observed in both doseeresponse functions (Table 1), when RH 60, the effect of SO2, and also HNO3 in case of Portland limestone, is not taken into account in the functions because when this occurs the parameter RH60 is “0”. Then, the calculated corrosion, and also the real corrosion rate measured in Madrid, is low regardless SO2 and HNO3 concentrations, even when RH is slightly higher than 60% due to the low value of RH-60. This is the reason why in a dry climate more pollution could be tolerated. According to these results, as can be observed in Fig. 5, all Cultural Heritage objects are located in areas where corrosion or recession rates are lower than the maximum tolerable. Anyway, the methodology developed could be useful if apply it to towns, regions or countries in order to quantify the percentage of Cultural Heritage at risk by means of the overlapped (corrosionCultural Heritage) maps and taking into account the established tolerable levels. Additionally, although the corrosion or recession rates are lower than the maximum tolerable values, it does not mean complete absence of degradation. During the in-situ inspections of the monuments carried out in order to prepare the Cultural Heritage database, a general good condition of the materials was observed due to the low corrosion rates but also for the importance of the restoration/maintenance works carried out, especially during the last decades of the 20th Century. In spite of that, some slight problems were also detected and therefore, maintenance is always necessary even at tolerable intervals. Management of heritage at local level is clearly complex and can require both reactive and proactive interventions. Anyway, it is clear that all future conservation and maintenance strategies should take into account the concept of sustainability. In that way, at was stated within the CultStrat project, buildings and monuments should be considered within the context of the overall built heritage and so repair and restoration should be seen as a conservation project within an overall conservation plan which draws on an underlying conservation philosophy. The key considerations for a conservation philosophy can be summarized as:
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Table 3 Tolerable corrosion rate based on background corrosion rates and n ¼ 2.5. Material
Background corrosion
Background corrosion/ recession depth
Factor for acceptable corrosion/ recession
Tolerable corrosion/ recession rate per year
Zinc
3.1 g m2
0.46 mm
2.5
Copper
2.8 g m2
0.34 mm
2.5
2
0.25 mm
2.5
3.2 mm 2.8 mm
2.5 2.5
7.8 g m2 1.1 mm 7.1 g m2 0.8 mm 5.25 g m2 0.6 mm 8.0 mm 7.0 mm
Cast Bronze Portland Limestone White Mansfield dolomitic sandstone
2.1 g m
- Conservation and restoration must have recourse to all the sciences and techniques which can contribute to the study and safeguarding of the architectural heritage. - Restoration and refurbishment should be based on a programme of “minimum intervention” whilst taking into account the need to balance the costs of such work and the disruption of activities on the site. Wherever possible interventions should be reversible, that is that they can reversed at a later date, for example if a better solution becomes available at some future date.
3.6. Tolerable and exceedance maps (n-factor maps)
Fig. 5. Overlapped map: corrosion of cast bronze-movable cultural heritage made of bronze in 2008 (upper) and recession of Portland limestone-immovable cultural heritage made of this material in 2008 (lower).
- An holistic approach: the buildings and their setting needs to be considered as an entity. - The historic environment must allow for new architecture and modern life-styles but with a presumption in favour of preservation.
Table 2 Tolerable corrosion rate based on tolerable corrosion before action and tolerable time between maintenance. Material
Type of surface
Tolerable Tolerable Tolerable corrosion time between corrosion before maintenance rate action
Portland Limestone Ornament, aged 100 mm Ornament, corroded 50 mm
12 years 6 years
8.3 mm y1 8.3 mm y1
Copper monument Ornament, aged 50 mm Ornament, corroded 10 mm
50 years 20 years
1.0 mm y1 0.5 mm y1
Bronze monument Ornament, aged 50 mm Ornament, corroded 10 mm
50 years 15 years
1.0 mm y1 0.7 mm y1
80 mm
50 years
1.6 mm y1
Zinc monument
Evenly corroded
As explained before, although Madrid case is not a good example for quantification of areas where corrosion/recession levels are tolerable or exceeds the maximum tolerable (Ktol ¼ 2.5Kb), i.e. (0.6 mm) in the case of cast bronze and 8.0 mm in the case of Portland limestone, n-factor maps have been also developed (Fig. 6). As can be observed, in 2008 the predicted corrosion of bronze from the doseeresponse function is in the range n ¼ 1.0e1.5 times the background level and the recession of Portland limestone in the range n ¼ 1.0e2.0 times the background level, always lower than the tolerable n ¼ 2.5. However, these maps could be useful if apply it to other towns, regions or countries in order to quantify the percentage of the area where corrosion/ recession exceeds 2.5Kb. 3.7. Future scenarios In order to analyze future scenarios climate and pollution evolution should be taken into account because both parameters have notable influence in the materials degradation, as it is described in the doseeresponse functions. Regarding the effect of climate change, the predictions of the Noah’s Ark project for both, near and far future, are a decrease in annual precipitation in Southern Europe (Sabbioni et al., 2010). Temperature and relative humidity were not specifically mapped but in principle the predictions seems to indicate a slightly increase in case of temperature and a slightly decrease of the relative humidity in Southern Europe. Although the Atlas claims that the models are not necessary true in the case of local sites, because at local scale many other considerations should be taken into account, the most probable situation in Madrid would be a slight increase in case of temperature, a slight decrease of the relative humidity and a slight decrease in precipitation. All those trends would always drive to a lower corrosion rate. Therefore, from the climatic point of view, the worst case future scenario would be to keep constant in
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Fig. 6. n-factor maps for cast bronze (left) and Portland limestone (right).
Fig. 7. Predicted cast bronze corrosion in 2010 and 2020 for different future scenarios.
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Fig. 8. Predicted Portland limestone recession in 2010 and 2020 for different future scenarios.
the predictions both, temperature and relative humidity and consider only the extra beneficial effect of pollution. Therefore, a study consisted in the estimation of the levels of corrosion and recession for cast bronze and Portland limestone in 2010 and 2020 was also carried out considering RH and T always constant and two possible different future scenarios regarding pollution: 1. A neutral trend during the period 2008e2020 (following the same trend than the observed in the period 1995e2008). 2. An optimistic trend during the period 2008e2020 (following a 10% higher reduction of mass loss and recession from 2008 to 2010, and the same reduction from 2010 to 2020). In Figs. 7 and 8 the maps for cast bronze and Portland limestone respectively are shown. As can be observed the annual mass loss and recession could be in 2020 very close to the background values (0.24 mm and 3.2 mm). 4. Conclusions Different maps have been developed: inventory of stock of cultural heritage at risk for each selected material (cast bronze and Portland limestone), selected pollutants (SO2, NO2, O3 and PM10), corrosivity for each material (by the application of doseeresponse functions), corrosion-Cultural Heritage overlapped maps, exceedance maps and future scenarios. The risk for the Cultural Heritage in Madrid, from the corrosion point of view due to pollution, is lower than in most cities of Central and North Europe, being the prediction of cast bronze corrosion and Portland limestone recession always lower than
the previously established tolerable levels for those materials. Nevertheless, maintenance/restoration is always necessary even at tolerable intervals and all future strategies should take into account the concepts of sustainablility and conservation philosophy. Anyway, the model and the methodology developed could be useful if apply it to towns, regions or countries in order to quantify the percentage of Cultural Heritage at risk or to quantify the percentage of the area where corrosion/recession exceeds the tolerable levels (2.5Kb). Acknowledgements The authors of this paper would like to thank the European Community 6th Framework Programme (CULT-STRAT: Specific Targeted Research Project, STREP, SSPI-CT-2004-501609) and the Ministry of Science and Innovation of Spain (MAT2005-23937-E) for the financial support. They thank also the Petrology Research Group of Miner Engineering School of Madrid and the municipal authorities for the help offered during the elaboration of the inventory of Cultural Heritage, as well as, the free access to the pollution and Cultural Heritage databases. References AIRBASE, 2008. Air Quality Data. European Environment Agency. http://www.eea. europa.eu/themes/air/airbase/map-statistics (2010). Bonazza, A., Messina, P., Sabbioni, C., Grossi, C.M., Brimblecombe, P., 2009a. Mapping the impact of climate change on surface recession of carbonate buildings in Europe. Science of the Total Environment 407, 2039e2050. Bonazza, A., Sabbioni, C., Messina, P., Guaraldi, C., De Nuntiis, P., 2009b. Climate change impact: mapping thermal stress on Carrara marble in Europe. Science of the Total Environment 407, 4506e4512.
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Brimblecombe, P., Grossi, C.M., Harris, J., 2006. Climate change critical to cultural heritage. In: Fort, R., et al. (Eds.), Heritage, Weathering and Conservation. Taylor and Francis Group, London, pp. 387e393. Clean air for Europe (CAFE), 2010. http://europa.eu/legislation_summaries/ environment/air_pollution/l28026_en.htm. Cult Strat, 2010. Assessment of air pollution effects on cultural heritage e management strategies, the CULT-STRAT project. http://www.corr-institute.se/ cultstrat/web/page.aspx. ICP-Materials, 2010. International cooperative programme on effects on materials, including historic and cultural monuments, convention on long-range transbondary air pollution (CLRTAP), United Nations Economic Commission for Europe (UN ECE). http://www.corr-institute.se/ICP-Materials/. Kucera, V., 2004. Chapter 4: mapping of effects on materials. In: Kucera, V. (Ed.), Manual on Methodologies and Criteria for Modeling and Mapping Critical Loads and Levels and Air Pollution Effects, Risks and Trends. UNECE convention on Long-Range Transbondary Air Pollution (CLRTAP), Geneva, pp. IV-1eIV-10. Kucera, V., Tidblad, J., Kreislova, K., Knotkova, D., Faller, M., Snethlage, R., Yates, T., Henriksen, J., Schreiner, M., Ferm, M., Lefèvre, R.A., Kobus. J., 2007. The UN/ECE ICP Materials multi-pollutant exposure on effects on materials including historic and cultural monuments. Acid Rain 2005 Conference, Prague, 12e17 June 2007.
Mikhailov, A.A., Tidblad, J., Kucera, V., 2004. The classification system of ISO 9223 standard and the doseeresponse functions assessing the corrosivity of outdoor atmospheres. Protection of Metals 40 (6), 541e550. Multi-Assess, 2010. Model for multi-pollutant impact and assessment of threshold levels for cultural heritage, MULTI-ASSESS project. http://www.corr-institute. se/MULTI-ASSESS/. Sabbioni, C., Brimblecombe, P., Cassar, C. (Eds.), 2010. The Atlas of Climate Change Impact on European Cultural Heritage. Scientific Analysis and Management Strategies. Anthem Press, London, p. 146. Sokhi, R.S., Kitwiroon, N., 2008. Air pollution in urban areas. In: Sokhi, R.S. (Ed.), World Atlas of Atmospheric Pollution. Anthem Press, London, pp. 19e34. Tidblad, J., Kucera, V., Mikhailov, A.A., Henriksen, J., Kreislova, K., Yates, T., Stöckle, B., Schreiner, M., 2001. UN ECE ICP materials: doseeresponse functions on dry and wet acid deposition effects after 8 years of exposure. Water, Air and Soil Pollution 130 (1e4), 1457e1462. Tidblad, J., Kucera, V., Mikhailov, A.A., Kreislova, K., 2002. Improvement of the ISO classification system based on doseeresponse functions describing the corrosivity of outdoor atmospheres. In: Townsend, H.E. (Ed.), Outdoor and Indoor Atmospheric Corrosion. American Society For Testing and Materials (ASTM), West Conshohocken (PA), pp. 73e87. Special Technical Publication ASTM STP 1421. Watt, J., Tidblad, J., Kucera, V., Hamilton, R. (Eds.), 2009. The Effects of Air Pollution on Cultural Heritage. Springer, New York, p. 306.