Air pollution, black crusts and Cairo monuments: A review

Recently, the degradation phenomena affecting built cultural heritage and relative to environmental pollution increased considerably. The monuments in Historic Cairo are particularly exposed to these processes and their conservation is seriously threatened. The present review considers the studies about degradation products such as black crusts and salt crystallization affecting the building materials of selected monuments. The minero-petrographical and geochemical characterization will allow establishing the connections between them and the environmental pollution, such as the atmospheric one in terms of heavy metals and carbonaceous fraction. All specimens underwent a multi-methodological approach, the results highlighted that black crusts and salt crystallization represent the most common degradation products affecting all the monumental sites. Additionally the correlation between the composition of black crusts and the main pollutant sources in Cairo such as vehicular traffic and industrial activities was clarified.