Atmospheric pollution impact on Moroccan architectural cultural heritage

Project leaders

Alessandra Bonazza, Mustapha Haddad

Agreement

MAROCCO - CNRST - Centre National pour la Recherche Scientifique et Technique

Call

CNR/CNRST 2014-2015

Department

Earth system science and environmental technologies

Thematic area

Earth system science and environmental technologies

Status of the project

New

Research proposal

State of the art and aims of the project.
Emissions from vehicular traffic and combustion processes in general are known to be the main causes of damage for built cultural heritage [1]. Airborne particulate matter, including air pollutants, deposits and accumulates onto architectonic surfaces and then interacts with the substrate compounds. The dry and wet deposition of air pollutants is demonstrated to be one of the most important damage factor in building material deterioration. In particular, airborne particulate matter and SO2 are the most aggressive and dangerous agents in case of limestone and marble materials. Therefore, in synergy with environmental parameters, they are responsible of chemical and physical processes that may lead to damage effects such as: color changes [2], loss of material, changes in mechanical properties. The studies performed on the elemental characterization of the deposit have indicated the differences in composition between various European sites [3]: this observation has been linked to different location and exposition to the local pollutants sources such as combustion process in industry, domestic heating or traffic. In this proposal the interest is focused on the monuments located in the Mediterranean Africa, where climate is influenced by Atlantic Ocean and Mediterranean Sea as well as Sahara desert. Moreover, regulations concerning the use of fuels are not in line with those adopted in European countries.
Recent studies dedicated to pollution impact on the monuments in North Africa, (ancient ramparts of the Moroccan city Salé) have highlighted the role of SO2, carbonaceous particles and marine aerosol deposition in black damage layer formation. Moreover, the strong impact of the vehicular emission was evidenced by the presence of the high amounts of organic carbon and nitrates [4].
Field exposure tests are currently under execution in Milan (Cathedral) and in Florence (loggia of S. Marco Museum), Italy, in order to investigate the mobility impact (vehicular traffic) on stone exposed to different environmental conditions (pedestrian area in Milan, close to a busy street in Florence) and geometries of exposure (horizontal, vertical and inclined). The data are currently being processed in order to correlate the concentration of carbon and soluble fraction of the total suspended particulate matter with the ones encountered in the surface deposit of the different lithotypes. The main objective is to measure the deposition flux of the major pollutants causing blackening and soiling.
The aim of this project is to enlarge the knowledge in the field of the pollution impact evaluation including an African site by: (i) performing an exhaustive characterization of deposits on local stones employed in heritage buildings (ii) identifying stationary and mobile combustion sources causing damage, (iii) evaluating the impact of mobility in relation to substrate type and environmental conditions. In this context, field exposure tests by using Carrara Marble, Candoglia Marble and a local stone (calcarenite) specimens are planned to be performed in two Moroccan sites: the Mosqué Al Qods, Roches Noires, in Casablanca and the tower Borj Al Klab/rempart in Salé. The selected lithotypes are known in their mineralogical and petrographic characteristics from literature: this will provide an enhance in understanding preferential depositions and/or interactions between suspended particulate matter and substrate.
Specimens are going to be exposed outdoor in a sheltered area for 18 months and analyses at 6-12-18 months of exposure. The result will be then compared and integrated to those obtained in the Italian sites.
Moreover, two seasonal (summer-winter) weekly campaigns for environmental monitoring are planned in order to characterize the total suspended particulate matter (TSP) in terms of soluble fraction and elemental and organic carbon. In particular, total suspended particular matter will be collected using four suction pumps working with circular filters. Two sampling lines working in parallel will be installed: one for carbon measurements, using quartz fiber filters, and the other one for the quantification of the ion fraction, working with polycarbonate filters. At the same time the microclimate (relative humidity and temperature) will be monitored.
Additionally, sampling of damage layers from selected monument will be carried out and subsequently analysed in order to contribute in the evaluation of the pollution impact on Moroccan calcareous stones.
Historical sites.
The Italian historical places selected have been target sites in previous (CARAMEL EC Project) and current (SYDDARTA EC Project) research studies concerning the impact of pollution on cultural heritage; thus consistent and relevant data on the atmosphere-material interaction from specific environmental and sampling campaigns are available to be compared with those obtained within this research proposal.
Here under a brief description:
Milan Cathedral is placed in the center of Milan in a pedestrian area. Its construction started in the XIV century in Gothic style (in place of the older Santa Maria Maggiore and Santa Tecla, the wintry and summer cathedrals, respectively) and ended only in the nineteenth century. Nowadays, this is one of the most important and attractive religious buildings of Milan.
San Marco Museum in Florence is an architectural masterpiece of Michelozzo, in San Marco square in the center of Florence. It hosts the best collection in the world of frescoes and easel paintings by Fra' Beato Angelico, Fra' Bartolomeo, Domenico Ghirlandaio, Alessio Baldovinetti, Jacopo Vignali, and others. Unfortunately, the Museum is close to a busy street, where every day hundreds of touristic busses stand and pass by.
In Morocco, the metropolis Casablanca and Rabat-Salé are subject to the problematic of architectural heritage disfiguration as the big cities of the world.
While Casablanca possesses historical monuments built of limestone belonging to the colonial period, in the city of Salé there are limestone monuments and walls dating from the late 12th century, edified by the Almohads dynasty. The disordered expansion of industrial and urban centers in these cities leading to the emission of gaseous pollutants and aerosols from various combustion processes and traffic (about 1.5 million of vehicles a day travel in the city of Casablanca) increases drastically the atmospheric pollution and its impact on all the environmental compartments including the built heritage.
Concerning Moroccan selected monuments, here under a brief description:
- The Mosque of Al-Quds at Roches Noires district in Casablanca, formerly St. Margaret Church, was built in 1923 by the French industrial Eugene Lendrat. It was built of limestone on the same architecture as the Saint-Martin church in the city of Pau in France from where Eugene Lendrat was originating.
- The Tower Borj AlKlab of Salé was built by the Almohads in the late 12th century. It is an octahedral monument, constructed on limestone, in complete accordance with the Andalusian architecture and identical to those of Cordoba. It is a military fortress that allowed for centuries, the control of Salé areas and roads to Ceuta and Fez.


Methodological approach and analytical techniques.
Analyses and characterization will be carried out both in Italian and in Moroccan laboratories, according to the following scientific approach.
Italian equipment.
- Non-contact color measurements for the determination of chromatic change of the surfaces using a KONICA MINOLTA Spectrophotometer CM700d, which is calibrated with its white reference (100% reflective) and zero calibration box (0% reference) in the 400-700 nm range. The measurement geometry is d/8° with a xenon light source with UV cut filter and a silicon photodiodes array detector. Color data will be evaluated for the D65 illuminant, 10° supplementary standard observer, and excluding the specular component of light. The data will be calculated for the CIEL*a*b* 1976 color space. For each measurement the spectrophotometer will be positioned on the same spot (Ø 8 mm) of each area by using a repositioning mask.
- Sampling of the deposit to be analyzed using a bistoury.
- Ion Chromatography (IC) analyses for the determination and quantification of soluble anions within the deposit by means of a Dionex Chromatograph 4500i Instrument, with a conductivity detector (Dionex CD II).
- Speciation and quantification of organic and elemental carbon within the deposit. In particular, the discrimination and measurement of carbon fraction - Total carbon (TC), Non Carbonate Carbon (NCC), Organic Carbon (OC) and Elemental Carbon (EC) - will be carried out following the thermal-chemical methodology set up by Ghedini et al. [5] using a CHNSO combustion analyzer (CHNSO EA 1108 FISONS Instruments)
- Morphological and elemental characterization of particulate matter by means of a ZEISS 1530 Scanning Electron Microscope (SEM) equipped with an Energy Dispersive X-Ray Spectrometer (EDX) for X-Ray microanalysis, and two different Secondary Electrons (SE) detectors, the InLens (IL) and the Everhart-Thornley detectors (ETD).
Moroccan equipment.
- Use of constant wavelength synchronous spectrofluorimetry by means of a Shimadzu RF-5301-PC apparatus for the identification of hazardous polycyclic aromatic hydrocarbons (PAHs) in: i) the sampled black crusts deposited on the limestones and iii) in the suspended matter deposited on the specimens exposed outdoor. spectrofluorimeter. Using the solid sample holder, it will be tried to carry out the SF spectra directly on the solid crusts and on the specimens without any solvation.
- µ-XRF analysis, by means of a Brucker XRF spectrometer, on the sampled deposits and for the identification of the composition differences among the external and internal parts of the samples.
- µ-Raman analysis. A Renishaw Raman spectrometer coupled to a Leica DMLM (UK) microscope with a laser at 632nm excitation wavelength and a Peltier cooled CCD detector will be used in view to determine the molecular composition of the deposits sampled on surface and on layers at different depths in the stone. A second Jasco RMP-200 Raman spectrometer with integrated microscope, laser excitation at 532 nm and a Peltier cooled CCD detector is also available.
- Magnetic resonance EPR (ESR) analysis on the samples, to probe locally the structures of the compounds deposited. Combined with reflectance UV-Vis./NIR and Raman analysis, it will give more insight on chromogen elements and color change induced by the pollutants on the monument facades. A Bruker ER 200 D, X-band, and a Jasco V570 UV/VIS./NIR will permit these investigations.

Collaboration.
Common interest is to continue and to extend the collaboration in the framework of the CNRST/CNR bilateral cooperation, in view to enlarge the knowledge of the pollution impact on the Moroccan architectural heritage built in limestone. CNR-ISAC and LASMAR of the University of Moulay Ismail already collaborated within European project "TeACH" -Technologies and Tools to prioritize assessment and diagnosis of air pollution impact on immovable and movable Cultural Heritage (www.teach-project.eu).

References.
[1] Bonazza, P. Brimblecombe, C.M. Grossi, C. Sabbioni, Carbon in Black Crusts from the tower of London, Environmental Science and Technology, 41, 2007, 4199-4204.
[2] C.M. Grossi, P. Brimblecombe, R.M. Esbert, F.J. Alonso, Color Changes in Architectural Limestones from Pollution and Cleaning, Color Research and application, 32, 2007, 320-331.
[3] C.M. Belfiore, D. Barca, A. Bonazza, V. Comite, M.F. La Russa, A. Pezzino, S.A. Ruffolo, C. Sabbioni, Application of spectrometric analysis to the identification of pollution sources causing cultural heritage damage, Environmental Science and Pollution Research, 2013, DOI: 10.1007/s11356-013-1810-y.
[4] I. Ozga, A. Bonazza, S. A. L

Research goals

The present proposal aims at the diagnosis and evaluation of damage on cultural heritage due to pollution impact by analyzing and identifying critical parameters related to atmospheric pollution and climate conditions. Combination of micro-invasive and non-invasive spectrometric and chromatographic techniques will be adopted for this purpose.
The main objectives of this proposal are:
- To evaluate the vehicular traffic (mobility) impact on different building stones
- To characterize deposits in order to identify stationary and mobile combustion sources causing damage
- To compare the obtained data with those related to the same stones exposed in two Italian sites (Florence and Milan)

Last update: 07/10/2024