Elements and Ions

In this section, the use elements and ions will be considered in the assessment of pollution sources (isotopic data will be discussed in the next section "Isotopic Tracers (Stable Isotopes)"). Qualitative studies about the presence of certain elements or ions could give indications about the presence of pollutants (see Sabbioni et al. 2003 on organic ions) and can give relevant information for the typology of decay features (Sanjurjo-Sanchez et al. 2008) . The present authors defend that qualitative chemical data regarding presence/absence of substances in decay features, such as those obtained from scanning electron microscopy, can be used for statistical assessment (e.g., contingency tables) of pollution conditions, for example, to compare pollution loads in different façades.

Absolute values of contents of elements and ions have been used to compare decay features and materials (Maravelaki-Kalaitzaki and Biscontin 1999; Valls-del-Barrio et al. 2002; Sabbioni et al. 2003) and to study patterns of distribution of substances in order to discuss the sources of the pollutants and differentiation processes (see, e.g., Wendler et al. 1990; Casal-Porto et al. 1991; Dorn 1998; Maravelaki-Kalaitzaki and Biscontin 1999; Alves and Sequeira Braga 2000; Steiger 2003). Quantification of elements and ions also allows the comparison of contents in different fractions by selective extraction (McAlister et al. 2006).

Enrichment factors are classically used in geochemistry to compare a certain sample with possible sources and evaluate the contribution of these sources. The enrichment factor for a given element or ion compares the concentration of that element or ion in the sample and the concentration of the same element or ion in the possible source (Reimann and Caritat 2000). Such comparison can be normalized by using a reference element or ion that is considered immobile or conservative (Reimann and Caritat 2000). A classical example is the use of chloride or sodium as a conservative ion for the evaluation of seawater and non-seawater fraction in rain composition (Appelo and Postma 2005). However, caution is needed in the use of enrichment factors (see Reimann and Caritat 2000) due to problems arising from the

Fig. 2.11 Schematic representation of the use of ternary diagrams in studies of pollutants effects on building materials: (a) comparison of groups of samples (see examples in Derbez and Lefèvre 1996; Begonha and Sequeira Braga 1996; Alves and Sequeira Braga 2000) where "1" represents a set of samples in which constituent "B" is predominant while "2" represents a set of samples with similar proportions of "A" and "C" and "B" is the minor component (lines could be used for definition of classification fields; see, e.g., Derbez and Lefèvre 1996); (b) trends of evolution, where "I" represents depletion in "A" (keeping similar proportions between "B" and "C") and "II" represents enrichment in "A" over "C" while "B" remains a minor constituent (for examples considering evolution with spatial position of samples see Alves and Sequeira Braga 2000; Moreno et al. 2006)

Fig. 2.11 Schematic representation of the use of ternary diagrams in studies of pollutants effects on building materials: (a) comparison of groups of samples (see examples in Derbez and Lefèvre 1996; Begonha and Sequeira Braga 1996; Alves and Sequeira Braga 2000) where "1" represents a set of samples in which constituent "B" is predominant while "2" represents a set of samples with similar proportions of "A" and "C" and "B" is the minor component (lines could be used for definition of classification fields; see, e.g., Derbez and Lefèvre 1996); (b) trends of evolution, where "I" represents depletion in "A" (keeping similar proportions between "B" and "C") and "II" represents enrichment in "A" over "C" while "B" remains a minor constituent (for examples considering evolution with spatial position of samples see Alves and Sequeira Braga 2000; Moreno et al. 2006)

representativeness of the contents considered as reference as well as to the effects of the fractioning processes. In the case of the built environment, there are examples of using enrichment factors to compare chemical characteristics of decay features with possible pollution sources and with the affected substrate in order to distinguish their contributions (Sabbioni 1995; Torfs and Van-Grieken 1997). Enrichment factors have also been used to compare different zones and different depths of decay features (Maravelaki-Kalaitzaki and Biscontin 1999).

Graphical procedures used in the study of both sources and evolution of pollutants include both bidimensional dispersion plots and ternary plots. Dispersion plots allow the comparison of elements or ions considering signatures of pollution sources and mineralogical relations (Begonha and Sequeira Braga 1996; Begonha et al. 1996) ; They are also useful to study variations in the amounts of elements/ions against a spatial parameter, such as height, in order to study the existence of possible processes of differentiation (Alves and Sequeira Braga 2000; Moreno et al. 2006).

Ternary plots have been applied in the study of pollution of the built environment (see illustration in Fig. 2.11) concerning both atmospheric pollution and salt contamination. Some examples of the use of ternary diagrams in the study of atmospheric pollution include the grouping of atmospheric particles deposited on surfaces (Derbez and Lefèvre 1996) and the study of decay features related to atmospheric pollution (Begonha and Sequeira Braga 1996) ; In relation to salt pollution, ternary diagrams have been used to discuss pollution sources (Alves and Sequeira Braga 2000; Moreno et al. 2006) as well as to assess evolution with spatial position (horizontal/height) of samples (Alves and Sequeira Braga 2000; Moreno et al. 2006).

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