Organic and inorganic compounds in limestone weathering crusts from cathedrals in southern and Western europe.

Limestone and weathering crusts have been studied at the major cathedrals of Sevilla, in southwestern Spain, and Mechelen, in northern Belgium. These cities have very different climatic and environmental conditions. The deterioration characteristics of the limestone in both localities have been compared. Detailed petrographical characterization was carried out for the different building stones, including restoration materials. The bulk and trace inorganic composition of the stones and crusts was assessed, and the leachable ions were analyzed, while elemental concentration profiles wi th depth were studied with electron microprobe analysis. The organic compounds in the black weathering crusts have also been studied and compared. In the different types of limestone, the deterioration is largely influenced by the petrographic characteristics ofthe stone. Gypsum crusts from Mechelen and Sevilla show variable textures, even on the same stone types. Sulfatation of calcite provides Ca for the gypsum crusts. Except for a part of the Sr and Fe fractions in the crust, all other elements may be of external origin. Concentrations of the various elements are more or less comparable in crusts from Mechelen and Sevilla. External inorganic particles consist of fly ash, quartz, clay, and glauconite. Most of the organic material appeared to be of anthropogenic origin, due to cornbustion processes, while a minor fraction originated from cuticular waxes of higher plants. Introduction Sevilla and Mechelen are cities located in very different climatic regions in Europe. Sevilla (700 000 inhabitants), in Andalucia, southwestern Spain (Figure 11, is one of Europe's southernmost cities. This part of the Iberian peninsula is among the regions with the highest average temperatures in Europe, 10.7 "C in January (average daily maxima and minima of 16 and 5 "C, respectively) and 26.8 "C in July (average daily maxima and minima of 35 and 19 "C, respectively), with an insolation of 2750 hlyear. It rains 620 mm/year in Sevilla, mostlyinwinter (the average rainfall in January and July is 66 and 0 mm, respectively), and the average relative humidity is only 59%. The climate in Mechelen (80 000 inhabitants) in Flanders, northern Belgium (Figure l), is much colder, with an average temperature of 2 "C in January (average daily maxima and minima Of 4 and -1 "C, respectively) and 18 "C in July (average daily maxima and minima of 22 and 12 "C, respectively), and it is also marked by a high relative humidity and by an average precipitation of 850 mmlyear, which is rather evenly spread over the year. Both cities have limestone cathedrals of very high historical value, which are seriously threatened presently by air pollution. The first stone of the cathedral of Sevilla was laid in 1402, and the construction lasted until 1927, when the Conception Gate was finished. Through the 15th century, stones from the quarries of the Cadiz and Sevilla provinces Uerez, Puerto de Santa Maria, Sanlucar de Barrameda, Alcala de Guadaira) and Portugal were used. During the 16th century, the origin of the stones was even more diverse (1). The most abundant stone type is a yellowish fossiliferous calcarenitic limestone of Miocene age, whereas white oolithic and micritic limestones were used duringthe 19th20th century construction. The mineralogical composition of the calcarenite is 45-97% calcite and 3-55% quartz, with traces of phyllosilicates; the micritic limestone is 95% calcite and 5% quartz, while the oolithic limestone is 100% calcite (2). The original yellowish or whitish colors turned gray or black due to air pollution exposure during the last century. The mean atmospheric SO2 and particulate matter levels in 1976-1980 were 87 and 174 pglm3, respectively, at a station near the cathedral. In 1980-1985, the mean SO2 level was 47 pglm3. After 1985, the station was discontinued. Today, higher levels are presumed because the cathedral neighborhood is characterized by dense traffic, areas of car parking, and narrow sheltered streets, a typical configuration of historic centers in old Andalusian cities. High-rising damp levels have been observed on the cathedral walls (2). These deteriorating factors are enhanced by the softness of the high-porosity limestone. The most important deterioration is caused by sulfatation of calcite and dissolution of calcitic cement. Technical characteristics of the building materials used in the Sevilla cathedral have been reported by Esbert et al. (31. The city of Mechelen is located on the industrial axis between the major cities of Antwerp and Brussels. Refineries, electrical power plants, and non-ferrous industries make this area the most important emitter of industrial SO2 and NO, in Belgium. Like many ancient buildings in northern Belgium, the 15th century St. Rombouts cathedral was built with materials of local origin: Balegem and