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Atmospheric Environment 45 (2011) 4986e4995

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Atmospheric Environment

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Diagnosis of surface damage induced by air pollution on 20th-centuryconcrete buildings

I. Ozga a,*, A. Bonazza a, E. Bernardi b, F. Tittarelli c, O. Favoni c, N. Ghedini a,d, L. Morselli b, C. Sabbioni a

a Institute of Atmospheric Sciences and Climate, ISAC-CNR, via Gobetti 101, 40129 Bologna, ItalybDepartment of Industrial Chemistry and Materials, University of Bologna, Viale del Risorgimento 4, 40136 Bologna, ItalycDepartment of Materials and Environmental Engineering and Physics, via Brecce Biance, 60131 Ancona, ItalydDepartment of Pharmaceutical Sciences, University of Bologna, via Belmeloro 6, 40126 Bologna, Italy

a r t i c l e i n f o

Article history:Received 30 July 2010Received in revised form25 May 2011Accepted 27 May 2011

Keywords:Concrete buildingBlack crustCarbon fractionEnrichment factorCombustion sources

* Corresponding author. Tel.: þ39 0516399569; faxE-mail address: i.ozga@isac.cnr.it (I. Ozga).

1352-2310/$ e see front matter � 2011 Elsevier Ltd.doi:10.1016/j.atmosenv.2011.05.072

a b s t r a c t

The present work focuses on the impact of anthropogenic multi-pollutants on modern concrete build-ings exposed in two different European urban areas: Centennial Hall in Wroclaw (Poland) and CasaGalleria Vichi in Florence (Italy). Through a range of analytical techniques the complete characterizationof the damage layer collected from the buildings under study has been achieved for the first time,including quantitative measurements of the carbon content. The experimental results allow the iden-tification and prioritization of the air pollutants responsible for the surface deterioration, findinggypsum to be the main damage product on surfaces sheltered from rain runoff, with embeddedparticulate matter, especially carbonaceous particles, responsible for darkening of the building walls. Thediscrimination of carbon fractions shows different concentrations of elemental and organic carbonwithin the damage layers, depending on the location of the buildings. This step is essential for identi-fying the anthropogenic sources causing deterioration on the buildings, including the aestheticimpairment of surfaces. The contribution of air pollutants is also reflected by the elements found in thedamage layers, while the evaluation of the enrichment factors is useful for identifying the elements ofanthropogenic origin.

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1. Introduction

It is now well known that air pollution accelerates surfacedeterioration on buildings, monuments and outdoor statues inurban areas (Steiger, 2003; Smith et al., 2008; Varotsos et al., 2009).The phenomenon has been extensively studied, focusing on lime-stone, marble and granite, in view of their widespread use in theconstruction of many famous European monuments (Del Monteet al., 1981; Sabbioni, 1995; Schiavon, 2007). Research performedon the deterioration of natural stones due to atmospheric pollut-ants indicates that SO2 and particulate matter, primarily due tofossil fuel combustion, are the most dangerous agents. Specialattention has been devoted to the dark component of aerosols,referred to as black carbon (soot), which causes the blackening ofbuildings. Experimental research has been performed on this issueas part of the EU project MULTI-ASSESS, with the measurement ofparticle deposition at 35 test sites in Europe in order to evaluate

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how qualitative and quantitative variations in atmospheric partic-ulate matter concentrations are connected to the corrosion ofmaterials (Ferm et al., 2006). The formation of so-called black crustsalso results in an increase in surface roughness and retention ofparticulate matter (Ghedini et al., 2006). The characterization ofblack crusts on carbonate stones, such as marble and limestone, hasindicated gypsum to be the main component, with embeddedairborne particulate matter, including carbonaceous particles(Bonazza et al., 2005). It is recognized that carbonaceous particlesare an important component of atmospheric aerosols, includingelemental carbon (EC), organic carbon (OC), sulphur and heavymetals (Kupiainen and Klimont, 2007). Their composition deter-mines the role they have in building deterioration: the elementalcarbon causes darkening, while the heavy metal content andspongy morphology catalyse the heterogeneous oxidation of SO2(Benner et al., 1982; Hutchinson et al., 1992). Papers providingquantitative data on elemental and organic carbon fractions indamage layers on stonemonuments are scarce in the literature. Thefew works published evidence that the discrimination andmeasurement of carbon fractions in damage layers may be animportant tool for identifying fixed and mobile combustion

Fig. 1. Centennial Hall, Wroclaw (Poland).

Fig. 2. Casa Galleria Vichi, Florence (Italy).

I. Ozga et al. / Atmospheric Environment 45 (2011) 4986e4995 4987

sources. They also show that the most recent damage layers arecharacterized by higher concentrations of organic carbon thanhistoric black crusts, and that local sources of pollution, particularlyvehicular traffic, play the leading role in building surface damage(Bonazza et al., 2005, 2007). It is now recognized that mobilecombustion sources are the most important factor determining theair quality in urban centres. In fact, while concerted Europeanpolicy actions have led to a decrease in sulphur dioxide emissions,increasing traffic densities have caused an increase in nitrogencompounds, ozone and particulates, thus giving rise to a newpollutant situation (Ferm et al., 2005).

Despite many studies devoted to environmental damage oncultural heritage, deterioration on cement mortars, characteristic of20th-century architecture, is still not well explored. The literature onthis issue mainly focuses on the following aspects, which still requiredeeper investigation: CO2/H2CO3 (carbonation), SO2/H2SO4 (sulpha-tion), NOX=HNO

�3 cement components interaction (Sabbioni et al.,

2001; Zivica and Bajza, 2001; Yates, 2003; Van Balen et al., 2003;Tittarelli et al., 2008; Ozga et al., 2009). Marinoni et al. (2003) showthat black crusts developing on inside walls of a concrete tunnel inMilan (Italy) have a similar composition to the typical crust found oncarbonate materials: gypsum as main component, with embeddedparticulate matter produced by fuel combustion.

The present work sets out to investigate the interactions betweencement materials and environmental multi-pollutants, to further theknowledge of the processes that cause soiling and surface blackeningon 20th-century buildings. For this purpose, two cement buildings inEuropean urban areas exposed to different pollution sources, wereselected for sampling and analysis of damage layers and black crusts:Centennial Hall, Wroclaw (Poland) and Casa Galleria Vichi, Florence(Italy). The main objective of the work is to identify and prioritize themain air pollutants responsible for surface deterioration, highlightingthe combustion sources contributing to the damage at each site.A complete characterization of the carbon fractions present in damagelayers on cement buildings is performed for the first time, this beinga key factor for understanding the role played by pollutant sources insurface deterioration.

I. Ozga et al. / Atmospheric Environment 45 (2011) 4986e49954988

2. Material and methods

2.1. Sampling

Sampling was performed on two concrete buildings: CentennialHall and Casa Galleria Vichi. The Centennial Hall (Fig. 1) is located inthe urban area ofWroclaw, a city in one of themost industrialized andpolluted regions of Poland, the Silesian Coal Basin. In addition, thebuilding is situated in the neighbourhood of coal-fired power stations,the closest of which is just 10 km west of the monument. TheCentennial Hall, a landmark in the history of reinforced concrete, wasbuilt in 1913 to the design of Max Berg, and in 2006 it was added toUNESCO’s prestigious list of World Heritage Sites, as one of the mostimportant achievements of 20th-century architecture.

The second building studied, Casa Galleria Vichi (Fig. 2), stands inthe historic centre of Florence, where traffic is the most significantsource of air pollution. The building is directly exposed to vehiculartraffic pollutants emitted from the adjacent road. The Casa GalleriaVichi was designed by architect Giovanni Michelazzi in 1911, in theArt Nouveau style, and is the only example of this style in the centreof Florence. The eccentric narrow facade includes structural andsculptural fantasy motifs composed of a mix of artificial stone, steeland glass.

The sampling sessions at both sites were performed at differentheights, starting from ground level and taking account of exposureto rain water. Details of the 36 samples collected are listed Table 1.

During sampling on Centennial Hall black crusts of a maximumthickness of 2e3 cm were observed in the highest part of thebuilding in areas protected from rain runoff. In the case of CasaGalleria Vichi, two types of damage layers were distinguished: dark

Table 1Description of the samples collected at Centennial Hall (Wroclaw) and Casa Galleria Vich

Sample Monument City Height (m) Side/sampling

CH2 Centennial Hall Wroclaw 1.5 NorthCH3 Centennial Hall Wroclaw 1.5 NorthCH4 Centennial Hall Wroclaw 1.5 SouthCH5 Centennial Hall Wroclaw 1.5 SouthCH9 Centennial Hall Wroclaw 12 EastCH14 Centennial Hall Wroclaw 14 SouthCH15 Centennial Hall Wroclaw 14 EastCH17 Centennial Hall Wroclaw 14 South-EastCH18 Centennial Hall Wroclaw 14 NorthCH19 Centennial Hall Wroclaw 14 SouthCH21 Centennial Hall Wroclaw 14 EastCH22 Centennial Hall Wroclaw 12 SouthCH23 Centennial Hall Wroclaw 12 SouthCH26 Centennial Hall Wroclaw 27CH27 Centennial Hall Wroclaw 27CH29 Centennial Hall Wroclaw 27 WestCH38 Centennial Hall Wroclaw 40 North WestCH39 Centennial Hall Wroclaw 40 EastCH40 Centennial Hall Wroclaw 40 EastCH41 Centennial Hall Wroclaw 40 North-EastCH42 Centennial Hall Wroclaw 12 North WestBOS1 Casa Galleria Vichi Florence 19 Dragon of theBOS2 Casa Galleria Vichi Florence 19 Central partBOS3 Casa Galleria Vichi Florence 19 Dragon on theBOS4(2) Casa Galleria Vichi Florence 19 Dragon on theBOS6 Casa Galleria Vichi Florence 15 Shell on the leBOS5 Casa Galleria Vichi Florence 19 Central partBOS7 Casa Galleria Vichi Florence 15BOS8 Casa Galleria Vichi Florence 15 Mask on the lBOS9 Casa Galleria Vichi Florence 15 FrameBOS10 Casa Galleria Vichi Florence 15 Mask on the rBOS11 Casa Galleria Vichi Florence 15 Frame on theBOS12 Casa Galleria Vichi Florence 11 FrameBOS13 Casa Galleria Vichi Florence 7 Mask on the rBOS14 Casa Galleria Vichi Florence 5 Sculpture on tBOS16 Casa Galleria Vichi Florence 5 Sculpture on t

coherent crust strongly attached to the surface, and incoherent greydeposit (contemporary dust) with a powdery consistency.

2.2. Analytical techniques

The structural, textural and petrographical properties of thecollected samples were provided by optical microscopy observations(OM) on thin sections in transmitted light, utilizing an Olympus BX51microscope. An X-ray diffractometer Philips PW 1730 was used toidentify themain crystalline phases in powdered samples. The surfacemorphological and elemental characterization of the damage layerswas obtained by scanning electron microscope equipped withdispersive energy analyzer (SEMeEDX Philips XL 20). The quantifica-tionof gypsumandcarbonateswasperformedbymeansofdifferentialand gravimetric thermal analysis (DTAeTGA) using a METTLERTOLEDO TGA/SDTA 851, equipped with a TSO 800GC1 programmablegas switch. The anion concentrations were measured employinga DIONEX 4500i Ion Chromatograph: the low concentration limit foranions is 0.01 ppm,with the exception of Cl�, NO3

�, where the limit is0.001 ppm, and the relative standard deviations (RSD) are alwayslower than 5%. The carbon fractions present in damage layers werediscriminated and measured by flash combustion/gas chromato-graphic analysis using a CHNSOEA 1108 FISONS Instrument, followingthemethodologypublishedbyGhedini et al. (2006). Themethodologydistinguishes total carbon (TC), composed of carbonate carbon (CC)and noncarbonate carbon (NCC) and, in turn, fractions of NCC, i.e.elemental carbon (EC) and organic carbon (OC); the RSD is 0.2e7.0%.Finally, the elemental chemical analysis was performed by coupledplasma-optical emission spectrometer (ICP-OES), Circular OpticalSystem CIR.O.S.CCD; the RSD for all the metals analyzed is 0.5e10.0%.

i (Florence).

area Protection from rain Description

Sheltered Grey coherent crustPartly sheltered Grey coherent crustPartly sheltered Fragment (substrate and damage layer)Sheltered Grey crustPartly sheltered Grey coherent crustPartly sheltered Grey coherent crustPartly sheltered Crust from partPartly sheltered Dark crustSheltered Dark crustSheltered Fragment (substrate and damage layer)Partly sheltered Fragment (substrate and damage layer)Sheltered Fragment (substrate and damage layer)Sheltered Fragment (substrate and damage layer)

SubstrateSubstrate

Partly sheltered Fragment (substrate and damage layer)Sheltered Thick dark crust, with rough surfaceSheltered Fragment (substrate and damage layer)Sheltered Fragment (substrate and damage layer)Sheltered Fragment (substrate and damage layer)Sheltered Coherent grey crust

left Sheltered Coherent dark crust, rough surfaceSheltered Fragment (substrate and damage layer)

right Partly sheltered Dark coherent crust, probably biologicalright Substrateft Sheltered Dark coherent material, smooth surface

Sheltered Grey incoherent depositSubstrate

eft Sheltered Incoherent dark grey deposit materialPartly sheltered Grey incoherent deposit material

ight Sheltered Dark coherent material, smooth surfaceright Partly sheltered Grey incoherent deposit material

Sheltered Grey incoherent deposit materialight Sheltered Incoherent dark crusthe right Partly sheltered Dark coherent crust, rough surfacehe left Partly sheltered Dark coherent crust, rough surface

Fig. 3. Optical micrographs, several black particles are clearly identifiable embedded inthe gypsum matrix, sample collected from Casa Galleria Vichi observed in planed-polarised light (a), damage layer with clearly visible crystal of gypsum, samplecollected form Centennial Hall observed in cross-polarised light (b).

I. Ozga et al. / Atmospheric Environment 45 (2011) 4986e4995 4989

To understand the origin of the elements detected in the blackcrust specimens, the data obtained during ICP-OES analysis wereanalyzed statistically. Firstly, to identify patterns in elemental data,highlighting similarities and differences, the calculation of principalcomponents and factor analysis (by Varimax rotation)was carried outusing the Q-Parvus 3.0 software package (Forina et al., 2001). Ina second phase, a preliminary screening was performed to identifythe elements with a significant positive difference between theirconcentrations in the damage layers and in the original substrate, bymeans of a one tailed t-test, at level of significance a ¼ 0.05. Theelementswere then considered in order to calculate, for the first time,the enrichment factor (EF) for cement materials, which indicates thepreferential associationof elements to the substrate or to atmosphericdeposition. The EF was evaluated using the following formula:

EFðXÞ ¼ ½X�blackcrust=½Al�blackcrust½X�substrate=½Al�substrate

where [X] and [Al] represent, respectively, the concentration ofa generic element X and aluminium in the black crust andsubstrate. Aluminium was employed as reference element, basedon the chemical composition of Portland cement mortar, assuminga smaller contribution of Al from pollution. It was assumed that, ifthe value of EF (X) > 5, element X was present in the crust due toatmospheric deposition, and did not belong to the original buildingmaterial (Gao et al., 2002; Arditsoglou and Constantini, 2005). Thenext step in the investigation was the discrimination between thenatural (soil dust) and anthropogenic origin of the elements fromatmospheric deposition (EF (X) > 5). This was done by calculatingthe crustal Enrichment Factor EFcrust (X) (Sabbioni and Zappia,1992) with respect to the composition of the Earth’s upper crust:

EFðXÞ ¼ ½X�blackcrust=½Al�blackcrust½X�uppercrust=½Al�uppercrust

;

where Al is used as reference element and X is the concentration ofa generic element X in the damage layer and in the Earth’s uppercrust (Rudnick and Gao, 2003). The elements with values of EFcrust(X) > 20 were considered to be typical of aerosols emitted byanthropogenic sources.

3. Results and discussion

3.1. Optical and scanning electron microscopy

The OM observations on transversal thin sections indicated thatthe external surfaces of the samples from both buildings werecovered by a non-homogenous damage layer (Fig. 3). The crustsanalyzed were characterized by different thicknesses: those fromthe Centennial Hall had a maximum thickness of 850 mm in areasprotected from rain runoff, whereas in the case of Casa Galleria Vichithe damage layer was thinner, with maximum thickness of 400 mmin areas not exposed to rainwater. At both sites, damage layers werecomposed mainly of gypsum, quartz and iron oxides. Additionally,black carbonaceous andwhite or yellow transparent aluminosilicateparticleswere frequently observed embedded in the gypsummatrix.

The OM observations of the underlying material (substrate)from the two buildings indicated it to be cement mortar, withcoarse texture and binder presenting the typical mineralogical andmorphological features of hydraulic components. The mineralog-ical composition of the aggregate was identified as mainly mono-crystalline and polycrystalline quartz, fragments of silicatic stonesand sporadic feldspar crystals. Furthermore, in samples of substratefrom Casa Galleria Vichi, fragments of carbonate stones and calcitewere identified.

The SEMeEDX analyses confirmed the presence of gypsum,withglobular and lamellar shape, in samples of damage layers from bothWroclaw and Florence. Two particle typologies were identifiedembedded in the gypsummatrix: (1) spherical shape particles withsmooth surface (Fig. 4), characterized by the presence of silicon andaluminium, the main elements typical of aluminosilicate particlesfrom coal combustion (Jab1o�nska and Smo1ka-Danielewska, 2003);(2) particles with spongy structure (Fig. 5) mainly characterized byS, typical of carbonaceous particles from oil combustion (Del Monteand Sabbioni, 1984).

3.2. XRD and DTAeTGA analyses

The crystalline phases of the samples, identified by X-raydiffraction analyses, are listed in Table 2.

The results obtained for the Centennial Hall samples show thatspecimen CH27, characteristic of the substrate, is composedprimarily of quartz and traces of calcite, portlandite and feldspar,attributable to the binder and aggregates of the mortar. Specimensof black damage layer, CH17 and CH38, collected from a partiallyand completely sheltered surface, respectively, show gypsum andquartz as the main components, followed by hematite andilmenite; in the case of CH17 calcite and rutile were also detected.Quartz and calcite may be linked to both the underlying material

Fig. 4. Scanning electron micrograph (a) with relative EDX spectrum (b) of alumino-silicate particles in a sample from Centennial Hall.

Fig. 5. Scanning electron micrographs (a) with relative EDX spectrum (b) of carbo-naceous particles in a sample from Casa Galleria Vichi.

I. Ozga et al. / Atmospheric Environment 45 (2011) 4986e49954990

and atmospheric deposition (soil dust, fly ash). The crystal phasesoccurring only in damage layers, such as gypsum, hematite,ilmenite, magnetite and rutile, are related mainly to atmosphericdeposition. The results for the Casa Galleria Vichi samples alsoshow quartz, calcite and feldspar as the main crystal phases of thesubstrate (BOS4(2)), associated with traces of rutile. The presenceof quartz, calcite and feldspar is attributable to the binder andaggregates of the concrete. In general, the minerals present only indamage layer samples are gypsum (most abundant in coherentblack crusts: BOS6 and BOS16), hematite and ilmenite.

The results of DTAeTGA analyses on the representative specimensare listed in Table 3. The data obtained for the sample representingthe substrate of Centennial Hall (CH27) show significant mass loss ofwater up to 230 �C. This effect can be ascribed to surface waterdesorption as well as water loss from CeSeH gel (Gabrov�sek et al.,2006). Moreover, the alumino and silicate cement phases under-went decomposition up to 429 �C. The further thermal reaction is thedehydroxylation of portlandite up to 520 �C, followed by decarbon-ation of carbonates up to 776 �C. The analysis of the damage layersfrom the Polish site highlighted the dehydration of gypsum between90 �C and 220 �C, with the highest amount of 87% in the sample ofthick black crust (CH38). The DTAeTGA analyses of the Casa GalleriaVichi samples showed that in specimen BOS4(2), representing theunderlying material, the decomposition of carbonates occurredbetween 600 �C and 850 �C, with an amount of 25%. Considering thedamage layer, gypsum showed significant amounts in samples withcoherent black crust (BOS6, BOS14, BOS16) ranging from 42% to 66%,

and smaller amounts in samples with incoherent deposit, 9e33%(BOS5, BOS12). Carbonates were also detected in both incoherentdeposits and crusts, in amounts ranging from 7% to 58%.

In both buildings, gypsumwas the main mineral encountered inthe damage layers, thus confirming the results from optical andscanning electron microscopy. Gypsum forms due to the depositionof atmospheric SO2/H2SO4 and the subsequent interaction withcement components (Martínez-Ramírez and Thompson, 1998;Pavlĭk et al., 2007).

3.3. Ion chromatography

Anion compositions and concentrations measured by ion chro-matography allowed a better understanding of acid deposition onthe building surfaces. The results for samples from Centennial Hall(Table 4) indicate that sulphate (SO4

¼) is the most abundant anion,observed in the highest values in black crust samples from shel-tered areas e.g. CH18 (50%), and CH38 (41%). Lower concentrationsare observed in samples from partly protected areas, witha minimum of 0.8% in sample CH15. In samples of damage layersfrom Casa Galleria Vichi, sulphate concentrations range from 2% to42%, with a greater contribution in samples of coherent black crusts(mean concentration equal to 36%) than in incoherent deposit(mean equal to 14%). The higher concentration of sulphate inspecimens of black crust is linked to the greater amount of gypsumin these samples. As revealed during DTAeTGA analyses, this maybe an effect of advanced sulphation and complete protection fromrain runoff. In studies performed on damage layers on granite,oolitic limestone, ancient mortars and Carrara marble, sulphate hasalso been found as the most abundant anion (Gobbi et al., 1998;Bonazza et al., 2005; McAlister et al., 2006).

Table 2Main crystalline phases revealed by x-ray diffraction in the analyzed damage layers and substrates collected at Centennial Hall (Wroclaw) and Casa Galleria Vichi (Florence).

Sample Gypsum Quartz Calcite Portlandite Feldspars Magnetite Hematite Ilmenite Rutile

Centennial HallCH17 þþ þþþþþ tr þ tr trCH27a þþþþþ tr tr trCH38 þþþþþ þ þ þ þCH41b tr þþþþþ þ þ tr tr þCasa Galleria VichiBOS2 þ þ þþþþþ þBOS4(2)a þþþþþ þþþþ þ trBOS5 þþ þþþþþ þ þ þ þBOS6 þþþþþ þþþ þþþ þ þBOS12 þþ þþþþþ trBOS14 þ þþþþþ trBOS16 þþþ þ þþþþþ þ tr

þþþþþ Main mineral present; þþþþ/þþþ very abundant; þþ abundant; þ present, tr: tracers.a Substrate.b Fragment of substrate and damage layer.

Table 4Anion concentration (mg g�1) measured by ion chromatography in damage layersand substrates collected at Centennial Hall and Casa Galleria Vichi.

Sample SO4¼ NO3

� NO2� Br� Cl� CHO2

� C2H3O2� C2O4

¼

Centennial HallCH2 110,685 921 338 673 486 1229 6370 1052CH3 84,269 1004 201 398 673 811 4507 1005CH4 70,903 400 291 333 520 989 3953 457

I. Ozga et al. / Atmospheric Environment 45 (2011) 4986e4995 4991

Nitrates (NO3�) and nitrites (NO2

�) were detected in very vari-able amounts, with higher concentrations of NO3

�, especially insamples from Casa Galleria Vichi, (Table 4), where NO3

� has thehighest concentration in samples of incoherent deposit (contem-porary dust), a fact that can be linked to intense traffic emissions inthe surrounding area (Schifter et al., 2000). The predominantconcentrations of NO3

� over NO3� have also been observed in

damage layers collected from stones (Ghedini et al., 2000).Concentrations of Cl� were also detected, which in the case of

Florence may be attributed mainly to marine aerosol deposition,since Florence is located around 100 km from the Tyrrhenian Sea.Moreover, amounts of Br� were detected, particularly in the Polishsamples, where its presence can be ascribed to gasoline combustion(Sabbioni, 1995).

The IC results also indicate the presence of significant amountsof organic anions, such as formate (CHO2

�), acetate (C2H3O2�),

oxalate (C2O4¼). Themean acetate concentration is higher than that

of other organic anions at both Centennial Hall (0.8%) and CasaGalleria Vichi (0.8%).

The role of short chain organic anions (acetate, formate, oxalate)in the deterioration of cement materials, and also in natural stones,is still not well understood. Studies investigating the presence oforganic anions on stones, such as limestone and sandstones, indi-cate three main origins: (1) deposition of primary and secondaryatmospheric pollutants, (2) biological weathering and (3) restora-tion treatments (Sabbioni et al., 2003; Saiz-Jimenez, 1993, 1995;Rossi Manaresi, 1996). However, in the cases of Centennial Hall and

Table 3Percentage (%) concentrations of gypsum, carbonates and portlandite in samplesfrom Centennial Hall (Wroclaw) and Casa Galleria Vichi (Florence) obtained byDTAeTGA analyses.

Sample Portlanditeb Gypsumc Carbonatesd

The Centennial HallCH27a 2.45 7.47CH38 87.35CH42 31.75Casa Galleria VichiBOS2 14.54 57.62BOS4(2)a 25.09BOS5 32.97 7.43BOS6 50.20 18.55BOS12 9.06 70.28BOS14 41.85 41.99BOS16 66.02 11.36

a Substrate.b Calculated as Ca(OH)2.c Calculated as CaSO4$2H2O.d Calculated as CaCO3.

Casa Galleria Vichi, no information on restoration treatments isavailable. It has been proved that organic compounds emitted bydiesel exhaust particulate (DEP), radial tyres used in summer, andasphalt in asphalted pavements, decalcify cement concrete (Tomotoet al., 2009).

Even though the samples were collected at different heights, novertical gradients were observed for any of the anions. It is knownthat the effect of a building on the dispersion of a stationary sourceplume is, in general, dependent on the building geometry, sourcelocation, prevailing wind distribution and wind-driven rain(Thompson,1993; Etyemezian et al.,1998; Tang et al., 2004). However,theoretical considerations are very difficult to attempt in the absenceof direct measurements. At the same time, it must be borne in mindthat damage layers are an integral result of accumulation over time.Thus, measurements of today’s atmospheric composition and climateparameters, such as wind, cannot be considered an exhaustiveexplanation for damage layer formation, although such data cansupport the development of preventive conservation strategies andprovide input for future damage assessment.

CH5 27,104 174 86 183 171 272 n.d. n.d.CH9 39,172 700 839 n.d. 137 4799 1659 367CH14 99,623 808 300 808 322 1375 5553 1353CH15 8228 144 n.d. n.d. 93 135 n.d. 173CH18 502,320 1751 n.d. 2503 794 5851 n.d. n.d.CH27a 2779 321 169 n.d 237 226 7684 461CH38 410,361 550 569 2015 664 9020 32,948 95CH42 135,684 659 332 394 561 4729 6082 n.d.Casa Galleria VichiBOS1 421,846 4823 148 1275 3100 2274 12,098 5568BOS4(2)a 7325 166 113 n.d. 363 286 2775 135BOS3 98,608 4460 363 710 3272 226 5688 2357BOS5 122,651 9950 626 n.d. 11,616 168 7878 3102BOS6 112,250 2148 28 n.d. 1890 111 7878 3538BOS8 206,734 8141 28 n.d. 8715 117 7932 1285BOS9 221,166 7439 28 n.d. 7606 158 9490 1743BOS10 389,626 3285 36 n.d. 1835 126 8462 386BOS12 25,676 879 70 n.d. 1557 278 3706 3999BOS13 202,441 19,003 70 n.d. 14,796 184 11,817 1561BOS14 251,455 3020 29 n.d. 1812 128 9791 1068BOS16 381,331 3989 29 n.d. 2505 2095 9504 n.d

n.d. ¼ Not detected.a Substrate.

I. Ozga et al. / Atmospheric Environment 45 (2011) 4986e49954992

3.4. CHNSO analyses

In Table 5 the discriminated carbon fractions in the damagelayers and their concentrations are expressed as percentages of thesample total mass. Considering the Centennial Hall, the total carbonranges from aminimumof 0.3% to amaximumof 3%. Non carbonatecarbon represents an important fraction of TC, ranging from 68% to96%, and it predominates over CC in all samples from CentennialHall. The strong contribution of NCC to TC reflects the input ofatmospheric deposition in the damage layer formation. In turn,taking into account the fractions of NCCe the elemental carbon andorganic carbon e it is observable that EC makes the highestcontribution to NCC in samples of black crust (CH18 and CH38),where the highest amounts of SO4

¼ are also present. Conversely, OCpredominates over EC in samples of grey crust (CH9, CH15, CH42),achieving 100% of NCC in samples CH9 and CH15.

The carbon fraction in the samples from Casa Galleria Vichi(Table 5) indicates that the total carbon concentration ranges from4% to 17%. The mean concentration of TC for all samples is 9%,higher than the value detected in samples from Centennial Hall,where the TC mean is 2%. Considering the fractions of TC in Flor-ence, NCC is present in highly variable amounts, from a minimumof 29% to a maximum of 91% of TC, with the greatest contribution insamples of coherent black crust. The CC predominated over NCC insamples BOS8 and BOS16. In the case of BOS16, this result is inagreement with the DTAeTGA analyses, where the contribution ofcarbonates was also identified. The CC observed in samples fromCasa Galleria Vichi could possibly be due to a low coherency of thebuilding material collected as samples. Considering the NCC frac-tions, in the case of Florence, the EC ranges from 3% to 5% of thetotal mass of sample, with higher concentrations than those foundin the Centennial Hall samples. The values of OC are very variable,with a maximum of 6% in sample BOS3.

It should be underlined that EC constitutes a qualitative index ofthe black carbonaceous particles embedded in damage layers(Lanting, 1986). Moreover, it is demonstrated that OC and ECconcentrations emitted into the atmosphere by combustionprocesses depend on the fuel used and burning efficiency (Cachier,1998). Coal and oil combustion at relatively low temperatures andpoor efficiency increase the EC emission factor. Elemental carboncomes from combustion-generated aerosols (Kupiainen andKlimont, 2007) and the areas of location of the two buildingsunder study are characterized by different, but intense, combustion

Table 5Total carbon (TC), carbonate carbon (CC), non carbonate carbon (NCC), elementalcarbon (EC) and organic carbon (OC) concentration (%) and OC/EC ratio in thedamage layers collected at Centennial Hall (Wroclaw) and Casa Galleria Vichi(Florence).

Sample TCa CCc NCCb ECb OCc OC/EC

Centennial HallCH9 1.01 0.20 0.81 n.d. 0.81CH15 1.57 0.31 1.26 n.d. 1.26CH18 3.12 0.99 2.14 1.26 0.88 0.69CH38 2.79 0.27 2.52 2.29 0.23 0.10CH42 0.26 0.01 0.25 0.03 0.22 8.02Casa Galleria VichiBOS1 3.68 0.32 3.36 3.01 0.35 0.12BOS3 11.23 2.34 8.89 3.13 5.77 1.84BOS5 10.03 4.18 5.85 2.64 3.21 1.22BOS8 16.73 11.88 4.85 4.52 0.33 0.07BOS13 7.30 1.29 6.01 2.80 3.21 1.15BOS16 8.59 4.59 4.00 3.13 0.87 0.28

n.d. ¼ Not detected.a Measured on bulk sample.b Measured on treated samples.c Calculated.

processes. In the case of Centennial Hall, EC is linked to stationarysources, such as coal-fired power stations and domestic heatingsystems. In case of Casa Galleria Vichi, surrounded by intense roadtraffic, the EC comes mainly from mobile fossil fuel combustion(principally diesel) (Kupiainen and Klimont, 2007). Organic carbon(like organic anions) can have different origins: primary airpollutants from incomplete fossil fuel combustion, secondary airpollutants, biological weathering and restoration treatments. Thecontribution of organic carbon to the total mass of sample is ingeneral higher in samples from Casa Galleria Vichi than in thosefrom Centennial Hall. Additionally, a significant contribution of OCwas observed in contemporary deposit (BOS5 and BOS13), wherethe highest concentration of NO3

� was also detected, thus provingthe strong impact of mainly diesel vehicle exhaust fumes (Schifteret al., 2000). The OC/EC ratio in the samples of contemporarydeposit is higher than 1, a phenomenon also observed in recentlydeposited material at the Vittoriano Monument in Rome, and onwalls exposed to the effects of traffic-bearing roads e.g. S. Maria DelFiore in Florence, Seville Cathedral (Bonazza et al., 2005).

3.5. ICP-OES

The results of elemental concentrations from ICP-OES, performedon selected samples from the two sites are listed in Table 6. Consid-ering the data from Wroclaw, the elements with highest concentra-tions are Si, Al, Ca, S, Fe and Na. Sulphur has the highest concentrationin a sample of black crust (CH38), thus confirming the DTAeTGAresults, which show the highest amount of gypsum for this sample,and the IC results, which indicate high concentrations of SO4

¼.The principal components analyses on ICP-OES data involved

the rotation of the first three PCs, accounting for 87% of the totalvariance, giving the results shown in Fig. 6. The first factor F1,accounting for 44% of variance, is mainly influenced by theelements characterizing the substrate (sample CH26); theseinclude Mg, Na, Al, Mn, and Fe, which are typical of Portlandcement. By contrast, the second and third factors, accountingrespectively for 22% and 21% of variance, are mainly influenced byAs, Ca, Cu, Pb, S Sn, Zn, characterizing the damage layer (samplesCH19, CH21, CH29, CH38, CH40) and having, therefore, a possibleatmospheric source (As, Bi, Ca, Cu, Cr, Ni, Pb, S, Sn, Zn). In the case ofthe second factor, there is also a clearly visible separation of the twosamples, CH22 and CH23, suggesting their different origin. In fact,these samples were collected from the south wall of an outbuildingof Centennial Hall, probably built in recent years, although infor-mation is lacking on this point. One tailed t-test (significant levela ¼ 0.05) confirmed that the elements of possible atmosphericorigin includemost of those suggested by the factor analysis (As, Ca,Cu, Pb, S, Sn, Zn). Samples CH22 and CH23 again yield quitedifferent results from those of the other samples, in agreementwith the hypothesis of a recent origin of the south wall.

The calculation of the EF showed that As, Cu, Pb, S, Sn, Zn arelinked to atmospheric deposition. Furthermore, the crustalenrichment factors (EFcrust) for these elements achieved valueshigher than 20, also indicating their anthropogenic origin. Sulphurhas the highest value of EFcrust, and can be considered as the mainelement linked to anthropogenic activity, principally emissionsfrom combustion processes (Sabbioni and Zappia, 1992). Consid-ering the location of Centennial Hall, the presence of sulphur,arsenic and tin can be ascribed to fixed combustion sources, such ascoal-fired power generation, industry, and the domestic combus-tion of fossil fuels (Querol et al., 1996). The presence of Cu, Pb andZn in the Centennial Hall damage layers can also be attributed totraffic exhaust (Caselles et al., 2002).

Looking at the data from Casa Galleria Vichi, themean elementalconcentrations indicate higher contributions of almost all elements

inthedam

agelayers

than

inthesu

bstrate,with

theexcep

tionofC

a.Th

emost

abundan

telem

ents

inall

analyzed

samples

areSi,C

a,S,Fe,

Al,

K,Na,

and

Mg.

The

maxim

um

concen

trationsof

Swere

observedin

samples

ofblack

crust

e.g.BOS10

and

BOS16.

This

findingis

ingood

agreemen

twith

thehigh

SO4 ¼

concen

trations

measu

redby

ICan

dwith

thehigh

estamou

nts

ofgypsu

mmeasu

redby

DTA

eTG

Ain

sample

BOS16.

Thefirst

three

prin

cipalcom

pon

ents,togeth

errep

resentin

g95%

ofthetotalvarian

ce,were

rotatedan

dtheresults

aresh

ownin

the

plots

inFig.7.H

ere,three

differen

tgroupsofelem

ents

aresh

ownin

relationto

incoh

erentdep

osit,coh

erentcru

stan

dsu

bstrate.Th

efirst

factor(exp

lained

variance:

56%)is

main

lyinfluen

cedby

elemen

tssu

chas

Ba,C

d,C

o,Cr,C

u,K

,Fe,Ni,Ti,V

,associatedwith

samples

ofincoh

erentdep

osit(BOS5,

BOS8,

BOS9,

BOS13),

and

Table 6Elemental concentrations (ppm) determined by ICP-OES for samples collected at Centennial Hall (Wroclaw) and Casa Galleria Vichi (Florence).

Sample Al As Ba Bi Ca Cd Co Cr Cu Fe K Mg Mn Na Ni P Pb S Si Sn Ti V Zn

Centennial HallCH19 14,324 4 454 210 104,629 5 31 198 52 9617 5600 1572 397 2568 108 n.d. 206 55,117 173,547 15 581 22 1066CH21 12,734 21 234 730 174,142 2 32 731 175 11,214 5434 1914 154 2390 409 n.d. 128 123,520 76,646 32 684 22 174CH22 10,434 n.d. 151 28 31,925 4 4 18 23 4881 4744 710 153 1503 10 n.d. 54 12,082 240,798 6 389 9 111CH23 10,647 n.d. 182 260 39,825 3 5 256 57 4446 4538 710 77 2351 135 n.d. 56 16,211 238,846 11 291 10 65CH26a 23,795 1 345 912 90,200 5 118 925 34 31,653 8252 15,039 602 9288 516 2 10 1522 200,236 2 3718 81 92CH29 11,277 11 207 1953 151,897 4 55 1996 355 14,763 3675 1427 188 2694 1078 n.d. 32 94,796 139,199 n.d. 502 17 141CH38 5174 16 210 32 130,204 2 24 27 73 6999 2238 1049 55 1056 23 n.d. 225 154,121 34,748 9 537 22 140CH40 8938 8 186 53 139,351 3 16 45 74 6377 4347 1460 169 1792 30 n.d. 111 83,261 140,779 10 420 20 225Casa Galleria VichiBOS5 7592 n.d. 976 n.d.. 109,688 4 209 192 1154 39,123 17,200 9252 624 19,979 87 1883 635 61,022 19,4711 4 253 119 568BOS7a 5011 n.d. 130 n.d. 368,702 n.d. 26 17 114 5174 4162 5874 248 6150 6 256 207 47,741 46,188 n.d 24 23 296BOS8 7312 n.d. 862 n.d. 127,231 4 167 129 605 31,525 15,471 7951 566 21,521 63 1328 927 79,069 192,937 11 201 86 955BOS9 6139 n.d. 1029 n.d. 118,928 4 215 197 988 40,118 16,000 8047 556 19,053 84 1711 931 96,346 198,533 4 263 116 525BOS10 7661 n.d. 658 n.d. 232,961 2 91 86 209 18,749 8728 4568 212 8114 30 1000 606 138,614 104,847 1 121 70 223BOS13 7762 n.d. 858 n.d. 92,439 4 202 173 708 32,136 13,773 8742 502 17,181 75 1441 838 83,636 143,457 4 203 102 571BOS16 5150 n.d. 495 n.d. 189,744 1 61 52 283 12,606 6155 3267 139 6465 21 695 603 152,938 68,410 1 74 44 300

n.d. ¼ Not detected.a Substrate.

Fig.6.

Resultsof

theFactor

Analysis

ondata

fromelem

entalanalysis

(ICP-OES),

CentennialHall

(Wroclaw

):F2

vsF1

(a),F3vs

F1(b).

I.Ozga

etal./

Atm

osphericEnvironm

ent45

(2011)4986

e4995

4993

I. Ozga et al. / Atmospheric Environment 45 (2011) 4986e49954994

therefore probably due to the deposition of airborne particulatematter. The substrate sample (BOS7) is on the opposite quadrantand clearly uncorrelated with these elements. On the first factor,a correlation can also be observed between Ca, Zn and Sn andsamples BOS7, BOS10 and BOS16. However, on the second factor(explained variance: 31%), these samples appear to be negativelycorrelated to Zn and Sn and mainly influenced by Ca, as can beexpected for samples coming from the substrate and black damagelayers. The third factor (explained variance: 8%) is essentiallydetermined by S and, secondarily, lead. Fig. 7b (PC3 vs PC1) high-lights the strong association of S to samples of black crust (BOS10and BOS16), where S and Ca can be related to gypsum, and thenegative correlation with the substrate (BOS7).

Fig. 7. Results of the Factor Analysis on data from elemental analysis (ICP-OES), CasaGalleria Vichi (Florence), F2 vs F1 (a), F3 vs F1 (b).

The t-test results also provide an indication as to the possibleorigin of elements (atmospheric deposition or substrate), suggest-ing that, except for Ca and P, almost all the analyzed elements insamples of grey incoherent material and black crusts could have anatmospheric origin. The enrichment factor calculation narrowedthe field, showing that in most of the samples the elements withatmospheric origin (EF > 5) are Ba, Cd, Co, Cr, Cu, Fe, Ni, Pb, S, Sn, Tiand Zn. The calculation of the EFcrust indicated that elements suchas Ba, Cd, Co, Cr, Cu, Ni, Pb, S, Sn and Zn derive from anthropogenicsources (EFcrust > 20). Sulphur again shows the highest enrichment(EFcrust > 1000), with a maximum in samples of black coherentmaterial. The EFcrust of Cd, Cu, Pb and Zn has higher values(EFcrust > 200) in samples with contemporary (incoherent) depositthan in black crusts.

All the elements showing EFcrust > 20 can be tracers of particlesfrom traffic emissions, wear of brake-linings and fossil fuelcombustion (Caselles et al., 2002; Gao et al., 2002; Monaci andBargagli, 2004). The presence of most elements, especially incontemporary (incoherent) deposits, is mainly due to motorexhaust, thus underlining the direct impact on damage layerformation of traffic emissions from roads around Casa GalleriaVichi.

4. Conclusions

The paper focuses on the impact of air multi-pollutants on 20th-century architecture, employing a complete analytical procedure tostudy for the first time the damage layers on two European build-ings mainly constructed in concrete: Centennial Hall, Wroclaw(Poland) and Casa Galleria Vichi, Florence (Italy). SO2 and particlesemitted by combustion sources have been proven to play thepriority role among multi-pollutants in damage layer formation atboth sites and the results obtained show a correlation betweenbuilding location and damage layer composition. In fact, in the caseof Centennial Hall the impact of coal-fired power stations and coaluse for domestic heating is fundamental in causing the surfaceblackening and soiling of the building surface (EC > OC in blackcrusts). The Polish site is located in one of the regions of Europemost polluted by SO2 and in proximity of coal-fired power stations.Conversely, mobile sources (traffic), main emitters of organiccarbon in urban atmospheres, are the principal cause of damagelayer formation at Casa Galleria Vichi, which is located close toa busy street. It has to be underlined that the quantification of ECand OC was a key factor in the discrimination between stationaryand mobile combustion sources of the pollutants affecting the twobuildings, confirming the dominant role of local pollutant sourcesin the respective damage processes.

The processing of elemental data (PCA, EF) has also allowed theidentification of the origin of elements present in the damage layers,confirming that Casa Galleria Vichi is more affected by pollutantsfrom traffic emissions (e.g. Ba, Pb, Zn) and oil fly ash from domesticheating, while the Centennial Hall surface deterioration is mainlycaused by multi-pollutants emitted by coal combustion (e.g. As).

Acknowledgments

This work was performed within “European Ph.D. in Science forConservation (EPISCON)”, promoted by the European Commissionwith 6FP EU- Marie Curie EST Action, and also within the EC Project“Technologies and Tools to prioritise Assessment and diagnosis ofair pollution impact on immovable and movable Cultural Heritage(TeACH)” funded by the European Commissionwithin 7FP (contractnumber: 212458). The authors thank Serena Ricci for her collabo-ration in the work performed on Casa Galleria Vichi.

I. Ozga et al. / Atmospheric Environment 45 (2011) 4986e4995 4995

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