IBIL analysis of road dust samples from San Bernardo tunnel

https://doi.org/10.1016/j.saa.2013.07.058Get rights and content

Highlights

  • Road dust samples of San Bernardo tunnel are characterized by IBIL.

  • Standard BCR-723 and possible sources of road dust particles are analyzed too.

  • Road dust samples and standard BCR-723 exhibit similar IBIL spectra.

  • Six spectral components and two inorganic compounds are identified.

  • IBIL is a useful tool to characterize complex environmental matrices.

Abstract

Road dust in urban or industrial sites is an important source of atmospheric particulate by re-suspension of finer particles that may contain potentially toxic pollutants. In this work Ion Beam Induced Luminescence (IBIL), Nuclear Magnetic Resonance and fluorescence spectroscopy analyses were used to characterize road dust samples with particle size lower than 250 μm collected on the walls and on the floor of the ventilation air shaft of “Traforo del San Bernardo” highway tunnel. Moreover, for comparison, IBIL analyses were performed both on some possible anthropic sources of particulate matter and on a road dust reference sample (BCR-723). IBIL spectra as a function of the fluence were analyzed with a multivariate approach in order to identify the spectral components evolving with different rate. Nuclear Magnetic Resonance and fluorescence spectroscopy analyses were performed on extracted samples of the road dust in order to study the contribution of organic compounds to the IBIL features. Results point out that IBIL, here performed for the first time for road dust analysis, can be applied for the identification of compounds by characterizing the sample origin.

Introduction

Road dust is composed by natural and anthropogenic particles collected on surfaces and along roadsides. This material contributes significantly to atmospheric particulate matter by re-suspension of finer particles [1]. In urban, suburban or industrial centers, it may even represents the dominant source of PM10 (particles with aerodynamic diameter less than 10 μm). Since road dust may contain potentially toxic pollutants such as heavy metals originating from a range of anthropogenic sources, the study of this material is therefore crucial for the choice of pollution reduction policies.

In literature several studies concerning this environmental matrix are reported. In most cases only the elemental composition is probed, for example Apeagyei et al. [2], Fujiwara et al. [3] and Prichard et al. [4] characterized the samples using X-ray fluorescence (XRF), Inductively coupled plasma optical emissions Spectrometry (ICP-OES) and Inductively Coupled Plasma Mass Spectrometry (ICP-MS), respectively. In other cases road dust samples are analyzed by several techniques in order to identify the potential sources. For instance Gunawardana et al. [5] probed road dust samples by Scanning Electronic Microscope (SEM), Energy Dispersive X-ray spectroscopy (EDX) and X-ray Diffraction (XRD) to study the morphology, the elemental and mineral composition, respectively. Instead Bardelli et al. [6] used X-ray Absorption Spectroscopy (XAS), X-ray Diffraction (XRD), Thermo-Gravimetric Analysis (TGA) and SEM–EDS techniques to determine the composition and the speciation of Fe and Mn in road dust samples.

Up to now Ion Beam Induced Luminescence (IBIL) has never been used so far to probe this kind of samples. IBIL is a spectroscopic technique based on the detection of UV, visible and IR radiation emitted by a solid sample excited with an ion beam (H+ or He+) at energy up to a few MeV [7], [8], [9]. The luminescence features in the IBIL spectra depend on the compounds, impurities and defects of the probed samples and on the recombination mechanisms of the excited charge carriers at the emitting centers. Moreover, the high energy density released by the probe induces the luminescence decrease during irradiation due to the damage of the luminescent molecules or to the formation of quenching centers. In some case, the ion-beam promotes the formation of new emitting centers, like defects or radicals, characterized by luminescence features whose intensity initially grows with the fluence [8], [9], [10]. The rate of this change depends on both the incident beam parameters (current density, ion species, and ion energy) and the radiation resistance of the probed material.

Both the luminescence features and the intensity evolution with the irradiation fluence can be used to discriminate the presence of different emitting centers or molecules in the inspected samples. Up to now, IBIL has been extensively used for the analysis of trace elements in geological samples [11], for the study of the defects formation under ion irradiation [9], [10], for the study of the radiation hardness of both inorganic and organic materials [8], [12], [13], [14], [15] and for the discrimination of pigments for cultural heritage [16], [17], [18].

Recently, Valotto et al. [19] developed a method to analyze time evolving IBIL spectra based on the multivariate analysis of a matrix of IBIL spectra collected at fixed time intervals during irradiation. Following this method the main eigenvectors of the covariance matrix of normalized IBIL spectra were studied as a function of the wavelength, allowing to determine the spectral components, evolving with different rate, without any assumption on the number or position of peaks [19].

The aim of this work is to study the effectiveness of IBIL in the analysis of road dust samples, deepening how this technique can get more information on the compounds participating to the formation of the particulate. In particular, road dust from the “Traforo del San Bernardo” tunnel is examined. The spectra collected during irradiation are analyzed by means of a multivariate method in order to identify the main spectral features and an attribution to the luminescence peaks is attempted. The observed components are compared with IBIL spectra collected from possible sources of particulate matter.

Section snippets

Materials and methods

San Bernardo tunnel is located at 30 km from Aosta at the Italian-Swiss border, at about 1900 m above the sea level. Its length is almost 6000 m and it is formed by a single two-lane carriageway with double-way street. Since 2000–2007, the average flux of vehicles has been of 576,000 cars per year and 66,000 truck per year. This is an ideal sampling area to study the particulate emitted from the vehicular traffic, because inside it the road dust: (i) represents the averaged emission from different

Results

Fig. 1 shows normalized IBIL spectra of BCR-723 road dust standard and of four representatives “Traforo del San Bernardo” road dust samples with different particles size (4<63, 4 63-250, A<63, A 63-250). They exhibit a comparable luminescence peak with the maximum located in the 610–620 nm range, a shoulder at about 750 nm, a broad less intense band centered at about 450 nm and a faint feature in the IR part of the spectrum around 850 nm.

Fig. 2 shows four IBIL spectra, acquired after an energy

Discussion

IBIL analysis can be a suitable technique for the analysis of organic and inorganic compounds, owing to the possibility to enlighten the presence of luminescent impurities or compounds, whose spectral features can be used as a signature of the origin of the inspected materials. Moreover, multiparametric analysis of IBIL spectra can give an additional tool for the discrimination of both spectral features and patterns characterizing the probed samples.

In IBIL spectra of road dust samples several

Conclusions

Road dust collect inside the ventilation air shaft of “Traforo del San Bernardo” highway tunnel and some matrices which are the possible sources of particulate matter that constitute it, were analyzed by IBIL spectroscopy. Moreover, it was also analyzed the standard reference material of road dust BCR-723.

All road dust samples of St. Bernardo tunnel and standard BCR-723 exhibit a comparable spectra characterized by an asymmetric luminescence peak with the maximum located in the 610–620 nm range.

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      Most of them are based on the study of the elemental composition (e.g: McKenzie et al., 2008; Amato et al., 2011; Han et al., 2011; Fujiwara et al., 2011b, 2011c; Gunawardana et al., 2012; Huang et al., 2012; Wijaya et al., 2012; Du et al., 2013; Liu et al., 2014; Zhang et al., 2015a), some other on the characterization of the organic compounds (e.g: Omar et al., 2007; Fang et al., 2004; Liu et al., 2007; Hassanien and Abdel-Latif, 2008; Han et al., 2009; Zhang et al., 2015b). X-ray powder diffraction (XRD), X-ray fluorescence (XRF), X-ray absorption spectroscopy (XAS) and Ion Beam Induced Luminescence (IBIL) techniques were also used to study RD samples (e.g: Fujiwara et al., 2011a; Apeagyei et al., 2011; Barrett et al., 2010; Bardelli et al., 2011; Varrica et al., 2013; Sakata et al., 2014; Valotto et al., 2014a); however, the use of a multi-technique approach to characterize this matrix is quite rare. Usually, RD samples are collected to determine the chemical differences among different areas of the same city such as industrial, urban, residential and background (e.g: Liu et al., 2007; Huang et al., 2012; McKenzie et al., 2008; Fujiwara et al., 2011a, 2011b, 2011c; Gunawardana et al., 2012; Du et al., 2013; Kumar et al., 2013b; Hassanien and Abdel-Latif, 2008; Zhang et al., 2015b).

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