Role of particulate matter from vehicle exhaust on porous building ...
ELSEVIER
The Scienceof the Total Environment187(1996)79-91
Role of particulate matter from vehicle exhaust on porous building stones (limestone) sulfation Carlos Rodriguez-Navarro*, Eduardo Sebastian htituto
Andaluz
de Geologia
Mediterranea, Departamento Mineralogia Fuente Nueva s/n 18003, Granada,
y Petrologia. Spain
CSIC-
hive&&d
de Gran&,
Received14 December1995;accepted6 March 1996 Abstract This work, for the first time, experimentally demonstrates the relationship between motor vehicle emissionsand the decay of ornamental calcareous stone, by means of sulfation processes(the well-known phenomenon of Black-crust formation). The critical catalytic effects of carbon (soot) and metal-rich particles from vehicle exhaust result in the acceleration of the rate of fixation of atmospheric SO, to form gypsum on the limestones (calcarenites)used to build Granada Cathedral (Spain). The analysisof particulate matter deposited on the building (carbonaceousand metal-rich particles), as well as of emissionsfrom both leaded-gasoline and diesel motor vehiclesconfirms that the origin of the particulate matter found in the surface of decayed building stones from Granada Cathedral is consistent with having been contributed by motor vehicle exhaust. Experimental data indicate the role played by this particulate matter in the fixation of atmospheric SO1as sulfates (gypsum) on calcareous materials in the presenceof humidity. We have also experimentally demonstrated that there is a close relationship between the composition of the particulate matter and the fixation rates of the SO, in the form of sulfate: (a) dieselengine exhaust, which is primarily composed of soot and metallic particles bearing Fe and Fe-S as major elements and of Cr, Ni, Cu, and Mn as trace elements, plays the largest part in the catalytic oxidation rates of SO,; (b) the emissionsfrom gasoline engines, composed of minor quantities of soot and high concentrations of Pb- and Br-bearing particles, cause a lower rate of SO, fixation as gypsum on limestones. From these experimental findings, a new hypothesis is proposed concerning the sulfation of the limestones. Keywords: Limestone; Vehicle emission; Building stone, decay; Black-crust formation; Granada, Spain
1. Introduction
The effects of atmospheric pollution and acid deposition on lakes, animals, forests, humans and buildings arouse considerable interest and are the * Correspondingauthor. Presentaddress:The Getty Conservation Institute, 4503 GlencoeAvenue,Marina de1Rey, CA 90292,USA. Fax: +l 310 821-9409,e-mail:cnavarroagetty. edu.
subject of extensive discussion. Air pollution has since the mid-19th century been suspected of accelerating the degradation of many types of construction materials [l]. Moreover, air pollution has been suspected to be a major factor in the degradation and, in some cases, the loss of large parts of our cultural heritage [2-51. Pollutants such as SOz and particulate matter, primarily from the combustion of oil-derived fuels, have
0048-9697/96/$15.000 1996ElsevierScienceB.V. All rights resewed PIZ SOO48-9697(96)05124-8
80
C. Rodriguez-Navarro.
E. Sebastian
/ The Science
been related by several authors [6-91 to the alteration by sulfating of ornamental stones (particularly carbonate ones: marbles, limestones, and dolostones), involving acid attack of these materials, and formation of sulfate compounds (i.e. gypsum). Nevertheless, many questions on the dynamics of this decay process remain unsolved. Novakov et al. [lo] established a relationship between sulfating processes from atmospheric SOI and the presence of carbonaceous particulate matter. This process, according to experimental data by Urone et al. [l I], accelerates in the presence of some transition and other metals (Fe, V, Cr, Ni, Pb, etc.), which catalyze the oxidation and hydrolysis of the SO, to form sulfuric acid, which is responsible for both the ‘acid rain’ and the stone sulfation. Del Monte et al. [7] made it clear that carbonaceous particles are invariably present in the weathered gypsum crusts (the so-called ‘Black Crusts’) that form on the surface of calcareous materials used in historical buildings. Cheng et al. [S] demonstrated under laboratory conditions that metallic-sphere pollutants exert a catalytic action in the oxidation of SOz and determined the role played by carbonaceous particles in aiding the nucleating reactions of gypsum on marble surfaces. Pye and Schiavon [12] demonstrated by means of S isotope ratios that the S found in gypsum crusts on building stones always comes from an atmospheric source. Hildemann et al. [13], by means of C isotopes, identified the origin of carbonaceous particulate matter in the urban environment and concluded that a major source of these particles is the emissions from motor vehicles, with diesel engine vehicles being the major vehicular source. A number of recent articles [ 14-181 have underscored the role played by the deposition of particulate matter (as a product of high urban pollution) in the formation of black crusts, mainly comprised of gypsum, (for an extensive review of this subject, see Lipfert [19] and Ross et al. [20]); however this paper presents the first experimental work supporting this theory. Our study provides new data on the action of particulate matter coming from motor vehicle exhaust in the sulfation of carbonate stones (limestones), that were so extensively used in the construction of historic buildings
of the Total
Environment
187 (1996)
79-91
in all of the Mediterranean Basin and especially in the South of Spain. Following building construction (and especially accelerated in the last few decades), limestones become covered by abundant black crusts in which gypsum and different types of particulate matter are normally found. The black crust and other products deposited in the initial stages of weathering in the limestones used in the construction of the Cathedral of Granada (southern Spain) have been examined This historic building is located in an area where the degree of environmental pollution is low (there is no highly contaminating industry nearby). The only source of pollution therefore is from traffic and, to a lesser extent, from the seasonal use of furnaces. We have also analyzed the dust deposited in the molding, under cornices, and in other areas of the building where black crusts had not yet developed (the so-called gray areas [21]). This layer of dust reaches a thickness of several centimetres in particularly protected areas and is considered to be the precursor of black crust formation, Data from Skiotis et al. [22] and Yocom [23] indicated that this type of dust is normally found in the early stages of decay of building stones. They also pointed out the possible role of metallic elements, such as Fe, Mn, Cu and Zn that are always present in the dust, as catalysts in the oxidation of SO*, which in the presence of humidity results in the formation of sulfuric acid. The main goal of this work is to demonstrate that the dust which enclosed particulate matter coming from vehicular traffic sources, plays a major role in fixing atmospheric SO* as CaSO,.2H20, and as a consequence, is the first stage of black-crust development. A secondary goal is to demonstrate the differences in catalytic power of particulates from gasoline and diesel vehicle exhausts on the oxidation of SO2 and its fixation as sulfates. 2. Materials and methods 2.1. Materials
Fifteen samples were taken of the weathering products (black crusts) and dust deposits from different heights and orientations of the Cathedral of
C. Rodriguez-Navarro,
E. Sebastian/The
Science
Granada. This XVI Century monument was primarily constructed of a Tortonian limestone (calcarenite) of high porosity (average value: 32%, [24]). Other characteristics of this material include a microsparitic matrix which, in some cases, may include a second generation of sparitic carbonate cement containing a great variety of bioclasts (molluscs, echinoderms, and foraminifera). Given their porosity, distribution of pore size, degree of cementation, and primarily carbonate composition, these materials are very susceptible to weathering processes caused by the generation of gypsum [24-271. The black crusts and accumulated dust from the most protected parts of the building were analyzed by chemical, mineralogical, and petrographical methods, using X-ray diffraction (XRD), polarizing microscopy (PM), scanning electron microscopy with energy dispersive spectrometry microanalysis @EM-EDS), X-ray fluorescence
of the
Total
Environment
I87
(1996)
79-91
(XRF) and ion coupled plasma emission spectrometry (ICP). Once the weathering products were identified, a study was made of the role of each of the components of the accumulated dust and gypsum crust, in limestone sulfation, focusing on the role of the enclosed particulate matter. 2.2. Experimental SO,
attack
Unweathered blocks of limestone (from the ancient quarries) used to build this monument were analyzed with XRF, ICP, XRD, PM, and SEM with EDS, before being submitted to SOZ attack in a static chamber with controlled temperature and relative humidity. Fig. 1 shows a schematic view of the chamber used, the sample dimensions, and the different runs carried out, as well as the experimental conditions. To speed up the process, SO, was administered at the beginning of the experiments at a dose of
CHAMBER (500 I)
Limestone
(4 slabs) Simultaneous
a) Blank b) Dust c) Gasoline exhaust
5cm Experimental
81
conditions
SO, static chamber (100 ppm SO,) Timing: run a) 24 h run b) 48 h Temperature: 30” C Relative Humidity: 100 %
Fig. 1. SO2 chamber scheme, sample dimensions, and experimental protocol (for detail see text).
82
C. Rodriguez-Navarro.
E. Sebastian/The
Science
100 ppm (50 ml of SO2 were introduced into a 500-l chamber, at 1 atm and 25%). This concentration is 2500 times higher than the average SO2 concentration near the cathedral (0.04 ppm), but, since one of the main goals of the experiment was to demonstrate that pollution particulate matter enhances SO2 fixation as sulfates on the stone surface, it was consider appropriate to obtain a high reaction rate. To evaluate the role of particulate matter coming from vehicular sources on stone sulfation, two types of particulates were collected directly from the exhaust systems of vehicles using leaded gasoline and diesel as fuels. These particles were analyzed by chemical, mineralogical and morphological means using SEM-EDS, ICP, XRF, and XRD, after which they were deposited on the limestone slabs (evenly spread over the upper surface with a brush). Then, each of the following limestone slabs were simultaneously exposed in the above described chamber: (a) a fresh slab of limestone as a control; (b) a slab of limestone covered with a thin layer of dust collected from the stone surface of the building (concentration: 100 mg cm-*); (c) a slab of limestone covered with a thin layer of solid residue emissions from a vehicle using leaded gasoline (concentration: 10 mg cm-*); (d) a slab of limestone covered with a thin layer of particulate matter emitted by a diesel engine (concentration: 10 mg cme2). To accelerate the process of SO2 attack on the limestone surfaces and to reproduce the natural condition of the building, all slabs were wetted. It was pointed out [28-301, this would accelerate the sulfate attack by means of SO2 dry deposition process. After 24 h from the beginning of the exposure, one set of samples (a-d) was removed from the chamber and immediately, their surfaces exposed to the attack, were submitted to XRD and SEMEDS analyses. After 48 h from the start of the experiment, the very same operation was performed on a second set of samples. 3. Results and discussion 3.1. Material from the building In rock samples with incipient weathering it was
of the Total
Environment
187 (19%)
79-91
Fig. 2. Polarizing microscopy photomicrographs of black crusts: (a) Incipient crust with particulate matter (indicated by arrows), plane light; (b) developed crust, mainly composed of acicular gypsum crystals (crossed Nicols). Bar scale, 200 pm.
possible, as a rule, to observe by means of polarizing microscopy, a thin layer of tiny acicular gypsum crystals surrounded by clay minerals and calcium oxalate (weddellite). These phases were immersed in a dark matrix (Fig. 2a) of very porous particulate matter (soot) in conjunction with smooth, metal-rich spheres (as deduced from SEM-EDS data). The samples of black crusts (Fig. 2b) contained acicular gypsum crystals (up to 200 pm). Also, in central areas that were in contact with the limestone, several types of pollutants enclosed in a matrix of calcite crystals and microcrystalline gypsum (Fig. 2a,b) were also seen. However, there were not properly identified by this technique, due to their small size (average diameter < 2 pm). XRD analyses of rock samples with incipient weathering (limestones with very thin, - 1 mm thick, black crusts), clearly indicated that calcite is
C. Rodriguez-Navarro. E. Sebastian / The Science oj the Total Environment 187 (19%) 79-91
83
Table 1 Comparison of the concentration of principal metallic elements of undecayed quarry limestone (fresh) and different samples from the building Sample
V
Fresh Initial Initial Initial Crust crust Crust Crust CNst
13 18
9 17
10 14 10 10
10 15 44
CNSt
Dust Dust Dust Dust Dust Dust
crust (1) crust (2) crust (3) (1) (2) (3) (4) (5) (6)
Cr
8 11
31
44 36 29 38 65 57
13
(4) (5) (6)
2 2 2 3 2 2 2 4 6 3 3 2 2 6
164
10
(2) (3)
Ni
30 18 22
17 22 36 26 24
(1)
co
44 53 56
cu 4.2 7.3 8.1 12.2 56.5 37.5
8
27.7 26.6 48.8 57.5 44.2 39.4
15.8 30.8 16.1 54.8 34.8 53.7 40.8 70.0 82.1 53.7 98.3 123.0 142.0
15
100.1
113.0
31 18
61.5 96.5
124.9 191.0
3 6 5 4
11 8
10.5
91 7 9 9
11 10
Zn
Pb
Fe 4 18 2 37 83 209 29 130 72
11300 260 3740 193 439 352 677
629 1538 1188 1503 3951 4720 1608 2308 4557 7203 7448 4021 4196
Mn 154 77 77 310 154 232 77 77 481 309 310 232 464
11 644
154
11480
225 463
11 826
All element concentrations in ppm. The fresh sample was taken from an ancient quarry and reflects the average composition of these materials. Samples from the building (Initial crust, Crust and Dust) are identified by number (reflecting their different locations).
the major phase, followed by clay minerals, quartz, and small amounts of gypsum. In the most developed black crusts (thickness greater than 2 mm and up to l-2 cm), gypsum is the major phase, with calcite, quartz, clay minerals, and oxalates (weddellite) as minor components. Analysis of the accumulated dust revealed the presence of a small amount of gypsum together
z
300
2 ;I a
225
+e Y z
150 75 0 1 0
I 20
40
60
80
100
Gypsum (wt%) Fig. 3. Gypsum concentration versus amount of Pb, Zn and Cu in black crust developed on limestone surfaces of Granada Cathedral.
with quartz and clay minerals, the latter being the most abundant. Minor quantities of weddellite, feldspars and iron oxides were also found. Detailed analysis of the
The Scienceof the Total Environment187(1996)79-91
Role of particulate matter from vehicle exhaust on porous building stones (limestone) sulfation Carlos Rodriguez-Navarro*, Eduardo Sebastian htituto
Andaluz
de Geologia
Mediterranea, Departamento Mineralogia Fuente Nueva s/n 18003, Granada,
y Petrologia. Spain
CSIC-
hive&&d
de Gran&,
Received14 December1995;accepted6 March 1996 Abstract This work, for the first time, experimentally demonstrates the relationship between motor vehicle emissionsand the decay of ornamental calcareous stone, by means of sulfation processes(the well-known phenomenon of Black-crust formation). The critical catalytic effects of carbon (soot) and metal-rich particles from vehicle exhaust result in the acceleration of the rate of fixation of atmospheric SO, to form gypsum on the limestones (calcarenites)used to build Granada Cathedral (Spain). The analysisof particulate matter deposited on the building (carbonaceousand metal-rich particles), as well as of emissionsfrom both leaded-gasoline and diesel motor vehiclesconfirms that the origin of the particulate matter found in the surface of decayed building stones from Granada Cathedral is consistent with having been contributed by motor vehicle exhaust. Experimental data indicate the role played by this particulate matter in the fixation of atmospheric SO1as sulfates (gypsum) on calcareous materials in the presenceof humidity. We have also experimentally demonstrated that there is a close relationship between the composition of the particulate matter and the fixation rates of the SO, in the form of sulfate: (a) dieselengine exhaust, which is primarily composed of soot and metallic particles bearing Fe and Fe-S as major elements and of Cr, Ni, Cu, and Mn as trace elements, plays the largest part in the catalytic oxidation rates of SO,; (b) the emissionsfrom gasoline engines, composed of minor quantities of soot and high concentrations of Pb- and Br-bearing particles, cause a lower rate of SO, fixation as gypsum on limestones. From these experimental findings, a new hypothesis is proposed concerning the sulfation of the limestones. Keywords: Limestone; Vehicle emission; Building stone, decay; Black-crust formation; Granada, Spain
1. Introduction
The effects of atmospheric pollution and acid deposition on lakes, animals, forests, humans and buildings arouse considerable interest and are the * Correspondingauthor. Presentaddress:The Getty Conservation Institute, 4503 GlencoeAvenue,Marina de1Rey, CA 90292,USA. Fax: +l 310 821-9409,e-mail:cnavarroagetty. edu.
subject of extensive discussion. Air pollution has since the mid-19th century been suspected of accelerating the degradation of many types of construction materials [l]. Moreover, air pollution has been suspected to be a major factor in the degradation and, in some cases, the loss of large parts of our cultural heritage [2-51. Pollutants such as SOz and particulate matter, primarily from the combustion of oil-derived fuels, have
0048-9697/96/$15.000 1996ElsevierScienceB.V. All rights resewed PIZ SOO48-9697(96)05124-8
80
C. Rodriguez-Navarro.
E. Sebastian
/ The Science
been related by several authors [6-91 to the alteration by sulfating of ornamental stones (particularly carbonate ones: marbles, limestones, and dolostones), involving acid attack of these materials, and formation of sulfate compounds (i.e. gypsum). Nevertheless, many questions on the dynamics of this decay process remain unsolved. Novakov et al. [lo] established a relationship between sulfating processes from atmospheric SOI and the presence of carbonaceous particulate matter. This process, according to experimental data by Urone et al. [l I], accelerates in the presence of some transition and other metals (Fe, V, Cr, Ni, Pb, etc.), which catalyze the oxidation and hydrolysis of the SO, to form sulfuric acid, which is responsible for both the ‘acid rain’ and the stone sulfation. Del Monte et al. [7] made it clear that carbonaceous particles are invariably present in the weathered gypsum crusts (the so-called ‘Black Crusts’) that form on the surface of calcareous materials used in historical buildings. Cheng et al. [S] demonstrated under laboratory conditions that metallic-sphere pollutants exert a catalytic action in the oxidation of SOz and determined the role played by carbonaceous particles in aiding the nucleating reactions of gypsum on marble surfaces. Pye and Schiavon [12] demonstrated by means of S isotope ratios that the S found in gypsum crusts on building stones always comes from an atmospheric source. Hildemann et al. [13], by means of C isotopes, identified the origin of carbonaceous particulate matter in the urban environment and concluded that a major source of these particles is the emissions from motor vehicles, with diesel engine vehicles being the major vehicular source. A number of recent articles [ 14-181 have underscored the role played by the deposition of particulate matter (as a product of high urban pollution) in the formation of black crusts, mainly comprised of gypsum, (for an extensive review of this subject, see Lipfert [19] and Ross et al. [20]); however this paper presents the first experimental work supporting this theory. Our study provides new data on the action of particulate matter coming from motor vehicle exhaust in the sulfation of carbonate stones (limestones), that were so extensively used in the construction of historic buildings
of the Total
Environment
187 (1996)
79-91
in all of the Mediterranean Basin and especially in the South of Spain. Following building construction (and especially accelerated in the last few decades), limestones become covered by abundant black crusts in which gypsum and different types of particulate matter are normally found. The black crust and other products deposited in the initial stages of weathering in the limestones used in the construction of the Cathedral of Granada (southern Spain) have been examined This historic building is located in an area where the degree of environmental pollution is low (there is no highly contaminating industry nearby). The only source of pollution therefore is from traffic and, to a lesser extent, from the seasonal use of furnaces. We have also analyzed the dust deposited in the molding, under cornices, and in other areas of the building where black crusts had not yet developed (the so-called gray areas [21]). This layer of dust reaches a thickness of several centimetres in particularly protected areas and is considered to be the precursor of black crust formation, Data from Skiotis et al. [22] and Yocom [23] indicated that this type of dust is normally found in the early stages of decay of building stones. They also pointed out the possible role of metallic elements, such as Fe, Mn, Cu and Zn that are always present in the dust, as catalysts in the oxidation of SO*, which in the presence of humidity results in the formation of sulfuric acid. The main goal of this work is to demonstrate that the dust which enclosed particulate matter coming from vehicular traffic sources, plays a major role in fixing atmospheric SO* as CaSO,.2H20, and as a consequence, is the first stage of black-crust development. A secondary goal is to demonstrate the differences in catalytic power of particulates from gasoline and diesel vehicle exhausts on the oxidation of SO2 and its fixation as sulfates. 2. Materials and methods 2.1. Materials
Fifteen samples were taken of the weathering products (black crusts) and dust deposits from different heights and orientations of the Cathedral of
C. Rodriguez-Navarro,
E. Sebastian/The
Science
Granada. This XVI Century monument was primarily constructed of a Tortonian limestone (calcarenite) of high porosity (average value: 32%, [24]). Other characteristics of this material include a microsparitic matrix which, in some cases, may include a second generation of sparitic carbonate cement containing a great variety of bioclasts (molluscs, echinoderms, and foraminifera). Given their porosity, distribution of pore size, degree of cementation, and primarily carbonate composition, these materials are very susceptible to weathering processes caused by the generation of gypsum [24-271. The black crusts and accumulated dust from the most protected parts of the building were analyzed by chemical, mineralogical, and petrographical methods, using X-ray diffraction (XRD), polarizing microscopy (PM), scanning electron microscopy with energy dispersive spectrometry microanalysis @EM-EDS), X-ray fluorescence
of the
Total
Environment
I87
(1996)
79-91
(XRF) and ion coupled plasma emission spectrometry (ICP). Once the weathering products were identified, a study was made of the role of each of the components of the accumulated dust and gypsum crust, in limestone sulfation, focusing on the role of the enclosed particulate matter. 2.2. Experimental SO,
attack
Unweathered blocks of limestone (from the ancient quarries) used to build this monument were analyzed with XRF, ICP, XRD, PM, and SEM with EDS, before being submitted to SOZ attack in a static chamber with controlled temperature and relative humidity. Fig. 1 shows a schematic view of the chamber used, the sample dimensions, and the different runs carried out, as well as the experimental conditions. To speed up the process, SO, was administered at the beginning of the experiments at a dose of
CHAMBER (500 I)
Limestone
(4 slabs) Simultaneous
a) Blank b) Dust c) Gasoline exhaust
5cm Experimental
81
conditions
SO, static chamber (100 ppm SO,) Timing: run a) 24 h run b) 48 h Temperature: 30” C Relative Humidity: 100 %
Fig. 1. SO2 chamber scheme, sample dimensions, and experimental protocol (for detail see text).
82
C. Rodriguez-Navarro.
E. Sebastian/The
Science
100 ppm (50 ml of SO2 were introduced into a 500-l chamber, at 1 atm and 25%). This concentration is 2500 times higher than the average SO2 concentration near the cathedral (0.04 ppm), but, since one of the main goals of the experiment was to demonstrate that pollution particulate matter enhances SO2 fixation as sulfates on the stone surface, it was consider appropriate to obtain a high reaction rate. To evaluate the role of particulate matter coming from vehicular sources on stone sulfation, two types of particulates were collected directly from the exhaust systems of vehicles using leaded gasoline and diesel as fuels. These particles were analyzed by chemical, mineralogical and morphological means using SEM-EDS, ICP, XRF, and XRD, after which they were deposited on the limestone slabs (evenly spread over the upper surface with a brush). Then, each of the following limestone slabs were simultaneously exposed in the above described chamber: (a) a fresh slab of limestone as a control; (b) a slab of limestone covered with a thin layer of dust collected from the stone surface of the building (concentration: 100 mg cm-*); (c) a slab of limestone covered with a thin layer of solid residue emissions from a vehicle using leaded gasoline (concentration: 10 mg cm-*); (d) a slab of limestone covered with a thin layer of particulate matter emitted by a diesel engine (concentration: 10 mg cme2). To accelerate the process of SO2 attack on the limestone surfaces and to reproduce the natural condition of the building, all slabs were wetted. It was pointed out [28-301, this would accelerate the sulfate attack by means of SO2 dry deposition process. After 24 h from the beginning of the exposure, one set of samples (a-d) was removed from the chamber and immediately, their surfaces exposed to the attack, were submitted to XRD and SEMEDS analyses. After 48 h from the start of the experiment, the very same operation was performed on a second set of samples. 3. Results and discussion 3.1. Material from the building In rock samples with incipient weathering it was
of the Total
Environment
187 (19%)
79-91
Fig. 2. Polarizing microscopy photomicrographs of black crusts: (a) Incipient crust with particulate matter (indicated by arrows), plane light; (b) developed crust, mainly composed of acicular gypsum crystals (crossed Nicols). Bar scale, 200 pm.
possible, as a rule, to observe by means of polarizing microscopy, a thin layer of tiny acicular gypsum crystals surrounded by clay minerals and calcium oxalate (weddellite). These phases were immersed in a dark matrix (Fig. 2a) of very porous particulate matter (soot) in conjunction with smooth, metal-rich spheres (as deduced from SEM-EDS data). The samples of black crusts (Fig. 2b) contained acicular gypsum crystals (up to 200 pm). Also, in central areas that were in contact with the limestone, several types of pollutants enclosed in a matrix of calcite crystals and microcrystalline gypsum (Fig. 2a,b) were also seen. However, there were not properly identified by this technique, due to their small size (average diameter < 2 pm). XRD analyses of rock samples with incipient weathering (limestones with very thin, - 1 mm thick, black crusts), clearly indicated that calcite is
C. Rodriguez-Navarro. E. Sebastian / The Science oj the Total Environment 187 (19%) 79-91
83
Table 1 Comparison of the concentration of principal metallic elements of undecayed quarry limestone (fresh) and different samples from the building Sample
V
Fresh Initial Initial Initial Crust crust Crust Crust CNst
13 18
9 17
10 14 10 10
10 15 44
CNSt
Dust Dust Dust Dust Dust Dust
crust (1) crust (2) crust (3) (1) (2) (3) (4) (5) (6)
Cr
8 11
31
44 36 29 38 65 57
13
(4) (5) (6)
2 2 2 3 2 2 2 4 6 3 3 2 2 6
164
10
(2) (3)
Ni
30 18 22
17 22 36 26 24
(1)
co
44 53 56
cu 4.2 7.3 8.1 12.2 56.5 37.5
8
27.7 26.6 48.8 57.5 44.2 39.4
15.8 30.8 16.1 54.8 34.8 53.7 40.8 70.0 82.1 53.7 98.3 123.0 142.0
15
100.1
113.0
31 18
61.5 96.5
124.9 191.0
3 6 5 4
11 8
10.5
91 7 9 9
11 10
Zn
Pb
Fe 4 18 2 37 83 209 29 130 72
11300 260 3740 193 439 352 677
629 1538 1188 1503 3951 4720 1608 2308 4557 7203 7448 4021 4196
Mn 154 77 77 310 154 232 77 77 481 309 310 232 464
11 644
154
11480
225 463
11 826
All element concentrations in ppm. The fresh sample was taken from an ancient quarry and reflects the average composition of these materials. Samples from the building (Initial crust, Crust and Dust) are identified by number (reflecting their different locations).
the major phase, followed by clay minerals, quartz, and small amounts of gypsum. In the most developed black crusts (thickness greater than 2 mm and up to l-2 cm), gypsum is the major phase, with calcite, quartz, clay minerals, and oxalates (weddellite) as minor components. Analysis of the accumulated dust revealed the presence of a small amount of gypsum together
z
300
2 ;I a
225
+e Y z
150 75 0 1 0
I 20
40
60
80
100
Gypsum (wt%) Fig. 3. Gypsum concentration versus amount of Pb, Zn and Cu in black crust developed on limestone surfaces of Granada Cathedral.
with quartz and clay minerals, the latter being the most abundant. Minor quantities of weddellite, feldspars and iron oxides were also found. Detailed analysis of the
